Conventional Aerobic Activated Sludge Treatment Systems

UEM has installed more than 70 high efficiency aerobic activated sludge systems. These systems incorporate fine bubble diffusers for aeration and most are designed with a removable headers concept. All of our systems have been able to produce treated water with very low organic pollutant (BOD, COD, etc.) concentrations, well within what is required to meet the client's discharge specifications. Many of these installations have been designed as extended aeration systems. These systems are designed for a low F:M ratio (0.1 kg BOD/kg MLSS-day) and a high SRT (20 - 30 days). The extended aeration process has many benefits, including a reduced sludge yield and an increased process stability. These systems have been successfully installed for various municipalities and industries such as distilleries, breweries, yeast, pharmaceuticals, textiles, soft drinks, food, petrochemicals, chemicals, paper, etc.

Sequencing Batch Reactors

A sequencing batch reactor is an activated sludge type wastewater treatment system in which different treatment operations are carried out in one vessel. This differs from conventional wastewater treatment where the wastewater flows from one vessel to another, each vessel performing a specific treatment operation.

Different environments are created in the SBR by controlling process equipment such as air blowers for diffusers, pumps and decanters during a cycle. The process is controlled and coordinated by a programmable logic controller (PLC).

Treatment in a SBR is accomplished in four distinct cycle events. The first event is FILL during which influent wastewater is distributed into the sludge blanket. The FILL event can take place under mixed or unmixed conditions and aerated or un-aerated conditions, depending on the treatment objectives. REACT events include mixing and aeration. The SETTLE event occurs when all mixing and aeration is turned off and the mixed liquor solids settle, allowing a clear supernatant to form in the upper part of the SBR.

The DECANT event occurs once a substantial depth of supernatant is drawn off the upper portion of the SBR. Sludge wasting can occur during this time, since the settled sludge bed will have a maximum concentration of solids.

The timing and sequencing of events in an SBR cycle depend on the influent wastewater characteristics and the treatment objectives. Aerated conditions serve to oxidize organic carbon, nitrify ammonia, and promote uptake of phosphorus in the sludge. Unaerated conditions encourage the denitrification of nitrite snd nitrate present and help select the proper bacteria required for phosphorus removal. Thus, the inclusion of sequenced anoxic, anaerobic, aerated, biomass settling and decanting events in the SBR allow organic carbon, suspended solids, ammonia, total nitrogen and phosphorus removal to all be accomplished within a single tank.

SBR technology offers a number of benefits and advantages over other activated sludge system such as:

Lower operating costs. Comparative cost analyses have shown that SBR operating costs are typically lower than conventional activated sludge treatment processes.
Greater ability to meet effluent limitations (both organic and nutrient) since the SBR utilizes `batch' kinetics - process reactions approach completion under high concentration gradients with no short-circuiting. The outlet BOD, COD are much lower than in conventional systems.
Better resistance to sludge bulking, since the biomass undergoes cyclic feast-famine conditions, which have been proven to produce a better settling sludge than in continuous flow conditions.
No need for external clarifiers and associated return sludge pumps and piping, since solids separation and clarification occurs in the same vessel as other treatment operations.
Easily adaptable to nutrient (nitrogen) removal, since all necessary treatment operations can be imposed without requiring multiple vessels.
Greater system flexibility and control since the cycle format can be easily modified at any time to offset changes in process conditions, influent characteristics or effluent objectives.
Less land required and less process equipment to maintain, since only one vessel is used for all process operations and external secondary clarifiers are not required.

Several plants with this innovative technology have been installed by UEM for various industries such as chemicals, petrochemicals, pulp & paper, municipal sewage, etc.