Application of automatic filter to water treatment process

Sewage treatment generally includes the following three levels of treatment: The first level of treatment is mechanical treatment through automatic filters, such as grilles, sedimentation or air flotation, to remove stones, sand, fat, and grease contained in sewage. The secondary treatment is biological treatment, the pollutants in the sewage are degraded and converted into sludge under the action of microorganisms. The tertiary treatment is the advanced treatment of sewage, which includes the removal of nutrients and the disinfection of the sewage through chlorination, ultraviolet radiation or ozone technology. Depending on the treatment goals and water quality, some sewage treatment processes do not include all the above processes.

The mechanical (first-level) treatment section includes structures such as grilles, grit tanks, and automatic filters for the purpose of removing coarse particles and suspended solids. The principle of treatment is to achieve solid-liquid separation through physical methods to remove pollutants from sewage Separation, this is a commonly used sewage treatment method. Mechanical (primary) treatment is a necessary project for all wastewater treatment processes (although some processes sometimes omit the primary sedimentation tank). The typical removal rates of BOD5 and SS in the primary treatment of municipal wastewater are 25% and 50%, respectively. In biological dephosphorization and denitrification sewage treatment plants, aerated grit tanks are generally not recommended to avoid the removal of rapid degrading organic matter; in the case of raw sewage water quality that is not conducive to dephosphorization and denitrification, whether or not the primary sedimentation is set The method needs to be carefully analyzed and considered according to the follow-up process of special injection of water quality to ensure and improve the quality of the influent water of the follow-up process such as dephosphorization and denitrification.

　　 Wastewater Biochemical Treatment

The biochemical treatment of sewage is a secondary treatment, with the main purpose of removing non-sinkable suspended solids and soluble biodegradable organic matter. Its process composition is diverse and can be divided into activated sludge method, AB method, A/O method, and A2/O Various treatment methods such as method, SBR method, oxidation ditch method, stable pond method, and land treatment method. Most urban sewage treatment plants have adopted the activated sludge method recently. The principle of biological treatment is to complete the decomposition of organic matter and the synthesis of organisms through biological action, especially the action of microorganisms, and convert organic pollutants into harmless gas products (CO2), liquid products (water) and organic-rich products. Solid product (microbial colony or biological sludge); excess biological sludge is separated in the sedimentation tank by solid-liquid separation in the sedimentation tank, and removed from the purified sewage.

　　In the process of wastewater biochemical treatment, the factors that affect microbial activity can be divided into two categories: matrix type and environmental type:

1. The matrix category includes nutrients, such as carbon-based organic compounds, namely carbon source materials, nitrogen sources, phosphorus sources and other nutrients, as well as trace elements such as iron, zinc, and manganese; in addition, it also includes some toxic and harmful chemicals Compounds such as phenols and benzene also include some heavy metal ions such as copper, cadmium, and lead ions.

　　 2. Environmental factors mainly include:

　　(1) Temperature. Temperature has a wide range of effects on microorganisms. Although certain types of bacteria are active in high temperature environments (50℃～70℃) and low temperature environments (-5～0℃), most of the microorganisms in sewage treatment are the most active. The suitable temperature range for growth is 20-30°C. In a suitable temperature range, the physiological activity of microorganisms is vigorous, and its activity increases with the increase of temperature, and the treatment effect is better. Beyond this range, the activity of microorganisms will deteriorate, and the biological reaction process will be affected. Generally, the maximum and minimum limits for controlling the progress of the reaction are 35°C and 10°C, respectively.

　　(2) PH value. The most suitable pH range of activated sludge system microorganisms is 6.5-8.5. The acidic or alkaline environment is not conducive to the survival and growth of microorganisms. In severe cases, the sludge flocs will be destroyed and the bacterial micelles will disintegrate. The treatment effect deteriorated sharply.

　　(3) Dissolved oxygen. For aerobic biological reactions, it is important to maintain a certain concentration of dissolved oxygen in the mixed solution. When the dissolved oxygen in the environment is higher than 0.3mg/l, both facultative bacteria and aerobic bacteria carry out aerobic respiration; when the dissolved oxygen is lower than 0.2-0.3mg/l close to zero, the facultative bacteria will turn into anaerobic respiration. Oxygen respiration, most aerobic bacteria basically stop respiration, and some aerobic bacteria (mostly filamentous bacteria) may also grow well, and often lead to sludge expansion after occupying an advantage in the system. Generally, the dissolved oxygen at the outlet of the aeration tank should be kept at about 2mg/l. If it is too high, it will increase energy consumption, which is not economically cost-effective.

　　Among all influencing factors, matrix factors and PH value are determined by the quality of influent water. The control of these factors mainly depends on daily monitoring and strict implementation of relevant regulations and laws. For general urban sewage, most of these factors will not have much impact, and the parameters can basically be maintained within an appropriate range. Temperature changes are related to climate. For 10,000-ton municipal sewage treatment plants, especially when activated sludge processes are used, temperature control is difficult to implement, and it is not very feasible economically and engineeringly. Therefore, it is generally through appropriate selection of design parameters to meet the processing requirements of different temperature changes in order to achieve the processing goals. Therefore, the main goal of process control falls on the activated sludge itself and the environmental factors that can be changed by regulating and controlling means. The main task of control is to take appropriate measures to overcome the influence of external factors on the activated sludge system, so that it can Continue to play a role steadily.

　　The key to achieving the process control of the biological reaction system lies in the selection of control objects or control parameters, which in turn is closely related to the treatment process or treatment goals.

As mentioned earlier, dissolved oxygen is a very important indicator parameter in the type and process of biological reactions. It can intuitively and relatively quickly reflect the operating conditions of the entire system. It is convenient for operation and management, and the installation and maintenance of instruments and meters are relatively simple. This is also the reason why my country's newly built sewage treatment plants have basically realized dissolved oxygen on-site and online monitoring in the past decade.