Wastewater, in general, refers to any water that isn’t fit for any kind of use. Typically, wastewater consists of domestic, industrial, and agricultural run-off. And the biggest challenge is separating each of these organic and inorganic compounds to obtain water that’s clean and safe for drinking and other purposes.
Since this is a massive task, treatment of wastewater is done in three stages; primary, secondary, and tertiary; each of which deals with a different aspect of cleansing.
What is wastewater treatment
Treatment of wastewater is a major step in preventing the pollution of our freshwater resources. The process uses specialized machines to remove pollutants such as metals, debris, microorganisms, and biowaste from the water before it is returned to its source, be it surface water or groundwater.
Been in use for decades now, wastewater treatment helps remove or destroy pollutants in wastewater to achieve water quality standards. From an environmental point of view, conservative wastewater treatment methods have proven their worth by making sure that harmful chemicals within the water are safely eliminated.
There are four types of wastewater treatments
Stages of wastewater treatment
Primary wastewater treatment
Primary treatment of wastewater refers to mechanical and biological processes that remove solids, settleable materials, and other impurities from wastewater contaminants that can’t be broken down into smaller components.
The first stage of wastewater treatment is done in a series of tanks and clarifiers. The clarification process involves the removal of 50 to 90 percent of solids and floatable materials from wastewater.
Solids removal relies on providing the right conditions for biochemical, physical, and other natural processes to remove solid matter. The basic aim of primary wastewater treatment is to stop human health hazards, protect freshwater ecosystems and preserve the quality of receiving waters.
This is achieved by screening (large solids removal), sedimentation (settling of heavy materials) or skimming (floaters or light materials), grit removal, chemical precipitation, biological treatment (sewage sludge settled on the bottom), flocculation (clumping of particles to form bigger particles) and disinfection.
Secondary wastewater treatment
Secondary wastewater treatment is a two-stage process. First, the wastewater is allowed to settle for several hours (or days). This allows large particles, such as grit and gravel, to settle to the bottom. The water is then removed from the top and sent to the next treatment stage.
The purpose of this stage is to remove suspended solids, settleable particles, dissolved chemicals, and other pollutants from anaerobically digested primary sludge.
Secondary treatment works to eliminate contaminants that weren’t fully taken care of by primary treatment. It does so using three methods; biofiltration, aeration, and oxidation ponds.
Tertiary wastewater treatment
Tertiary wastewater treatment is the process that follows primary and secondary wastewater treatment. While the primary and secondary treatments target the physical and inorganic removal of large solids, tertiary focuses on making the water safe for drinking.
This stage of treatment includes a number of processes that improve the quality of the already treated wastewater to the point where it can either be returned directly into the natural environment or used for household purposes.
Tertiary treatment processes include activated carbon filtration, advanced oxidation processes, ozone injection, and reverse osmosis. The aim is to dilute water enough so that it won’t have adverse effects on the environment, plants, wildlife, or humans.
Wastewater in this final stage is treated in two parts; disinfection and dichlorination.