Garduno Jimenez, Andrea Lorena
(2021)
Analysis and behaviour of bioactive pollutants in wastewater and reuse for irrigation: addressing country specific issues in Mexico and the UK.
PhD thesis, University of Nottingham.
Abstract
Treated and untreated municipal wastewater reuse for agricultural irrigation is a widespread worldwide practice that has many benefits. These include reusing a waste stream, its year-round availability and the presence of nutrients in wastewater. However, municipal wastewater has been identified as one of the main sources of bioactive chemical pollutants or BACs (also known as emerging pollutants) in the environment. Many unknowns remain in terms of the extent of the removal of these pollutants using conventional wastewater treatment, seasonal and geographical variation on the prevalence of these pollutants, the extent of natural attenuation and the behaviour of these pollutants once in the environment. The aim of this thesis was to address some of these knowledge gaps by developing environmentally-relevant targeted and untargeted analytical methods, modelling tools, and undertaking an evaluation of wastewater treatment plants and the aquatic environment in the UK and Mexico.
The two wastewater treatment plants monitored in the UK were Stoke Bardolph wastewater treatment plant (PE~650,000) which has advanced biological treatment and Sutton Bonington wastewater treatment plant (PE~2,000) which has conventional trickling filter and a tertiary sand filtration step. Both of these plants were monitored using targeted methods, Stoke Bardolph for a year and Sutton Bonington for seven months. It was found that sulfamethoxazole, acetaminophen, acetyl-sulfamethoxazole and ibuprofen were better removed by Stoke Bardolph, while the estrogen hormones, diclofenac, morphine, erythromycin, trimethoprim, o-desmethylvenlafaxine, propranolol and codeine were better removed by Sutton Bonington. Despite their differences in removal efficiencies, both plants have risk coefficients consistently above 1 for the same 8 out of 36 pollutants; namely, codeine, diclofenac, erythromycin, morphine, oxytetracycline, propranolol, salicylic acid, simvastatin, sulfamethoxazole, tramadol and trimethoprim. Furthermore, the equivalent estradiol concentrations were found to be at least 8 times above the predicted no effect concentration. Significant (p<0.05) seasonal variations in removal for Stoke Bardolph wastewater treatment plant for 12 pollutants were identified, including diclofenac, sulfamethoxazole and carbamazepine. Eight strong and significant correlations were identified among several pollutants and between pollutants and water quality parameters, these are important in pinpointing removal efficiencies in relation to process operating conditions. For example, a correlation between temperatures >15°C and increased removal for o-desmethylvenlafaxine in Sutton Bonington treatment plant was identified.
In order to address the knowledge gaps in relation to metabolites, transformation products and unknown BACs, an untargeted method was developed and used to analyse samples from Stoke Bardolph and Sutton Bonington wastewater treatment plants. Twenty-five compounds not previously identified in relation to wastewater pollution were identified, as well as 10 biomarkers (including caffeine, nicotine, saccharin and acesulfame), 2 illicit drugs rarely reported in wastewater, and 3 pollutants identified in relation to potential disease monitoring. Partial least square analysis provided insights on the removal efficiencies of both plants for these pollutants. This work helps to address the knowledge gap on the environmental toxicity which remains unmonitored using targeted approaches, as well as identifying pollutants relevant for wastewater-based epidemiology.
Both targeted and untargeted methods developed were used to study an agricultural area in Mexico known as the Tula Valley, which has been irrigated using wastewater from Mexico City for over 100 years. Seven BACs were quantified which had not been previously studied in the Tula Valley, of which 4-tert-octylphenol, levonorgestrel, simvastatin and tramadol were found to have environmental risk quotients above one. Five BACs were found with measurable concentrations in spring groundwater, indicating prevalence and poor natural attenuation, with sulfamethoxazole found with an environmental risk quotient above one. The total estradiol equivalent was found to have environmental risk quotient above 1, with influence from estriol and its sulfate conjugate which have not been previously measured in the Tula Valley. Using the untargeted method, over 10 pollutants which have not been previously detected in the aquatic environment and with likely bioactive effects were detected in the Tula Valley. For example, 4-hydroxyindole which is used in the hair dyes and banned by ASEAN. More than 20 pollutants known for their toxicity and bioactivity, but not previously detected in the Tula Valley were identified. For example, the benzotriazole 5-methylbenzotriazole, cocaine metabolite benzoylecgonine and the antibiotic, ciprofloxacin. Potential biomarkers (e.g., caffeine and nicotine), which were also found in the UK wastewaters were detected. It is significant that common biomarkers were found in two locations using an untargeted method, because this makes them strong candidates to use in future international wastewater-based epidemiology studies.
The data gathered using targeted and untargeted methods in field studies in Mexico and the UK was used to identify pollutants of environmental significance for further study. These were then shortlisted as sulfamethoxazole, carbamazepine and tramadol. The first modelling investigation of BAC sorption in soil using data obtained from the literature enabled identification of gaps in the literature and unveiled experimental biases about these pollutants once they reach the soil compartment following water application. Six specific gaps which require further study were identified. 1) Further data is required for understudied pollutants such as tramadol and for pollutants which present inconsistencies across the literature like sulfamethoxazole. 2) Sorption studies are needed with environmentally-relevant concentrations, as they are usually carried out at higher concentrations. 3) In order to rule out biodegradation, different biodegradation quenching methods are used. These methods were found to influence sorption, with sodium azide having a greater influence than autoclaving, pointing towards the need for further study. 4) Sorption studies at different temperatures that account for variations which occur seasonally and geographically need to be carried out. 5) Sorption studies using treated and untreated liquid phase (realistic irrigation water) are needed. 6) Untargeted analysis of soil and liquid phases in sorption studies could elucidate competitive sorption effects as well as transformation process which may account for discrepancies in the literature.
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