Recovery of sludge humic acids with alkaline pretreatment and its impact on subsequent anaerobic digestion

摘要

Sludge humic and fulvic acids (HAs and FAs) can be utilized as a source of organic fertilizer. After alkaline sludge pretreatment, recovery of HAs and FAs and the impact on subsequent anaerobic digestion were studied. RESULTS: Total content of HAs and FAs in the raw sludge was 112.5mg g-1 total solids, and HAs constituted the major fraction. After the raw sludge was disintegrated with NaOH, an ultrafiltration membrane with a molecular weight cut-off of 30 000 D was chosen for humic recovery from the alkaline lysate. 22.9% of HAs and FAs in the raw sludge were recovered and their total concentration was 4083mgL~(-1) in the retentate. HAs and FAs provided 30% of the organic carbon in the recovered retentate, which could be processed for humic fertilizer together with the other co-recovered macromolecular organic substances. After alkaline pretreatment and humic recovery, the biogas yield increased by 29.4-49.2% during subsequent sludge anaerobic digestion. Due to the recovery of humic substances and the enhanced organic biodegradation, the removal rate of sludge volatile solids was improved by about 70% compared with the control. CONCLUSION: HAs, FAs and other macromolecular organic substances can be recovered from sludge by alkaline pretreatment and ultrafiltration separation, and subsequent anaerobic digestion improved significantly.