Evaluation of the potential of feedstock combinations and their biochars for soil amendment

One of the approaches for recycling and reusing agricultural and animal wastes is to pyrolyse the residues and subsequently use them as soil amendments. The prevalence of several feedstocks suggests that it is necessary to investigate the optimal combinations of feedstocks and pyrolysis temperature for use as soil amendments. This study was done to evaluate five combinations of raw materials (sugarcane bagasse, rice husk, cow manure and pine wood) and their biochars produced by slow pyrolysis at 300°C and 500°C for soil amendment. Several physicochemical properties (electrical conductivity (EC), pH, cation exchange capacity (CEC), total organic matter content (C) total porosity (TP), total nitrogen (N), particle density (PD) and bulk density (BD)) were investigated. Comparison among feedstocks showed that the highest PD, BD and CEC were observed in WM (cow manure-pine wood). The pyrolysis process increased the PD, TP, N and monovalent cations and decreased EC, CEC and BD. Compared to the feedstock, pyrolysis increased the N content, but higher temperatures lowered the N content. Pyrolysis at 500°C reduced the EC, N, CEC and biochar yield by 18%, 13%, 21% and 24% respectively, compared to 300°C. Pyrolysis at 500°C increased the pH, Na⁺ and K⁺ by 17%, 12% and 22%, respectively, compared to 300°C. Considering the physicochemical properties of biochar and the costs, the bagasse-wood-rice (BWR) combination and temperature of 300°C are suggested for biochar production for soil amendment.

Improving the quality of stabilization pond effluents using hybrid constructed wetlands

Water shortage and excessive use of water resources in arid and semi-arid regions, such as Iran, highlights the importance of using treated wastewater, especially for the highly demanding agricultural sector. Constructed wetlands (CWs) are among green technologies that offer an efficient and cost-effective wastewater treatment. This study investigates the complementary treatment of effluent from the Fooladshahr wastewater treatment plant, Isfahan, Iran, using pilot-scale CWs with horizontal (H-CW) and horizontal-vertical flow (HV-CW). The performance of two substrates, pumice and gravel, and the effect of using plants (Phragmites australis) was compared. Maximum removal efficiencies of total suspended solids (TSS) and biochemical oxygen demand (BOD₅) were observed in the case of unplanted and planted HV-CW with pumice bed, respectively. In the case of gravel bed, planted H-CWs demonstrated maximum chemical oxygen demand (COD) removal efficiency. The highest mean outflow concentrations for TSS, BOD₅ and COD were obtained in unplanted H-CW with pumice bed, likely due to shorter retention times compared to HV-CWs, as well as due to the absence of plants providing the required physicochemical and biological conditions for high performance treatment. Phosphate (PO₄^3-) removal efficiency demonstrated seasonal dependency, where the highest values were obtained in warm seasons. In the case of fecal coliforms (FC), no significant differences were observed between the studied HV-CWs during the whole study period. Based on our results, planted H-CW with gravel bed provided an optimum removal efficiency while requiring a smaller footprint and lower expenditure than HV-CWs. This study demonstrates the application of CWs as an affordable solution for treating domestic wastewater for various reuse application in developing countries with water crisis, such as Iran.