Performance of coagulant-aided biomass filtration to protect ultrafiltration from membrane fouling in biogas slurry concentration

This study investigated the performance of a novel coagulant-aided biomass filtration for rapid pretreatment of biogas slurry to prevent subsequent membrane concentration from severe fouling for maximum resource recovery. Potassium aluminum sulfate (PAS) and chitosan were used as representative inorganic and organic coagulant, respectively. Cornstalk was used as the biomass media. Results show that blending PAS with cornstalk as filtration media could increase the removal of suspended solids (SS), organic matter, and nutrients from biogas slurry in comparison with single PAS coagulation or cornstalk filtration. Thus, PAS-aided cornstalk filtration could significantly reduce membrane fouling to double water flux in subsequent ultrafiltration of biogas slurry. Compared to PAS, chitosan with polyacrylamide led to more SS sedimentation in coagulation of biogas slurry. Nevertheless, chitosan has low dissolution and could be flushed to permeate when mixed with cornstalk to compromise the filtration performance. After biogas slurry pretreatment, the spent PAS-aided cornstalk was highly compostable with rapid temperature increase to above 60 °C within three days. Heavy metals and antibiotics retained from biogas slurry could be effectively passivated and removed in composting, respectively. As such, spent PAS-aided cornstalk media could be transformed to mature compost with seed germination index of >120%.