Production of acetic acid from thermally treated sewage sludge in an upflow anaerobic reactor

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This research project demonstrates the potential for converting the materials present in partially digested sewage sludge to acetic acid for environmental protection purposes, e.g. use in production of calcium magnesium acetate for road deciding salt or scrubbing sulfur dioxide from atmospheric emissions to prevent acid rain problems. Thermal treatment at 121°C for diluted sewage sludge (5:1) in 0.1 N Ca(OH) 2 proved to be successful for solubilizing the suspended volatile solids in the digested sewage sludge. The reduction of such solids reached 57% on a dry weight basis. The more soluble sewage sludge could then be treated in a flow-through, low hydraulic retention time, packed column anaerobic reactor to produce acetic acid. The laboratory pilot process first involved suppressing the methane producing bacteria using 0.0005 N bromo ethane sulfonic acid (BES), then feeding the 2.5-1 up-flow anaerobic reactor with thermally conditioned sludge broth in batch and then in continuous feed modes operated at hydraulic retention times of 24, 8 and 4 h. The effluent was monitored for acetic acid production, COD destruction, pH, alkalinity, ammonia, and total nitrogen. Electron scanning microscope photographs were taken to examine the attachment of the acid producing bacteria to the support media. The efficiency of the production of total volatile fatty acids (TVFA) from the treated sewage sludge was 80, 87 and 90% of the theoretical bioconversion possible based on the amount of COD reduced (40–62%). Acetic acid was the major volatile acid form produced.