Finding and maintaining a clean water supply for drinking and other uses has been a constant challenge throughout human history.
Today, significant technological developments in water treatment, including monitoring and assessment, help ensure a drinking water supply of high quality. The source of water and its initial condition prior to being treated usually determines the water treatment process. [See also Water Recycling.]
Just as the earth’s hydrologic cycle continually recycles water, water is repeatedly cleansed through several natural processes. For instance, solids settle to the bottom of water bodies and impurities are filtered out when water percolates or seeps through rocks, gravel, or sand and back into groundwater sources.
Similarly, water treatment technology has been developed to mimic nature’s cleansing process but at a faster rate and with greater control over completeness and efficiency.
Advanced treatment processes are used to reach the water quality levels necessary for the intended usage.
In general, surface water treatment problems involve more microbial types of contamination, or suspected carcinogens produced by the standard chlorine disinfection process. Groundwater problems often are related either to naturally occurring contaminants, or to seepage of chemicals from industrial manufacturing, septic tanks or farming into water supplies.
Water Treatment Overview
Water treatment technology must deal with a number of potential perils resulting from the movement of water from its source to tap.
These contaminants can include naturally occurring sulfur, zinc, or arsenic-laden formations. Groundwater can pick up contamination from fertilizers, septic tanks, mine drainage, or naturally occurring minerals. Rivers and streams sometimes carry harmful microorganisms from animals or humans, presenting a risk of disease. Storm drains can carry polluted runoff from cities into rivers and streams. Pollutants and contaminants also can enter the water from farm drainage and sewage treatment plants.
Other potential sources of pollution include landfills where rainwater can soak into the ground and leach out harmful substances and carry them into groundwater. In homes, factories and buildings, corrosive water can dissolve lead in water pipes.
The Treatment Process
Primary treatment removes wastewater solids by sedimentation. During this treatment, wastewater flows slowly through a tank allowing suspended particles that are heavier than water to settle to the bottom of the tank. From there, the solids are pumped to digesters for stabilization. Primary-treated municipal wastewater is not used in California for irrigation or any other use.
Secondary treatment is a biological treatment process involving oxidation and sedimentation of primary treated wastewater. It uses bacteria to remove approximately 90 to 95 percent of the solids remaining from the primary treatment.
Tertiary treatment – often called Title 22 in California under the California Code of Regulations – involves coagulation, flocculation, clarification, filtration and disinfection of secondary treated water.
Finally, at most wastewater treatment plants scum and biosolids undergo significant treatment, often through a process called anaerobic digestion. This includes heating material to 100+ degrees to help break it down and destroy pathogens. Other processes include composting and heat drying.