The combination of sequential chlorination and flow equalization will satisfy the first objective, reliably meet Title 22 disinfection requirements for unrestricted use at permitted capacity, because sequential chlorination requires less contact time and an equalization tank will reduce the peak concentration and flow rates. During periods when the influent contains high levels of ammonia or when the flow rate to the plant exceeds a predetermined level, some flow can be diverted to the equalization tank. The diversions will result in lower constituent loadings on the plant and lower overall flow rates.
The second objective, increase volume and availability of recycled water for reuse, will be satisfied by this alternative because the effluent flow rate from the plant will be more constant and the minimum effluent flow rate will be higher than it would be without flow equalization. This is a result of feeding flow collected in the equalization tank back into the process when flows are lower, therefore increasing the flow and production of recycled water during that time.
Institution of sequential chlorination will fulfill the requirement of the final objective, minimize formation of disinfection byproducts at the permitted capacity, because both THMs and NDMA will be reduced. Free chlorine added to fully nitrified secondary effluent reacts with NDMA precursors, therefore reducing subsequent NDMA formation. Chloramines are then added to media filtered effluent to stop formation of THMs. Sequential chlorination reduces NDMA formation by 50 to 85 percent in comparison to chloramination and produces effluent consistently meeting the total THM limit for recycled water (Maguin et al. 2009).
Los Angeles County Sanitation District
Provide chlorination and flow equalization to increase the volume and availability of recycled water for reuse.
Project Benefits a Disadvantaged Community (or SDAC):