Biological Wastewater Treatment: COD/BOD/N Removal Solutions

Biological waste water treatment is a wastewater treatment method that uses microorganisms to consume and transform pollutants in water. In simple terms, bacteria act like a living treatment workforce: they use organic matter as food, convert ammonia nitrogen through nitrification, and help reduce pollutant concentration before final discharge or reuse.
A typical biological treatment process may include:

Pretreatment is important before biological units. Screens remove large solids, while equalization tanks balance flow and pollutant concentration. If wastewater contains oil, grease, high suspended solids or toxic substances, oil-water separation, DAF dissolved air flotation, pH adjustment or chemical dosing may be required. Good pretreatment protects microorganisms and improves system stability.
The biological stage is selected according to wastewater quality. Activated sludge is a common process where microorganisms grow in suspended flocs under aeration. MBBR uses floating biofilm carriers to increase microbial surface area and improve resistance to load fluctuation. MBR combines biological treatment with membrane separation, providing clearer effluent and compact layout. SBR treats wastewater in timed cycles, including filling, aeration, settling and decanting, which is useful for variable-flow projects.
For nitrogen removal, anoxic and aerobic zones are often combined. In the aerobic zone, ammonia nitrogen can be converted into nitrate through nitrification. In the anoxic zone, nitrate can be converted into nitrogen gas through denitrification when suitable carbon source and operating conditions are available. If phosphorus removal is required, biological phosphorus removal or chemical dosing may be added.
Biological treatment is suitable for biodegradable wastewater, such as domestic sewage, food and beverage wastewater, hotel sewage, community sewage, commercial wastewater and some industrial effluent. However, it has boundaries. Wastewater with strong toxicity, high salinity, heavy metals, extreme pH, high oil content or poor biodegradability may inhibit microbial activity and require pretreatment or pilot testing.
System selection depends on daily flow, peak flow, COD, BOD, BOD/COD ratio, TSS, ammonia nitrogen, total nitrogen, phosphorus, oil content, pH, temperature, salinity, discharge standard, available space, operation schedule and automation level. These parameters affect tank volume, aeration design, carrier filling ratio, membrane area, sludge production and total cost.
A common mistake is choosing a biological process only by equipment price. Under-designed aeration, insufficient tank volume, poor sludge control or weak pretreatment can cause unstable effluent. Qingdao Jinwantong provides customized biological wastewater treatment equipment and process support. Send your water quality report, flow data and discharge target for technical selection and quotation.