Slow Sand Filtration for Disinfection of Secondary Effluent From a Wastewater Treatment Plant.

摘要

Low-cost, reliable disinfection of secondary effluent is needed at wastewater treatment plants in small communities in developing countries to reduce pathogens to a level required for reuse. There is currently a wastewater treatment plant in Solola, Guatemala that reuses all of the effluent for crop irrigation. The reuse of this wastewater poses a public health risk to the community because the treatment plant lacks disinfection. In treatment plants such as this, a simple, gravity-fed disinfection system is needed. Five pilot scale slow sand filters were tested in three phases to determine the feasibility of slow sand filtration as a disinfection step in small wastewater treatment facilities, as well as to characterize the level of treatment achieved in the process. In the first phase, secondary effluent from the UC Davis treatment plant served as the influent to the sand filters. The time required between maintenance events in Phase 1 ranged from 7 to 114 days. In the second phase, effluent from a pilot scale wastewater treatment system (i.e. a septic tank treating municipal wastewater from UC Davis followed by a plastic-media trickling filter) intended to replicate the treatment system in Solola was used to feed the sand filters. The third phase focused on investigating the effect of various sand sizes on maintenance frequency and treatment capability. The experimental results indicate that when fed low-turbidity influent water (e.g. < 2 NTU), slow sand filters can achieve significant turbidity reduction and 1.18-log to 1.67-log removal of coliform. However, when fed high-turbidity water, slow sand filters clog quickly and produce effluent high in turbidity, and therefore may need additional pre-treatment in order to be feasible in communities such as Solola.