Most water treatment facilities employ a variety of physical/chemical treatment processes and involve the addition of a variety of chemicals for an array of purposes, such as to oxidize iron and manganese, coagulate suspended solids, render the water less corrosive and disinfect the water. While the industry standard treatment processes are tried and true, there are a number of “natural” low-tech treatment strategies that when used alone, or in conjunction with conventional strategies, can reduce chemical usage and sludge production, and lower operation and maintenance costs.
Natural pH Adjustment Strategies
Typical water treatment strategies require an optimal pH range and thus some form of pH adjustment for a variety of reasons such as chemical process optimization, corrosion control and minimization of disinfection system byproduct formation. Typically the pH adjustment is done with chemicals, such as caustic soda, lime, soda ash, or sodium bicarbonate. There are a couple of natural alternatives as profiled blow.
Low pH groundwater sources are frequently very high in dissolved carbon dioxide and require an excessive amount of chemical addition to adjust the pH (because of the excessive buffering capacity from the carbon dioxide). One natural way to raise the pH of the ground water is through aeration. Aeration will strip off dissolved carbon dioxide and raise the pH of the water. If there is radon present in the water, it will also be stripped. Aeration can be a cost effective alternative for water with the appropriate characteristics.
Another natural way to raise the pH of water is by allowing the finished water to flow through a bed of crushed limestone (limestone contactor). Limestone is a naturally occurring rock that can be crushed and processed to produce a uniform granular material, which, when used in a properly designed limestone contactor, will allow the pH finished water to be in the range of 7.2 – 8.3. With a limestone contactor there is no chemical feed facilities to maintain and no concern for over feeding a chemical such as caustic soda.
Low-Tech Filtration Strategies
Most surface water treatment systems involve coagulation, flocculation and filtration systems to remove colloidal/suspended solids and pathogens and produce water low in turbidity. These processes tend to use a fair amount of chemicals, they require operational oversight, and produce significant quantities of sludge. One natural way to pre-treat the water and improve the quality of the water entering the treatment plant is to employ bank filtration. Bank filtration involves installing a well near the surface water source to allow pulling water through the ground to effect some natural filtration. This concept requires granular soils adjacent to or under the surface water source. Where these conditions exist, there can be significant benefits with employing bank filtration.
Slow Sand Filtration
Another low-tech way to filter surface water is with a slow sand filter. Slow sand filters are large open sand beds without any backwashing mechanism, appropriate for small water treatment systems. They are excellent at removing coliform bacteria and protozoans such as Giardia and Cryptosporidium. A slow sand filter not only physically filters the water, but also provides biological treatment from an organic mat which naturally forms on the filter surface. A slow sand filter can reduce microbial contaminants without the high cost of coagulation or pre-treatment chemicals needed for common high rate filters.
Biological Iron and Manganese Removal
Iron and manganese have been major aesthetic concerns in many groundwater supplies for years. While these constituents have been regulated with secondary standards for years, manganese in particular, is gaining new notoriety and is being considered for regulation as a primary standard. The most commonly used treatment for iron and manganese removal has been some variation of greensand filtration. In this case a chemical is added to the water to oxidize the iron and manganese so they can be filtered out. Membranes and ion exchange systems have been used in cases where oxidation/filtration removal has been difficult. An alternative to these processes is the use of “natural” bacteria to remove iron and manganese. Bacteria can be grown on a filter media that will remove iron and manganese. The bacteria are aerobic and require dissolved oxygen and an appropriate pH range. The benefits of this type of removal include less chemicals and less sludge generated in the process.
While natural low tech water treatment strategies are not applicable everywhere, they can be very effective in the right application. Wright-Pierce has been a leader in employing alternative natural processes for pH adjustment, filtration and iron/manganese removal.