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Removal of pharmaceutical micro-pollutants from waste water by anaerobic digestion and its effect on nitrogen recovery from digestate by micro-algae.

Periodic Reporting for period 1 - PHARM AD (Removal of pharmaceutical micro-pollutants from waste water by anaerobic digestion and its effect on nitrogen recovery from digestate by micro-algae.)

Reporting period: 2015-08-01 to 2017-07-31

In recent years there has been increasing attention towards identification, effect and abatement of residues of pharmaceutical (PR) in the environment. PRs generally originate from within the urban-environments and may finally reach the natural aquatic environment as some of them are only partially removed in Waste Water Treatment Plants (WWTP). They are typically found at very low concentrations in the environment and are unlikely to affect human health but could cause damage to aquatic organisms and are included as watchlist-substances in the Water Framework Directives.
Anaerobic digestion (AD), a common tertiary treatment, is a biological process where different microorganisms take part. PRs may have an effect on the microorganism of this process inhibiting the system. The treatment of sewage sludge is a common application of AD in the wastewater industry. Whilst removal of PRs by AD in sludge has received some research interest, this project investigated the application of AD for the removal of PRs from wastewater, which contains many of these compounds. Previous studies have shown that advanced treatment of the aqueous phase of wastewater is expensive and energy intensive whilst only providing partial removal of PRs. Removal of PRs by AD would reduce the financial and carbon cost of treatment due to its potential to generate energy from waste, and this would thus provide a viable technique to reduce a proportion of PR pollution of water in all EU member states.
Typical barriers to wastewater treatment by AD are washout of bacteria and corresponding low turnover, process sensitivity to inhibitors and lack of nitrogen (N) and phosphorous (P) removal from wastewater. Therefore, the aims of this project were:
1. Investigate the efficacy of AD for the removal of PR.
2. The application of AD to the direct treatment of waste waters.
3. Combine PR removal by AD with nutrient recovery by microalgae cultivation.
4. Elaborate the scope for river water quality improvement by these techniques, thus contributing to the European aims of water protection and resource efficiency.
The fellow evaluated the effect of PR and their removal by AD. A new method was developed to enable rapid assessment of the system inhibition and estimation of the biogas produced. Based on the results obtained, it was concluded that the presence of high PR concentrations in wastewater may inhibit the anaerobic process; however, the system recovered producing the same biogas amount than samples without PRs. The AD microbial diversity appears to be a key factor that influences the sensitivity of the system: the higher microbial diversity, the less inhibition observed.
Some PRs were highly removed during AD (atenolol, caffeine, clarithromycin, erythromycin, propranolol, simvastatin, oxytetracycline and ciprofloxacine) achieving removals higher than 85%. However, other compounds such as bezafibrate, carbamazepine and lidocaine were only removed by between 25-40%.
These batch tests were built on by the design of a laboratory scale AD process to evaluate the long term effect of PR in the system. This settling was not adequate to retain the solids in the system, as low biogas productions were achieved as a consequence of a lack of anaerobic microorganisms in the system, instead of an inhibition due to the amount of pharmaceuticals added. Therefore, further research is needed to evaluate the long term effect of these PR in AD.
AD does not remove N and P from the wastewater and therefore further action is required for a safe effluent disposal. Microalgae can consume nutrients and Chlamydomonas acidophila in particular has been shown to be a promising agent for the removal of nutrients from anaerobically treated effluents. Furthermore, it can operate at low temperatures and requires low light intensities, which is well suited for use in North-West European Countries. Laboratory scale studies were conducted to evaluate the effect of PRs on nutrient recovery by C. acidophila. This microalgae was unaffected by PRs and additionally, it appeared to increase the removal of the antibiotic erythromycin and clarithromycin, two of the three antibiotics added in 2015 to the WFD watch list of priority substances.
Growing microalgae on surfaces for effluent treatment is an attractive option as it is much easier to separate the biomass from the medium and the costs of scaling up the system can be reduced. Therefore, we studied the nutrient removal by C. acidophila using different carriers as a first stage in investigating the suitability of this alga for nutrient recovery processes from effluents. Wool appeared to be a suitable material for microalgae cell attachment. Thus, a semi-continuous experiment was carried out to study the long term feasibility of immobilized cells on this material to remove both nutrient and 3 selected antibiotics: erythromycin, clarithromycin and a third problematic antibiotic, ciprofloxacin. It was observed that microalgae were not affected by a constant long-term addition of antibiotics and both erythromycin and clarithromycin decreased during the 50 days of incubation with average removals of 100% and 61% respectively. However, ciprofloxacin was not removed during the 50 days of incubation. These results lead to the construction of a unique fixed bed reactor for effluent treatment. For that purpose, a reactor was designed were microalgae were grown in wool columns. Based on the preliminary results, it seems that wool columns are as efficient as the suspended cells for recovering nutrients.
The fellow attended and presented results at a combination of research conferences in order to get involved in different networks and get in contact with different European organizations. The promising results obtained in the experiments with microalgae led to GCU being a principal partner and the fellow to be a joint Principal Investigator in an Interreg NWE project based on P recovery from wastewaters. This new project allows the fellow to continue the research on scaling-up the microalgae reactor to a demonstration unit to treat municipal wastewaters at small WWTPs.
MSCA Fellowship allowed the fellow to develop her skills in research management and to acquire technical expertise in a wide range of disciplines and industry sectors.
Additionally, the fellow’s existing knowledge in AD, together with the supervisory training provided by GCU, provided a useful input in the supervision of three PhD and 11 postgrad/undergraduate students working on the topic. At the same time, this input has benefited the researchers’ publications quality and increased the European knowledge base on water protection (from pollution by pharmaceuticals).
Working with GCU’s existing pool of contacts, further collaborations, proposals and networks have been built up in this emerging research field, culminating in a research funding success. Both the fellow and the GCU research group were awarded funding through INTERREG for a project aimed at P recovery from wastewater (PhosForYou). At GCU, the fellow will investigate microalgae technology specific for municipal small-scale water treatment works. GCU will construct the demonstrator for a typical location of 200 PE.
Through this follow-on project, which includes collaboration with industry, regulators and other stakeholders, there will be additional and sustained impact of the work undertaken during the MSCA fellowship.