Sigma can custom design specific aerobic biological process based on the treatment application. A variety of aerobic biological systems are available for treatment of industrial and municipal wastewater. Selections of the process are dependent on the specific application, area available, future expansion needs, and operating costs. Systems offered under aerobic biological treatment systems include:

o Activated Sludge
o Extended Aeration
o Aerated Lagoon / Aerated Ponds
o Trickling Filters-Solids Contact (TFSC) Hybrid Systems
o Moving Bed Hybrid Systems
o Membrane Bio Reactors (MBR)
o Sequencing Batch Reactors (SBR)
o Solids Contact Processes
An overview of the Sigma TFSC and Sigma MBR processes are provided below.


A BIOfilter system designed as a trickling filter (TF) is used as a primary step to remove soluble organics from the wastewater. The TFSC system comprises of a TF tank, a solids contact tank and a reaeration tank. Generally, the TF tank is aerated by means of subsurface fine pore diffusers to keep the contents of the tank completely mixed. Recycle pumps recirculate incoming wastewater blended with the wastewater in the TF tank through a TF structure housing engineered TF media. The wastewater is applied on the surface of the media by a uniform distribution system. Air vents are provided to ensure sufficient air circulation through the media to maintain a aerobic atmosphere. The TF system can be operated in a “low, medium, high and super high rate” modes. This is dependant on the application and the system is custom engineered accordingly. The TF is often used for nitrification application such as in the palm Oil industry. The biological removal process in a TF system depends on biochemical oxidation of complex organics in the wastewater to carbon dioxide and water with a portion oxidized for energy used to sustain and promote the growth of filter organisms.

Oxygen for the aerobic metabolism is supplied from the circulation of air through the interstices between the filter media and partially from the dissolved oxygen in the wastewater. The growth of microorganism on the filter media is facultative in nature with the anaerobic bacteria in direct contact with the media and the surface growth exposed to the air being aerobic.

The bio-slime growth will increase as the organic load increases until a maximum effective thickness is reached. This maximum growth is controlled by physical factors including hydraulic dosage rate, type of media, type of organic matter, amount of essential nutrients present, and temperature. Once a maximum thickness is exceeded, the slime is sloughed (falls) off. Engineered uPVC media is used for the application. High surface area to volume (100 m² per m³) ratio provides a competitive advantage over generic suspended growth processes. The Solid Contact System (SC) unlike the trickling filter is a suspended growth process. The solid contact portion of the secondary treatment system is a polishing step for the effluent. The SC system is operated in a high rate mode with the reaeration tank serving as a sludge aeration tank. It is highly resilient to shock loading. The SC tank is aerated by fine pore subsurface diffusers to ensure adequate oxygen transfer to degrade the organic matter.

The solids contact system is compact in nature and often used in conjunction with the trickling filter system for higher industrial loadings and high flow scenarios when space available for installation is limited. The overflow from the SC tank enters the secondary clarifier for biological sludge clarification. The Sigma TFSC system used for industrial waste treatment is very compact and modular in design permitting vertical expansion to accommodate future expansions. The expansion shall require increasing the media height in the trickling filter tower.


A membrane biological reactor is generally offered for polishing the effluent to recycle standards. An MBR is an activated sludge process with the conventional secondary clarifier and any tertiary filtration systems replaced by a membrane. The air lift MBR is an external MBR and not submerged within the tank. This allows easier control of the MBR system during operation and maintenance. The system incorporates a closed boundary (absolute barrier) on TSS and many other COD/BOD compound enabling a high level of separation with the use of ultra filtration membranes.

Figure 1.0: Schematic diagram of MBR where ultra filtration unit is directly connected to the solid contact tank confining the biological mass and other TSS compound by recycling the concentrate back to the solid contact tank.

Figure 1.0 shows the schematic diagram of the MBR system. Biological mass and suspended solids are confined in the MBR loop of ultra filtration and the bio reactor tank. The activated sludge from bio reactor is wasted to a sludge tank for disposal.

The advantages of SMBR unit can be summarized below:

o Secondary clarifiers in the activated sludge process eliminated reducing plant footprint.
o The separation of solids from the effluent is not dependant on the quality of mixed liquor suspended solid. This allows the elevated mixed liquor concentration in the bioreactor tank reducing aeration basin volume and hence further reducing the plant foot print.
o Requires less monitoring of the mixed liquor level as there is no reliance on settleability.
o Produce high quality effluent ready to be recycled or reused.

The expected treated effluent parameters of MBR are as below:

Sigma’ MBR system offers the latest technology in wastewater treatment. The MBR system is simple to operate, and extremely efficient in size requirements, and operating costs.

The Sigma MBR process demonstrates numerous advantages, including:

o Reduced sludge production
o Modular and compact design, easy to expand economically.
o Greatly reduced plant area
o Improved stability of suspended growth biomass
o Capability to respond and treat shock loads
o Improved settlement and concentration of solids at MBR
o Improved economics