Switchgrass and Giant Reed Energy Potential when Cultivated in Heavy Metals Contaminated Soils

The cultivation of energy crops on degraded soils contributes to reduce the risks associated with land use change, and the biomass may represent an additional revenue as a feedstock for bioenergy. Switchgrass and giant reed were tested under 300 and 600 mg Cr kg−1, 110 and 220 mg Ni kg−1, and 4 and 8 mg Cd kg−1 contaminated soils, in a two year pot experiment. Switchgrass yields (average aerial 330 g.m−2 and below ground 430 g.m−2), after the second year harvest, were not affected by Cd contamination and 110 mg Ni kg−1, but 220 mg Ni kg−1 significantly affected the yields (55–60% reduction). A total plant loss was observed in Cr-contaminated pots. Giant reed aboveground yields (control: 410 g.m−2), in the second year harvest, were significantly affected by all metals and levels of contamination (30–70% reduction), except in 110 mg Ni kg−1 pots. The belowground biomass yields (average 1600 g.m−2) were not affected by the tested metals. Contamination did not affect the high heating value (HHV) of switchgrass (average 18.4 MJ.kg−1) and giant reed aerial fractions (average 18.9 MJ.kg−1, stems, and 18.1 MJ.kg−1, leaves), harvested in the second year, indicating that the biomass can be exploited for bioenergy

Development and Characterization of Na₂CO₃-Activated Mozambican Bentonite: Prediction of Optimal Activation Conditions Using Statistical Design Modeling

A calcium bentonite clay from Boane region (Mozambique) was subjected to an Na2CO3 activation process. The methylene blue test together with energy-dispersive X-ray spectroscopy (EDX) analysis indicated the successful ion exchange of Ca2+ by Na+ ions since the cation exchange capacity (CEC) increased from 67.5 to 74 meq/100 g and the Na/Ca ratio from 2.91 up to 15.8, as the concentration of Na2CO3, activation temperature, and activation time were varied from 2 to 6 wt.%, from 25 to 65 °C, and from 2 to 4 h, respectively. However, the increase in the CEC did not follow the same trend as the increase in the Na/Ca ratio, and for the case of Na2CO3 concentration, the increase in the CEC was limited. The X-ray diffraction (XRD) patterns also confirmed that Ca-rich bentonite was effectively modified into Na-bentonite since after the activation, the d(001) decreased from 1.52 nm to 1.30 nm. The statistical design of the experiments showed that as well as the time and the temperature × time linear interactive effect, all the other independent factors and their interactive effects had a significant influence on the CEC. The response surface methodology (RSM) indicated that higher values of the CEC can be obtained under the optimal activation conditions of 4 wt.% Na2CO3, at a temperature of 45 °C, and with an activation time of 3 h. A statistical model was used to predict the CEC, and the R2 value was 0.99529, which denotes a satisfactory result in predicting the CEC

Development and Characterization of Na2CO3-Activated Mozambican Bentonite: Prediction of Optimal Activation Conditions Using Statistical Design Modeling

A calcium bentonite clay from Boane region (Mozambique) was subjected to an Na2CO3 activation process. The methylene blue test together with energy-dispersive X-ray spectroscopy (EDX) analysis indicated the successful ion exchange of Ca2+ by Na+ ions since the cation exchange capacity (CEC) increased from 67.5 to 74 meq/100 g and the Na/Ca ratio from 2.91 up to 15.8, as the concentration of Na2CO3, activation temperature, and activation time were varied from 2 to 6 wt.%, from 25 to 65 °C, and from 2 to 4 h, respectively. However, the increase in the CEC did not follow the same trend as the increase in the Na/Ca ratio, and for the case of Na2CO3 concentration, the increase in the CEC was limited. The X-ray diffraction (XRD) patterns also confirmed that Ca-rich bentonite was effectively modified into Na-bentonite since after the activation, the d(001) decreased from 1.52 nm to 1.30 nm. The statistical design of the experiments showed that as well as the time and the temperature × time linear interactive effect, all the other independent factors and their interactive effects had a significant influence on the CEC. The response surface methodology (RSM) indicated that higher values of the CEC can be obtained under the optimal activation conditions of 4 wt.% Na2CO3, at a temperature of 45 °C, and with an activation time of 3 h. A statistical model was used to predict the CEC, and the R2 value was 0.99529, which denotes a satisfactory result in predicting the CEC

Comparing the growth and yield of kenaf (Hibiscus cannabinus L.) produced in two different climatic types in soils contaminated by zinc, copper, chromium and lead

Soil is an important natural resource for agriculture and deserves special attention to possible problems that may arise. Heavy metal contamination of the soil can cause serious problems for the ecosystem in general, with consequent impact on water resources, soil quality, crop yield and human health due to the potential for heavy metal bioaccumulation in the different trophic levels of the food chain. Remediation of heavy metal contamination in soils can be done by using crops that have potential of growth and biomass production in marginal soils. The main objective of this work was to compare the growth and biomass production of Kenaf (cultivar H328, developed by IBFC in China) in soils contaminated by zinc (Zn), copper (Cu), chromium (Cr) and lead (Pb) in two different climate types (Tropical climate and Mediterranean climate). The study was performed in a pot essay and the plants were tested in clay soils. The soils were artificially contaminated, and the concentrations chosen were based on the limits established by the Decree Law 276 of 2009 (Portuguese regulation that establishes the regime for the use of sewage sludge in agricultural soils) - Zn: 450 mg/kg; Cr: 300 mg/kg; Pb: 450 mg/kg and Cu: 200 mg/kg. Results indicate that the growth in Mediterranean climate contaminated soils was more affected than in tropical climate. On average, the yields in Mozambique were 4900 g/m2, and in Portugal, merely 107 g/m2. Characterization of biomass indicate that kenaf can phytoextract zinc, copper, chromium, and not so much lead

Phytoremediation potential of the perennial crops giant reed and switchgrass to soils contaminated with heavy metals

Among the various impacts caused by man to the environment, soil contamination deserves attention. This gives rise to a number of environmental problems such as desertification, contamination of water resources and contamination of food crops, which can lead to serious health problems for humans directly or indirectly. To avoid these situations, it is necessary to decontaminate the soils, which can occur through various techniques (physical, chemical and biological methods). The use of plants for the decontamination of soils (phytoremediation), and specifically the use of energy crops, is an interesting alternative. Along with the decontamination action, the biomass produced may provide an additional income, when used for bioenergy or biomaterials, and the process contributes to the bioeconomy by reducing the dependence on fossil fuels. Therefore, the aim of this work was to study the effects of different heavy metals (Zn, Cr, Pb, Cd, Ni, Cu) on giant reed (Arundo donax L.) and switchgrass (Panicum virgatum L.) growth, productivity and biomass quality. The soils were artificially contaminated and the concentrations chosen were based on the limits established by the Decree Law 276 of 2009 (Portuguese regulation that establishes the regime for the use of sewage sludge in agricultural soils)-Zn: 450 mg/kg; Cr: 300 mg/kg; Pb: 450 mg/kg; Cd: 4 mg/kg; Ni: 110 mg/kg and Cu: 200 mg/kg. Results indicate that both switchgrass and giant reed are crops tolerant to Zn and Pb contamination. In contrast, for both crops, in Cr contaminated soils, a significant decrease in productivity was noted. Switchgrass was unable to grown in the Cr contaminated soils. Cadmium, nickel and copper also affected the yields of both crops, but not so significantly as chromium. In this establishment year, giant reed was three times more productive than switchgrass, and therefore showed to be more promising in heavy metals contaminated soils. Biomass is being characterized to evaluate the phytoremediation ability of both crops to the heavy metals studied

Understanding the potential of kenaf in heavy metals contaminated soils

The increasing demand for biomass for the production of bioenergy is generating land-use conflicts which might be avoided through the establishment of dedicated energy crops on marginal land, e.g. heavy-metal contaminated land. Yet, heavy metals contaminated soils might induce the reduction of crop yields and the quality of agricultural products, desertification, and the loss of ecosystem services. Therefore, assessment of bioenergy from marginal land should take into account constraining factors, such as productivity and biomass quality. Hence, the aim of this work was to study the effects of soils contaminated with heavy metals (Chromium, Copper, Lead and Zinc) on growth and productivity of kenaf. The study was performed in a pot essay and the plants were tested in sandy soils and clay soils. The soils were artificially contaminated, and the concentrations chosen were based on the limits established by the Decree Law 276 of 2009 (Portuguese regulation that establishes the regime for the use of sewage sludge in agricultural soils)-Zn: 450 mg/kg; Cr: 300 mg/kg; Pb: 450 mg/kg and Cu: 200 mg/kg. Results indicate that all the contaminated soils affected the growth and yields of kenaf. Highest yield reduction was observed in sandy contaminated soils than in clay contaminated soils, although this trend was not statistically significant. Copper was the metal that affected most yields and growth of kenaf in clay soils. In sandy soils, it was chromium that affected most, yields and growth of kenaf. Overall, yield reduction due to heavy metals contamination was above 50%, which may hinder its economical exploitation. Biomass is being characterized to evaluate the phytoremediation ability of this cultivar to the heavy metals studied