Wastewater treatment is removal or elimination of harmful impurities and contaminants in water. The purpose of wastewater treatment is to ensure access to clean water by avoiding contamination of water sources.
The following are the steps involved in wastewater treatment process:
Step 1: Screening
The incoming wastewater passes through screens, removing objects such as rags, wood fragments, plastics, and grease. After screening, the wastewater is then conveyed to another step called grit removal.
Step 2: Grit removal
This process involves separating heavy but small materials like sand and gravel from the wastewater. The grit is also disposed of at landfills.
Step 3: Primary settling
In this stage, big round tanks known as clarifiers are used to remove material with settling rates that are slower than the grit. Within the clarifier, particles collected at the bottom of the unit and form sludge, debris such as grease, float and wastewater leave from above. The primary sludge is pumped out while the float is skimmed off the top to the digesters. Phosphorus is also removed by adding chemicals at this stage.
Step 4: Aeration/activated sludge
At the aeration step, wastewater receives most of its treatment. Aeration is the process by which air is circulated through, mixed with or dissolved in a liquid so that oxygen is provided to bacteria for treating and stabilising the wastewater. Through biological degradation, the pollutants are consumed by micro-organisms and transformed into cell tissue, water, and nitrogen.
Step 5: Secondary settling
Large circular tanks called secondary clarifiers allow the treated wastewater to separate from the biomass from the aeration tanks, yielding an effluent, which is now over 90% treated. At this
stage, the bacteria that have grown in the previous process precipitate to the lower part of the settling tank, generating a mixture of water and solids termed biological sludge. This biological sludge, also known as activated sludge, is continuously pumped from the clarifier back to the aeration tanks in step four.
Step 6: Disinfection
Disinfection is done by ultraviolet, chlorine gas or any other disinfectant to ensure that treated wastewater is virtually bacteria-free.
Common problems in wastewater treatment
Often, wastewater treatment is shrouded with problems that may compromise the quality of treated water for consumption by humans and animals. These problems are prone to every treatment plant and should, as a result, be avoided at all costs. Here are four of the most common problems encountered in the overall system of treatment plants:
Maintenance Issues
Wastewater treatment technology, facilities, and systems must always be monitored, inspected, and maintained. Otherwise, neglect of these protocols may cause serious implications for the overall quality and safety of treatment processes. Failing to regularly maintain equipment and other assets can result in costly repairs, grave damage to systems, and compromised human safety.
Inefficient Bacterial Control
While some bacteria are essential to treatment operations, failing to monitor and manage bacterial growth can endanger the quality of effluent. Hence, having a tested and proven bacterial control system helps avoid such a risk and hamper the treatment cycle.
Inadequate Training
Those working in treatment plants or facilities, such as operators and specialists, deal with highly technological processes. As such, there is a need to prevent any misunderstanding of certain aspects of work due to poor training. Compromised quality of training can affect not just workers’ safety but also the overall treatment cycle quality.
Poor Monitoring and Record-keeping
Monitoring and good record keeping must be maintained to ensure that protocols are being followed and that there is evidence of it being so. Common problems encountered in these situations are best resolved through corrective and preventive actions that help address gaps discovered in monitoring and recordkeeping processes. Without these protocols in place, treatment plants may suffer from a lack of traceable data and patterns in order to benchmark their processes and discover improvement opportunities. In the local context, LEWA developed Water and Sewage Treatment Facilities Safety Standards 2013 which apply to the operation and maintenance of all water and sewage treatment facilities operated by Water and Sewerage Company (WASCO). The objectives of the safety standards are to avert accidents on water and sewage treatment plants, to mitigate health risks to workers and to ensure protection of the environment. It is the duty of the licensee to ensure that installations on its water and sewage treatment plants and the operation of the plants comply with the standards.
LEWA carries out inspections of WASCO’s infrastructure in order to monitor compliance with these standards. Inspections reveal the Company’s failure to meet some set standards for effluent quality and poor up-keep of treatment plants.
