The problem of contamination of water bodies with biogenic elements and protection of the environment is essential. The main source of contamination, which worsens water quality and disrupts ecosystems is the release of insufficiently treated wastewater.
Municipal treatment facilities, where biological treatment of water is performed through the traditional arrangement of aerotank and a secondary settling tank, cannot ensure high enough quality of the processed water to meet the requirements sufficient for release into water bodies, due to high concentrations of various forms of nitrogen and phosphorus.
The reasons of low efficiency of treatment plants are many: design flaws, obsolete technology, incorrect operation, water and contaminant composition different from anticipated due to the development of the industry.
The solution to the problem of pollution by inefficiently treated waste is to reconstruct most of the sewage facilities using advanced technology and new wastewater treatment developments. Most attention is now directed at processes, which can simultaneously remove phosphorus and nitrogen from wastewater. Considering the environmental factors, removal of nitrogen and phosphorus using biological denitrification and biological dephosphorization.
Removal of biogenic materials from wastewater can be done in several ways. All methods are divided into anaerobic, anoxic and aerobic.
Three areas must be created in aerotanks for biological denitrification and dephosphorization:
- aerobic (high concentration of solved oxygen), with removal aerobic removal of organics, nitrification (biooxidation of ammonia nitrogen to nitrate nitrogen) and dephosphorization (rapid consumption of phosphates by bacteria);
- anoxic (practically no solved oxygen, but nitrates and organics are present), with denitrification;
- anaerobic (no solved oxygen, no nitrates and nitrites, organics present), with fermentation of organics to acetate, consumed by bacteria with formation of phosphates.
Anoxic and anaerobic conditions are created by changing aeration to mechanical agitation, although such reconstruction is costly for existing facilities. There is an alternative: to create anoxic conditions in the aerotank by low (the minimum required to prevent settling of biological sludge) intensity of aeration.
For existing aerotanks in traditional aerobic mode, implementation of biological denitrification and dephosphorization while keeping treatment capacity requires intensification of purification. Increasing the rate of aerobic process, including nitrification and biooxidation of organics, can reduce the volume of aerobic zone to allocate space in the tank for anoxic and anaerobic zones.