Sewage Treatment Plant (STP)

Sewage Treatment Plant (STP)

Sewage treatment or wastewater treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges.

Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can rangefrom decentralized systems (including on-site treatment systems) to large centralized systems involving a network of pipes and pump stations Called sewerage) which convey the sewage to a treatment plant. For cities that have a Combined sewer, the sewers will also carry urban runoff (storm water) to the sewage treatment plant.

Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter (measured as biological oxygen demand) from sewage,?using aerobic or anaerobic biological processes.

A so-called quaternary treatment step (sometimes referred to as advanced treatment) can also be added for the removal of organic micro pollutants, such as pharmaceuticals.

Design of MBBR Systems:- 

It uses a combination of activated sludge process i.e. suspended growth and biofilter i.e. attached growth. It uses the entire tank volume for biomass growth by implementing the carriers for attached growth of biofilm. Movement of carriers is enabled by air bubbles through agitation. The reactor can be in any shape and support different load depending on carrier filling.

MBBR design of reactor depended on the actual wastewater characteristics and locality. The plants come either with vertical or horizontal mounted rectangular mesh sieves. The reactor can also be fitted with cylindrical bar sieves. MBBR carriers are cylinders having a cross inside and fins outside to increase the surface area.

The standard used is below 70% of carriers in an area of not more than 465m2 per m3. MBBR is used together with a septic tank or a pre-coagulation step for pre-treatment. MBBR technology can be designed with additional non-mechanical or mechanical system to enhance phosphorus and fecal coliform reduction.