Characterisation of treated effluent from four commonly employed wastewater treatment facilities: A UK case study

Abstract

Sewage treatment systems are a common feature across the landscape of the United Kingdom, serving an estimated 96% of the population and discharging approximately eleven billion litres of treated wastewater daily. While large treatment facilities are ubiquitous across the landscape, they are not the only method employed in domestic wastewater treatment. This study investigates whether differences in nutrient export (carbon, nitrogen and phosphorus) and organic matter composition (determined by optical indices, SUVA254, S350-400 and E2:E3) from treated effluent could be detected between four of the most common facilities employed in the treatment of wastewater across the U.K. Set in the context of the River Wylye, a small headwater catchment, treatment facilities studied included; a septic tank system, small packet treatment works, and two large sewage treatment works, one of which employed phosphorus stripping for phosphorus removal. Inorganic N and P concentrations ranging between 7.51 and 42.4 mg N l-1 and 0.22 and 8.9 mg P l-1 respectively, with DOC concentrations ranging between 1.63 and 11.8 mg C l-1. Optical indices were comparable to those observed in microbially dominated endmember aquatic systems suggesting the dominance of low molecular weight material when compared to values observed across temperate aquatic systems. Combining data from both the Environment Agency and Ordinance Survey we estimate that only 25% of domestic properties in the study catchment have a corresponding Environment Agency consent/exemption permit meaning the numbers of small discharges are significantly underestimated, thus undermining efforts under current legislation to improve stream ecosystem health.

Variation in dissolved organic matter (DOM) stoichiometry in U.K. freshwaters: Assessing the influence of land cover and soil C:N ratio on DOM composition

“…In addition to inputs of DOM from agricultural land, lower DOC : DON ratios observed in our study could be explained by the presence of effluent discharge from septic tank systems often associated with rural riverside properties, as well as larger STWs where these were present within these two study catchments (Yates et al ). Due to regulation surrounding septic tank system design in the United Kingdom, such systems are often indistinguishable from diffuse nutrient sources.…”

“…In marked contrast to the acidic soils and geology of the Conwy, the Nadder catchment drains land underlain by base‐rich sedimentary rocks, supporting intensive arable production on the chalk to the middle and north of the catchment and intensive cattle production on heavy clay soils to the west of the catchment. The Nadder catchment also receives significant nutrient and organic matter input from treated wastewater discharges from large urban conurbations and riverside villages (Yates et al ). Elevation across the Nadder catchment ranges between 51 and 283 mAOD and has a mean AAR of 875 mm (1961–1990; station: Nadder at Wilton).…”

“…In most natural or seminatural catchments, allochthonous sources dominate the aquatic DOM pool, derived mainly from the degradation of vascular plant material and soils and its incorporation into animal and microbial biomass, with soil biogeochemical processes acting to mediate the delivery of this material to aquatic systems (McDowell and Likens ; Mattsson et al ). However, catchments impacted by agricultural intensification (Graeber et al ; Yates et al ), subject to urbanization (Aitkenhead‐Peterson et al ), or heavily impacted by sewage treatment works (STWs; Sickman et al ; Yates et al ), have demonstrated increases in both DOM concentration and its relative nutrient richness (measured as DON and DOP). Not only is DOM concentration therefore known to vary in relation to catchment character (Palviainen et al ) but also a wide range of studies have observed compositional differences in DOM related to specific catchment sources (Mattsson et al ; Spencer et al ; Hernes et al ; Yates et al ).…”

Untargeted characterisation of dissolved organic matter contributions to rivers from anthropogenic point sources using direct‐infusion and high‐performance liquid chromatography/Orbitrap mass spectrometry

“…The concentration and presence/absence of target compounds across different sewage treatment works have been found to vary between different sites and over time. 13,15,16,18,19 With over 9000 sewage treatment works in the UK and numerous other point sources, the identification of potentially ecotoxicological compounds remains a challenge. Without identifying these micropollutants; the determination of ecotoxicity, effective mitigation solutions and environmental monitoring cannot be carried out.…”

Phosphorus stocks and flows in an intensive livestock dominated food system

“…In common with other rural populations (e.g. Yates et al., 2019 ), opportunities for using advanced P removal technologies, such as struvite recovery, in wastewater treatment are not yet cost effective, though different nature based technologies such as constructed wetlands ( Vymazal, 2011 ) or short rotation coppice willow plantations grown for bio-resources ( McCracken and Johnston, 2015 ) could provide cost effective opportunities for reducing P loss to water in these situations.…”