Aerobic wastewater treatment converts the organic pollutants (COD/BOD) present in the water into excess sludge and carbon dioxide with the help of oxygen.
Aerobic Post Treatment
Biothane proposes complimentary aerobic post treatment of previously treated wastewater with an anaerobic process. This can be necessary when stringent discharge standards have to be met. The aerobic treatment step can also effectively remove nitrogen and phosphorous, the priority pollutants at that stage.
Biothane has extensive experience with the design and operation of combined anaerobic/aerobic installations.However, whenever appropriate, Biothane recommends anaerobic treatment processes as the costs for aeration, sludge treatment and sludge disposal are notably higher than anaerobic treatment steps.
Conventional Activated Sludge System
The conventional activated sludge system comprises an aeration tank and a clarifier. Aerobic biomass degrades COD in the aeration tank. The mixed liquor (ML) in the clarifier is separated into a water phase and a concentrated ML by sedimentation. The clarified water overflows weirs at the top of the clarifier whereas the sludge (biomass) is removed at the bottom. The major part of the biomass is recycled to the aeration tank to maintain the required amount of biomass in the system. Redundant biomass, produced by growth of microorganisms due to COD degradation, is withdrawn from the sludge stream and discharged to a storage tank or further sludge treatment facilities.
SBR (Sequence Batch Reactor)
The SBR process consists of two reactor tanks with a common inlet system. The bio-selector at the influent section contains baffles to mix the reactor content and enhances digestion. The treatment step is followed by a settling phase, which runs parallel with the filling and aeration of the second tank. The treated water is discharged and the solids are extracted at the reactor bottom.
MBR (Membrane Bioreactors)
In membrane bioreactors ultrafiltration (UF) or microfiltration (MF) membranes are used for separation of the treated water from the mixed liquor (ML). The UF/MF membranes guarantee a constant and very high effluent quality as particulate matter (SS, microorganisms) cannot pass through the membranes. Furthermore, MBR installations require less space than conventional activated sludge systems because more biomass can be retained in the system allowing a higher treatment capacity in smaller reactors.
Anox Kaldnes™ MBBR (Moving Bed Biofilm Reactor)
The MBBR™ biofilm technology is based on specially designed plastic biofilm carriers or biocarriers. Biofilm grows protected within these engineered plastic carriers, which are carefully designed with a high internal surface area. An aeration grid located at the bottom of the reactor supplies oxygen to the biofilm along with the mixing energy required to keep the biocarriers suspended. Treated water flows from reactor through a grid or a sieve, which retains the MBBR™ biocarriers in the reactor.
Nitrification and Denitrification (N-removal)
Biological N-removal is achieved through a combination of nitrification and denitrification. During the first step, nitrification, nitrifying bacteria converts ammonia into nitrate in the presence of oxygen. The nitrate is then reduced to nitrogen under anoxic conditions by denitrifying biomass. These two processes are realized in modified aerobic systems by increasing the sludge age (allowing growth of nitrifying biomass) and providing an anoxic zone.
Biological- and chemical phosphate removal (P-removal)
Phosphate can biologically be removed from wastewater or by means of chemical precipitation. Biological phosphate removal is achieved by a special design of the biological treatment with combination of anaerobic and aerobic conditions. However, biological removal is often not sufficient. Then phosphate is removed from the water by means of precipitation with Fe or Al salts. Precipitated phosphorous is also removed with the surplus sludge.
