Wintgens, Thomas
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Microbial communities and processes in biofilters for post-treatment of ozonated wastewater treatment plant effluent
Impact of ozonation and biological post. Treatment of municipal wastewater on microbiological quality parameters
Ozonation is an established process for advanced wastewater treatment, with a dose-dependent degree of disinfection. It is generally followed by biological post-treatment with the main objective of oxidation by- product abatement. However, there is little research on the impact of the combination of ozonation and biological post-treatment on microbiological quality parameters. This long-term study investigated pilot- scale ozonation with six different filtration processes (4 deep-bed filter systems and 2 vertical flow constructed wetlands) as biological post-treatment. A broad spectrum of microbial parameters has been monitored for a comprehensive evaluation of the disinfection performance. While vegetative bacteria (Escherichia coli and enterococci) were inactivated to a large extent by ozone, spore-forming Clostridium perfringens and viral indicator somatic coliphages exhibited a high ozone tolerance and could only be effectively retained in subsequent filtration steps. Extended hydraulic retention times as well as fine filter materials in post-treatment proved to be beneficial for faecal indicator abatement. In deep-bed filters, coagulant dosing was an additional important factor for the disinfection performance. Post-treatment also played a crucial role in the reduction of the antibiotic resistance gene sul1 and the indicator genes intl1 (mobile genetic element) and 16S rRNA (total bacterial number), whereas inactivation of antibiotic resistant bacteria was dominated by the ozonation process. In summary, the combined disinfection mechanisms of ozonation (chemical) and filtration (physical) resulted in an effective abatement of a wider range of microbial parameters than the individual processes. Regrowth during post-treatment has only been observed for the parameters intact cell counts and Pseudomonas aeruginosa with mean concentration increases of 0.5–1 log units.
Deep-bed filters as post-treatment for ozonation in tertiary municipal wastewater treatment. Impact of design and operation on treatment goals
Ozonation followed by biological post-treatment is an established technology for abatement of organic micropollutants (OMP) from municipal wastewater. Although the necessity of biological post-treatment for oxidation by-product (OBP) removal is widely accepted, there is still discussion about the appropriate design and operation. The presented pilot-study investigates the impact of filter material and contact time on the removal efficiency of bulk organics, OMP, and OBP in three different deep-bed filters operated in parallel as post-treatment after ozonation (biological activated carbon (BAC) filter, dual-media filter sand/BAC and dual-media filter sand/anthracite). The use of BAC instead of non-adsorptive filter material resulted in higher removal of DOC and dissolved oxygen which indicates increased biological activity. Moreover, both BAC containing filters showed additional removal for a number of OMP even at high treated bed volumes of >50 000 whereas no removal was observed in the sand/anthracite filter. Analysis of N-nitrosodimethylamine (NDMA) and several carbonyl compounds revealed a clear formation of these biodegradable OBP during ozonation. A strong correlation was found between carbonyl formation and the specific ozone dose. Removal of OBP in the sand/BAC and the sand/anthracite filter was tested at different empty bed contact times (EBCT). While NDMA was efficiently removed independent of EBCT changes, there was a slightly negative impact of shorter EBCT on the reduction of carbonyl compounds. Furthermore, it was demonstrated that the integration of enhanced phosphorus removal into post-treatment is feasible with relatively low efforts by inline coagulant dosing (FeCl3) in the filter influent.