SWITCH TO CHLORAMINATION IMPROVES DISINFECTION EFFICIENCY OF AWT EFFLUENT TO MEET STRINGENT TOTAL COLIFORM STANDARD

The recent improvements at the City of Henderson (NV) Water Reclamation Facility have brought to the forefront the difficulties experienced at many POTW's to consistently meet stringent disinfection limits of high quality effluents. The City of Henderson practices reclamation with a self-imposed effluent standard of less than 2.2 MPN total coliform. Shortly after a switch to hypochlorite disinfection, there was a substantial increase in chlorine demand for disinfection and the ineffective use of the chlorine applied. The problem was traced to the lack of ammonia in the well-nitrified effluent, which resulted in chlorine reacting rapidly with organics rather than being available for disinfection. After evaluating possible solutions, the City decided to install an ammonium hydroxide feed system to create chloramines to improve disinfection. Pilot testing was performed to determine the effectiveness of the ammonium hydroxide, to determine if a reduction in chlorine usage could be realized, and determine the feasibility of eliminating the practice of rechlorination to create a residual for the reclaimed water distribution system.