Harnessing the power of the census: characterising wastewater treatment plant catchment populations for wastewater-based epidemiology

Wastewater studies that provide per-capita estimates of consumption (influent) or release (effluent) via wastewater systems rely heavily on accurate population data. This study evaluated the accuracy of WasteWater Treatment Plant (WWTP) reported populations, as well as hydrochemical parameters, against accurate populations from a population census. 104 catchment maps were received from WWTPs, geo-located in geospatial software and overlaid with the smallest area unit of the Australian census, equating to 14.9 million Australians or 64% of the national population. We characterised each catchment for population counts, as well as by age profile, income profile and education level. For a subset of sites, population estimates using hydrochemical parameters BOD, COD and dissolved ammonia were evaluated for accuracy against census populations. Compared to census-based estimates, population estimates provided by WWTP personnel were overestimated by 18% on average. Similarly, hydrochemical-based population estimates had high RSD (> 44%) for BOD, COD and ammonium between sites, suggesting their applicability for use in population estimation may not be appropriate for every WWTP. Surprisingly, 46% of catchments had a skewed age distribution; 6% skewed older and 40% younger. Through this process WWTP catchment populations can be characterised in a way which will enhance the interpretations of per-capita estimates