Treatment Optimization of the Twin Oaks Valley WTP

This paper presents a firsthand account of how water quality and operational challenges have been addressed to improve plant reliability. The overall methodology to address each challenge, including treatability and monitored data, will be presented. ZLD facilities present unique challenges since any constituents that enter the facility in the untreated water or through chemical addition must be efficiently removed in the residual solids or leave in the treated water at permissible levels. Accumulation of these constituents can quickly impact plant capacity, and thus must be monitored and controlled proactively. Due to the closed loop nature of the ZLD system, mitigation strategies need to balance competing requirements. For example, pH suppression was evaluated to improve solids stream clarifier performance, but high source water alkalinity and subsequent needs for pH addition for treated water corrosion control drove costs too high. Polymer addition and relocation of the centrate return stream were ultimately effective, but even these required evaluating the potential for membrane fouling due to polymer carryover and speciation of DOC fractions in the recycle stream.

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