At present, the treatment and disposal technology of sludge mainly refers to the processing process of thickening, regulating, dewatering, stabilizing, drying or incineration of sludge, in order to achieve reduction, stabilization, and harmless treatment of sludge. The commonly used sludge treatment and disposal technologies currently include anaerobic digestion technology, aerobic fermentation technology, deep dehydration technology, thermal drying technology, lime stabilization technology, and incineration technology. Anaerobic digestion technology Anaerobic digestion of sludge refers to the process in which facultative and anaerobic bacteria decompose biodegradable organic matter in sludge into carbon dioxide, methane, and water under anaerobic conditions, resulting in stable sludge. It is one of the commonly used methods for sludge reduction and stabilization. Anaerobic digestion of sludge has advantages such as reducing sludge volume, stabilizing sludge properties, and producing methane gas. Traditional anaerobic digestion of sludge has the disadvantages of slow reaction, low organic matter degradation rate, and low methane production, which limits the advantages of anaerobic digestion technology. According to Bryant's three-stage theory, hydrolysis is the rate limiting step in the anaerobic digestion process of sludge. Therefore, since the 1970s, research has been conducted on various physical and chemical methods, including high-temperature hydrolysis, ultrasonic pretreatment, alkaline hydrolysis pretreatment, and ozone pretreatment, to enhance anaerobic digestion of sludge. By breaking down the cell wall of sludge, organic matter inside the cell is transferred from the solid phase to the liquid phase, promoting sludge hydrolysis and improving the anaerobic digestion efficiency of sludge. With the increasing amount of sludge in various countries and the increasing demand for energy and the quality requirements of treated sludge, some existing anaerobic sludge digestion facilities are facing expansion and renovation. The sludge pretreatment technology can improve the anaerobic digestion effect of sludge, improve the dewatering effect of sludge, and increase the biogas production. To a certain extent, it can replace the benefits brought by the expansion of digestion tanks, so it has been widely studied and applied. Among them, high-temperature hydrolysis technology is relatively mature. Currently, this technology has developed various processes such as Cambi hydrolysis, Biothelysis hydrolysis, and Monsal enzymatic hydrolysis. In recent years, it has been promoted and applied in Europe, with successful cases in Norway, the United Kingdom, and Australia. In response to the limitation of low solid content in traditional anaerobic digestion of sludge, research on anaerobic digestion technology for high solid content sludge has also become a hot topic. The advantage of anaerobic digestion of high solid sludge is that the efficiency of biogas production is higher than that of traditional anaerobic digestion. The reason is that the solid content of the incoming sludge is significantly increased, and the amount of organic matter that can be digested per unit of microbial mass in the anaerobic digestion tank is greatly increased. As a result, its gas production efficiency and treatment load are also improved. At present, various anaerobic digestion technologies for high solid sludge have been developed abroad and have been applied in practical engineering, such as Finland's HLAD process, which controls the solid content of sludge entering the pre reaction tank to be 10% -15%, and the gas production efficiency is 30% higher than traditional anaerobic digestion of sludge.
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