As for the composites reinforced with 30 vol% hemp fabric, it was noted a larger number of broken fibers and holes characteristic of pulled out fibers, which could be related to greater interaction of the hemp fibers in the fabric with the epoxy matrix. Table 5 shows the ANOVA for the tensile strength of the composites. According to the values in this table, it is possible to state, with 95% confidence, that the tensile strength averages are different since the F > Fc . The HSD results for the tensile test are shown in Table 6. Based on the obtained HSD, all the values were considered statistically different. Therefore, it confirms the initial hypothesis that the 30 vol% hemp fabric epoxy composites exhibited the highest tensile strength in comparison to all tested conditions. As a material for engineering application, the results presented for hemp fabric reinforced epoxy composite disclose a potential substitute for common composites reinforced with glass fiber. Indeed, the epoxy matrix reinforced with 30 vol% of glass fibers reveals a specific tensile strength of 64.5 MPa$cm3 /g. Comparatively, it is only about 40% higher than that for hemp fabric reinforced epoxy composites .The hemp plant and the building industry have a lot in common, especially when it is about sustainability. At the European Union level, the construction industry is answerable to 35% of the GHG-greenhouse gases emissions, 30% of the water consumption and waste generation, 42% energy consumption, and the highest percent is 50% of the extracted materials. Therefore, the concept of sustainability in the construction sector tries to find solutions to develop the materials building market in the way in which the future of the coming generations will not be compromised, as Brundtland report defines development in 1987 – to make development sustainable to ensure that it meets the needs of the present without compromising the ability of future generations to meet their own needs.

The increasing needs to develop and deepen the research on sustainable materials, which can be defined as building products with low density, hydroponic grow tent composed of affordable raw materials and which have a positive impact on the environment are made in order to find solutions to use the materials as naturally as possible to reduce energy consumption during transport and processing and help retain a higher percentage of CO2 in the environment where they are located. However, finding solutions to decrease the 50% of extract materials connects more the building sector with the agricultural one, in the pursue of two of the main goals of sustainable development: number 11- sustainable cities and communities by implementing affordable building materials and number 12- responsible consumption and production which can be focus on decreasing the percentage of extract raw materials. In the last years, many studies were made in the sector of building materials having a perspective on the raw materials derived from the agricultural sector, as hemp, flax, jute, and so on, which can represent an alternative to the natural extracted materials. For this reason the research is focused on the hemp plant, finding a proper composition which can respond to three aspects: improving the impact upon the unwanted sounds, decreasing the energy consumption and obtaining a composite which reduce the percentage of the extract materials. The hemp plant is known as Cannabis sativa L., which has a low concentration of THC, and allows the plant to be cultivated for the seed and fiber, without having psychoactive effects as marijuana. It is a plant which grows rapidly, having an annual regeneration rate. The hemp plant is used for the seeds, fiber and shiv. The seeds are used especially in the food and cosmetics industry, while the fibers are more met in the paper, textiles, automobiles industry.

The hemp shiv represents the highest percentage from the plant and it is considered a form of waste obtained after the extraction process of the fibers. The shiv is used for bedding and recently, after 1990 in the building industry. Today, more than 25000 products have in their composition hemp elements. One hectare of the hemp culture for fiber represents 6 to15 kg of dry plant from which it results 75% of hemp shiv, 20% of long fibers and 5% dust. In the scientific literature the hemp plant, shiv or fiber, or both of them, are found in mixtures with various natural or artificial binders, to obtain hemp based composited building materials which have the role to decrease the negative percentages on the enviroment of the building industry. Regarding the building materials based on hemp and cement, the scientific literature presents the study of Guillaume Delannoy which compared the composition of the hemp shiv with a binder based on cement and one with lime and showed that the acoustic, thermal and hydric properties of the compositions are similar, Hakamy analyzed the characteristics of hemp fabric reinforced nanoclay–cement nanocomposites, Balčiūnas studied the impact of hemp shives aggregate mineralization on the physical–mechanical properties and structure of composite with cementitious binding material, Çomak deepens in the subject of the effects of hemp fibers on the characteristics of cement based mortars, Hamzaoui analyzed the mechanical performance of mortars modified with hemp fibres, shiv and milled fly ashes and Balčiūnas presented a paper about the physical properties and structure of composites made from hemp hurds and different binding materials. Starting from the studies presented in the literature, the present research discusses more in-depth the composition of hemp elements and white cement and identifies the acoustical and thermal properties of the hemp based building materials.The sound absorption coefficients of the hemp based building materials are presented in Figure 5 and 6. The values of the acoustic parameter are presented in the diagrams 5a and 6a on a frequency spectrum from 50-6400 Hz and on the diagrams 5b, respectively 6b, on standardized frequency bands. In the first diagram, Figure 5a, the two curves of the sound absorption coefficient of the composition with fiberblue line and the composition with shiv- orange line can be noticed. After evaluating the values of the samples, the most performing composition is the one based on fibers which present the highest point of absorption at 90% on the 1500 Hz frequency. At the frequency of 2500 Hz, the monolayer composition with fibers and cement solution presents the lowest value on the interval between 500-6400Hz of sound absorption which is around 65%.

The sound absorption coefficient for the monolayer sample with shiv presents a maximum of absorption of the sound on the frequency of 1000Hz around 80%. From de 1000Hz until 6400 Hz the lowest value of the sound absorption is around the frequency of 2000Hz where only 45% of the sound is absorbed. For the results of the sound absorption coefficients presented on the standardized frequency bands, Figure 5b, it can be noticed that the both samples have similar values on the average frequency of 1000Hz, but a substantial difference is recorded on the 500Hz frequency where the shiv sample presents less than 30% sound absorption comparative with the fiber sample. Sustainable building materials are considered materials which have a minimum impact on the built and natural environment. These materials are designed to accomplish economic, social and environmental performances and also to contribute to reduce the energy consumption, to avoid the utilization of the limited natural resources and to have a positive impact on the environment and human life. Every type of sustainable building materials is defined by three major stages in its life cycle time: the pre-building stage, when a material is manufactured , the in-building stage when the product is used in a building and post-building stage when a material is disposed of . Researchers who are studying the building materials emphasize the fact that since the preconstruction stage it is necessary to design a material which has a positive impact on the environment. For this reason, the focus of the scientific studies in the last years is to establish a connection among different sectors, such as the agricultural and building sector. The raw materials coming from the agricultural sector together with different binders can represent an alternative to the synthetic building materials.The two components allow the production of a bio based building material. The presence of the earth-clay in the building industry is considered the most natural and friendly binder for the environment. It has been used as a building material since ancient times because of the characteristics that it shows: availability, low carbon footprint, low embodied energy, but also clay is considered a natural humidity regulator due to the fact that it has the capacity to transfer and store the heat and the moisture,cheap grow tents which contribute to a high heat capacity. This binder can usually represent also a waste from the construction sector, coming from the foundation of a building and it is completely recyclable. The hemp plant is known especially for the fiber in the textile sector, but in the last years many studies were made on hemp shiv which represents the woody core of this plant. The potential of the hemp shiv in the construction sector is due to the fact that this natural resource shows a high porosity which has a low density. The hemp shiv components are defined by cellulose , hemicellulose , lignin and other compounds.

To complete a wider investigation on the acoustic, thermal and mechanical properties of hemp-clay building materials, several studies about these bio-based materials were found in the scientific literature. Degrave-Lemeurs studied the acoustical properties of the hemp-clay concrete which showed that the concentration of the hemp influence upon the acoustic parameters, while the clay type and the binder fluidity did not have any effect. Mechanical properties of the hemp clay building materials were studied by Mazhoud and Brummer. Mazhoud observed that all the samples had a ductile behavior and the resistances strongly depend on the hemp to binder ratio.Brummer concluded the work by mentioning that in different mixtures of hemp and clay, stabilized with lime, varieties of hemp influence the recipes that need to be adequate to obtain the maximum performance. Relative to the mechanical properties, the use of lime for the stabilization of the mixture decreased the compressive strength and increased the flexural strength. The thermal conductivity of the hemp-clay building materials was analyzed by Bursbridge. The mixture between hemp and clay is not very used in the construction sector; for this reason there is a small number of studies that analyze the physical properties of the hemp-clay building materials.The agricultural industry uses pesticides to optimize food protection for the growing human population . Once crops are infected by fungi, no curative treatment is actually available, leading to crop loss. As a consequence, preventive treatments are often applied. Among treatment options, triazole-based formulations are preferred in agriculture because they specifically target fungi . Triazole molecules are broad-spectrum fungicides used for disease control in cereals, vegetables, fruits and other field crops . They represent 26.1% of total fungicides sales for agriculture and horticulture in Europe, with 31 molecules available . However, triazole molecules do not only control the targeted pathogenic fungi, such as the species responsible for septoria, fusarium ear blight and rust, but have also unintended impacts on other nonphytopathogenic fungi . Among them, Aspergillus fumigatus is a collateral damage especially worrying. This fungus causes invasive aspergillosis in immunocompromised patients, an invasive fungal infection with a mortality rate of 50% which can reach 100% in cases of infections involving antifungal resistant strains. Medical triazole antifungal drugs are indeed used to treat patients, but many cases of antifungal resistance have been reported for 20 years. Two routes of resistance selection are described: the first is linked to the long-term treatment of patients , the second is likely caused by fungicides largely used in the environment for crop protection . Triazole molecules used in medicine and agriculture have similar chemical structures as showed in Scheme 1. Thus, resistant strains with spontaneous mutations are selected byfungicides, or sensitive strains can become resistant through phenotypic plasticity . These environmental resistant strains, in contact with fungicides in fields, would be also resistant to antifungal therapies .

The input–output data were collected by Agris Sardegna under the framework of the “CANOPAES” project at two experimental sites located in Sardinia . The first experimental site contains low levels of HM-contaminated soil, while the second experimental site contains high-level HM-contaminated soils . At both experimental sites, the “Futura 75” industrial hemp cultivar was sown at a rate of 40 kg ha− 1 and fertilized with 60 kg ha− 1 nitrogen , while the irrigation water was distributed at a rate of approximately 4,500 m3 ha− 1 based on the thermopluviometric trend and soil moisture content. The input–output data of the processes after the field gate were gathered from the most recent scientific literature and from the Ecoinvent database . As recommended by Siregar et al., to meet the data quality requirements, data verification must be conducted. The data adopted in this study were checked and verified according to the data quality parameters proposed by ISO 14044. Specifically, the data quality included the time coverage, geographical coverage, precision, completeness, representativeness, consistency, reproducibility, data sources, and information uncertainty. In addition, an uncertainty analysis was performed to address any parameter uncertainties and to test the robustness of the Life Cycle Impact Assessment . The Monte Carlo simulation method was conducted by using 1,000 Monte Carlo analysis runs. This analysis was carried out by collecting a set of uncertainties for the parameters that affected the variation of each scenario. Specifically, the uncertainties for industrial hemp cultivation, seed processing plants, anaerobic digestion plants, biomass-fired power plants and transportation were accounted for. Where available, uncertainty was explained by the results of this study , while for the other subsystems, greenhouse benches the mean and standard deviation were provided from the referenced sources or recalculated based on available published data.

The selected functional unit of this study consisted of 1 kg of dry matter industrial hemp product and 1 ha of phytoremediated area. An assessment of the cumulative energy demand and environmental impacts of each production phase, from raw material extraction, the manufacturing process, cultivation, transportation and biomass utilization, to the end of life, was analyzed in this study, and 4 different industrial hemp supply chain scenarios were designed . The system boundaries of the 4 scenarios were defined from cradle-to-grave. Scenario 1 – Industrial hemp supply chain scenario 1 includes, as shown in Fig. 1, industrial hemp cultivation and harvesting of the crop at the full ripening stage of the seeds , with two main products obtained, namely, industrial hemp seeds and residual straw. These two products share the same on field activities; thus, the energy and environmental burdens were distributed between these products by following the economic allocation method. After transportation, the industrial hemp seeds were treated in a processing plant to obtain several final products , while the industrial hemp straw was pressed and delivered to an anaerobic digestion plant for biogas production. The biogas produced was used to generate electricity and heat, where a portion of the heat was used to dewater the digestate. Next, the dry digestate was transported to a biomass power plant to produce electricity for the grid. Scenario 2 – Fig. 2 shows industrial hemp supply chain scenario 2 , which consists of, as specified in HSC1, industrial hemp cultivation, management and harvesting of the seeds and straw, and the treatment of industrial hemp seeds in a processing plant. The industrial hemp seeds and residual straw share the same on-field activities; thus, the energy and environmental burdens were distributed between these products by following the economic allocation method. In this scenario, the straw bales from the field were transported directly to the biomass power plant for electricity generation. Scenario 3 – Industrial hemp supply chain scenario 3 includes industrial hemp cultivation and then mowing the dried plants to obtain a dried whole plant product . Industrial hemp straw bales, after transportation, were used as solid fuel in a biomass power plant to produce electricity for the grid. Scenario 4 – Industrial hemp supply chain scenario 4 includes, as shown in Fig. 4, industrial hemp cultivation and harvesting of the crop after the complete flowering stage by using a self-propelled forage harvester to obtain a chopped whole plant with a short cutting length .

The industrial hemp biomass was transported to an anaerobic processing plant where after an ensiling process, the product was used as a substrate for biogas production. The successive steps of this industrial hemp supply chain scenario were the same as those presented for HSC1. An LCI includes an extended set of inputs and outputs that are associated with the studied system. Analyses of the inventoried data were conducted by splitting the overall processes into 5 subsystems, as described below. 1- Industrial hemp field cultivation for the phytoremediation of HMcontaminated soil. A field-level dataset was obtained from on-site measurements that included the overall inputs , outputs and detailed descriptions of each cultivation activity for each designed scenario . Specifically, the information consisted of the field task conducted, the type and power of the agricultural machinery used and the time spent per activity, which were collected for industrial hemp cultivation. The equations applied to assess the requirements for the amount of diesel fuel are available in the associated dataset .Moreover, as suggested in other energy and environmental studies, the indirect energy requirements of capital goods for on-field activities were included to obtain a broader overview of the examined system. For these reasons, the embodied energy of the machinery and equipment that was used for the field operations was considered in this study. 2- Seed processing plants transform seeds into refined products. After the harvesting operations, the industrial hemp seeds were delivered to a processing plant for further treatment in scenarios HSC1 and HSC2. The industrial hemp seeds were immediately dried with air ventilation because improper moisture levels of the seeds may cause considerable problems in their conservation and in subsequent processing phases. The preprocessing activities consisted of sieving and ventilation by rotary sieves. Then, the industrial hemp seeds were processed in an expeller screw press to extract the oil and to obtain the cake byproduct. The cumulative energy demand and environmental burdens of industrial hemp seed processing were offset by the savings that were obtained from the replaced products. Industrial hemp oil and its byproducts are widely used in the nonfood sector to produce biofuels and other industrial products. The seed processing dataset for this work comes from the processing trials that were carried out and are still in progress at the experimental stations of Agris. 3- Anaerobic digestion plants for biogas production and energy conversion. The industrial hemp byproducts for scenario HSC1 and fresh industrial hemp biomass for scenario HSC4 were used in an anaerobic digestion plant for biogas production. Based on the available literature, it was assumed that the fresh industrial hemp biomass was ensiled at the ADP with a dry matter loss of 12%, while the industrial hemp straw bales were stored at the ADP.

Both the industrial hemp silage and industrial hemp straw bales were mechanically pretreated with a cross-flow grinder before feeding the anaerobic reactor, and an energy expenditure of 12 kWh t− 1 of feed stock was adopted. The quantity and quality of the biogas may vary based on the input material compositions and operational parameter settings . A specific methane yield of 92 m3 t− 1 of volatile solids was adopted for the industrial hemp straw residues under mesophilic conditions of VS for the industrial hemp silage was used. Moreover, it was assumed that 1.73% of the methane produced was lost as diffuse methane emissions in the combined heat and power unit. The produced biogas was converted into a CHP unit for electricity and heat generation; electricity was conveyed to the national grid, while heat was used for dewatering the digestate. According to the national directive, the agronomic use of digestate, which is produced with the addition of biomass derived from contaminated areas, is not allowed, while the energy valorization of the digestate is encouraged after a rigorous dewatering process. Other studies have indicated that dewatering digestates improves their disposal , but the water content of the digestate should be reduced to 50–60%. Several technologies are available to reduce the water content of digestates obtained from anaerobic digestion , such as a belt conveyor dryer. In this study, the heat from the CHP unit is used to dewater the digestate, since only a minor proportion of the heat produced from the CHP unit is used to maintain the optimal thermal conditions of the anaerobic reactor, while the remaining heat proportion is generally not exploited in commercial ADPs due to their locations in rural areas and because there are only a few potential heat consumers for bulk consumption. For these reasons, in this study, the surplus heat that was produced from the CHP unit was released as waste heat into the atmosphere. The production of capital goods was excluded from the inventory assessment of this study since the capital equipment of ADPs is commonly not considered due to their long life spans and low environmental impacts. 4- Biomass-fired power plant for industrial hemp biomass incineration and energy generation. The dewatered digestates from scenarios HSC1 and HSC4, the industrial hemp straw bales from scenario HSC2 and the dried whole plant bales from scenario HSC3 were incinerated in a biomass-fired power plant for electricity generation. The exploitation of the waste heat that was derived from the BFPP was not considered in this study since reliable energy and emissions factors were not available.

Additionally, growers equipment the limited availability of national district heating structures causes the exploitation of waste heat to be difficult to pursue. Accordingly, the BFPP dataset was compiled from the available scientific literature. The BFPP was assumed to have a life span of 20 years and a power generation efficiency of 20%. In addition, due to the nonnegligible capital goods burdens, the cumulative energy demand and carbon emission impacts of BFPP upstream manufacturing were 0.35 MJ kWh− 1 and 0.036 kg CO2e kWh− 1 , respectively. The dewatered digestate and industrial hemp straw bales were stocked at the BFPP. The industrial hemp straw bales were mechanically pretreated with a cross-flow grinder before incineration, with an energy expenditure of 12 kWh t− 1 of biomass. The specific lower heating values adopted in the hemp supply chain scenarios are available in the associated dataset . In this study, the BFPP employed a mixture of biomass in the furnaces; thus, the suitability of ash as a mineral soil amendment is unknown and requires further investigation. In fact, Cavalcanti et al. and Ferreira et al. found that the contribution of the final disposal of biomass ash was not significant or was excluded from the study boundaries. For these reasons, the disposal of biomass ash was considered to be outside the system boundaries. This aspect represents a limitation of the study. 5- Transportation phases. The transportation of the products among the different processing sites was included in the system boundaries of this study. The transportation data were obtained from the Ecoinvent 3 dataset and from onsite information. Specifically, the industrial hemp seeds and industrial hemp straw bales were transported from the field gate to the seed processing plant and to the ADP , respectively, and 16–32-t Euro 5 trucks for road transportation were used. The fresh industrial hemp biomass that was harvested in scenario HSC4 was transported to the ADP by tractors . The dewatered digestates were delivered from the ADP to the BFPP in scenarios HSC1 and HSC4 with 16–32-t Euro 5 trucks for road transportation. These trucks were also used in scenarios HSC2 and HSC3 for industrial hemp bale transportation from the field gate to the BFPP . When addressing the cumulative energy demand and environmental impacts of the field subsystem inputs, the overall scores were reported based on the amount of product that was harvested; thus, lower production yields had greater impacts. Moreover, the working times that were related to on-field activities were likely influenced by the biomass yields. In fact, the harvesting operations in S1 were slightly greater than the activities carried out in the S2 experimental field.

The fibre bundles were then taken out from the containers and washed several times with distilled water until all the sodium hydroxide from the surface of the fibres was eliminated.This was verified by the neutral response of pH measurement of water in which fibres were washed.Afterwards,the fibre bundles were cut to the required length.Additional treated fibres were prepared for evaluation of their water absorption percentage share measured at different time intervals,i.e.the same intervals as for the non-treated fibres.The treated fibres resulted with the same percentages of their total water absorption as for the non-treated fibres.For all mortar mixtures,the fly ash to sand mass ratio was set to 1:3.The activator to fly ash dosage was defined by equaling the mass of Na2O from the activator with 10% of the fly ash mass.All mortar specimens were prepared according to the EN 1015-11.From each mixture,six prism specimens with dimensions of 40 × 40 × 160 mm3 were cast.The exact composition of all the mixtures is listed in Table 2.After the mixture is poured into the moulds and left for one hour in laboratory conditions ,the specimens were covered with a plastic foil,placed in an oven and cured at 80 ◦C for six hours.The oven was turned off and the specimens were left to rest inside the oven for the next 12 h.The specimens were demoulded and kept in a climate chamber until their testing at the age of 28 days.Non-treated hemp fibres have many small fibrous materials that are connected to the main fibres’ structure.These filaments result from the fibres’ processing and are not to be confused with the small structural fibres.Besides,mobile vertical rack other impurities and wax materials could be found on the surface of non-treated fibres.Generally,one single hemp fibre bundle consists of many fibrils that are glued together with waxy and oily materials.

During the fibres’ surface examination,it was noticed that 3% concentration of sodium hydroxide solution can significantly clean the fibres’ surfaces and remove small filaments.With the sodium hydroxide treatment also waxy and oily materials can be rinsed off and removed from a fibre,which leads to the separation of larger fibre bundles into smaller fibrils with cleaner surfaces.Using higher concentrations of sodium hydroxide treatment leads to further significant improvements in the cleaning of the fibres’ surface.The positive impact on the morphology of natural fibres after the sodium hydroxide treatment has also been proven in the study of others.Mwaikambo and Ansell showed that after the treatment with 0.24% sodium hydroxide solution,the surface of hemp fibres became cleaner and fibre bundles more separated,with a highly serrated surface.Sedan et al.proved that the hemp fibre treatment with 6% sodium hydroxide solution removed hemicelluloses,waxes and impurities from the fibres’ surface and thus increased its homogeneity.Edeerozey et al.showed that the treatment of kenaf fibres with 3%,6% and 9% of sodium concentrated solutions significantly enhances the purity of the fibres’ surface.They concluded that the optimum concentration of sodium solution for fibres’ treating in regards to fibres’ surface cleanness and tensile strength is 6%.After the chemical treatment of the fibres even by touching them and with visual inspection could be noticed that the fibres are rougher and show jagged edges.The level of roughness before and after the treatment can provide important information for further interfacial adhesion between the fibres and matrix.Measuring the roughness on the surface of non-treated hemp fibres was very difficult.Due to the inhomogeneous surface of the fibres ,the cantilever from the AFM could not move easily on the surface of the fibres.After the chemical treatment of the fibres it is indicated that sodium hydroxide not only cleans the fibres surface ,but also attacks more sensitive surface parts,disrupting them and providing the roughness and jagged edges of the fibres surfaces.

Chemically treated fibres had more uniform surface structure in the longitudinal direction.The fibres after alkali treatment also resulted in higher root mean square roughness,which indicates that the treatment increases the roughness of the fibre surface.After the alkali treatment,fibres also decrease their water absorption capacity ,due to the elimination of the fibres’ filaments and washing out the hemicellulose and waxes.The pore diameters in the range of 2.5–10 nm,10–50 nm and 50 nm − 10 µm are considered to be the small,medium and large capillary pores,respectively and were adopted according to Mindess et al..All pores with diameters larger than 10 µm are considered as entrained air pores.Plain mortar is characterized by 31% lower total pore volume and 24% lower porosity in comparison to the non-treated hemp reinforced mortar.The main pore structure parameters and the pore sizes distribution give evidence of the finer pore structure formed in the plain mortar than in the non-treated fibre reinforced mortar.In a plain mortar,the entrained air pores occupy only around 10% of its total porosity ,whereas in nontreated hemp fibre reinforced mortars even up to 25%.The fibre reinforcement contributes to aeration of the matrix by the entrained air,as in cement-based matrices,and consequently to pore structure coarsening.The medium capillary pores occupy in both mortars around 70% of their total porosity,however,the ratio of small capillary pores significantly differs,i.e.,in the plain mortar,it is around 20%,whereas in hemp fibre mortar – only around 7%.The pore size distribution curve of the plain mortar has a lower slope in the area of the coarser pores than in hemp fibre-reinforced mortar ,which also indicates its finer pore structure.However,the mortar’s total porosity and the effect of the pore structure coarsening by fibres addition are lowered when the fibres are previously treated with sodium hydroxide solutions.After the fibre treatment,reinforced mortars resulted in a lower volume of total pores and lower porosity.When fibres are treated with 3%-,6%- and 9% sodium hydroxide solution,the total pore volume of the fibre reinforced mortars’ decreases by 28%,3% and 20% and their total porosity – by 22%,3% and 19% respectively.The fibre treatment leads to a pores refinement of the reinforced mortar.Furthermore,the fibre treatment results in a decrease of the entrained air pores by 46%,19% and 22% when the fibres are treated with 3%-,6%- and 9% sodium hydroxide solution,respectively.Additionally,the alkali treatment of fibres results in a reinforced mortar’s lower slope of the pore size distribution curve in the area of coarser pores followed by a more pronounced rise in the small range pore area around 1 µm.

The alkali treatment leads to a cleaner fibres’ surface and better separation of the fibre bundles and consequently in a better mixability with more optimal distribution within a matrix.All this could be the reason for lower porosity and pore refinement in reinforced mortars containing treated fibres.In addition to this,treated fibres show higher surface roughness.Consequently,it is expected that treated fibres have a better bond with the matrix than non-treated fibres,resulting in fewer pores on the fibre–matrix interface itself.As a result of the entrained air,no fibre-reinforced mortar achieves the pore structure parameters of the plain mortar.Nevertheless,no significant deterioration is observed in the case of alkali-treated fibre reinforced mortars.In cementitious mortars,a similar but not so pronounced trend of total porosity change was obtained by Jo et al..It was shown that when using 5 mm-long 0.5% sodium hydroxide treated jute fibres in a dosage of 1 wt%,cement-based mortars reduced their porosity by 3.5% when compared to non-treated jute fibre reinforced mortars.After wet/dry cycles,the porosity of plain mortar measured with MIP is 41% lower than in the case of non-treated fibre-reinforced mortar,which shows a significant decrease.The reason could be that nontreated fibres absorb water and swell,causing micro-cracks in the matrix.The alkali treatment of fibres seems to lower the reinforced mortar’s porosity also after the wet/dry cycles.Reinforced mortars show a decrease in the total pores volume by 33%,35% and 26% and in porosity by 27%,28% and 23%,after the fibres treatment with 3%,6% and 9% sodium hydroxide,respectively.In addition to this,the alkali-treated fibre reinforced mortars show a more distinctive drop of the pore size distribution curve in the area of the main curve’s peak ,which is evidence of a pore refinement.Lower porosity in alkali-treated fibre reinforced mortars could arise from the reduced water absorption capacity of treated fibres ,which consequently reduces the fibres’ swelling under wet/dry cycles.Additionally,cleaner fibres’ surfaces and removal of surface filaments are expected to reduce the fibre agglomeration and improve the distribution of fibres within the matrix.In comparison to non-aged mortars,after wet/dry cycles,the porosity of the plain mortar increases by 15%,whereas the porosity of the non-treated fibre reinforced mortar increases significantly,i.e.by 47%.The alkali treatment of fibres decreases this value.Decreased porosity by 36%,10% and 40% is observed for 3%-,6%- and 9% sodium hydroxide treated fibres,respectively.Most importantly,it is noticed that mortars reinforced with 6% sodium hydroxide treated fibres experience a smaller change in porosity after wet/dry cycles in comparison to the plain mortars.It could be concluded that 6% sodium hydroxide treatment helps to clean the fibres’ surface sufficiently and at the same time,it is not a too strong concentration for a possible deterioration of the structure of the fibres.

Water ingresses in open pores that are larger than approximately 1 μm.These pores belong to the large capillary and entrained air pores.The plain mortar results in 19% lower water absorption in comparison to non-treated fibre reinforced mortar.This occurs due to an increase of the coarser pores after the addition of non-treated hemp fibres.Since the fibres alkali treatment decreases the water absorption capacity of the fibres itself and refines the pore structure of mortars ,it also leads to an overall decrease in the fibre reinforced mortar’s water absorption capacity.The same trend was reported in cement-based mortars reinforced with 5 mm-long jute fibres with a dosage of 1% in the matrix.The addition of non-treated jute fibres to the matrix increased the water absorption of the plain mortar by 5.55%.Due to a better interface between 0.5% sodium hydroxide-treated jute fibres and the matrix,the water absorption of alkali-treated fibre reinforced mortars was 3.16% lower than by non-treated fibre reinforced mortars.After the wet/dry cycles,vertical grow rack the plain mortar shows 12% lower water absorption capacity when compared to the non-treated fibre reinforced mortar.The alkali treatment of the fibres,after the wet/ dry cycles,helps to reduce the water absorption capacity of the fibre reinforced mortars to almost the same level as the plain mortar’s absorption.On average 11% lower water absorption capacity is noticed for alkali-treated fibre reinforced mortars than for the non-treated fibre reinforced mortar.Comparison between the water absorption capacities of the mortars after the wet/dry cycles and their non-aged counterparts ,shows a decrease in the mortars’ water absorption capacity.It can be seen that fibre reinforced mortars experience a higher water absorption capacity drop in comparison to plain mortars.The alkali treatment results in a reduced water absorption capacity of the reinforced mortar after wet/dry cycles.The sodium hydroxide concentration itself has no influence on the fibre treatment in terms of the mortars’ water absorption capacity since all mortars showed on average the same capacity reduction,i.e.23%.The addition of non-treated fibres to the mortar has almost no influence on the mortar’s density,i.e.,a negligible decrease was observed.The decrease results from the entrained air and the increase of the total pore volume by the addition of fibres to the mortar.Additionally,hemp fibres have a lower density than plain mortar ,which in turn slightly decreases the composites’ overall density.In the case of sodium hydroxide treated fibres,the density of the reinforced mortar remains almost the same,.The different sodium hydroxide concentrations used for fibre treatment had no influence on the bulk density of the mortar.In fibre-reinforced cement-based composites,the same trend was reported.After the addition of 1% of 50 mm-long coir fibres to the matrix,the density of the composite decreased by 1.7%.In the case of 5% sodium hydroxide solution-treated fibres,the density of the composite increased by 0.4% in comparison to the nontreated fibre reinforced composite.The same trend with no significant change in density was noticed by Jo et al.in the case of jute fibre reinforced cementitious mortars.The addition of the 5 mm-long,non-treated jute fibres,in the dosage of 1% ,decreased the density of the mortars by 1%.However,after the addition of the 0.5% sodium hydroxide-treated fibres,the density of the nontreated fibre reinforced mortars was increased by 0.7 %.Similar to the results of our study,there was no significant change in density after the fibres were chemically treated.Compared to the non-treated fibre-reinforced mortar,after the wet/ dry cycles,the plain mortar’s bulk density was only 4% higher.

When extraction is performed on retted material,the scutching step has a significant impact on the strength and modulus compared to the breaking step.However,as a large part of the fibres weakened by the scutching stage are eliminated during hackling and transformed into hackling tows,this explains the slight rise in modulus observed at the hackling stage.In this case,the modulus and breaking strength after hackling are not significantly different to the ones determined after the breaking step.The tensile property analysis also shows that dew-retting has no significant impact on the strength and modulus of the fibres after hackling.Student’s tests have also shown that there is no significant difference between the fibres obtained at the end of hackling and the reference material,both for retted or un-retted stems.The mechanical potential of the elementary hemp fibres is not affected by the scutching/hackling steps and the level of tensile property and modulus of elasticity.This is globally lower than the potential of flax fibres extracted manually and reported in the literature by about 20 %,but highly sufficient for load bearing composite use.The properties obtained in this work cannot be compared directly as very few studies considered the tensile properties of hemp fibres after scutching and hackling extraction.In most of the studies,the fibres were extracted by hand or with more aggressive devices such as hammer mills,or a mechanical fibre opener.The tensile properties obtained in this work are also larger than the ones obtained by Liu et al.for hemp extracted manually,therefore showing the quality of the fibre extraction.The results obtained at the end of hackling are also compared to those collected at the end of industrial scutching/hackling devices carried out on retted stems from the same batch as the one extracted on the lab-scale device.Fig.8 shows that industrial extraction has a strong and significant impact on both the modulus and the strength with strong decreases compared to extraction on the lab scale device.

At this stage,cannabis grow equipment it has not been possible to identify which process is the most damaging for the fibres in comparison to the lab scale.Both processes are expected to contribute to the fibre property loss in comparison to the lab scale results.In any case,the process parameters used at the industrial scale are expected to be too aggressive and probably damage the fibre by generating defects on their structure.In order to confirm these observations,an analysis of the kink-band defects observed on the fibres at the end of hackling for the two batches extracted with the lab scale and industrial scale equipment was carried out.The results presented in Table 3 show that the number of kink bands varies little from one batch to the other.When the scutching/hackling of the retted material is carried out industrially,there is still no significant difference in the number of defects in the fibres,but the percentage of the fibre surface occupied by the kink bands has been increased ,but still insignificantly,from 12.2 % to more than 17 %.Industrial scutching/hackling therefore probably causes larger defects on the fibres and this may explain the decrease in both modulus and strength for industrially extracted fibres.To improve both fibre yield and tensile properties after industrial extraction,the authors recommend to reduce the processing speed especially with well-retted stems which are more delicate and to introduce the hemp stems as homogeneously as possible.The magnitude of the processing speed will depend of the hemp level of retting,but a reduction by a factor ranging from 1.5 to 2 is recommended and needs to be tested in next trials.Of course,the reduction in scutching speeds will lead to a reduction in the rate of production.However,it should be considered that the decrease in speed should be accompanied by an increase in the long line fibre yield and the preservation of mechanical properties adapted to load-bearing composite materials,which is not currently the case.With such improved process parameters and way of introduction of the stems it is expected to improve both fibre yields and tensile properties of the fibres to values close to the ones of flax.Phytoremediation is a mainly solar energy-driven technology that uses plants and agronomic techniques to remediate and restore contaminated soils.This method has several advantages ,as well as limitations.The first approach of phytoremediation was to use hyperaccumulators for phytoextraction or accumulators for phytostabilization.However,as the research and field application results were released,it became obvious that a crucial bottleneck in the technology was its slowness and economic viability.

A new phytoremediation approach was subsequently developed,the so-called phytomanagement,in which high-biomass and high-value industrial cash crops are cultivated on contaminated lands to produce useful biomass feedstock for bioproducts and bioenergy.The main advantages of this method are they: produce economic revenue for farmers and rural areas,contributing to the wellbeing of the local population; boost local economies by developing innovative entrepreneurship for industrial applications of the biomass produced; increase the availability of domestic raw materials and the ability for them to be used in new emerging markets; exploit land that cannot be used for food production; mitigate the route of exposure for the intake of contaminants by humans,etc.The main bottleneck of this method is that it becomes effective only when the contaminated site is a large area of unused/abandoned arable land,in which agricultural practices and mechanization can be applied.A group of crops that have many attractive characteristics for phytomanagement purposes are fiber crops.Among them,flax ,kenaf and hemp  are very promising candidates since they have been reported to show a tolerance to toxic trace elements in soils,are fast-growing and yield a high biomass,have low input requirements,use well-known agricultural practices,and are multipurpose.Several scientific works showed that flax is relatively tolerant to and in some cases an accumulator of Cd,Cu,Pb,and Zn ; kenaf accumulates Cd,Pb,Zn,and Cr;and hemp accumulates Cd,Ni,Pb,Zn,Cu,Cr,Hg,As,Mn,Se,Rn,Tl,and Sr.These crops have well-known large-scale agronomic and harvest practices and a plethora of industrial uses.Attention most certainly has to be paid to biomass exploitation since a small amount of heavy metals and metalloids may be taken up by the biomass produced.Especially if fibers are used for clothing,they might represent a risk to health and should be carefully monitored.Nevertheless,De Vos et al.demonstrated that hemp fibers concentrated Cd and Pb in levels far below the thresholds for textile product according to STANDARD 100 by OEKO-TEX 2020,while Zn is not considered a toxic element in textile production.The aim of this work was to find crop and variety differences between FKH in their tolerance and potential for Cd,Ni,Pb,Zn,Cu,and Sb accumulation.

The research should generate data for the possible use of each crop/variety for phytomanagement of contaminated soils.Before sowing,water was added to each pot to adjust the soil moisture to 70% of the field capacity,which was measured by the static approach as defined by Reynolds.The seeds of each crop and variety were sown into pots on 4 March 2020.The initial seed germination rate was taken under consideration,and the target seedling number per pot and the actual sowing number for each variety and crop are shown in Table 3.Ten days after sowing,the number of seedlings per pot was recorded to determine the effect of HM&M stress on the germination rate of each variety.During the experimental period,the seedlings were observed for phytotoxicity symptoms every three days.The soil was kept moist by spraying pots every five days with a 100 mL of water.Weeds and pests were controlled in a timely manner.Seven weeks after sowing,the aboveground part of each crop was harvested and the plant height,stem diameter,number of leaves,and the fresh biomass per pot were measured.Then the plants from each pot were dried ,weighed and ground into powder using a cross-hammer beater mill.Plant samples were digested with 5–10 mL nitric acid in vessels,left for 1 h,and then heated in a microwave digestion apparatus.Subsequently,the vessels were placed on a temperature-controlled electric heating plate for 30 min at 100 ◦C to reduce the volume of the solution to approximately 2 mL and the sample volumes were adjusted to 25 mL with deionized water.The resulting solutions were filtered through a Whatman No.42 filter paper and were analysed for HM&M using ICPMS.At this point it should be noted that under Cu and Zn treatments,the seeds of all varieties did not germinate,indicating the severe toxicity of the applied contamination levels of both heavy metals to FKH.Several studies have been published on the phytoremediation potential of FKH; generally,in these studies,low to moderate soil contamination levels were examined.However,in this experiment,extremely high concentrations of the applied HM&M were used in order to evaluate the tolerance of FKH and their uptake potential.The plants were subjected in even higher stressing conditions since this was a pot experiment with artificially contaminated soil,resulting in higher soil availability of the toxic elements.The presented study was quite complex,covering three varieties of each of three crops in three replicates,while for each treatment,eight measurements were taken.The scientific questions to be answered were: which fiber crop and variety is most tolerant to the tested HM&M; which crop/variety takes up the most HM&M for phytoextraction purposes; and which crop/variety does not take up the tested elements,thereby producing a clean biomass for further transformation to bioenergy and/or bioproducts.

These findings will play a key role when designing a phytomanagement plan for areas heavily contaminated due to manufacturing,mineral extraction,abandonment of mines,accidental spills etc.In this work,vertical grow system seed germination per variety and crop was tested since it is the simplest and rapid method for evaluating the phytotoxic effects of inorganic contaminants on plants.The germination of seeds and the early stages of seedlings growth are more sensitive to metal stress as several defense mechanisms have not yet been developed.The heavy metals Zn and Cu are classified as essential micronutrients,involved in many important biochemical and physiological processes of plants.However,their presence in excess can lead to a significant reduction of seed germination and seedling growth.In this study and throughout the experimental period,no seedlings emerged for the pots under Cu and Zn treatments,indicating that the pollution levels of both metals were beyond the endurance of the supplied varieties.Thus,no further analysis was made for these two metals.Compared with the control,the addition of each heavy metal and Sb significantly affected the seedling emergence rates of all the varieties of FKH.Flax: Low Cd contamination increased the rates of emergence of three flax varieties when compared to the control,with the highest rate of 67.1% for Y2I329 and the lowest of 49.5% for Zhongyama No.1.The high Cd concentration reduced the emergence of all flax varieties,with the highest emergence rate of 53.3% for Y2I328 and the lowest one of 35.2% for Zhongyama No.1.Compared with the control,the three flax varieties did not emerge in Ni220; the emergence rate of Y2I329 was reduced for Ni110,but was significantly increased for Y2I328,and was slightly increased for Zhongyama No.1.Compared with the control,Pb1500 showed a tendency to increase the emergence rate of the three flax varieties,among which Zhongyama No.1 obtained the highest rate but Y2I239 the lowest; Pb3000 had no significant effect on the emergence of flax compared with Pb1500.Compared with the control,Sb50 increased the emergence rate of flax varieties; Sb100 reduced the emergence of Y2I328 and Zhongyama No.1 but increased that of Y2I329.Kenaf: Different metals significantly influenced the emergence rate of this crop.Treatment Cd40 notably or slightly increased the emergence rates of the three kenaf varieties,while Cd80 significantly reduced them.Ni110 significantly reduced the emergence of GSS,but did not notably affect the other two varieties,Ni220 significantly reduced the emergence of HP and slightly reduced that of GSS.Pb in this study showed no significant effects on kenaf emergence rate; these results are not in accordance with the findings of Sultana et al.,when two kenaf varieties were subjected to a combined Pb and Cr treatment of 120 and 120 mg/L,respectively.Treatment Sb50 significantly increased and Sb100 significantly reduced the emergence of Hongyou No.2,but did not notably affect that of GSS and HP.Heavy metal stresses also significantly affected the emergence rate of hemp.Compared with the control,Cd40 significantly improved the emergence of Guangxibama and slightly increased that of Zhongdama1,but notably reduced the emergence of Yunma No.1; compared with Cd40,Cd80 significantly reduced the emergence rate of Guangxibama and Yunma No.1 but did not significantly affect that of Zhongdama No.1.An increased germination rate under Cd treatment was also reported by Linger et al.and Seregin and Ivanov.A possible explanation for this is the expression of stress-inducible genes during germination that adjust seedlings’ metabolism to the stressing conditions and better protect them compared with the control seedlings.

The partition coefficient of the solute i was then calculated according to Eq. 1. LLC experiments were carried out on a counter current chromatography column, model HPCCC-Mini Centrifuge from Dynamic Extractions , with a column volume of 18.2 mL. Two isocratic Gilson 306 pumps , equipped with an 806 Manometric Module , were used for delivering the mobile and stationary phases. The elution profiles were monitored with a DAD 171 diode array detector at a wavelength of 220 nm. The CCC experiments were performed at room temperature. All LLC separations were carried out as pulse injections in DSC mode, where the lower phase is used as mobile phase. At the beginning of each experiment, the column was filled with stationary phase. Afterwards, the rotational speed was set to 1900 rpm and the mobile phase was pumped through the column at 1 mL min−1 until no more stationary phase eluted from the column. The samples were dissolved in the corresponding mobile phase , filtered and then injected via a 1 mL sample loop with a manual injection valve, with the mobile phase continuously pumped at 1 mL min−1. All CCC runs were manually fractionated after injection in fraction intervals of 1 min. The collected fractions were analyzed by HPLC-DAD. Based on the analysis of the fractions, a reconstructed offline LLC-chromatogram was generated for each separation run. GC-TCD analysis was performed using a Nexis GC 2030 coupled with a thermal conductivity detector from Shimadzu . A Restek Rxi-624Sil MS capillary column was used, with helium as carrier gas at a linear velocity flow of 40 cm s−1. The temperature of the injection port was set to 250 °C, at a split-ratio of 50 during injection. After an isothermal step of 1 min at 35 °C, a linear temperature gradient of 31 °C min−1 to 190 °C was applied. The TCD temperature was set at 260 °C. The biphasic solvent systems were prepared in 20 mL vials by mixing the corresponding portions of the solvents at ambient temperature and pressure.

The mixture was then vigorously shaken and equilibrated at 25 °C for 2 h. Then, 100 μL of upper and lower phases were separately diluted with 900 μL THF and their compositions were analyzed by GC-TCD, using six-point calibration curves established for each of the analyzed solvents. In this work, a computer-aided approach for selecting biphasic solvent system candidates for preparative LLC isolation of CBD from hemp extracts,cannabis grow supplies with simultaneous removal of contaminating pesticides that might be present in the starting material is proposed. First, a list of biphasic solvent systems from a predefined pool of solvents was created. After that, a fully predictive thermodynamic model was used to screen for potential systems . The objective of the screening was to identify biphasic solvent systems in which the partition coefficient of the target component CBD is within a predefined range. Three of the most promising solvent systems were next evaluated in terms of their ability to separate the target compound CBD from a list of pesticides as impurities. In this work, pesticides whose limits in cannabis products are regulated by the state of Oregon were considered. Consequently, a list of critical pesticides was determined for each solvent system based on separation factors αCBD/PEST values predicted by COSMO-RS and validated by shake-flask experiments . For the proof-of-concept, a hemp extract spiked with seven pesticides was subjected to LLC separations with each of the three selected solvent systems . To demonstrate the applicability and validity of the approach shown above for the selection of solvent systems for the preparative LLC separation of CBD from potentially contaminated hemp extracts, seven representative pesticides from the red, orange and yellow zones were selected. These were added to a decarboxylated hemp extract that was further subjected to LLC separations with each of the three solvent systems. The separations were performed on a lab-scale CCC column, in DSC mode at 1 mL min−1 and 1900 rpm. The feed mixture was injected in the column in a concentration of 5 mg mL−1 hemp extract spiked with 50 ppm of each pesticide. In all separations, a stationary phase retention of 0.6 was achieved.

Even though the pesticide concentrations for spiking might exceed those existing in real hemp batches, they were selected taking into consideration the higher LODs and LOQs of the UV detector of the HPLC-DAD system used to perform the off-line analyses of the collected fractions. The reconstructed off-line chromatograms presenting the individual fraction concentrations vs. elution time are depicted in Fig. 5. The peak shapes in Fig. 5 for CBD and each pesticide were obtained by fitting the experimental data points into Gaussian equations with Origin2020 software. The on-line chromatograms recorded with the DAD detector of the CCC set-up is presented in Fig. S1 . As expected from PCBD EXP values from Table 2, the yellow-zoned and green-zoned pesticides as well as trifloxystrobin were completely removed during the LLC separation with solvent system I . Nevertheless, ethoprophos and kresoxim methyl, cinerin I and pyrethrin II were partly co-eluting with CBD peak. In the case of solvent system II, the pesticides from yellow and orange zones were eliminated, with the exception of the highly critical pesticides cinerin II and pyrethrin II that strongly overlapped with the CBD peak; trifloxystrobin only partly co-eluted. Since none of the selected pesticides were in the red zone in solvent system III, the separation with this system showed the best outcomes, most of the pesticides being totally eliminated, while ethoprophos and cinerin II slightly overlapped with the CBD peak . Lignite is still an important source of energy in many countries of the world. Poland is the second lignite producer in European Union after Germany , and fourth in the world . Presently about 30 % of Poland’s energy is generated from brown coal . Lignite mining in Poland covers approximately 16 000 ha while the area of land degraded as a result of open mining activity is over 67 000 ha . Opencast mining is the most common technique used for mining of coal and other minerals when they occur close to the surface . Surface coal mining causes a lot of disturbances in the ecology of the natural environment. Sometimes, far-reaching geological and ecological changes may even lead to international conflicts and legal disputes . Opencast mining leads to significant geomechanical transformations and degradation of the natural structure of the soil profile and the layers of the natural cover of humus, one of the basic components of soil that determines its fertility. Before the lignite can be excavated by the open-mining method the top layer over the lignite deposit – so called overburden – has to be removed together with all the vegetation and the soil.

Surface mining drastically alters soil properties, destabilizes soil organic carbon and depletes SOC pools. Carbon is initially lost from mined soils in the same manner that organic C is lost from tilled soils due to the disintegration of soil aggregates that leads to organic matter being decomposed and carbon is ultimately respired . After the coal deposit mined with the opencast method is exhausted, a dead excavation remains, which is filled with material from the outlay as the excavation progresses. The surface of such terrain is leveled.The humus content in such a layer is trace, it does not have a biologically active surface layer consisting of mineral and organic particles of varying degrees of disintegration. When natural components of the environment have lost the capability to autoregenerate in a timely manner, their rehabilitation is only possible through anthropogenic correction. Natural processes of soil formation are slow and can take decades or centuries to form new soil. To speed up soil formation processes and to achieve a normal soil productivity level different procedures of land reclamation ale implemented, leading to construction of a new soil. The characteristics of this new soil or minesoil depend on the kinds and sequences of reclamation procedures employed . There are many possible options for the productive uses of reclaimed mine lands. This does not necessarily imply restoring precisely the characteristics of the premine soil and landscape but rather involves the establishment of geological and hydrologically stable landscapes capable of supporting a natural mosaic of ecosystems. The implementation of any one of the land use possibilities is conditioned by technical, economic, social, and environmental aspects . There are three main directions for the restoration of the post-mining areas. These are agricultural use when arable lands, cannabis grow facility permanent grassland or orchards are set up, afforestation of reclaimed areas that have a production or protective function and a special direction based on recreational, ecological or aesthetic and protective management. Agricultural reclamation is not the most common. The direction of reclamation in each country is selected for each case separately. In Great Britain for example, as well as in Germany and Hungary, the agricultural approach of reclamation is preferred while in the United States and Turkey the forestry approach dominates. In Poland many disturbed areas are used for recreational purposes . Among lignite mines in Poland, agricultural reclamation is used on a larger scale by only two mines – “Adam´ ow” and “Konin” .

Globally, agricultural reclamation is carried out mostly by cultivating a small number of non-food plants, which are then used industrially. In our opinion, this is not the optimal solution. From an industrially degraded area, where the process of creating a humus layer has just begun, biomass is extracted, resulting in low yields of succeeding crops, and the reclamation process is ineffective and extended over time. Devastated soil has a diverse geomechanical composition and deficiencies of some essential nutrients are common, which makes it unsuitable for the production of food or fodder plants. We propose here the use of fiber hemp cultivation as a pioneering plant, when all the produced biomass is not removed from the field but is reintroduced into the soil in order to restore the missing humus layer as quickly as possible. Hemp is an herbaceous plant that can grow from about 1–6 m tall, depending on factors such as cultivar and environmental and agronomic conditions. It can produce high amount of biomass. Some authors reported very high yields of hemp reaching more than 22 tons per hectare , however more typical values are lower and other authors report yields of fiber hemp on the level of 7− 15 tons per hectare . Fibre hemp is a traditional industrial crop in many regions of the world. For many centuries hemp has been cultivated mostly as a source of strong stem fibre and seed oil . Recently this species gains a lot of attention for its alternative use directions, these include using hemp for biomass and biofuel production. Hemp is a rapidly growing plant that tolerates high planting density and the total biomass of hemp per hectare is similar to other energy crops, including giant miscanthus, poplar or willow. However, hemp may provide a key advantage; its bast fibers contain high amount of cellulose and low amount of hemicelluloses and lignin comparing to other biomass crops. The stem biomass in hemp consists of high cellulose fiber; thus, the ratio of digestible sugars to lignin is higher in hemp than in other similar-yielding biofuel crops . In addition to a high amount of biomass, the plant has a well-developed taproot system, growing into the soil to a depth of about 2 m or more. Hemp’s short growing cycle, decreased need for pesticides, and low plant maintenance makes it an ideal candidate for phytoremediation utilization . Cannabis sativa is also plant potentially usable for the detoxification of contaminated soils due to its resistance to soil contamination, its ability to accumulate heavy metals and possibility of cultivation in different climatic conditions . All these unique characteristics of hemp and the awareness that vegetation plays a major role in improving the properties of mine soils, where increased biomass production, root residues and exudates, and the greater activity of microbes following revegetation have positive effects on the accumulation of soil organic matter has encourage us to test the study the usefulness of fibre hemp as a species for experimental reclamation of the 7.5 ha area degraded by previous lignite mining operations.

The selected representative SEM images of structural electrolytes with various contents of hemp fiber are presented in Fig.4.As the content of hemp fiber increases,wider inter layer voids are found in the matrix.The processed images of structural electrolyte with various contents of hemp fiber are shown in Fig.5.Area considered here is defined as the number of pixels.The white part represents pore structure,while the black part is matrix.The pore structure here is mainly macro-pores,which have the greatest influence on storage of aqueous electrolyte and ionic migration.Interconnected pore structure is consisting of some isolated macro-pores in the matrix.Thus,the porosity P of structural electrolyte is calculated by P = S1/S,where S1 is the area of all the white parts,and S is the area of the overall area.And the pore connectivity PC of structural electrolyte is measured according to PC = S2/S,where S2 is the area of all the interconnected pore structure.The porosity and pore connectivity of structural electrolytes with various contents of hemp fiber are depicted in Fig.6.It is found that the volume of hemp fiber is between 5 vol% and 15 vol%,a gradual increase from 8.3% to 18.6% in porosity and from 5.6% to 15.5% in pore connectivity of the structural electrolyte.The increase in porosity and pore connectivity attributes to the interlayer voids trapped beneath the fiber during casting.However,as the content of hemp fiber increases to 5 vol%,the porosity of the sample decreases from 10.8% and the pore connectivity decreases from 7.2%.It is consistent with that low volume of fiber is effective in reducing free plastic shrinkage and pore structure development.Moreover,cannabis grow racks as the content of hemp fiber is higher than 15 vol%,the porosity and pore connectivity of the samples decreases due to the disorganized arrangement and massive stacking dispersion of hemp fiber in the matrix.Thus when compared with foaming method by adding air entraining agent,synchronized changes of porosity and pore connectivity of the structural electrolyte by adding hemp fiber show better.

This is mainly due to that the macropores created by air entraining agent are independent bubbles and difficult to connect with each other,but lots of interconnected pore structure can be formed by adding large content of hemp fiber.Fig.7 shows the pore size distribution curve and porosity of structural electrolytes with various contents of fibers tested by MIP.It is clear that most probably aperture diameter is about 115 μm,54.6 μm and 86.5 μm for the structural electrolyte with 0 vol%,15 vol% and20 vol% of hem fiber,respectively.As the content of hemp fiber increases to 15 vol%,the pore number of structural electrolyte dramatically increases.The structural electrolyte has a total porosity of 13.0%,24.2% and 21.1% with 0 vol%,15 vol% and 20 vol% of hemp fiber,respectively.The pore content obtained by MIP is a little higher than by image analysis,which is mainly due to sampling,but the variation trend of porosity is consistent with that of image analysis.Fig.8 displays the CV curves of structural super capacitors with different contents of hemp fiber.All the CV curves are relatively in rectangular shapes and exhibit near mirror-image current response on voltage reversal,meaning ideal capacitive behavior.Based on the area of CV curves,the specific capacitance of the structural super capacitor initially increases with the increasing content of hemp fiber and then decreases,which are resulted from the porosity and pore connectivity of structural electrolytes.Here,as the volume content of hemp fiber increases from 15 vol% to 20 vol%,the area of CV curves decreases,which is mainly due to that the pore structure of structural electrolyte decreases by 33.5%.Thus the pore structure of structural electrolyte significantly affects the specific capacitance of structural super capacitor.From Fig.9a,the typical triangular-shaped galvanostatic charge discharge curves of the structural super capacitors with different contents of hemp fiber are highly linear and symmetrical without obvious iR drop,exhibiting nearly perfect capacitive behavior.In Fig.9b,as the content of hemp fiber increases from 5 vol% to 15 vol%,the specific capacitance of structural super capacitor gradually increases from 35 F·g−1 to 51.4 F·g−1,which ascribes to the increase in porosity and pore connectivity of structural electrolyte.However,as the volume of hemp fiber is lower than 5 vol% or higher than 15 vol%,the specific capacitance of structural super capacitor decreases with the increasing volume of hemp fiber due to the reduction of porosity and pore connectivity of structural electrolyte.It can be deduced that aqueous electrolyte can be stored in the pores of matrix to assemble structural electrolyte,and aqueous electrolyte can pass quickly from the surface to underlying layers of the matrix through the interconnected pore channels during charge-discharge.

Similar findings have been reported by J.M.Xu,W.Y.Ma and N.Shirshova,they all agreed that ionic conductive phase was not only stored in the pore structure of matrix,but also transmitted to the electrode surface through the pore structure during charge-discharge.Yet they didn’t discuss the effect of pore structure on the specific capacitance of the structural super capacitor in depth.The higher porosity in the matrix,the more KOH aqueous stored.And the higher pore connectivity in the matrix,the more passageways provided for ion movement.Thus the specific capacitance of structural super capacitor is mainly affected by the porosity and pore connectivity of structural electrolyte.Furthermore,the specific capacitance  of the structural super capacitor reaches to 41% of solid state super capacitor  under the same test conditions,which is promising to develop structural electrolyte combining magnesium phosphate with KOH aqueous.Fig.9c shows the Nyquist plots of structural super capacitors with various contents of hemp fiber.The nearly vertical line in the low frequency region is a result of ion diffusion in the electrolyte to the electrode surface,signifying an ideal capacitive behavior and the high frequency region represents an arc-like shape.The internal resistance Rs of the structural super capacitor can be obtained from Nyquist curves by the intercept at real part of horizontal axis.The charge transfer resistance Rct at the electrolyte/electrode interface is represented by the arc formed in a high frequency region.Seen from Fig.9d,as the volume fraction of hemp fiber increases from 5 vol% to 20 vol%,the curve trend of Rs and Rct are negatively related with that of porosity and pore connectivity in structural electrolyte.In addition,as the content of hemp fiber increases to 5 vol%,Rs of the structural super capacitor sharply reduces from 40.2 Ω to 17.4 Ω and Rct decreases from 21.2 to 4.4 Ω due to the strong absorption capacity of hemp fiber for aqueous electrolyte.Thus the internal resistance Rs and charge transfer resistance Rct are mainly affected by absorption capacity of hemp fiber to aqueous electrolyte when small content of hemp fiber is added,yet they are mainly affected by the porosity and pore connectivity of matrix when larger content of hemp fiber is added.Low Rct value of the structural super capacitor reflects the improved transfer mechanism at the interface of electrode/electrolyte.

Therefore,structural super capacitors in this work show better electrochemical performance than that of epoxy system.The long-term cycling stability of the structural super capacitor is evaluated by CV method with a scan rate of 100 mV·s−1 for 2000 cycles.From Fig.10,the specific capacitance of the structural super capacitors with 0 vol% and 15 vol% of hemp fiber retain about 92.2% and 88.2% after 2000 cycles,respectively.The cycling stability of the structural super capacitor slightly decreases after adding 15 vol% of hemp fiber,which is due to the increase of pore structure of the structural electrolyte.It can be concluded that the structural super capacitors in this work have good cycling stability during long-term charge discharge processes.Fig.11a depicted the compressive strength of structural super capacitors with various contents of hemp fiber.It is seen that an increase in the content of hemp fiber causes a gradual reduction in compressive strength of structural super capacitor.Although hemp fiber has been used to enhance the mechanical properties of cement pastes,it has been reported that hemp fiber has a negative effect on the compressive strength of cement matrix,even a small content.In general,high porosity of structural electrolyte can reduce the compressive strength of structural super capacitor,but it is not the only factor.Except for porosity,there are still many reasons for the reduction in compressive of structural super capacitor,such as disorganized arrangement of fiber,agglomeration of fiber and surface interactions between matrix and fiber.To analyze multifunctional properties of the structural super capacitor,two performance parameters are employed in this work,specific capacitance and compressive strength.However,as the mechanical performance and ion conductivity are in a trade-off relationship,an ideal structural super capacitor is designed in this work.The ideal structural super capacitor exhibits the highest values of the two parameters among all the samples,with a compressive strength of 24.1 MPa and a specific capacitance of 51.4 F·g−1.Fig.11b presents the multi-functionality of structural super capacitors with various contents of hemp fiber.It is known that the shorter the distance of scatter to the ideal point,the closer to the ideal structural super capacitor.As the content of hemp fiber increases from 5 vol% to 15 vol%,multi-functionality of the structural super capacitor gradually increases.Nevertheless,as the content of hemp fiber is smaller than 5 vol% or N15 vol%,the multi-functionality of structural super capacitor decreases with the increasing content of hemp fiber.It can be inferred that the multifunctional properties of the structural super capacitor is mainly affected by the porosity and pore connectivity of structural electrolyte.Lots of pore structure causing by adding large content of hemp fiber result in low compressive strength of structural super capacitor,yet such pore structure are beneficial to improve electrochemical properties of structural super capacitor.Moreover,when specific capacitance and compressive strength are combined for evaluation of structural super capacitor,cannabis grow system the porosity and pore connectivity are positively correlated with its multi-functionality.

The sample containing 15 vol% of hemp fiber appears for the optimum balance,displaying a specific capacitance of 51.4 F·g−1 and a compressive strength of 13.2 MPa.The comparison of this study with other relevant structural super capacitors is listed in Table 3.It can be seen that the structural super capacitor with 15 vol% of hemp fiber in this work shows good electrochemical and mechanical properties.In fact,perfect performance of structural super capacitor is still difficult to achieve,but this work is highly encouraging to improve the multi-functionality of structural super capacitor by developing pore structure of structure electrolyte with hemp fiber.Hemp   is one of the plants domesticated and used by humans.This important natural bast fiber crop originated from the central Asia and is belonging to the genus Cannabis,in the family of Cannabiaceae.Hemp is extensively used for paper,textiles,food,medicine,synthetic plastics,and fiberglass production.According to its usage,hemp can be divided into three types,seed hemp,industrial hemp,and drug hemp.For seed hemp,the seeds can generate oil rich in omega-3 and omega-6 polyunsaturated fatty acids that are useful in treating atopic dermatitis symptoms.For industrial hemp,the bast fiber of hemp is widely used in garment production as an environmentally friendly raw material because of its excellent features including biodegradable,heat resistance,softness,and fitness.Also,hemp has a great value in the production of cosmetics and building materials.Because of these significance aspects,hemp has received much considerations from plant breeders in the recent years.As one of the largest transcription factor families in plants,WRKY gene family is widely distributed and is an important part of plant transcription regulation and signal transduction.It regulates the expression of related genes by combining cis-elements or interacting with other regulatory factors,thereby playing an important role in plant growth and development,defense against abiotic stresses,and other biological processes.All known WRKY proteins contain at least one DNA binding domain of about 60 amino acids residues,a highly conserved WRKYGQK heptapeptide at the N-terminus,and a C2H2 or C2HC zinc finger motif at the C-terminus.WRKY proteins can be classified into three groups  based on the number of the conserved WRKY domains and the type of zinc finger structure,and group II was further divided into five subgroups.Previous studies have shown that WRKY genes in group I exist not only in higher plants but also in ferns while group III WRKY genes only exists in higher plants and responds to abiotic stress.WRKY proteins usually preferentially recognizing and binding the W-box cis-element of the target gene to regulate gene expression,respond to environmental stresses,and regulate plant growth and development.The first WRKY gene  was cloned in sweet potato and then identified in Arabidopsis,corn,rice,rapeseed,potato,tomato,cotton,cucumber  and other plants.Previous studies have demonstrated that WRKY transcription factors play a vital role in response to biological/abiotic stress and plant development.In Arabidopsis,WRKY8 and WRKY75 regulate salt tolerance,while multiple WRKY genes  participate in drought stress response through different signaling pathways.In rice,over-expression of OsWRKY53 can promote cellulose synthesis in leaves,WRKY47 and WRKY80 participate in drought stress,while OsWRKY11 over-expression can improve the tolerance of high-temperature stress,and OsWRKY31 is also found to be related to lateral root growth.In addition,recent studies showed that the expression patterns of VviWRKY40 and VviGT14 are negatively correlated with that in grapefruits.