Reactions and Reactors | Biological Processes for Wastewater Treatment

Unit : 3 

Concept of Reactions: Types of reactions and reaction rates

In Biological Wastewater Treatment, there are several types of reactions that take place, including: 

Hydrolysis: This is the first step in the breakdown of complex organic compounds. It involves the use of enzymes to break the bonds between the atoms in the organic compounds, resulting in the formation of simpler compounds. 

Acidogenesis: After hydrolysis, the simpler compounds formed are then converted into volatile fatty acids (VFAs) and other short-chain organic acids by acidogenic bacteria.

Acetogenesis: Next, the VFAs and short-chain organic acids are converted into acetate, hydrogen, and carbon dioxide by acetogenic bacteria.

Methanogenesis: In the final stage of the breakdown process, methanogenic bacteria convert the acetate, hydrogen, and carbon dioxide into methane and carbon dioxide.

Nitrification: This process involve two step, In the first step, Nitrosomonas convert the ammonia into Nitrite and in the second step Nitrobacter convert Nitrite into Nitrate.

Denitrification: Denitrifying bacteria convert nitrate into nitrogen gas, which is released into the atmosphere.

The reaction rate in biological wastewater treatment is affected by several factors, including the type and concentration of pollutants, the temperature and pH of the wastewater, and the presence of nutrients and oxygen. 

The rate of reaction can be increased by adding nutrients to the wastewater to promote the growth of microorganisms, or by increasing the temperature and pH of the wastewater. However, it is important to note that the reaction rate should not be increased too much, as this can lead to the production of harmful byproducts and can also cause the death of microorganisms.

In summary, biological wastewater treatment relies on the action of microorganisms which use different types of reactions to breakdown the pollutants present in the wastewater. The reaction rate is affected by several factors and can be manipulated to optimize the treatment process. 

Temperature effects and
Enzyme Reactions in Biological Wastewater Treatment 

Enzyme reactions are a key aspect of biological wastewater treatment, which is a process that uses microorganisms to break down organic pollutants in wastewater. Enzymes are proteins that catalyze specific chemical reactions in cells, and they play a crucial role in the metabolism of microorganisms. 

In wastewater treatment, enzymes produced by microorganisms are used to degrade complex organic compounds, such as sugars and fats, into simpler compounds that can be further broken down and removed from the water. 

This process helps to improve the overall quality of the wastewater and reduce the amount of pollutants that are discharged into the environment. 

Temperature can have a significant effect on enzyme reactions in biological wastewater treatment. Enzymes are proteins that catalyze chemical reactions, and their activity is affected by temperature. 

Generally, enzymes have an optimal temperature at which they function best. If the temperature is too low, the enzyme's activity will be slowed, and if the temperature is too high, the enzyme's activity will be reduced or destroyed.

Therefore, the temperature of the wastewater must be carefully controlled to ensure that the enzymes are able to function effectively. Additionally, enzymes are also sensitive to pH, and their optimal pH range must also be considered in order to achieve the best results.

Concept of reactors : Types of reactors and reactors in series in Biological Wastewater Treatment 

Reactors are devices used in biological wastewater treatment to provide a suitable environment for microorganisms to break down organic matter. 

There are several types of reactors used in biological wastewater treatment, including:

Aerobic reactors: These reactors use oxygen to support the growth of microorganisms that break down organic matter. Examples include the activated sludge process and the extended aeration process.

Anaerobic reactors: These reactors do not use oxygen and instead rely on microorganisms that can survive in the absence of oxygen. Examples include the anaerobic digester and the upflow anaerobic sludge blanket reactor.

Aerobic-anaerobic reactors: These reactors use both aerobic and anaerobic microorganisms to treat wastewater. Examples include the sequential batch reactor and the integrated fixed-film activated sludge reactor.

Reactors in series refer to the use of multiple reactors in a treatment process. For example, anaerobic reactors may be used first to break down organic matter, followed by aerobic reactors to remove remaining pollutants. This approach allows for more efficient and effective treatment of wastewater.