Biogas slurry purification-lettuce growth nexus: Nutrients absorption and pollutants removal

Graft copolymerization synthesis of chitosan-polyferric sulfate composite coagulant to improve biogas slurry treatment toward effective irrigation

Biogas slurry from anaerobic digestion of organic wastes can be a potential biofertilizer for agricultural irrigation, which however, is challenged by suspended solids and contaminants. Thus, this study synthesized a composite coagulant and optimized its performance to advance biogas slurry treatment. A natural-synthetic polymer, chitosan (CTS), was modified by 2-methacryloxyethyltrimethyl ammonium chloride (DMC) via graft copolymerization and then combined with polyferric sulfate (PFS) to formulate the composite CTS-g(DMC)-PFS coagulant. Results show that CTS-g(DMC)-PFS exhibited stronger electrical neutralization and adsorption bridging to destabilize and aggregate colloidal particles, thus, exhibiting higher removal of suspended solids, heavy metals, and antibiotics over individual and pristine coagulants. Graft copolymerization of CTS with DMC at the mass ratio of 1:9 maximized its water solubility. Further blending this mixture with PFS at the mass ratio of 1:2 effectively improved the coagulation of biogas slurry, particularly for the removal of antibiotics and heavy metals (e.g. enrofloxacin and Cu). Moreover, CTS-g(DMC)-PFS produced dense and compact flocs for effective sedimentation. Detailed characterization attributed such improvement to the hydrolysis of cationic quaternary ammonium groups on grafted monomers and further coordinative effects between CTS-g(DMC) and Fe to enhance molecular chains and positive charges in CTS-g(DMC)-PFS to facilitate particle aggregation, contaminant adsorption, and then floc sedimentation.

Synchronously degradation of biogas slurry and decarbonization of biogas using microbial fuel cells

Two-chamber microbial fuel cell (MFC) with biogas slurry (BS) of corn stover as the anode substrate and Chlorella as the cathode substrate was investigated to solve the problem of the accumulation of wastewater generated from biogas plants and to achieve low-cost separation of CO2 from biogas. A simple two-compartment MFC was constructed using biocatalysis and inexpensive materials without expensive catalysts. The performance of MFC (X1-W, Y1-W, Z1-W) with different biogas solution concentrations as anode substrate and MFC (X2-C, Y2-C, Z2-C) with Chlorella as biocathode were compared, respectively. The MFCs (Z1-W,) can start quickly and maintain a stable power production (286.82 mV ± 184.59 mV). The growth rate of Chlorella at the MFCs (X2-C, Y2-C, Z2-C) biocathode was highly coincident with the output voltage. The MFC (Z2-C) has a maximum power density of 489.7 mW/m2 when the external resistance is varied to 200 Ω. The removal rates of chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) are 93.42% and 92.59%. The maximum cell growth (Xmax) of Chlorella was 125.61 mg d-1, biomass productivity (Pmax) was 95.60 g L-1 d-1 and the maximum CO2 biofixation rate (RCO2) was 175.26 mg L-1 d-1. The microbial community analysis showed that the microorganisms in the anode solution were mainly from the biogas slurry and belonged to the hydrolytic bacteria. At the same time, the electroactive microbial community was mainly from anaerobic sludge. Therefore, MFCs can effectively degrade the organic matter in the biogas solution and generate electricity, and use Chlorella to absorb CO2 from the biogas, providing a new method for the development of biogas industry.

Concentrated biogas slurry and biogas residue can improve the yield and quality of pepper

The organic fertilizer (biogas slurry and biogas residues) was produced by the self-developed integrated device of "Pressure swirl / inclined plate sedimentation separation pretreatment (P/I) combined with ultrafiltration / reverse osmosis two stages membrane separation (UF/RO)". The paper focuses on the effect of concentrated biogas slurry and biogas residue produced by this technology on the yield and quality (vitamin C, soluble sugar, protein and nitrate content) of pepper as organic fertilizer compared with chemical fertilizer. The concentrated biogas slurry and biogas residue separated by this technology contained active substances such as N, P, K, trace elements and humic acids with stable composition and potential for good fertilization efficiency. The experiment of seed soaking for pepper sprouting confirmed the best effect of seed soaking with a concentration of 80% biogas slurry. Compared with chemical fertilizer treatment, the application of concentrated biogas slurry and biogas residue can improve the yield and quality of pepper, which is related to the nutrient elements in concentrated digestate. Meanwhile, the results of pepper cultivation trials show that the base fertilizer treatment of biogas residue is best with 2000kg/667m2 and foliar spraying of 75% biogas slurry. The results strongly demonstrate the great potential of the concentrated biogas slurry and biogas residue produced by the self-developed digestate concentration technology for pepper cultivation.