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Waste Treatment
The HRS DCS ( Digestate Concentration System ) reduces the costs of storage , transport and application of digestate . Image courtesy of HRS Heat Exchangers
The benefits of anaerobic wastewater treatment
Conventional wastewater treatment in many regions consists of three distinct phases : primary , secondary , and tertiary . The primary treatment involves the mechanical removal of solids by sedimentation or flotation and is followed by a secondary treatment which removes organic matter through microbial decomposition . A further final , or tertiary , treatment may also be required depending on the final destination of the wastewater – such as re-entering the mains water supply .
The choice of secondary treatment depends on a number of factors including the wastewater ’ s chemical and biological oxygen demand ( COD
& BOD ), operational and maintenance costs , sludge production , desired effluent quality , and microbial concentration . The choice is generally between aerobic or anaerobic treatment , although a combination of both methods can also be used .
By Matt Hale , Global Key Account Director , HRS Heat Exchangers
In recent years we have seen a steady increase in the use of anaerobic digestion treatment techniques for the treatment of wastewater ( and other effluent streams ), but before we can examine what is driving this , it is important to understand the differences between aerobic and anaerobic treatment , as well as the pros and cons of each .
Aerobic vs anaerobic treatment Anaerobic and aerobic systems are both forms of biological treatment which use microorganisms to breakdown and remove organic materials from wastewater . The key difference between aerobic and anaerobic treatment is the presence of oxygen . Aerobic treatment is typically applied to efficiently treat low strength wastewater ( with relatively low BOD / COD values ) when the treatment requires the presence of oxygen . In contrast , anaerobic treatment is typically applied to treat wastewater with higher organic loading . In aerobic treatment , oxygen ( air ) is used to circulate the material , providing the right conditions for aerobic bacteria to reproduce . These bacteria assimilate and then break down organic matter and other pollutants like nitrogen and phosphorus into carbon dioxide , water , and biomass ( sludge ). As the name suggests , anaerobic digestion utilises bacteria which do not need oxygen . They break down organic material in the wastewater into methane , carbon dioxide , and biomass ( digestate ). Some of the factors in favour of aerobic treatment include the fact that it has less odours ( as hydrogen sulphide and methane are not produced ), and nutrient removal from the wastewater to the sludge can be more efficient – meaning that treated water can often be discharged directly into the environment . However , oxygenation of the wastewater can require large amounts of energy ( or a large surface www . heat-exchanger-world . com Heat Exchanger World October 2024
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