ACID ADDITION SIMPLIFIES SWITCH TO SODIUM HYPOCHLORITE BASED DISINFECTION

The City of Henderson (NV) Water Reclamation Facility recently switched from chlorine gas to liquid sodium hypochlorite based solution for disinfection and in-plant use to eliminate the safety hazards associated with gas storage. The new hypochlorite system maintained the existing production of a chlorine solution to feed multiple application points throughout the plant, making the conversion straightforward for the operators. The early success of the conversion was tainted due to calcification that was occurring in the solution lines. Several alternatives were considered to reduce the calcification in the hypochlorite feed system. Including pH adjustment, dilution to lower pH of solution, softening or R.O. treatment of dilution water, and conversion to a “neat” feed system. Pilot testing was performed on an acid feed system with this alternative selected for implementation. pH adjustment was straight forward to implement, low cost, and with minimal maintenance required. It was found that though a final solution pH of 6 produced a solution free of precipitates, operation at a pH of 7.5 would not result in the deposition of carbonate precipitate, thus minimizing chemical costs.