September 26, 2015 Water Pollution Written by Greentumble
Waste water treatment
To maintain a healthy human population and

to prevent waterborne diseases, proper wastewater treatment is necessary. There are two types of biologically-based wastewater treatment processes: aerobic and anaerobic wastewater treatment.

The following chart explains the main differences between these two treatment processes:

Aerobic TreatmentAnaerobic Treatment
How it Works

Aerobic processes use bacteria that require oxygen, so air is circulated throughout the treatment tank.These aerobic bacteria then break down the waste within the wastewater.


Some systems utilize a pretreatment stage prior to the main treatment processes, as well as more treatment and sanitizing prior to release into the environment.


Electricity is required for system operation.


Pretreatment Process: Some systems reduce the solids that the aerobic bacteria could not easily break down (such as toilet paper) prior to the main treatment to reduce the chance of clogging the system.


Main Treatment: Treats household wastewater, and includes both domestic greywater and blackwater.


Forced air from an air blower or compressor is mixed with the wastewater, where the aerobic bacteria feed on the waste in the water and reproduce.


Solid wastes that the bacteria are unable to process settle out as sludge. Some aerobic treatment systems include a secondary settling tank to facilitate this settling process.


The sludge is frequently pumped out of the system to reduce opportunities for clogging.


Final Treatment and Disposal:

The final treatment processes prepare the water for return to the environment. These processes may include disinfection using chlorination or UV light, discharging the water to a soil absorption field, filtering through sand filters, drip irrigation, or evapotranspiration.

How it Works

Anaerobic bacteria (bacteria that live in environments that contain no oxygen) transform organic matter in the wastewater into biogas that contains large amounts of methane gas and carbon dioxide.
Energy-efficient process.


Often used to treat industrial wastewater that contains high levels of organic matter in warm temperatures.


Can be used as a pretreatment prior to aerobic municipal wastewater treatment.


Why it is Used
Used in rural areas or small communities where central sewage systems would be costly or impractical to implement.


Used when site or soil conditions are not amenable for septic (anaerobic) systems.


Used when the water table is too high for effective septic system use.


Provides a high-quality alternative to septic systems when properly cared for.


Often used to replace failing septic systems.


Why it is Used
No air input required and generates much less sludge (50-80% less) than aerobic treatment.


Sludge is safe to use as a soil enrichment.


Uses less energy and fewer chemicals than aerobic treatment.


The biogas produced can be used for a renewable energy source as a replacement for fossil fuels such as oil and natural gas.


Small-scale systems can be used to treat individual households or several households in a shared facility. In developing countries where centralized wastewater treatment systems are cost-prohibitive to build and implement, small scale anaerobic treatment systems are a viable option, and may include on-site, community on-site or off-site systems.

Maintenance Issues
Electrical and Mechanical parts require regular inspection and maintenance.


More expensive to maintain than septic tanks.


In most cases, systems require professional inspection and maintenance.


Solids must be pumped out of units frequently.


Maintenance Issues
Optimal operation of municipal anaerobic treatment systems is dependent upon warmer temperatures that exist around 35°C.


Bacterial activity decreases at cooler temperatures.


Due to these temperature constraints, anaerobic systems that are utilized in temperate climates require the use of insulation and heating systems. Generally, only a small volume of wastewater being treated in cold climate countries is treated using anaerobic process, with the majority of water volume treated using aerobic processes that utilize aerators in open and closed ponds.

Costs and Concerns Associated with Use
Aerobic treatment units (ATUs) are more expensive to operate than typical septic systems.


Costs and Concerns Associated with Use
Require lower costs to handle sludge than aerobic treatment systems.


The methane-rich biogas produced through anaerobic treatment must be collected, treated and used to avoid release into the atmosphere, as methane is a potent greenhouse gas and has a bad odor associated with it.


The biogas can be used in cogeneration units to produce electricity and heat.


Minimally, the methane should be flared to reduce its impact on the environment.


In developed countries, both anaerobic and aerobic treatment processes are often involved in municipal wastewater treatment. In developing countries, however, only basic treatment of wastewater typically occurs today, utilizing aerobic processes without the digestion of sludge or anaerobic processes that do not include post-treatment of wastewater[sc:1].


Chart Sources