Removal of pharmaceuticals from hospital wastewater by staged biofilm and ozone polishing

Publication: ResearchPh.D. thesis – Annual report year: 2018

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Research on the removal of micropollutants (i.e. pharmaceuticals) has received a lot of attention in the last few decades. Wastewater treatment plants (WWTPs) act as the final checkpoint in controlling the quality of wastewater before discharge into receiving water. However, conventional WWTPs are not able to remove every pharmaceutical, including the majority of hardly biodegradable compounds and effluents that eventually affect the aquatic environment. Therefore, either upgrading traditional processes in WWTPs or the onsite treatment of pharmaceuticals at the point source (i.e. hospital wastewater), before release into the sewer system, must be considered, in order to overcome the above issues.
Moving bed biofilm reactors (MBBRs) as an alternative to activated sludge have been already proven highly capable of removal of pharmaceutical. Based on 36 pharmaceuticals in hospital wastewater, the concentrations of which are limited through DHI (Institute for Water and Environment), these targeted compounds are investigated in this research despite no current regulations for the presence of pharmaceuticals WWTP effluent.
Concentrations of substrate in wastewater can affect the degradation of organic micropollutants, due to a number of involved biodegradation mechanisms, including co-degradation and competitive inhibition. The effect of humic acid, as a model complex organic substrate, was investigated in relation to the biodegradation of pharmaceuticals in WWTP effluent via a laboratory-scale polishing MBBRs. Twelve investigated pharmaceuticals were significantly biodegradable. The biodegradation rate constants of ten of these compounds increased in line with increased humic acid concentrations, which shows that the presence of complex substrates stimulates degradation via a co-metabolism-like mechanism rather than competitive inhibition.
Staged MBBRs were applied for polishing of the effluent of an activated sludge treatment plant, in order to enhance the removal of pharmaceuticals. To address the issue regarding effluent not containing sufficient organic matter to sustain enough biomass, a novel feeding approach, namely intermittent feeding to MBBRs reactor with WWTP effluent and settled raw wastewater, was implemented for the first time. First-order rate constants for pharmaceutical removal, normalized to biomass, were significantly higher compared to other studies on activated sludge and suspended biofilms, especially for diclofenac, metoprolol and atenolol. Due to intermittent feeding, diclofenac degradation occurred with a half-life of only 2.1 hours and was thus much faster than any hitherto described wastewater bioreactor treatments.
An onsite pilot-scale of staged MBBRs, involving only the MBBR technique, was applied to remove pharmaceuticals existing in raw hospital wastewater, in order to achieve relevant Danish regulation standards on discharge. Furthermore, a pilot-scale of staged MBBRs, involving MBBR and MBBR combined with activated sludge (Hybas) techniques, was applied to treat raw municipal wastewater, with the aim of attaining a high degree of pharmaceutical degradation. The strategy of intermittent feeding was carried out for both studies. In general, the majority of pharmaceuticals were removed sufficiently compared to other biological treatment processes, and the removal of diclofenac occurred in the reactors following the implementation of intermittent feeding.
A pilot ozonation system was introduced to treat effluents from the staged MBBRs that were applied to treat hospital/municipal wastewater. This was able to attain further removal of remaining pharmaceuticals and toxicity. Concentrations of pharmaceuticals decreased when ozone dosage increased, and then the ozone dose reaching 90% removal of pharmaceutical was normalized by DOC, following that relevant removal efficiency was comparable to literature studies of ozonation. Natural fluorescence as an easily measurable parameter for the oxidation of organic matter in wastewater appeared to degrade quickly along with an increase in ozone doses. Microtoxicity in the wastewater of staged MBBRs decreased along the treatment train, and ozone was able to remove half of the remaining toxicity in MBBR effluents. Polishing MBBRs applied after ozone, with the ultimate aim of reducing ozone by-products, removed almost all water toxicity.
Original languageEnglish
Place of PublicationKgs. Lyngby, Denmark
PublisherTechnical University of Denmark (DTU)
Number of pages48
StatePublished - 2018
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