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.
