Secondary water treatment methods vs. tertiary water treatment
Wastewater undergoes a series of treatment processes before it is released to the environment to minimize danger to human health and/or the natural environment. The three main stages of wastewater treatment are Primary treatment (removal of large, settling and floating solid waste through sedimentation and skimming), secondary treatment (further removal of residual solids from the water using biological processes) and tertiary treatment (removal of dissolved substances).
Secondary and tertiary wastewater treatments are subsequent processes in water treat and have some similar aspects. Notably, both utilize biological processes. Secondary treatment principally uses bacteria to digest pollutants. The tertiary process called Biological Nutrient Removal (BNR) also uses bacteria to remove phosphorus and break down ammonia into nitrogen gas and nitrate, removing them from the water (Environmental Protection Agency, EPA Victoria, 2003).
Secondary wastewater treatment involves the removal of biodegradable colloidal and dissolved matter from the water using aerobic biological processes. The water is forcefully mixed with bacteria and water and allowed to settle to help digest the pollutants faster (Helgeson, 2009). There are multiple methods of secondary water treatment. Some of these are: rotating biological contactors, oxidation ditches and activated sludge processes. The methods differ in the manner oxygen is supplied to the microorganisms (bacteria) also in the rate at which the organisms metabolize organic matter. Secondary water treatment removes 90-95% of pollutants from water but do not remove dissolved substances (United States Environmental Protection Agency, (USEP) 2007).
Tertiary wastewater treatment removes dissolved substances from the water. These substances include metals, organic chemicals, colour and nutrients such as nitrogen and phosphorus (USEP, 2007). Contrary to secondary treatment which relies strictly on biological processes, tertiary water treatment utilizes biological, Physical and chemical processes to remove residual substances (Helgeson, 2009). According to the EPA, Victoria (2003), tertiary water treatment processes can be incorporated in the primary and secondary processes to remove the dissolved substances and non-biodegradable waste.
Uses of reclaimed water
Most regulatory agencies ban the use of reclaimed water for bathing, drinking and filling swimming pools. Reclaimed water can find a number of non-potable uses in the agricultural, municipal and industrial sectors. It can be used to recharge groundwater aquifers, irrigation, industrial cooling, fire suppression and dust control. For instance, several Los Angeles counties have used the water to irrigate parks, as well as golf courses since 1929, (USEP, 2007).
In some places, the reclaimed water has been recommended fit for all purposes except drinking. Other than reducing the impacts of waste disposal, waste water has reliable supply, saves cost by supplementing primary water sources and has potential to increase productivity (Irrigation). However, care should be taken to prevent consumption of reclaimed water since it has potential to harm human and animal health.
Use of treated water to recharge groundwater aquifers
Water is life. This by extension means that the more of it there is the more the life on earth. Water reclaimed through the secondary and tertiary treatment processes is suitable for recharging groundwater aquifers from which drinking water is drawn. This is because improved technology in water treatment has enabled the removal of most of the dissolved chemicals and substances increasing the safety and reliability of the water for drinking purposes. In case the reclaimed water is to be used to replenish groundwater aquifers from which drinking water is drawn, the water is treated to be safer and more reliable. Moreover, groundwater undergoes treatment processes before it is released for drinking making it even safer. Some municipalities are already investigating the Indirect Potable Use (IPU) of recycled water. The water is percolated down to the groundwater aquifers, drawn and re-treated for drinking. Use of reclaimed water to replenish groundwater aquifers increases the supply of drinking water for an increasing population.
References
United States Environmental Protection Agency. (2007). Septic Technologies: Background and
Technology. Retrieved from:
http://www.epa.gov/owm/septic/pubs/septic_technologies.pdf.
Environmental Protection Agency, (EPA) Victoria (2003). Environmental Guidelines for the
Disinfection of Reclaimed Water. EPA Victoria, Publication No. 730.1.
Helgeson, T. (2009). A Reconnaissance-Level Quantitative Comparison of Reclaimed Water,
Surface Water, and Groundwater. Alexandria, VA: Water-Reuse Research Foundation.
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