Anaerobic Treatment of Wastewater and Different Reactor Types
Wastewater which contains a large amount of toxic chemical is treated well before releasing it into the environment to prevent harm to humans, animals and plants. The anaerobic process is one of the most effective and efficient biological processes for the treatment of wastewater where micro-organisms are used to degrade the organic matter. The process is undertaken in the absence of oxygen.
With increasing industrialization and urbanization, a large amount of effluents is generated which contains high organic content. Anaerobic treatment is considered to be the most suitable to treat the organic matter. The simple and inexpensive technology makes it popular among Effluent Treatment Plants – ETP’s. All kinds of industrial waste, biowaste, animal manure, sewage, waste from agricultural, dairy, pulp, food, textile as well as municipal solid waste is treated through this process.
One of the major highlights of anaerobic treatment of wastewater is that it consumes less energy and produces energy in the form of biogas.
Most, if not all anaerobic treatment process involves some form of bioreactor which helps to maintain the oxygen-free environment and assists anaerobic digestion. Generally, the bioreactor contains sludge which contains a community of anaerobic bacteria which acts upon wastewater as it enters bioreactor.
The first step involves the hydrolysis of complex organic and biodegradable material to basic monomers, organic acids and hydrogen. Secondly, acetogenesis step is followed where volatile organic compounds are turned into acetate and hydrogen. Finally, methanogenesis takes place where methanogens act to form methane and carbon dioxide. Necessary environmental conditions are a must to carry out the anaerobic degradation of organic matter.
Depending upon the applications and requirements, a variety of bioreactor configurations are designed and developed for anaerobic treatment of wastewater. Some of the common types are elucidated below: –
- Anaerobic contact process
A set of reactors are placed in series with the recycling process. The recycled material is taken to the bottom of the first reactor which is an up-flow reactor. The material leaving is a mixture of solid, liquid and gas, therefore, a vacuum degasifier is used to separate the gas.
- Anaerobic filter – AF
These reactors consist of a tank fitted with a fixed filer media which ranges from plastics, gravels, bricks or other material. The anaerobic microorganisms establish themselves on the filter media, generating what is known as a biofilm. In AF reactor, wastewater is made to pass through the filter, exposing it to the microbes. It has a high capability of biosolids retention and used widely in food processing, pharmaceutical and chemical industries.
- Fluidized and expanded bed reactors
It comprises of small media like sand or granular activated carbon. The bacteria are attached to it. Large biomass can be developed due to mass transfer and high flow rate around the particles. Due to the small size, fluidized bed reactors are highly efficient.
One of the most utilized bioreactor types is the Upflow anaerobic sludge blanket digestion – UASB.
- UASB – Upflow anaerobic sludge blanket digestion
It is one of the most utilized bioreactor types in anaerobic wastewater treatment. UASB is a methane-producing anaerobic bioreactor which has seen great development and acceptance. The wide applications for municipal wastewater treatment, industrial wastewater treatment, especially in food, chemical and pulp industries have made it popular. It is processed by anaerobic microorganisms and forms a blanket of granular sludge.
The treatment process consists of a sludge bed and sludge blanket. The wastewater flows upwards through the blanket and is broken down by the anaerobic microorganisms. The upward flow combined with the settling action of gravity suspends the blanket with the aid of flocculants. The sludge bed consists of a high concentration of biomass and substrates pass through it. The sludge blanket has biomass with less density through which remaining substrate pass.
The blanketing of the sludge enables a dual solid and hydraulic (liquid) retention time in the digesters. Solids requiring a high degree of digestion can remain in the reactors for periods up to 90 days. Sugars dissolved in the liquid waste stream can be converted into gas quickly in the liquid phase which can exit the system in less than a day. The technology needs constant monitoring when put into use to ensure that the sludge blanket is maintained, and not washed out.
Biogas with a high concentration of methane is produced as a by-product, and this may be captured and used as an energy source, to generate electricity and cover its own running power. It has three-phased separator called GLSS – Gas, liquid, solid separator which helps the reactor to separate solid, liquid and gas under highly turbulent conditions. The multiple gas hoods allow the separation of biogas.
As mentioned before, for effective anaerobic wastewater treatment, microorganisms are required to convert organic material to biogas via hydrolysis and acidification. Organica Biotech’s Bioclean ANB consists of a diverse & well-balanced ecosystem of bacteria for the treatment of wastewater.
The natural and effective solution supports biogas production and its output too can be significantly enhanced. It is powerful against odour and maximizes COD/BOD reduction.
Bioclean ANB is effective in chemical industries, pharmaceutical industries, petrochemicals, food processing plants, paper and pulp industries, breweries, milk dairy & cheese processing, fisheries & meat processing units and many more.