Basic theory of wastewater and wastewater treatment process

Specifically, in specific industries such as textile, paper and pulp, wastewater often has an average pH of 9 - 11, biochemical oxygen index (BOD), chemical oxygen (COD) up to 700mg / 1 and 2,500mg / 1, the content of suspended solids ... many times higher than the permitted level. Wastewater content of these sectors contains cyanide (CN-) up to 84 times, H2S exceeds 4.2 times, NH3 + content exceeds 84 times the permitted standard, causing pollution to surface water sources in residential areas. but not to mention industries that have heavier impacts on the environment (such as plating, steel, food production, drinking water, etc.) and domestic wastewater.

Waste water treatment is a common problem of the whole society in general and of industries in particular. Today, agencies under the Department of Natural Resources and Environment are strictly implementing methods to minimize the amount of waste caused by production.

Waste water treatment process

Wastewater from the plant's sources is directed into the receiving tank, with a coarse leaching device. The raw mud is separated from the wastewater.
After flowing through the receiving tank, waste water is passed through the fat separator (for systems where required). Wastewater is pumped, submersible sewage is pumped to fine garbage separator to separate solid waste of small size before flowing into the regulating tank. The fine mud is also separated.
Air conditioning tank is responsible for regulating the flow and concentration of pollutants in the waste water before putting into the works behind the unit. Air blowing device is supplied to the tank to disturb to avoid anaerobic phenomenon.
Waste water from the regulating tank is pumped to the flocculation tank, at the same time, it is used to conduct PAC (flocculation aid) and Polymer (flocculation aid) to perform the flocculation - flocculation process: bonding and stimulate the bonding of colloids in wastewater to create larger particles from small particles that cannot be treated by coarse and fine filtration. Larger particles after coagulation, flocculation in wastewater will be deposited and discharged into sludge.
The waste water then flows through the flotation system, where the mixture of gas and waste water is mixed to form fine bubbles under atmospheric pressure, the air bubbles separate from the water and entrainment of floating oil scum and some suspended sediments. The amount of grease and suspended solids is separated from the wastewater by an automatic scraper which is directed to the sludge tank. Flotation tank combined flotation process and flocculation achieve high removal efficiency. At the same time, the phosphorus removal efficiency of the whole system is also improved thanks to this work.
Waste water is directed through anaerobic treatment tank. Wastewater with high pollution levels will come into contact with the anaerobic sludge layer and all biochemical processes will take place in this mud layer, including hydrolysis, acidification, acetate, methane formation, and other final products.
Waste water after leaving the activated sludge tank will flow over the sedimentation tank. Here, the phase separation phase occurs and retains the sludge (microorganisms). Sludge after sedimentation is pumped to anaerobic tanks and lack of air to maintain the concentration of microorganisms in the tank. The excess mud is pumped to the sludge tank. All treated sludge is stored (pressed sludge) and the unit has a collection and disposal function.


Chemical treatment in wastewater treatment

Most common wastewater treatment processes use the above steps, depending on the characteristics of the wastewater, one or more parts are discarded. For other special procedures that are outside the scope of the above procedure, one or more of the following main processing systems are also followed:

Mechanical treatment: remove trash, sediment, ... through filters, regulating the flow and concentration of wastewater.
Chemical treatment: flocculation - flocculation - sedimentation (not counting the chlorination output process).
Biological treatment (activated sludge) combined with denitrification (Nitrification and Denitrification): remove organic pollutants from waste water.
Treatment of sludge: reduce the moisture of mud before being discharged as prescribed.


So, in the wastewater treatment system, in addition to the fixed investments for other parts (mechanics, biology, sludge, ...), the chemical treatment system is a continuous investment. Due to the specific nature of chemicals, chemical products often have a high price when compared with the economic benefits of the wastewater treatment system. Therefore, the flocculation - flossing (plays an important role in handling suspended particles smaller than 10–4mm) with the correct flow not only helps to complete the task of the process. settling small particles, but also help to save associated costs.