DBPs removal in GAC filter-adsorber

Abstract

A rapid sand filter and granular activated carbon filter-adsorber (GAC FA) were compared in terms of dissolved organic carbon (DOC) and disinfection by-products (DBPs) removal. A water treatment plant (WTP) that had a high ammonia concentration and DOC in raw water, which, in turn, led to a high concentration of DBPs because of a high dose of pre-chlorination, was investigated. To remove DBPs and DOC simultaneously, a conventional rapid sand filter had been retrofitted to a GAC FA at the Buyeo WTP in Korea. The overall removal efficiency of DBPs and DOC was higher in the GAC FA than in the sand filter, as expected. Breakthrough of trihalomethanes (THMs) was noticed after 3 months of GAC FA operation, and then removal of THMs was minimal (<10%). On the other hand, the removal efficiency of five haloacetic acids (HAA 5) in the GAC FA was better than that of THMs, though adsorption of HAA 5 decreased rapidly after 3.5 months of GAC FA operation. And then, gradual improvement (>90%) in HAA 5 removal efficiency was again observed, which could be attributed to biodegradation. At the early stage of GAC FA operation, HAA 5 removal was largely due to physical adsorption, but later on biodegradation appeared to prevail. Biodegradation of HAA 5 was significantly influenced by water temperature. Similar turbidity removal was noticed in both filters, while better manganese removal was confirmed in the sand filter rather than in the GAC FA.