Pretreatment of Water at a Water Management Plant
Water that comes from lakes, rivers, and streams must be treated before it can enter your household tap. This is because water supplies may contain germs, chemicals, and/or toxins.
Sewage water includes all the toilet and laundry wastewater as well as waste liquids from industries. The water flows through various treatment processes before it reaches the sewage plant.
Pre-treatment
The pretreatment of water at a water management plant helps reduce the risk of contamination. This process removes organic matter, phosphates, and other contaminants from the water before filtration. The water is then disinfected to kill any harmful microorganisms that are still present.
A primary function of pretreatment is to protect filtration equipment from fouling and scaling. Fouling occurs when suspended particles, organic matter, and microorganisms accumulate on membrane surfaces and obstruct water flow. Scaling results from the precipitation of minerals on membrane surface, reducing filtration efficiency. Prefilters remove these contaminants before they reach the finer filtration equipment.
The pretreatment plant processes incoming Hanover County sewage effluent (grey water), backwash water from the oily wastewater collection system, and power block blowdown waste. The incoming raw water enters the plant through a rapid mix unit that creates turbulent mixing energies to disperse chemical coagulants into the water and start the coagulation process. It then flows into a clarifier and two 100% flow dual media anthracite/sand depth filters.
Primary treatment
A wastewater treatment plant may use a combination of methods to treat sewage, and the first step in this process is primary treatment. This process is designed to remove any large debris and organic matter from the water. It also contains processes that reduce the amount of nitrogen and phosphorus in the water.
This step involves chemical dosing and coagulation of the water. The dosing process uses a rapid mix unit that creates turbulent mixing energies to evenly disperse chemical coagulants. The coagulants are used to help break down naturally-occurring organic material and to make it easier to remove other chemicals from the water.
The aeration tanks at this stage contain bacteria and microorganisms that degrade the organic waste in the water. These organisms eat the organic short-chain carbon molecules from the food, soap, and detergent in the water. After this step, the resulting biological sludge is separated from the water in large circular tanks called clarifiers.
Secondary treatment
A water treatment plant works to provide clean water for a community. This process removes germs, chemicals, and particles that may be harmful to humans and animals. Depending on the source of water, it may require additional treatment to meet quality standards. These standards include reducing bacteria, viruses, and other contaminants to acceptable levels.
The treatment process also involves screening and removing large materials that may clog or damage equipment. This includes twigs, leaves, paper, and other debris that might obstruct flow. These materials are screened and sent through a comminutor for grip disposal. The sludge is then pushed through a dual media depth filter and a clarifier.
The sludge from this process is then thickened and dosed with polymer before it is sent to the dewatering press. The facility is currently undergoing two large clarifier replacements to increase the capacity of the facility. A contingent valuation method was used to determine the cost-benefit of the project and to identify determinants of willingness to pay (WTP). The result is a sustainable management strategy that has the potential to address the community’s needs for clean water.
Tertiary treatment
Tertiary treatment of water at a wastewater plant takes place after the primary and secondary stages. It involves additional filtration and disinfecting. It also removes nutrient and pathogenic content and other non-biodegradable compounds.
This final stage of sewage water treatment allows for more stringent levels of cleanliness than that achieved with only primary and secondary treatments. These stricter standards are needed when the treated water is to be used in water-intensive processes or as drinking water.
After the tertiary treatment stage, the water is clean and safe for human consumption. It should be free of harmful microorganisms, nutrients and heavy metals, and other chemical pollutants. The JC France Industrie team has assessed the various tertiary treatment methods available by evaluating their technical efficiency, economic feasibility, and environmental impact. The photo-Fenton process was found to be the most effective. It significantly reduced the microbial load and pharmaceutical concentration of secondary effluent by 4.9 log and 84%, respectively.