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Re-evaluation of temperature correction in microbial biodegradation kinetics

Periodic Reporting for period 2 - ReArrhenius (Re-evaluation of temperature correction in microbial biodegradation kinetics)

Reporting period: 2018-04-01 to 2019-03-31

Recent years have seen a marked increase in micropollutants concentrations in water bodies, emphasizing limitations of wastewater treatment plants (mostly biological systems) in providing steady and effective pollutants removal. A better understanding of what causes such performance variability is one important contribution to preventing long-term adverse ecological effects and human exposure. Environmental parameters, such as temperature, likely have a direct impact on chemical exposure from wastewater treatment plants, as they directly influence pollutants biodegradation rates. As such, temperature is also explicitly used as predictor variable when modelling pollutant degradation half-lives in chemical fate and exposure models used for risk assessment purposes.
The ReArrhenius project aims at investigating the temperature dependence of micropollutants biotransformation kinetics in aerobic biological systems, taking into account both physico-chemical and taxon trait changes. Experimental data, for both biotransformation rate constants and community composition and activity from high-throughput sequencing, were used to test the validity of currently used temperature-correction models for the prediction of biotransformation rates of micropollutants in biological systems.
As full scale biological systems are affected by short (daily) and long (seasonal) term temperature fluctuation, the experimental work in the ReArrhenius project has been developed in two main phases: (i) short-term studies, where the impact of short-term temperature variation on a biological system was explored through a series of parallel small-scale batch reactors; (ii) long-term studies, where the implication of adapting activated sludge communities at different temperatures on the micropollutant biotransformation kinetics was investigated using laboratory-scale sequencing batch reactors. For both groups of experimental assays, the bioreactors were seeded with the activated sludge from a Swiss full-scale wastewater treatment plant, and spiked with a mixture of 93 environmentally relevant micropollutants, whose biotransformation kinetics under different temperatures (in the 4-40°C range) was monitored over time. The microbial composition and activity in each system were also assessed by high-throughput sequencing.
The results obtained so far have indicated a wide spectrum of responses to temperature variation (for both short- and long-term shifts). The micropollutants biotransformation kinetics in “temperature shocked communities” (short-term studies) failed to fit an Arrhenius model at higher temperatures (>20°C) for the majority of the micropollutants tested, where important microbial changes, not only in activity but also in composition, were found. Our results were in contradiction with the current European guidelines, which suggest that the Arrhenius model is valid in the 0-30°C range. Contrarily, fully adapted communities (long-term studies) showed an overall median increase in biotransformation kinetic rates with temperatures, following an Arrhenius-like behaviour, suggesting predominant enzymatic changes in the system. However, individual micropollutants still revealed various responses, which did not always parallel the observed effects of the short-term temperature shifts. Our results so far have highlighted the limitation of standardizing temperature kinetic models, based on the Arrhenius assumption, to predict the fate of micropollutants in biological systems, and the importance of the system microbial potential, which should be taken into account in developing such models.
This work was presented at the Environmental Chemistry Seminar series at Eawag (March 2018, Dübendorf, Switzerland), international workshop (Athene ERC Meeting, March 2017, in Koblenz, Germany), and conference (10th Micropol&Ecohazard Conference, Vienna). The work has also been accepted to be presented at the Society of Environmental Toxicology and Chemistry (SETAC) Europe 28th Annual Meeting (May 2018, Rome, Italy), and at the 17th International Symposium on Microbial Ecology (ISME17, August 2018, in Leipzig, Germany). Also, the ReArrhenius project was included in the cover page of the monthly newsletter at Newcastle University, which contains details of EU and international funding opportunities and other relevant news and targets the academic audience across the university.
In addition, dissemination of the Arrhenius research to general public and schools took place during a cultural event (“Women in Science: Forgetting to Remember”) organised at the Sage, a musical venue in the North East of England. The MSC fellow worked with composers and performers, from faculties across Newcastle University (UK) and the Electric Voice Theatre (UK contemporary music theatre ensemble), to disseminate her MSC scientific research through music and interactive games.
The work carried out in the ReArrhenius project has reopened the debate concerning the adaptability of physico-chemical models for the description of biological systems. If a handful of studies have attempted to justify the use of Arrhenius-based model for predicting the pollutants biotransformation kinetics in biological systems, the lack of a consistent experimental dataset has limited the validation of such approach. The Arrhenius project has built up a solid and comprehensive experimental evidence concerning micropollutants biotransformation in biological systems under different environmentally relevant temperatures, by closely investigating responses in both chemical rates and microbial community physiological status and structure. This new knowledge will lead to the identification of new parameters that should be integrated into existing physic-metabolic-ecological models, which will allow more accurate predictions for potential chemical exposure under different temperature regimes.
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