Water resulting from our everyday life activities like domestic, industrial, agricultural, medical and transport activities is called wastewater. Water can only become waste water if its quality, composition and temperature are changed. It is also defined as a complex mixture of both organic and inorganic materials. It can be in two categories;
- Gray water – this comes from showers, baths, dishwashers and all sinks except the kitchen sink.
- Blackwater – this is from toilets and kitchen sinks.
It has a high concentration of microscopic organisms which break down organic components. It’s composition is constantly changing. This is due to the active microbial content. Before entering a sewage plant, wastewater is known as raw sewage.
The most measured characteristics of wastewater are suspended solids and biological oxygen demand.
Wastewater can be transported in a combined sewer or in a sanitary sewer. Treated wastewater is usually discharged into a receiving water body. If it is discharged into the environment without being treated, it causes water pollution.
Areas with low populations have on-site sanitation systems. The most common one is the septic tank. There are many ways to purify wastewater depending on how contaminated it is.
Wastewater Treatment Process
This is a process by which contaminated water is cleaned and consequently released back into the environment
· Collection of Wastewater.
Systems are put in place to collect all the unwanted water. after that, they take it to a central point. In addition, it is transported to a treatment plant.
· Odor Control
Treatment processes to contain the bad smell in wastewater are done. Hence, a better working environment.
This is where large objects like nappies, bottles, etc. are removed and later on disposed in a landfill.
· Primary Treatment
Involves separation of solid matter from wastewater. However, the solid matter is then put under further treatment.
· Secondary Treatment
Involves adding seed sludge to wastewater to make sure it is broken down more. As a result, large particles usually settle down at the bottom of the huge tanks.
· Handling Bio-solids
The resulting solids are usually exposed to anaerobic digestion. Eventually, they release biogas which is a great fuel.
· Tertiary Treatment
This can remove up to 99% of impurities. However, it is more expensive due to the special equipment required. It also requires highly skilled personnel.
This is the process of removing the remaining disease-causing organisms. This leads to pure water.
Wastewater treatment methods
Physical Water Treatment
There are no chemicals used in this process. Instead, physical processes like screening, sedimentation and skimming are used in removing solids.
First, you separate the solids. Thereafter, pass air through them to provide it with oxygen. After that, filter out all the contaminants.
Biological Water Treatment
It can be through aerobic processes where bacteria, apparently, use Oxygen to decompose organic matter. Anaerobic processes also occur where bacteria act at a specific temperature without Oxygen. Another process is composting where you mix wastewater with carbon sources. As a result, it is treated. It removes most solids.
Chemical Water Treatment
Here Chlorine is used to kill bacteria. Hence, it purifies the water. Ozone can also be used to purify. It is an oxidizing agent.
This whole process involves using chemicals. They prevent bacteria from reproducing in water. These bacteria usually decompose the water by adding contaminants to it.
This is the separation of solids and liquids. A centrifuge is used for removing solids from the wastewater. The separated liquid should have very little solids while the solids should have very limited moisture.
Treating wastewater is not only beneficial to thriving animals, but it also protects the planet as a whole.
Wastewater Treatment Plant
This is a facility that contains the necessary equipment and manpower to remove pollutants from water. They are designed to have distinct water treatment process combinations. They release wastes that contain very harmful contaminants.
Efficient plants produce effluents which are less polluted than the water bodies they will be discharged into.
Wastewater treatment plants are composed of several stages of water purification. They include; physical, biological and chemical methods. In some countries, factories are required to pretreat their wastewater before releasing it. This is because they contain some pollutants that a sewage system cannot remove.
When there is excess rainfall, the flooding water can be guided into natural reservoirs to protect treatment systems from overload.
In the treatment plants, the processes are divided to ensure none interrupts the other. Some use chemicals while others don’t. Moreover, each process gives out different results.
The primary process separates the solid matter from wastewater. The secondary process breaks down the wastewater even more to give large settling particles. And finally, the tertiary stage removes the remaining impurities leaving the water pure enough to be discharged into the environment.
The treatment plants are responsible for controlling and preventing water pollution.
Removing Solids – Simple sedimentation techniques are used to remove solids. As a result, most are recovered as sludge. Ultrafiltration may be required sometimes.
Oil and Grease Removal – Skimming devices are often used to recover oils from open water surfaces. They prevent filters from premature blinding. It is cost-efficient.
Removing Bio-degradable Organics – Activated sludge or trickling filters can be used to treat some of these materials. However, the wastewater must not be too diluted with washing water.
Activated Sludge Process – Oxygen is injected and thoroughly mixed with wastewater to oxidize the wastewater.
Trickling Filter Process – Involves adsorption of organic compounds in the wastewater by the microbial slime layer. Air is then diffused into this layer to oxidize the organic compounds.
Treating Other Organics – Modified forms of wastewater treatment can be used to get rid of synthetic impurities like pesticides.
Treatment of Acids and Alkalis – Neutralization is required under controlled conditions. Sometimes gases may be evolved requiring treatment for the gas stream.
Treatment of Toxic Materials – Advanced Oxidation processes can separate dissolved organics from wastewater. Chemicals are used in treating some organics while others are resistant to treatment.