Mitigating Variable TDS Levels in Wastewater Biotreatment

Wastewaters characterized by elevated Total Dissolved Solids (TDS) levels and high organic content are produced by food, petroleum, and petrochemical facilities.  High TDS effluents have been traditionally treated by primary physical and chemical means.  Following pretreatment, water characterized by high organic content combined with high TDS effluents can be treated by biological means to achieve carbon, nitrogen and phosphorous removal.  Stable performance of primary and biological treatment steps is essential for meeting effluent discharge limits and for optimizing performance of posttreatment steps.

For high TDS wastewater, biological performance depends on the proper adaptation of the biomass to changes in wastewater conditions. Adaptation potential can be enhanced by the introduction of halophilic microorganisms to the wastewater biomass.  Another critical design consideration for TDS treatment is that concentrations are often subject to fluctuations, including variation in the rate of change.  When TDS is not maintained within acceptable limits, the operability of biological treatment systems can be adversely impacted by concentration fluctuation, such as that arising from upstream process changes.

This paper discusses the effects of TDS concentration changes when treating combined high TDS and high organic strength wastewater.  The objectives of this discussion on TDS concentration changes are to: (1) define from literature sources the observed response of biomass characteristics, such as the impact on biokinetics, and the cited industry design margins for treatment systems; and (2) present a case study that explores process design options for buffering variable TDS levels.  The Case Study is of a wastewater treatment system from chloralkali by-product manufacturing.

The process design for a biological treatment system depends on the wastewater characteristics and equalization capacity.  To most effectively treat wastewaters, an acceptable level of influent TDS fluctuation must be defined.  The proper determination of acceptable variability is critical to the design of a biological treatment system for high strength TDS and organic wastewaters to maintain the required operating efficiencies.