Chemistry for the Treatment of Surface and Borehole Water
Understanding the type of issues associated with surface and borehole water facilitates the process of selecting the correct chemistry for the water treatment plant.
When it comes to determining which chemicals need to be incorporated into your water treatment system, one critical factor in making that decision will come down to the type of issues associated with the particular water source. In this article, the two water sources that will be unpacked, along with their respective issues and solutions, are surface and borehole water.
Surface water, such as dams and rivers, is the primary source of water for most people.
The two major issues with surface water are:
The variability of volume and quality
The quality of the water
In terms of quality, the main points of concern of surface water are usually low pH levels, low alkalinity, suspended solids (such as sand and grit), organics, microbial content (bacteria), and low concentrations of inorganic metals, e.g. iron and manganese.
The main chemical processes used to address the abovementioned issues affecting the quality of the surface water are pH and alkalinity correction, coagulation, and disinfection. These are discussed below.
pH and alkalinity correction: Chemistry such as calcite, lime and sodium hydroxide can be introduced to the water treatment system in order to increase the levels of pH and alkalinity in the water. This also assists in the precipitation of the metals.
Coagulation: Suspended pollutants, such as solids and organics, that are either too small to be filtered or remain stubbornly stable in solution, require the addition of a coagulant to allow them to either settle out of solution or clump together in order to be filtered.
Disinfection: Chemistry such as sodium hypochlorite and chlorine dioxide can be used as an oxidant and, in turn, a disinfectant. This keeps biological growth at bay through to point of use, ensuring that the water remains clean, clear and bacteria-free.
Boreholes are typically not subject to variation in volume and quality. The quality, however, differs drastically from one borehole to another.
The groundwater from boreholes tend to contain large quantities of metals such as iron and manganese; high levels of total dissolved solids (TDS); excess amounts of sodium; and a high level of microbial content.
The main chemical processes used to address these issues are listed and explained below:
pH and alkalinity correction: As with surface water treatment calcite, lime or sodium hydroxide is often introduced in a borehole water treatment system. This maintains the pH and alkalinity at the required set point and, in turn, also increases the LSI (Langelier Saturation Index).
Oxidation: Sodium hypochlorite or chlorine dioxide is often introduced to assist in the oxidation of dissolved metals, organics and microbial content before filtration commences.
Disinfection: Sodium hypochlorite or hydrogen peroxide is introduced, ensuring all water sent to and stored in the final water tanks has a small residual disinfectant present. The presence of a disinfectant will keep biological growth at bay through to point of use.
If you are ever in need of a tailored water treatment solution, WPS is available to provide expert assistance anywhere in South Africa. Contact us anytime to discuss your water-related challenges. We would be honoured to help out in any way we can!