Activated Sludge Process – MBBR Technology (Moving Bed Bio-film Reactor)

Conventional wastewater treatment technologies like submerged aerated fixed film (SAFF) reactor, Fluidized Aerobic Bio (FAB) reactor, Rotary biological contactors (RBC), Trickling filters or other activated sludge processes have inherent disadvantages of large area of operation, higher power inputs and constant operator attention.

The MBBR process refers to the operation of activated sludge tanks in various configurations in a combination of

  • Suspended biomass,
  • MLSS (Mixed Liquid Suspended Solids) and
  • Attached biomass, which is attached to the MBBR media

Such kind of operation is generally classified as Moving Bed Bio-film Reactor (MBBR).

Basic Principle

The Flock forming organisms form clusters or’ attach to available surfaces. The MBBR carrier material allows High biomass concentrations per cubic meter of material, which:

  • Increases the specific volumetric capacity of activated sludge tanks
  • Controls biomass activity
  • Reduces operating cost

MBBR Scheme

MBBR

The MBBR technology is a single tank design unit, incorporating

  • A bar screen,
  • A specially designed tank with synthetic media & air grid system,
  • A Tube settler,
  • A chlorine contact tank & Clear water tank

The bar screen removes larger floating matter and suspended particles. Screened sewage flows into the MBBR tank, which contains MBBR media. The MBBR media significantly increases the surface area for bacteria growth. Air is supplied through fine diffusers. The Bacteria oxidizes the organic particles present in the sewage. Oxidized sewage overflows in the tube settler. Suspended particles in the treated wastewater settles, with a part of the settled sludge sliding back to the aeration tank. The lamella plates provide larger surface area, thus reducing the settling tank size. Treated water overflows into a chlorination tank, where-in the treated water is disinfected by dosing hypo-chlorite solution through an electronic dosing system.

Advantages using MBBR

  • Significant reduction in space requirement due to high surface area & loading rate of MBBR media
  • Reduced power and operating costs
  • No Sludge recycles
  • No moving parts, less maintenance

Applications of MBBR

I) Decentralized compact sewage treatment plants for Residential complexes/Hotels & Healthcare industry / Commercial Center’s / Office Premises / Industries and Rural Communities
II) Industrial wastewater treatment from:

  • Food & Beverage
  • Textiles
  • Pulp & Paper
  • Chemicals
  • Pharmaceuticals
  • Petro-Chemicals
  • Dairy Production

Process Details

Bar Screen
Raw sewage from the source is usually received into the bar screen chamber by gravity. Screen provided will remove all floating and big size matter such as plastic bottles, polythene bags, glasses, stones, etc., which may otherwise choke the pipeline and pumps.

Oil and Grease Trap (Civil Construction)
If the sewage generated includes maximum quantity from kitchen and canteen, there is a possibility of higher concentrations of oil and grease in the raw sewage. It needs to be removed before biological treatment as it otherwise may cause problems for biological treatment. Usually, a small civil construction tank with a baffle wall and slotted oil pipe skimmer is provided. The oil and grease removed by gravity floats to the surface, which is removed by the oil skimmer.

Equalization Tank (Civil Construction)
Usually, sewage generation is more during morning hours and evening hours. Visually no sewage is generated during night hours. Any biological system needs constant feed for bacteria to work efficiently. Hence, it is important to put an equalization tank to collect the excess flow during peak hours and feed sewage in lean hours. A typical equalization tank has a capacity of 8 – 12 hours of average flow rate. The tank is generally of civil construction by client. Provision of air grid is to be made for thoroughly mixing the sewage to make it of homogenous quality and to keep the suspended matter in suspension and to avoid septic conditions.

Transfer of Sewage
Our scope starts from transfer of sewage from Equalization Tank to MBBR tank. The distance of transfer should not exceed beyond 5 meters. The transfer pump can be either submersible or non-submersible type for this application. However, we have considered centrifugal non-submersible type. The pump should not run dry and Client to ensure enough sewage is available in the Equalization Tank.

Moving Bed Bio-film Reactor (MBBR)
As the name indicates consists of floating media of various shapes and sizes. The main objective of adding this media is to make available more surface area for bacteria to grow on, thereby maintaining and retaining maximum possible bacterial population in a limited volume. The MBBR media material allows biomass concentration of 20 – 40 Kgs/m3 material. Thus, MBBR consists of combination of biomass in attached as well as suspended form. High concentration of biomass enables reduction of aeration tank and in turn reduction in overall cost. Volume of the media shall vary from 6 to 25 % based on the concentration of organic matter.

Another main feature of the MBBR is its compactness. The MBBR consists of biological system for removal of organic matter (BOD, COD), tube settler for clarification and chlorine contact tank for disinfection. As all units are placed inside a single tank, it saves space and also increases operational ease.

In MBBR, raw sewage enters at the top of the tank. Air is introduced at the bottom of the tank through fine bubble diffusers. Media will be in suspension because of the turbulence created by the air. The bacteria required for the oxidation of the organic matter is attached to the media and some part is suspended in the tank. After oxidation, the bacteria grow in number and need to be separated from the aeration tank liquor. The lamella section inside the MBBR helps in clarification and separation of the bacteria (sludge) and clear overflow flows into chlorine contact tank. Lamella plates helps in increasing the settling area and removing the particles effectively in a smaller plan area. In chlorine contact tank, Sodium hypo Chlorite (NaOCl) is added for disinfecting the clarified sewage. Baffle plates are provided to make better contact. The chlorinated treated sewage then flows out of MBBR either for further treatment or for disposal.

Treated Water Collection Tank
The treated water collection tank can be of civil construction by client in case required. The treated water can be collected either from the chlorination chamber in Scheme I or’ from Activated Carbon Filter in Scheme II.

Sludge
The sludge from the Clarifier to be removed from the bottom of the Clarifier once in a day by client and transferred to sludge drying bed either by gravity or through pump depending on site condition. Before starting the De-sludge, shut off the aeration for 30 minutes and allow the sludge to concentrate at the bottom.After concentration, the bottom sludge valve can be open to drain the required quantity of sludge. An air scour pipe is provided to dislodge any media choking the drain outlet. Open the air scour valve for short time to remove the clog.

Flow Diagram

MBBR Flow Diagram