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This post was last edited by yinkuilin6868 on 2015-11-23 08:26. The anaerobic process can generally be divided into the hydrolysis stage, the acidification stage, and the methanation stage. Through research and engineering practice, it has been shown that by controlling the anaerobic process at the hydrolysis and acidification stages, a high removal rate of suspended solids can be achieved in a short time under relatively high loads. Moreover, complex organic macromolecules that are difficult to degrade can be broken down into simpler organic molecules that are easier to degrade, thereby **improving the biodegradability and solubility of wastewater. Unlike anaerobic treatment processes, the hydrolysis-acidification process does not require sealed tanks nor complex three-phase separators. The effluent lacks the unpleasant odors associated with anaerobic fermentation, so it does not affect the environment around the wastewater treatment plant. Additionally, it has the advantage of lower energy consumption compared to aerobic processes. In recent years, with the rapid development of the dye and dye auxiliary industry and the widespread use of biodegradably difficult dyes and auxiliaries, the biodegradability of printing and dyeing wastewater has become increasingly poor. As a result, the hydrolysis-acidification process has been widely adopted in the treatment of printing and dyeing wastewater. The hydrolysis-acidification process is widely used in the treatment of printing and dyeing wastewater, with different hydraulic retention times and water distribution methods employed depending on the characteristics of the wastewater. Summarizing our existing engineering experience, the effectiveness of hydrolytic acidification depends on: ① sufficient sludge concentration, ② good mixing of sludge and water, ③ adequate hydraulic retention time for the wastewater, and ④ an appropriate method for retaining the sludge. During the operation of wastewater treatment plants, with constant sludge concentration and hydraulic retention time, the mixing of sludge and water as well as the retention of sludge determine the effectiveness of the hydrolysis-acidification treatment. The hydrolysis-acidification process can employ stirring mechanisms to promote mixing of sludge and water, thereby achieving good mixing throughout the tank. However, this requires additional stirring equipment. Moreover, a sedimentation tank and an anaerobic sludge return system are needed for the effluent in order to maintain the sludge concentration in the hydrolysis-acidification tank; such measures increase the project cost and also expand the required floor space. In the hydrolysis-acidification process, multi-point water inlet methods are also employed, but this often leads to poor distribution of water and inadequate mixing of sludge and water. Over time, the anaerobic sludge, which is difficult to stir, tends to settle in certain areas at the bottom of the tank, resulting in short-circuits in the water flow from the water inlet to the outlet. As a result, the capacity of the hydrolysis-acidification tank cannot be fully utilized, and the actual hydraulic retention time is **less than the theoretical hydraulic retention time; consequently, it is difficult to achieve good results with this process. This is also the reason why many current hydrolytic acidification treatment processes fail. In the hydrolysis-acidification process, a upflow hydrolysis sludge bed reactor is used; the wastewater is evenly distributed across the bottom of the tank, enabling good mixing between the sludge and water as well as efficient biochemical reactions. As the wastewater rises, it passes through the entire sludge layer, resulting in separation of the sludge from the water. The supernatant then flows out through a collection tank and enters the subsequent aerobic treatment stage. The uniformity of water distribution and the mixing of sludge and water are controlled by a pulse water distributor. Water first enters this distributor, where it is stored for 3–5 minutes; thereafter, a siphonic pulse is generated automatically. The water within the distributor is distributed evenly across the bottom of the tank within about ten seconds, through a fan-shaped pipeline system. The flow rate at the outlets of the distribution holes in these fan-shaped pipes is greater than 2 meters per second. As a result, the sludge and water at the bottom of the tank mix vigorously, ensuring thorough reaction. The pH value of wastewater treated by hydrolytic acidification can be reduced from 10 to around 8, and the color intensity of some printing and dyeing wastewaters (such as those containing reactive red) can be reduced by 70%–80%. An effective hydrolysis-acidification treatment process can **improve the biodegradability of wastewater, thereby enhancing the removal efficiency in subsequent aerobic treatments; it is an important measure to ensure that the water quality meets the required standards in the entire wastewater treatment process.