Method and principle of sewage treatment

In the process of sewage biochemical treatment, the factors affecting microbial activity can be divided into two categories: substrate and environment:

The matrix includes nutrients, such as organic compounds dominated by carbon, namely nutrients such as carbon source material, nitrogen source and phosphorus source, and trace elements such as iron, zinc and manganese; In addition, it also includes some toxic and harmful chemicals such as phenols, benzene and other compounds, as well as some heavy metal ions such as copper, cadmium, lead ions and so on.

Environmental factors mainly include:

(1) Temperature. The influence of temperature on microorganisms is very extensive, although some types of bacteria are also active in high temperature environments (50 ° C ~ 70 ° C) and low temperature environments (-5 ~ 0 ° C), the most suitable temperature range for the growth of most microorganisms in sewage treatment is 20-30 ° C. In the appropriate temperature range, the physiological activity of the microorganism is vigorous, and its activity is enhanced with the increase of temperature, and the treatment effect is better. Beyond this range, the activity of microorganisms becomes worse, and the biological reaction process will be affected. In general, the maximum and minimum limits for controlling the reaction process are 35 ° C and 10 ° C respectively.

(2) The bacterial micelle disintegrated, and 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 mixture. When the dissolved oxygen in the environment is higher than 0.3mg/l, both facultative and aerobic bacteria perform aerobic respiration. When the dissolved oxygen is less than 0.2-0.3mg/l and close to zero, the facultative bacteria are transferred to anaerobic respiration, most of the aerobic bacteria basically stop breathing, and some aerobic bacteria (most of them are filamentous bacteria) may also grow well, which often leads to sludge swelling after dominating the system. In general, the dissolved oxygen at the outlet of the aeration tank is appropriate to maintain about 2mg/l, and too high will increase energy consumption, which is economically uneconomical.

Among all the influencing factors, matrix factors and PH value are determined by the influent water quality, and the control of these factors mainly depends on daily monitoring and the strict implementation of relevant regulations and regulations. For the general municipal sewage, most of these factors will not constitute too much impact, and the parameters can be basically maintained within the appropriate range. The change of temperature is related to the climate, and it is difficult to control the temperature for the 10,000-ton municipal sewage treatment plant, especially when the activated sludge process is used, and it is not very feasible economically and engineering. Therefore, it is generally through the appropriate selection of design parameters to meet the processing requirements of different temperature changes in order to achieve the processing target. Therefore, the main goal of process control falls on the activated sludge itself and the environmental factors that can be changed by regulatory means, and 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 stable role.

The key to the process control of biological reaction system is the selection of control objects or control parameters, which is closely related to the processing technology or processing target.

As mentioned above, dissolved oxygen is a very important indicator parameter in the type and process of biological reaction, which can intuitively and quickly reflect the operation of the entire system, convenient operation and management, and simple installation and maintenance of instruments and meters, which is also the reason why the newly built sewage treatment plants in China have basically realized on-site and online monitoring of dissolved oxygen in the past decade.

Precipitation filtration

The purpose of sediment filtration is to remove suspended particulate matter or colloidal matter from the water source. These particulate matter, if not removed, can cause damage to other sophisticated filtration membranes used in dialysis water or even block waterways. This is the oldest and simplest water purification method, so this step is commonly used in the preliminary treatment of water purification, or if necessary, several more filters will be added to the pipeline to remove larger impurities. There are many types of filters used to filter suspended particulate matter, such as mesh filters, sand filters (such as quartz sand, etc.) or membrane filters. As long as the particle size is larger than the size of these holes, it will be blocked down. For ions dissolved in water, there's no stopping them. If the filter is not replaced or cleaned for too long, more and more particulate matter will accumulate on the filter, and the water flow and pressure will gradually decrease. People use the difference between the inlet water pressure and the outlet water pressure to determine the degree of blockage of the filter. Therefore, the filter should be timed to reverse to eliminate impurities accumulated on it, and the filter should be replaced within a fixed time.