Performance assessment of advanced water treatment processes for the removal of unregulated trace organic chemicals

The detection of a variety of chemicals in impaired water sources has raised concerns about the potential presence of wastewater-derived chemical contaminants in water produced by planned and unplanned indirect potable reuse systems. Regulatory agencies and utilities have struggled with this issue because the wastewater-derived chemicals often are present at extremely low concentrations and it is difficult to assess human health or ecological risks associated with indirect potable reuse because chemical and toxicological data for the hundreds of compounds potentially present in recycled water are lacking. Therefore, a conservative approach for monitoring indirect potable reuse systems has evolved that assumes that certain bulk measurements and a limited list of wastewater-derived organic contaminants can be used to assess the removal of all of the wastewater-derived organic contaminants of concern. The objectives of this project were to identify surrogate parameters and indicator compounds for wastewater-derived chemical contaminants that might be useful in the assessment of indirect potable reuse systems; and to validate the ability of chosen surrogates and indicators to predict the occurrence and removal of wastewater-derived contaminants in indirect potable water reuse systems. The approach for monitoring wastewater-derived contaminants developed in this study is utilizing a combination of surrogate parameters and indicator compounds tailored to monitor the removal efficiency of individual unit processes comprising an overall treatment train. Selecting multiple indicators representing a broad range of properties will allow accounting for compounds currently not identified ("unknowns") and new compounds synthesized and entering the environment in the future (i.e., new pharmaceuticals) provided they fall within the range of properties covered. The underlying concept is that absence or removal of an indicator compound during a treatment process would also assure absence or removal of unidentified compounds with similar properties. Thus, a system failure will be indicated by poor removal of the indicator compound while normal operating conditions will be indicated by partial or complete compound removal. This concept was validated through monitoring efforts at pilot- and full-scale water reuse facilities. Indicator compounds and surrogate parameters identified were classified into categories of different treatability and for each treatment process, a master list of indicator compounds was provided by recruiting compounds, for which analytical methods existed, from the final list of viable indicator compounds present in secondary or tertiary treated wastewater effluents. As expected, results of these efforts also revealed that surrogate parameters are not strongly correlated with the removal of indicator compounds occurring at ng/L-level concentrations.