Environmental contextDecades of research tried to understand the inherent complexity of biodegradation of contaminants. We describe calculus of biodegradation driven by bioavailability, redox,... Show moreEnvironmental contextDecades of research tried to understand the inherent complexity of biodegradation of contaminants. We describe calculus of biodegradation driven by bioavailability, redox, geometry and acclimation (adaptation) of microbiota. We tested predictions for thousands of contaminants across wastewater treatment plants, explaining up to 70% of the variance in observations. This competes with more intensive methods, and enables more efficient monitoring, experimentation and data interpretation.RationaleRelease of harmful contaminants of emerging concern (CECs) in the environment prompts possible adverse toxicological effects. Increasing population, water use and process wastewater generation require more efficient removal of contaminants that allows for effluent discharge within environmental regulatory limits. Wastewater treatment plants (WWTPs) can remove hazardous contaminants, limiting unwanted release. Fine-tuning WWTP settings to fit the location, time, season, wastewater type, etc. may enhance removals to reduce CEC concentrations and toxic pressures.MethodologyFor this purpose, we need robust tools to calculate removal efficiencies. We studied influences of operational settings and CEC properties on their removal in WWTPs. For this purpose, we parameterised thermochemical properties of CECs: for their (1) speciation and acidification, (2) (re/im)mobilisation due to (de)sorption into solid/water, (3) redox-mediated biotransformation and (4) acclimation of biomass so to utilise metabolic pathways for biotransformation. By combining these parameters, we developed an energy-based framework for calculating biotransformation rates.ResultsWe evaluated our calculus using removal efficiency (%) data for 373 measurements of 60 CECs in 14 different Dutch WWTPs and an additional 667 CECs in 49 WWTPs across the world. Our prediction precision, R2 ≈ 0.65 (P < 10−5), captures influences of wastewater characteristics (multiple measurements for each WWTP). It is higher than R2-values of modelling approaches currently available. Our model explains CEC removal with appreciative certainty. We identified outliers during evaluation. These outliers were attributed mostly to back-transformation and uncertainty in long-term background concentrations of contaminants, causing consequent acclimation of microbial consortia.DiscussionBiodegradability and CEC-degrading biomass can be estimated from concentration and environmental residence time. Our framework and underlying parametrisations have a mechanistic basis, utilising simple WWTP operational information (CEC concentration, temperature, suspended solids concentration, oxygen demand, etc.). Thereby, our work has wide potential for implementation. Our approach can supplement current fate assessment for CECs for improved environmental risk assessments. We conclude by discussing the potential for removal enhancement. Show less
Chemistry describes transformation of matter with reaction equations and corresponding rate constants. However, accurate rate constants are not always easy to get. Here we focus on radical... Show moreChemistry describes transformation of matter with reaction equations and corresponding rate constants. However, accurate rate constants are not always easy to get. Here we focus on radical oxidation reactions. Analysis of over 500 published rate constants of hydroxyl radicals led us to hypothesize that a modified linear free-energy relationship (LFER) could be used to predict rate constants speedily, reliably and accurately. LFERs correlate the Gibbs activation-energy with the Gibbs energy of reaction. We calculated the latter as the sum of one-electron transfer and, if appropriate, proton transfer. We parametrized specific transition state effects to orbital delocalizability and the polarity of the reactant. The calculation time for 500 reactions is less than 8 hours on a standard desktop-PC. Rate constants were also calculated for hydrogen and methyl radicals; these controls show that the predictions are applicable to a broader set of oxidizing radicals. An accuracy of 30–40% (standard deviation) with reference to reported experimental values was found suitable for the screening of complex chemical systems for possibly relevant reactions. In particular, potentially relevant reactions can be singled out and scrutinized in detail when prioritizing chemicals for environmental risk assessment. Show less
