A process that is carried out in the absence of oxygen is an anaerobic process. Any system which operates in the absence of oxygen is called an anaerobic system. An example of anaerobic system is a Fermentor. Anaerobic treatment is a biological process which is an ideal method used for the pre-treatment of high strength industrial waste waters. The principle of an anaerobic system is to break down biodegradable content of the industrial waste stream using a biological aid that is naturally occurring bacteria. Many organisms esp. microbes can survive in the absence of oxygen and hence cause anaerobic digestion and decomposition of food and waste matter. To prevent any infiltration of air or odor they are enclosed or isolated against atmosphere.
What are the Applications of Anaerobic System?
An anaerobic system is used for waste treatment in 2 ways:
It is used before aerobic treatment. It is very efficacious and economical in the BOD and COD reduction . The anaerobically treated water is then sent to aerobic reactors.This system is called co-ordinated anaerobic treatment of waste water and can also treat very toxic wastes.
It is used alone for biological treatment of waste waters and to a very high degree it decomposing the organic matter. High BOD waste streams can be separately treated in reactors where aerobic treatment takes place, after which it can be combined with total flow.
The anaerobic treatment is of significant industrial value. It finds place in
Bakeries, Beverage production facilities, Dairies, Food processing plants
Chemical and Pharmaceutical plants
Pulp and paper mills, Textile mills
What are the various Types of Anaerobic Systems?
An anaerobic system can be of the following types,
Packed Anaerobic bed reactors : These are hybrid systems having suspended growth and fixed film sections. Their speciality is that they can handle high hydraulic and organic loading at short retention times. Their application is in processing of high strength and low solid waste waters.
Hybrid Anaerobic Lagoons : Generally used for high strength waste water treatment these are suspended growth systems. Their special characteristics like improved mixing and flow management facilitates high efficiency.
Packaged Anaerobic systems : These are modular systems available in configurations of both suspended growth and fixed film types. Modular design provides for expansion and easy relocation and thereby complete delivery to site is possible, with only power and piping connections required. These are used to treat small waste water volumes.
What is the mechanism of Anaerobic Waste Water Treatment?
Anaerobic system uses bacterial activity for clarifying wastewater, disintegration, digestion or reduction of the solids. As a result, the solids float or settle out of the wastewater and can either be skimmed off or separated from the water for sludge dewatering.
What are the Benefits of an Anaerobic System?
The advantages of an anaerobic system are:
Low sludge yield : As compared to sludge produced during aerobic treatment, the fraction produced during anaerobic process is less.
Lower power requirement : No need of surface aerators or blowers which reduces high horse power requirements.
Higher organic loading : Anaerobic systems are able to reduce BOD concentrations (1000-20000mg/L). Their effectiveness in COD removal is greater than aerobic systems.
Energy production : During anaerobic digestion methane is a byproduct which is of high value as a fuel for it can replace natural gas used in plant boilers, generators and similar energy systems.
Process stability : It is very stable under varying hydraulic and organic load and conditions that may estabilize other bio-systems.
Reduced nutrient requirement: Lower fraction of nutrients like nitrogen and phosphorous required.
Economy : Less nutrients and electrical input leads to lower operating costs.
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