Wastewater Treatment
Wastewater consists of a large amount of solids (total solids 350-1200 mg/l), heavy metals, nutrients, microorganisms (up to 109/ml), micro-pollutants, and dissolved and particulate matter (chemical oxygen demand 250-1000 mg/l) ) Complex matrix composition. Urban, industrial and agricultural activities generate wastewater. This is a process that removes pollutants from wastewater or sewage and converts them into wastewater. After treatment, the wastewater is safely returned to the water cycle with minimal impact on the environment or directly reused. The latter is called water recovery because the treated water can be used for many purposes. It occurs in a sewage treatment plant (WWTP), also known as a water treatment facility or sewage treatment plant.
Wastewater treatment method
Sewage treatment methods are divided into:
1. Source therapy
2. Pretreatment
3. Main treatment
4. Secondary treatment
5. Tertiary or advanced treatment of sewage
6. Sludge treatment
1. Source therapy
In this process, toxins and other unwanted pollutants are removed to prevent mixing with other wastes. Ingredients like metals can be reused from this step.
2. Pretreatment
Traditional sewage treatment includes pretreatment, primary treatment and secondary treatment. When necessary, a three-stage process is included in the sequence to remove the lowest residual level of specific ingredients. Pretreatment is used to make wastewater suitable for subsequent treatment processes. The pretreatment process includes equalization, pH adjustment, addition of nutrients, removal of oil, grease and toxic substances, and removal of solids by flotation, precipitation and filtration.
3. Main treatment
Primary treatment involves a subset of pretreatment methods, including physical separation through screening, sand removal and sedimentation. The primary treatment can remove a considerable amount of biological oxygen demand (BOD) according to the concentration of organic matter in the wastewater. The removal rate of cod in urban sewage is 35-40%, and the removal rate of precipitateable solids is 60-65%, which can be carried out in a rationally designed primary treatment plant.
4. Secondary treatment
The secondary treatment involves aerobic biochemical processes. This step involves trickling filters or activated sludge from municipal sewage streams. The improved suspension growth system is used in industrial wastewater to obtain high-quality treated effluent. In a well-designed secondary treatment plant, the removal rate of biochemical oxygen demand and suspended solids can reach 85-95%.
5. Tertiary treatment
Tertiary treatment is used to remove toxins, unconventional pollutants and persistent organic pollutants. This treatment method is often referred to as the Economically Achievable Best Available Technology (BTEA), which meets the allowable sewage standard. This includes filtration, coagulation and flocculation, gas stripping, filtration, adsorption, membrane processes, ion exchange, nitrification and/or denitrification, and other processes. Any desired removal efficiency can actually be achieved through tertiary or advanced wastewater treatment.
6. Sludge treatment
Sludge is usually difficult to treat because of its high water content and contains pollutants such as viruses and protozoa that are harmful to the environment and public health. Through aerobic/anaerobic digestion and lime stabilization, organic sludge needs to be stabilized before final disposal. Methods such as flotation, gravity or centrifugation can be used to achieve sludge concentration. The final disposal options include landfills, incineration or other reusable methods.
The need for sewage treatment
Water is very important to life, but now the world's water resources are drying up. The world’s population is increasing every day. The use of pure water is very important to the survival of life. In order to overcome the shortage of clean water, water treatment is necessary. Water care services treat wastewater, and then the water can be used for various purposes. In this way, the shortage of water will be reduced.
Sewage treatment application
The applications of sewage treatment are as follows:
■The biosolids formed by the local government and industrial wastewater during the mechanical/biological cleaning process.
■Do not directly use or remove sludge in an environmentally acceptable way.
■Fully ferment the sludge in the fermentation tank.
■Organic components are partially decomposed.
■Use the produced biogas to meet the energy demand of the sewage treatment plant.
■Reduce the amount of sludge treatment.
■Reduce the count of bacteria in wastewater.