An investigation of domestic wastewater treatment systems impacts on surface waters and applicability of wastewater fingerprinting compounds

Abstract

This research estimated the P and N loading to surface water arising from domestic wastewater treatment systems (DWWTS) and compared a range of wastewater fingerprinting techniques for identifying sources of surface water contamination. In particular, the aim was to quantify the extent of pollution from DWWTS as distinct from agricultural sources. Four small catchments, each containing a high density of DWWTS (15 - 32 DWWTS km-2) and underlain by either poorly permeable subsoil or shallow, impermeable bedrock, were selected for study.

Using a catchment P loading schematic, the P loading arising from DWWTS was found to represent between 1.5 % and 9 % of the annual P loading from the four study catchments. Likewise, between 10 % and 29 % of the annual N loading was estimated to arise from catchment DWWTS. These results were found to be in close agreement with those generated by the EPA?s Source Load Apportionment Model (SLAM) software for the same catchments.

A number of models were examined with the aim of estimating the P contribution of a given DWWTS as a function of its distance from the stream. Across the four catchments studied, a power inverse model was found to provide a good description of DWWTS-P loading with distance, describing a gradual decrease in P loading to the stream with increasing distance.

A range of fingerprinting parameters aimed at identifying chronic and incidental contamination arising from domestic wastewater inputs was also studied. This list of chemical and biological domestic wastewater ?fingerprinting? compounds comprised ammonium, faecal indicator organisms, human-specific Bacteroidales, faecal sterol ratios (FSR), fluorescent whitening compounds (FWCs), caffeine, artificial sweeteners and pharmaceutical compounds.

Based on observations of the success of the DWWTS tracers examined in this study, a ?tiered-approach? into the investigation of malfunctioning DWWTS is proposed, wherein the tracers that were studied in this research can be applied in a step-wise manner to isolate the DWWTS(s) causing water quality issues in a given catchment.