Performance evaluation of 1 MLD MBBR type sewage treatment plant

Screening (Bar screen and grit chamber)

The raw sewage first be screened through a manual bar screen, where all particles with diameter below 5 mm as well as small pieces of the fibre and floating suspended matters like polythene paper, polythene bags, rags and others materials are removed. These units are used to protect downstream equipment such as pumps, pipelines, valves etc. from damage and clogging by rags and other large objects. The bar screen and grit chamber is cleaned manually by means of rakes. The screened clean effluent flows by gravity to an equalization tank.1, 2

Oil & grease chamber

The screened wastewater then gets skimmed properly to remove Oil and Grease. The removal principle based on density and viscosity of the sewage.

Equalization tank

The raw wastewater collected in the equalization tank, where it is equalized with respect to its characteristics, homogeneity, flow and uniform pollution load as well as to make bacteria acclimatized. The equalization tank is designed for hydraulic retention time of around 6 hours. Proper equalization process minimizes the shock loadings and stabilizes the pH to improve the biological oxidation reaction in the next downstream units.

Anoxic tank

Anoxic zones in wastewater are useful for nitrogen removal. Wastewater has a high nitrate and nitrite content, and the treatment process must break down those compounds to avoid causing nutrient pollution when the plant discharges its effluent back into the environment. In anoxic zones bacteria break down the nitrogen products and release nitrogen gas into the atmosphere.

MBBR tank (Secondary-treatment) 3, 4, 5

The process of Oxidation, synthesis and endogenous respiration happens in the MBBR tank or aeration tank. Eco-friendly available in the sewage facilitates the above process; hence the complex organic compound gets converted to simpler organic substance. Bacteria or bio augmenter staying in MBBR Media surface and does the job utilizing the supplied oxygen through Air blowers.

Figure 1

MBBR media

Figure 2

Bacterial attachment

Figure 3

STP 1 MLD front view

Figure 4

MBBR aeration zone

Figure 5

Biological process happens in aeration zone

Tube settler

The oxidized sewage will be dosed with coagulants and flocculants and allowed to pass through the Tube Settler. Here the suspended solid gets settled inside the tube settler through the intact arrangements of tube settler media. A substantial amount BOD and COD are also removed in the coagulation and flocculation process.

Disinfection System

Chlorine disinfection system installed to oxidize the pathogenic bacteria from the treated sewage water and then allowed to pass through the filtration units like PSF and ACF.

Pressure Sand Filter (PSF)

From the filter feed tank, the clear water is pumped to the pressure sand filter. The filtration takes place in the downward mode. The filter is filled with a layer of graded sand media supported by a layer of graded gravel. The suspended matters from the effluent get filtered.

Activated carbon filter (ACF)

In this unit the feed flow is downward through a layer of granular activated carbon filter in which dissolved organics of the effluent are absorbed. It is necessary to backwash the carbon filter every eight hours.

Sewage treatment plant existing

Project Name: Rajiv Gandhi Institute of Medical Sciences (RIMS), Kadapa A.P

Project Type: Sewage Treatment Plant.

Design Capacity: 1 MLD.

Operation Hours: 24 hrs.

Technology: Moving Bed Bioreactor (MBBR).

System Erected by: M/S. Green Enviro Polestar, Pondicherry.