Performance of direct anaerobic digestion of dewatered sludge in long-term operation

Direct anaerobic digestion of dewatered sludge with total solids (TS) content of 15–20% was tested in a horizontal digester for one and half years. The system kept stable with pH 7–8. The concentration of volatile fatty acids was lower than 800 mg/L, free ammonia nitrogen was lower than 200 mg/L, and total alkalinity kept higher than 6000 mg/L. The performance was influenced by organic load rate (OLR) and organic content in feed sludge. When...