Safe Drinking-Water Supply for Small and Rural Communities in Newfoundland and Labrador with a Case Study of Pouch Cove
Chlorine is the most common disinfectant used in the province of Newfoundland and Labrador. However, in the presence of natural organic matter (NOM) in drinking-water sources, disinfection by-products (DBPs) are formed when chlorine is used to treat drinking water. The two largest groups of DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs), are frequently studied by researchers because of their toxicity and high levels in drinking water.
In 1998 Newfoundland and Labrador began monitoring THMs and HAAs and it was found that several water utilities had THMs and HAAs above the specified Canadian guidelines, mostly in small, rural drinking-water systems. Pouch Cove was selected for this study as elevated levels of THMs and HAAs were found in their drinking-water system.
This study focused on the development of a simple and affordable filtration technology. A passive carbon barrier was studied in the lab to remove NOM, commonly measured as total organic carbon (TOC), before chlorination. The carbon barrier was made from extracted unburned carbon from oil fly ash (OFA), which is abundant within Canada and abroad. The passive nature of this barrier makes it easy to operate and its extremely low cost makes the system affordable for small communities. The OFA samples used for this study were obtained from the Rabigh power plant in Saudi Arabia, which currently generates about 60 tons of OFA daily and currently being disposed into landfills.
Since raw OFA contains organic and inorganic impurities, study samples were cleaned and treated through one of two processes, acid leaching or NaOH modification, followed by physical activation. Activated carbon (AC) samples were then applied to reduce the TOC and UV in the Pouch Cove drinking-water samples. In this adsorption treatment, a Split Plot design was employed to investigate the effects of different factors (pH, temperature, carbon dosage, sample volume, and contact/adsorption time), as well as the interaction effects among these factors. The results indicate that pH, temperature, carbon dosage, and sample volume are significant factors in designing a filtration technology. The optimal condition for TOC and UV reduction is a low temperature and a low pH. When the temperature is over 35 degrees Celcius, or the pH is greater than 8, no reduction was observed. The overall TOC removal by activated OFA is relatively low; the maximum removal rate can reach 66% within 30 minutes. Compared with NaOH-modified AC, acid-leached AC is a better adsorbent to achieve TOC and UV reduction.