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Research Notes: The wastewater headache after taking an aspirin

Trace contaminants, including chemicals from pharmaceutical and household products that are part of our daily lives, are a growing area of concern in the water environment. Cranfield University's Dr Pablo Campo-Moreno summarises the latest research on the issue

by Dr Pablo Campo-Moreno, Lecturer in Applied Chemistry, Cranfield University

Got a headache? Most people wouldn’t think twice about taking an aspirin to alleviate the pain, but they might when they realise the cumulative effect this (and other perceived benign activities) are having on our environment, wildlife, and ourselves. From chronic toxicity to antibiotic resistance, trace contaminants from both the unusual (and usual) suspects are a cause for real concern, yet amazingly there are currently no regulatory standards in terms of water quality.

Addressing this situation, the EU Water Framework Directive aims to improve levels in water quality. In response to this, a collaborative effort involving Cranfield University and other leading institutions resulted in the Chemical Investigation Programme – a first step in combating the problem of unrecognised or recorded trace contaminants.

What are trace contaminants?

Just within the last decade, scientific studies reporting the presence of trace contaminants in aquatic environments can be counted by thousands. The expression ‘trace contaminant’ groups an array of compounds, mainly natural and synthetic organic chemicals, to which no regulatory standards apply in terms of water quality. Owing to significant improvements in analytical sensibility and accuracy, the driving force behind this intensive search for trace contaminants has been advances in instrumentation. Consequently, more powerful equipment has facilitated the detection of contaminants at the part-per-trillion or part-per-billion concentration levels in surface and ground waters, something otherwise unattainable by means of conventional techniques.

In addition to effluents from chemical manufacturing, food industry and agricultural activities, the occurrence of trace contaminants in water is, for most of the part, due to domestic streams. In our daily living we utilise personal care products, pharmaceuticals and household cleaners, among others substances, that contain these chemicals as ingredients and active components. Thus common practices such as body hygiene, doing the laundry or taking a tablet to alleviate a headache contribute organic compounds, in tiny amounts, to waterways. For instance, drugs enter sewage systems after being excreted by patients, via human waste, or because in some places the preferred method of disposal for old medicaments is flushing them down the toilet; hence more than 200 pharmaceuticals have been found in river waters worldwide.

While traditional wastewater treatment plants - mainly biological processes - are the main point of convergence for trace contaminants, these facilities were designed for the removal of bulk organic matter as well as nutrients (nitrogen and phosphorus), without further consideration for the elimination of trace contaminants. In fact, the amounts in which the trace contaminants exist in wastewater are insufficient for supporting microbial growth. As a result, freshwater bodies such as rivers, lakes and reservoirs closer to industrial and population sources are the environmental compartments receiving the greatest percentage of trace contaminants. The presence of these chemicals has escalated concerns as their potential impact on the biota and human health is not well understood. In general, trace contaminants are often associated with harmful effects such as acute and chronic toxicity, endocrine disruption, antibiotic resistance as well as bioaccumulation.

The Chemical Investigation Programme

From a normative point of view, however, trace contaminants are not monitored on a regular basis and no compulsory discharge limits are established in the United Kingdom or the European Union. Nevertheless, the implementation of the EU Water Framework Directive (WFD) has translated into an effort towards achieving good levels in water quality. In response to this challenge, a collaborative effort involving UKWIR, Atkins, Brunel University and Cranfield University resulted in the implementation of the Chemical Investigation Programme (CIP) in England and Wales.

Under CIP1, which took place from 2007 to 2013, different pollutants including trace contaminants were monitored at a selected number of wastewater treatment works. Collected data showed that current treatment processes are capable of removing many of the pollutants in a fairly effective way. Nevertheless, as discharge requirements will eventually become more stringent (e.g. the watch list of high risk substances has been incremented to seventeen organic compounds in EU Commission Decision 495/2015), effluents from some wastewater plants may constitute a risk to water quality in receiving water bodies.

Lasting for five years until 2020, the Programme’s second phase, CIP2, has established a more ambitious plan that encompasses chemical monitoring, treatment technology trials, sludge investigations and options appraisal. In this case, around 600 treatment works were selected based on their potential risk for compliance failure. At these sites, both upstream and downstream sampling campaigns are taking place to gain insight into the occurrence, fate and impact of trace contaminants as well as to assess compliance risks. The chemicals included in CIP2 are those on the current WFD priority substances list, the watch list, metals, and other supporting sanitary determinands.

Cranfield’s contribution

Our contribution at Cranfield University to knowledge about trace contaminants centres around gauging the efficiency of conventional activated sludge (CAS) processes. We are currently conducting research aimed to explain how treatment operational parameters affect the biodegradation of trace contaminants. From an engineering point of view, hydraulic retention time (HRT), solids retention time (SRT) and temperature are the governing factors in CAS systems. Longer HRTs and SRTs as well as higher temperatures are assumed to favour the elimination of trace contaminants. Nevertheless, the precise effects of those operational parameters on the microbial diversity and community structure in CAS treatments remain uncertain.

With this idea in mind, we adapted analytical protocols (phospholipid-derived fatty acids and next-generation sequencing) to determine the microbial ecology of activated sludge from a qualitative and quantitative point of view. As we treat our wastewater at Cranfield the protocols are being applied to monitor changes in the microbial community under varying HRTs and SRTs in a CAS pilot plant connected to the university’s wastewater works, which processes 1,000 m3 per day of wastewater produced by a population equivalent of 3000. In these tests we utilise fresh sewage from the university fortified with oestrogens.

Preliminary results indicate that changes in both SRT and HRT significantly affect the microbial diversity and oestrogen removal. For instance, extending the SRT from 3 to 10 days reduced the proportion of gram negative bacteria by 6%, while the extent of removal for oestrone increased from 20 to 80%. Part of this research is also the application of the protocols to full-scale facilities. We recently concluded a survey of microbial diversity at twelve CAS facilities: sampling events were carried out at different points during winter and summer months to capture variation in performance due to seasonal changes, if any. Upon completion of the analytical work and subsequent data interpretation, our results will contribute to define those parameters that are most conducive for microbial species capable of degrading trace pollutants, without compromising the main objective of CAS treatments, that is, the removal of organic matter and nutrients.

Future challenges

What are the future challenges regarding trace contaminants? Evolving methodologies for sample preparation and detection of analytes will bring to light more trace contaminants in the environment. These new protocols will add to the list of trace contaminants, not only well-known commercially available chemicals, but their unknown intermediates or metabolites that result from biotic or abiotic transformations during treatment and exposure to environmental conditions. Such advances in analytical chemistry need to be accompanied with suitable toxicological assays in order to elucidate whether these trace contaminants and their transformation products indeed represent a hazard for humans and the environment. Last but not least, costly investments in state-of-the-art instrumentation and extensive laboratory work may prove useless in the absence of well-designed sampling procedures. Clear objectives, characterisation of flow patterns, selection of sampling mode and sampling frequency have to be considered to minimise wrong conclusions.

-Find out more about the Chemical Investigation Programme at WWT's Wastewater conference in Birmingham, 31st January 2017. For information and booking details see: http://events.wwtonline.co.uk/wastewater/

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