Active sludge is a general term for microbial populations and the organic and inorganic substances to which they belong. It was discovered in 1912 by Clark and Gage in the United Kingdom. Activated sludge can be classified into aerobic activated sludge. And anaerobic granular activated sludge, activated sludge is mainly used to treat sewage wastewater. The activated sludge process is a kind of aerobic treatment method for treating organic sewage by using suspended microbial flocs.

Complex microbes in activated sludge and organic nutrients in wastewater form a complex food chain.
The first to carry out the purification task are the oxygen-producing bacteria and the saprophytic fungi. The bacteria, especially the globular bacteria, play the most important role. The activated sludge with excellent function is a fungal group composed of globular bacteria with filamentous bacteria as the skeleton. The sedimentation is good. With the normal operation of the activated sludge, the bacteria multiply and begin to grow protozoa, which is a predator of bacteria.

Common protozoans of activated sludge are flagellates, meat caterpillars, ciliates and pipeworms. When the activated sludge matures, the ciliate and the bell worm are dominant;

The metazoan is a secondary predator of bacteria. For example, rotifers, nematodes, etc. can only appear when the dissolved oxygen is sufficient, so when the metazoan occurs, the water quality improvement indicator is treated.

Performance indicators include: mixed liquid suspended solids (MLSS), sludge settling ratio (SV), sludge index [sludge volume index (SVI), sludge density index (SDI).

How to cultivate activated sludge in the water treatment section?

The sewage treatment plant is based on the preliminary acceptance of the unit test and the linkage test. The quality and quantity of sewage entering the water can meet the requirements of the initial operation, and the trial operation can be carried out. First, it is necessary to cultivate activated sludge, which is usually directly cultured through sewage.

After the urban sewage is introduced into the aeration tank, the water is suspended and aeration is performed. When the water temperature and temperature are suitable, flocs will appear in 1~2 days. At this time, a small amount of continuous water can be introduced, or intermittent water can be introduced continuously for continuous aeration. After one week of continuous aeration, the microscopic examination shows that the growth of the fungus can be gradually increased from small to large to the design amount, and put into trial operation.

If the nutrition is insufficient, some feces, nitrogen and phosphorus-rich waste liquid from the food processing industry, and rice bran water in the restaurant can be added to increase the speed of cultivation.

Also note that in the early stage of culture, because aerobic bacteria are not formed in large quantities, the amount of aeration should be controlled to avoid aging of aerobic bacteria.

How to cultivate anaerobic sludge in the sludge treatment section?

Large and medium-sized sewage treatment plants generally have good residual sludge after the water treatment section is normal, and it is more advantageous to cultivate anaerobic sludge.

First, the digester is filled with secondary effluent, and the anaerobic sludge strains of other digester are added, or the excess sludge of the water treatment section is connected.

In the place where the source of digested sludge is lacking, organic waste such as human feces, cow dung, pig dressing, distiller’s grains, and remaining starch may be diluted to a nitrification tank with a solid content of 1% to 3%.

When cultivating digestive sludge bacteria, it is necessary to control the pH value and the organic matter dosing load, and the pH should be maintained between 6.4 and 7.8. The organic load is controlled below 0.5 kg VSS / (m3 • d). Too high a loading load will result in a large accumulation of volatile fatty acids, a decrease in pH, and a too long acid decay phase, thereby prolonging the incubation time.

Stir the mixed sludge in the digester thoroughly. At medium temperature digestion, the water temperature in the digester should be kept at 35 °C ± 2 °C, and heated while entering the mud. After adding to the required temperature and mixing, the mud is suspended. After the anaerobic digestion and normal production of gas, the amount of mud can be increased one by one until the normal mud is added.

Analyze the biogas composition daily. When the required data is normal, take the sample for ignition test (pay attention to fire prevention and explosion protection) before the biogas utilization work can be formally carried out.

What should I pay attention to during the test run?

When the activated sludge is successfully cultured, the sewage treatment plant can be put into trial operation. The amount of water for the test run can be arranged according to the incoming water condition. Generally, when the test run is started, it runs according to half of the design amount, and when it is normal, it is put into the other half of the test run.

In order to determine the optimum process operating conditions during the test run, the main factors considered as variables are the temperature, pH, conductivity of the sewage, dissolved oxygen and sludge concentration in the aeration tank, mud temperature in the digester, pH値, and heated sludge system. The operation, the operation of the biogas cabinet, and the operation of the dehydrator.

The important parameters of the activated sludge process, BOD5, CODcr, MLSS, MLVSS, ammonia nitrogen, total phosphorus, etc., need to be monitored daily by the laboratory to adjust the process parameters. SV, SVI, microscopic examination, can be tested several times per day according to actual needs, and the process can be adjusted at any time.

Sewage treatment and sludge treatment should be controlled and adjusted in the trial operation stage. The control and observation, recording and analysis of the sludge should be carried out, and the sewage treatment volume, sludge treatment volume, sludge production, Biogas production, chemical consumption, production electricity consumption, and tap water consumption should be recorded in detail. Adequate analytical data should be provided for the quality of the influent and effluent, the aerobic sludge index, the anaerobic activated sludge index, the dewatered sludge index, and the biogas composition, so as to improve the quality of the sewage treatment.