Enhancement of anaerobic digestion operational efficiency for guar gum production wastewater using a microaerobic-biochar coupled system

The 1，2-propanediol in guar gum production wastewater tends to trigger propionate accumulation during traditional anaerobic treatment， leading to microbial activity inhibition. Microaerobic conditions can create a favorable environment for fermentative bacteria metabolism and promote the conversion of organic substrates. Biochar can facilitate the formation of anaerobic microbial aggregates and enhance the oxygen tolerance of anaerobic microorganisms. In this study， actual guar gum production wastewater was used as the research object， and a blank control group， an anaerobic group， and a microaerobic-biochar coupled （O2/BC） group were set up to investigate the operational efficiency of anaerobic digestion under the microaerobic-biochar coupled system. The results showed that through the regulation of micro-aeration ［0.2 mL/（g VS·d）］ and biochar dosage （15 g/L）， efficient wastewater treatment was achieved under mesophilic （37 ℃） conditions， with a COD removal efficiency reaching 90%， which was 10.6% higher than that of the anaerobic control group. The effluent COD concentration and propionate concentration were reduced to 3800 mg/L and 0.15 g/L， respectively， representing decreases of 49.6% and 98.4% compared to the anaerobic control group. The biogas production was 1.64 times that of the anaerobic control group， with the maximum methane concentration reaching 77.2%. Fourier transform infrared spectroscopy （FT-IR） revealed that the quantities of —OH， —CH2— and C—O functional groups on the surface of the sludge increased significantly， revealing the enhanced adsorption effect of biochar on microorganisms. Scanning electron microscopy （SEM） observations showed that the microaerobic-biochar coupled system formed dense microbial aggregates dominated by long bacilli， which were significantly different from traditional anaerobic sludge. The analysis of the microbial community composition revealed that the microaerobic-biochar coupled condition increased the abundance of Clostridium and Comamonas species， thereby modulating the propionate-to-acetate ratio and thus enhancing the efficiency of complex organic matter degradation.