Sewage Treatment Plant: STP Plant Manufacturers

• In the sewage treatment plant, water passes through a bar screen to remove all large objects like cans, rags, sticks, plastic packets, etc., carried in the sewage stream.

Primary treatment: Horizontal flow grit chambers at a sewage treatment plant in grit consists of sand, stone, rocks, and additional weighty materials. Immediate treatment may contain a sand or grit removal channel or chamber. Grit removal is necessary to:

• Reduce the formation of deposits in primary sedimentation tanks, aeration tanks, anaerobic digesters, pipes, channels, etc.
• Reduce the frequency of tank cleaning caused by excessive accumulation of grit.
• Protect moving motorized equipment from abrasion and attending abnormal wear.

Grit removal is essential for equipment with closely machined metal surfaces, such as comminutors, fine screens, centrifuges, heat exchangers, and high-pressure diaphragm pumps.

Equalization inlets achieve flow equalization to reduce peak dry-weather flows or peak wet-weather flows in the case of combined sewer systems. The benefits are performance improvements in the biological treatment processes, the secondary clarifiers, and filtration equipment.

In some larger plants, fat and grease pass the sewage through a small tank where skimmers collect the fat floating on the surface. Air blowers in the tank's base may also help recover the fat as a froth. Many plants use primary clarifiers with mechanical surface skimmers for fat and grease removal.

Primary treatment is the "reduction of an amount of the suspended solids and organic matter from the sewage." It allows sewage to pass via an inlet where rich solids can settle to the base while lubricant, grease, and soft solids flow to the surface and skim off. These bases are called "primary sedimentation tanks" or "primary clarifiers" and typically have a hydraulic retention time (HRT) of 1.5 to 2.5 hours. The rigid and floating materials remove, and the remaining liquid may be discharged or subjected to secondary treatment. Preparatory settling tanks are usually equipped with mechanically moved scrapers that continuously drive the collected sludge toward a hopper in the tank's base, pumped to sludge treatment facilities.

The main processes in secondary treatment remove as much substantial material as possible. They use biological processes to recapitulate and clear the remaining soluble material, especially the organic fraction. This process suspends growth or biofilm procedures. The microorganisms that forage on the organic matter present in the sewage grow and multiply, constituting biological solids or biomass. These products and groups are in the form of flocs or biofilms and granules in some specific processes. In several treatment processes, the biological floc or biofilm and remaining fine solids can then be settled as sludge, leaving a liquid substantially free of solids and a significantly reduced concentration of pollutants.

Advanced sewage treatment generally involves three main stages: primary, secondary, and tertiary treatment but may also include intermediate steps and final polishing processes. The tertiary treatment (also called "advanced treatment") is to provide a final treatment stage to improve the effluent quality further before it is discharged to the receiving water body or reused. It is always the final process.

Sludge is especially water with some quantities of stable material extracted from fluid sewage. Primary sludge contains settleable solids released during immediate treatment in prior clarifiers. Secondary sludge is sludge separated in secondary clarifiers that are operated in secondary treatment bioreactors or processes using inorganic oxidizing agents. In intensive sewage treatment processes, the sludge produced needs to be removed from the liquid line continuously because the volumes of tanks in the fluid line have the insufficient volume to store sludge.