Sewage water recycling
Sewage water recycling involves removing of impurities from the water through various physical, chemical and biological processes. If the sewage water goes untreated, there may be bitter consequences in the future with impacts on human health. Several governments in the world have made in mandatory for allocating sewage treatment plant for a particular area. The treatment of sewage is a very big process and the resulting water is safe to use and does not cause any disease to the human beings. The recycled water can be used to irrigate golf course thus saving gallons of drinking water. It can be used for irrigation in agricultural lands thus saving ample amount of ground water. It can be used for car wash in servicing centres. The other common domestic usage of recycled water can be for vehicle wash or gardening in homes.
Sewage Water Treatment
There are two types of sewage treatment. The first is the decentralised system where the process of recycling like aeration and filtering takes place close to where the sewage is collected. The other method of treatment is the centralised system where the sewage is transported through pipelines to a central municipal unit where several processes are done before discharging water into the environment. The main steps in sewage water treatment include pre-treatment, primary, secondary and tertiary treatments.
Pre-treatment
In this process, the solids that can be easily removed from the waste liquid is removed. The bigger solids like tree branches, sticks and plastics which could possibly cause damage to the pumps and pipe lines are removed. The water moves through a screening layer for removing all heavy materials. There is a grit removal section in pre-treatment which allows for constant velocity of sewage flow for the next treatment section.
Primary Treatment
The primary treatment involves removal of physical solids from the water by the process of sedimentation. The entire content is held in a huge basin and allowing the physical impurities to settle. The floating materials are removed by a special process and the liquid is alone transferred to the secondary treatment. A saponification process is carried out to remove the oil and grease from the water. The greasy materials come to the surface as froth and they are skimmed off.
Secondary Treatment
In secondary treatment, micro-organisms are used to treat the sewage water. They remove the dangerous microbes from the liquid, changing its colour and odour. However the micro-organisms are later removed before getting discharged to the tertiary treatment. The secondary treatment comprises of activated sludge process and aerobic granular sludge process which has an aeration tank to provide oxygen for bacteria helping to convert organic materials. The main conversion done here is changing ammonia to nitrates and then to nitrogen gas. Sometimes rotating biological contractors are used which are huge in size and holds the organic matter and bacteria while the conversion takes place. Finally before going to the tertiary treatment, secondary sedimentation is done which removes almost all suspended and organic matters.
Tertiary Treatment
This involves high degree of filtration involving lagoons or micro filtrations. Initially sand filtration is done to eradicate suspended impurities or sometimes carbon adsorption is done so that all dangerous microbes are removed. This is followed by nutrient removal process. This process is very important as the resulting water now contains large amount of nitrogen, phosphorous, etc. which helps in algal growth leading to eutrophication. After removing nitrogen and phosphorous, finally the disinfection process is carried out where the water is treated with UV or ozone and then the resulting water is discharged to nearby irrigation centres or any other place through pipelines.
