Evolution of the sewage treatment plant model SimpleTreat: Use of realistic biodegradability tests in probabilistic model simulations

Abstract

Given the large number of chemicals under regulatory scrutiny, models play a crucial role in the screening phase of the environmental risk assessment. The sewage treatment plant (STP) model SimpleTreat 3.1 is routinely applied as part of the European Union System for the Evaluation of Substances to estimate the fate and elimination of organic chemicals discharged via sewage. SimpleTreat estimates tend to be conservative and therefore only useful for lower-tier assessments. A probabilistic version of SimpleTreat was built on the updated version of the model (SimpleTreat 3.2, presented in a parallel article in this issue), embracing likeliest as well as worst-case conditions in a statistically robust way. Probabilistic parameters representing the variability of sewage characteristics, STP design, and operational parameters were based on actual STP conditions for activated sludge plants in Europe. An evaluation study was carried out for 4 chemicals with distinct sorption and biodegradability profiles: tonalide, triclosan, trimethoprim, and linear alkylbenzene sulfonate. Simulations incorporated information on biodegradability simulation studies with activated sludge (OECD 314B and OECD 303A tests). Good agreement for both median values and variability ranges was observed between model estimates and monitoring data. The uncertainty analysis highlighted the importance of refined data on partitioning and biodegradability in activated sludge to achieve realistic estimates. The study indicates that the best strategy to refine the exposure assessment of down-the-drain chemicals is by integrating higher-tier laboratory data with probabilistic STP simulations and, if possible, by comparing them with monitoring data for validation.

Estimation of the Contribution Made to Down‐the‐Drain Emissions of D5 by Personal Care Product Categories in the European Union

“…Removal in a WWTP was estimated with SimpleTreat 4.0 (Struijs ), using temperature‐dependent physicochemical properties from Panagopoulos and MacLeod () and no degradation. Compared with the default version of SimpleTreat 4.0, the concentration of total suspended solids in the final effluent (default 30 mg/L) was adjusted to the mean value (8 mg/L) measured in 2010 to 2012 from 53 WWTPs in the United Kingdom, which was used in the parameterization of a probabilistic version of the model (Franco et al ). SimpleTreat estimated removal is 98.2%, close to the value of 98.3% reported by van Egmond et al () for 1 WWTP in the United Kingdom.…”

Integrated fate assessment of aromatic amines in aerobic sewage treatment plants

“…The calculation process of C-STP(O) was similar as SimpleTreat model (Franco et al 2013). The Level III fugacity-based C-STP(O) model can provide a steadystate distribution of a chemical in a three-stage STP consisting of a primary settling tank, an active sludgebased aeration tank, and a secondary settling tank.…”

“…The OECD laboratory simulation test 303 A (OECD 2001) for aerobic sewage treatment can only test the total removal rate and residual percentage in the effluent and cannot determine the fraction released to the air and sludge, while the removal rate, including absorption to surplus sludge and evaporation to the air, is critical for ERA to calculate the predicted environmental concentrations in the air and soil. Several complementary mathematical models can predict the degradative, absorptive, and evaporative fate of chemicals in STPs (Prata et al 2018;Franco et al 2013). These models, such as SimpleTreat (Franco et al 2013), have been used as standard models in the European Union (EU) and in the USA to estimate the exposure in the STP and the environmental compartment.…”

“…Several complementary mathematical models can predict the degradative, absorptive, and evaporative fate of chemicals in STPs (Prata et al 2018;Franco et al 2013). These models, such as SimpleTreat (Franco et al 2013), have been used as standard models in the European Union (EU) and in the USA to estimate the exposure in the STP and the environmental compartment.…”

From consumption to harvest: Environmental fate prediction of excreted ionizable trace organic chemicals

“…Although significant uncertaintydresulting from scarcity and/or variability of available datadis usually associated with the input of fate models (e.g., excretion rates, biochemical properties), uncertainty-based approaches were adopted in few cases (Ort et al, 2009;Franco et al, 2013b).…”