Biological treatment plants 

Treatment facilities for domestic wastewater are designed to remove mechanical impurities, nitrogen compounds (nitrates, nitrites), surfactants, fats, oil products and other pollutants.

Wastewater treatment is carried out using a combination of mechanical and biological treatment methods, including aerobic and anaerobic processes, which makes it possible to reduce BOD, COD, suspended solids, and nitrogen compounds to regulatory limits.

Biological wastewater treatment plants are widely used for the treatment of domestic wastewater from residential complexes, shift camps, administrative buildings, and industrial facilities where stable system performance under variable loads is required.

The design of biological wastewater treatment plants is performed taking into account the composition of wastewater, design capacity, climatic conditions, and operating режимes, which is especially important for facilities located in areas with significant temperature fluctuations and subzero conditions.

The use of properly designed wastewater treatment plants ensures not only compliance with applicable sanitary and environmental regulations, but also reliable long-term operation of the system throughout its service life without loss of treatment efficiency.

The principle of operation is based on several stages of treatment:
1.Mechanical cleaning - retention of large impurities and sedimentation of ine suspended solids.
2.Biological treatment - sorption and oxidation of organic compounds.
3.Additional wastewater treatment - biosorption and biochemical oxidation of solutions of protein substances, organic acids, low carbohydrates,
synthetic surfactants and phenols.
4.Disinfection - removal of pathogenic bacteria, pathogenic viruses and fungi.
According to the type of execution, treatment facilities are subdivided into surface and underground.

Above-ground wastewater treatment plants are modular structures of full factory manufacture. Treatment facilities with a capacity of more than 100 m³/day consist of individual block modules that are easily assembled into a single integrated system at the installation site. The block modules are equipped with thermal insulation and external cladding, allowing the treatment plants to operate reliably in harsh climatic conditions.

Materials used for manufacturing technological modules:

Carbon steel with anti-corrosion coating

Stainless steel

Underground wastewater treatment plants represent a complex of prefabricated factory-made cylindrical units. The technological blocks are divided into a grit chamber, primary clarifier, biological treatment unit, ultrafiltration unit, secondary clarifier, and disinfection unit.
The process tanks are installed on a pre-prepared foundation and interconnected by technological piping.

Materials used for manufacturing technological modules:

Polymer composite materials

Polyethylene

The operating principle of both above-ground and underground treatment plants is based on a complete wastewater treatment process, which includes:

Mechanical pre-treatment (removal of sand, grease, and suspended solids);

Biological treatment (removal of carbon-based pollutants);

Gravity sedimentation (separation of sludge from treated water);

Disinfection of treated effluent.

Mechanical treatment is carried out by passing wastewater through a mechanical screen, grit chamber, and primary clarifier.

The biological treatment process begins in the receiving equalization chamber, where anaerobic denitrification processes occur with the release of gaseous nitrogen. This process takes place due to the mixing of return activated sludge with incoming wastewater. The design of the equalization chamber ensures minimal water displacement velocity, creating favorable conditions for biological processes.

The wastewater then flows into the bioreactor, where organic matter is degraded by activated sludge. The bioreactor is equipped with modern pneumatic aeration systems and polymer bio-media. The use of polymer bio-carriers increases the concentration of activated sludge by 6–10 times compared to conventional aeration tank–nitrification systems.

Treated wastewater subsequently enters the secondary clarifier, where activated sludge is separated from the clarified water. The activated sludge is returned to the beginning of the treatment process by an airlift system, while the clarified water flows into the clean water tank.

Pumps installed in the clean water tank supply the treated wastewater to a filtration system for tertiary treatment. After filtration, the treated water undergoes final disinfection.

After the disinfection stage, the treated effluent may be discharged into a water body, a stormwater drainage system, or reused for technical purposes, depending on the design solutions and regulatory requirements. The quality of the treated water meets applicable sanitary and environmental standards, provided that the technological scheme and operating modes are correctly selected.

The overall performance of the treatment system largely depends on the accuracy of process calculations, proper equipment selection, and stable operation. During the design of wastewater treatment systems, parameters such as average daily and peak capacity, pollutant concentrations, wastewater temperature, seasonal load variations, and flow regime are taken into account.

Special attention is given to operating conditions in the climate of Kazakhstan, where sharp temperature fluctuations and subzero winter temperatures require the use of thermally insulated structures, reliable materials, and robust technological solutions. For above-ground treatment plants, additional heating and ventilation systems are provided to ensure stable equipment operation during the winter period.

The design of wastewater treatment plants is carried out with consideration of reliability, ease of maintenance, and minimization of operating costs. A properly selected process scheme reduces electricity consumption, optimizes reagent usage, and ensures a long service life of the equipment without loss of treatment efficiency.

ERSEM designs and implements wastewater treatment plants tailored to the specific conditions of each project, providing a full scope of services—from initial data analysis and design to equipment supply, installation, commissioning, and final handover.