Use of activated carbon from oily fly ash to remove disinfectant by-products from drinking-water supply systems in small communities
Disinfection by-products (DBP) are formed in drinking-water supply systems due to chlorination and the presence of precursors such as dissolved organic carbons (DOC). Some of these disinfection by-products are harmful to human health and have been shown to be carcinogenic. There are hundreds of different types of known DBPs associated with different forms of disinfection, and it is difficult to monitor all of them. Recent focus has, however, been on two groups of DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs), since these have been identified as the largest class of DBPs detected in chlorinated drinking water.
In the province of Newfoundland and Labrador, chlorine is the most commonly used form of disinfection. Out of 536 public water supply systems, 459 use chlorine. The province started monitoring trihalomethanes and haloacetic acids in 1998; it found that 124 water systems had high levels of THMs and 184 had high levels of HAAs, levels above the specified Canadian guidelines. Most of these exceedances occurred in small, rural drinking-water systems.
The formation of disinfection by-products in drinking water is due mainly to the presence of natural organic matter (NOM) in the raw water which react with residual chlorine, forming DBPs in the chlorinated water. This study shows that the effective way to reduce THMs and HAAs in the drinking water is to remove the NOM, measured as total organic carbon (TOC), before chlorination. There are several treatment options, such as coagulation, reverse osmosis, and activated carbon filtration, but among these options, activated carbon filtration is the most effective to remove NOM. However, for small communities activated carbon technology is expensive due to the cost of the raw materials used in the development of the technology. In order to find a cost-effective and affordable raw material, a research study is being conducted on the beneficial uses of oily fly ash (OFA) generated by the burning of heavy fuel oil. This fly ash contains 80-90% unburned carbon. This study shows that the carbon extracted from OFA efficiently removed 70-90% of the total organic carbon (TOC) from the intake water in Torbay and Pouch Cove. These communities have high levels of THM and HAA in their drinking-water systems. Both raw and filtered water were chlorinated to study the formation potential of THM and HAA. It was found that the filtered water had much lower THM and HAA levels, even lower than the limits specified by Health Canada, than the raw water. The cost of extracting carbon from OFA is one-fifth to one-sixth of the cost of the activated carbon available in the market; spent carbon can also be regenerated.