The influencing factors of sludge anaerobic digestion are briefly described, and how to operate it is explained.

Under the condition of oxygen isolation, the organic matter in sludge is first metabolized by saprophytic bacteria into organic acids, and then anaerobic methanogens degrade the organic acids into methane and carbon dioxide. The progress of the process depends on the cooperation of these two bacteria. The growth conditions of methanogens are extremely strict. Organic acids produced by saprophytic bacteria must be degraded in time. If they accumulate, once the pH value is lower than 6.5, the growth of methanogens will be restricted, the balance will be destroyed and the digestion time will be greatly prolonged. Generally, the normal process is maintained by stirring the sludge (making it uniform) and controlling the organic acid and alkalinity. The organic acid (calculated by acetic acid) should be controlled below 1000 mg/L, and the process will be affected when it is around 2000 mg/L, and the alkalinity (calculated by calcium carbonate) should be controlled above 2000 mg/L. When the organic acid has an upward trend, the feeding (raw sludge) should be stopped immediately. Lime can be added when the alkalinity is insufficient. Temperature is also an important growth factor. The process can be carried out at 33 ~ 35℃ (medium temperature digestion) or 50 ~ 56℃ (high temperature digestion). Moderate temperature digestion is usually used. Digestion time varies with stirring; When fully stirred (called high-load sludge digestion), it is often less than 15 days; Without stirring (called traditional sludge digestion), it usually takes 30 ~ 60 days. High temperature digestion is often fully stirred, and the digestion time is about 6 ~ 10 day. The gas production rate is high, which can kill more than 90% of parasite eggs, but it consumes a lot of heat and energy.