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Highlights Performic and peracetic acid disinfection of combined sewer overflow was evaluated  Sewer overflow water for laboratory studies was made with diluted raw wastewater  The bathing water indicator E. coli was always easier to disinfect than Enterococcus  Peracetic acid required long contact time (2 ppm, 6 h) for efficient disinfection  Performic acid was short lived but potent, efficient disinfection by 2 ppm, 20 min Abstract We investigated the possibility of applying performic acid (PFA) and peracetic acid (PAA) for disinfection of combined sewer overflow (CSO) in existing CSO management infrastructures. The disinfection power of PFA and PAA towards Escherichia coli (E. coli) and Enterococcus were studied in batch-scale and pre-field experiments. In the batch-scale experiment, 2.5 mg·L -1 PAA removed approximately 4 log unit of E. coli and Enterococcus from CSO with a 360 min contact time. The removal of E. coli and Enterococcus from CSO was always around or above 3 log units using 2-4 mg·L -1 PFA; with a 20 min contact time in both batch-scale and prefield experiments. There were no toxicological effect measured by Vibrio fischeri when CSO was disinfected with PFA, a slight toxic effect was observed on CSO disinfected with PAA. When the design for PFA based disinfection was applied to CSO collected from an authentic event, the disinfection efficiencies were confirmed and degradation rates were slightly higher than predicted in simulated CSO.Keywords: disinfection, combined sewer overflow, peracetic acid, performic acid; chemical disinfection; stormwater treatment, Escherichia coli, Enterococcus. 2 1.0 INTRODUCTION Combined sewer overflow (CSO) is a well-known phenomenon in combined sewer systems where wastewater and rain water are transported in the same sewers. CSOs occur when the rainfall exceeds the design capacity of sewer systems and needs to be discharged to surface water near cities, either directly, or after a short retention in detention tanks or outfall pipes (see graphical abstract, supplementary Figure S1). Discharge of untreated CSOs deteriorates the quality of receiving waters, since CSOs contain a variable mixture of rain water, raw sewage, watershed runoff pollutants, variable pathogenic organisms, viruses, cysts, suspended solids, chemicals and floatable materials (USEPA, 1999). In recent years, the effect of CSOs on water bodies used for recreational purpose has caught a lot of attention in Europe. Particularly the dedication from 2002 of Copenhagen harbor for recreational purposes including swimming and water sports has yielded an economically significant added service and tourism industry to the harbor area. Corresponding economic loss when CSO events close the harbor for bathing has inspired construction of significant retention basins which should limit the CSO events frequency, but due to the climate change related increased number of extreme rain events in 2000-2011 20, rain events caused temporary closing of the bathing (NYC Global Partners, 2011).According to European Un...

Highlights:  Ozone dosage was determined for pharmaceuticals removal in hospital wastewater  The ozone dosage required varied 2-fold with both DOC and pH experienced over time  DOC normalized ozone dosage for 90% removal of 32 pharmaceuticals was determined  At low pH, pharmaceuticals need less ozone while ozone lifetime increased to 20 min  H 2 O 2 dosing shorten the ozone lifetime at low pH to 5 min similar to neutral pH 2 Abstract: Ozonation aimed at removing pharmaceuticals was studied in an effluent from an experimental pilot system using staged Moving Bed Biofilm Reactor (MBBR) tanks for the optimal biological treatment of wastewater from a medical care unit of Aarhus University Hospital. Dissolved Organic Carbon (DOC) and pH in samples varied considerably, and the effect of these two parameters on ozone lifetime and the efficiency of ozone in removing pharmaceuticals were determined. The pH in the effluent varied from 5.0 to 9.0 resulting in approximately a doubling of the required ozone dose at the highest pH for each pharmaceutical. DOC varied from 6 to 20 mg-DOC/L. The ozone required for removing each pharmaceutical, varied linearly with DOC and thus, ozone doses normalized to DOC (specific ozone dosis) agreed between water samples (typically within 15%). At neutral pH the specific ozone dose required to remove the easiest degradable pharmaceutical, sulfadiazine, was 0.50±0.04 mg-O 3 /mg-DOC and the most recalcitrant, diatrizoic acid, required 4.7±0.6 mg-O 3 /mg-DOC. The lifetime of ozone increased drastically in the higher end of the indicated dosage. At the lowest observed pH of 5.0, its lifetime was quadrupled to 20 min which influences the design of the reaction tank. The addition of 0.1 mg-H 2 O 2 per 1 mg-O 3 mitigated the prolonged lifetime without a corresponding influence in the pharmaceutical removal efficiency of ozone.

Hospital wastewater contains high concentrations of pharmaceuticals, which pose risks to receiving waters. In this study, a pilot plant consisting of six moving bed biofilm reactors (MBBRs) in series (with the intention to integrate Biological Oxygen Demand (BOD) removal, nitrification and denitrification as well as prepolishing Chemical Oxygen Demand (COD) for ozonation) was built to integrate pharmaceutical removal and intermittent feeding of the latter reactors aimed for micropollutant removal. Based on the experimental resultss, nitrifying MBBRs achieved higher removal as compared to denitrifying MBBRs except for azithromycin, clarithromycin, diatrizoic acid, propranolol and trimethoprim. In the batch experiments, nitrifying MBBRs showed the ability to remove most of the analysed pharmaceuticals, with degradation rate constants ranging from 5.0 × 10 h to 2.6 h. In general, the highest degradation rate constants were observed in the nitrifying MBBRs while the latter MBBRs showed lower degradation rate constant. However, when the degradation rate constants were normalised to the respective biomass, the intermittently fed reactors presented the highest specific activity. Out of the 22 compounds studied, 17 compounds were removed with more than 20%.

EXTENDED ABSTRACTMany old cities are drained by combined sewer systems in which wastewater mix with rainwater for transport to the wastewater treatment plant. When intense rainfalls occurs the design capacity of combined sewer systems exceeds resulting in discharge of combined sewer overflows (CSO) to nearby surface water resulting in contamination with various pathogenic organisms, suspended solids and chemicals. The European Union has stated that good microbial quality for bathing water should not exceed 500 MPN/100 mL for E. coli and 200 MPN/100 mL for Enterococcus. Bathing water quality can be maintained by disinfecting the CSOs. This study was conducted to characterize the disinfection by peracetic acid in combination with chemical coagulation in a HydroSeparator® system for CSO. HydroSeparator® CSO system is a patented and specialized system consisting lamella settler and mess filter (20 microns). The entire system was installed in Middelfart to treat the CSO from the towns of Båring and Asperup (Denmark) and contains a traditional CSO structure before the HydroSeparator and a constructed wetland to polish the disinfected effluent. Samples for experiment were collected from inlet and outlet of HydroSeparator at different flow to optimize the PAA dose without coagulation. In experiment II, samples were collected from the inlet of the HydroSeparator to optimize the coagulation dose in a Jar test using PAX-XL 100. Experiment III was performed in full scale by applying PAX-XL 100 as flocculent (5 mg-Al/L) followed by disinfection with 10 mg/L PAA in the HydroSeparator. In order to confirm the PAA dose delivered in the field, comparable PAA treatments were made in the laboratory on samples collected after coagulation. Turbidity and phosphorus was reduced by applying increasing flocculent doses, but higher than 5 mg-Al/L achieved insignificant improvements. In experiment III the removal of turbidity was 92%, COD 28%, total nitrogen 61% and phosphorus 27% with 5 mg-Al/L. The stability of PAA increased after the HydroSeperator treatment, but was markedly further improved by the coagulation. Consistently with this, PAA disinfection was more efficient after the HydroSeparator, and further improved by the coagulation. In experiment III, removal of Enterococcus was 2.2 log for onsite disinfection and 2.4 log for the laboratory disinfection, which confirms the field dosing considering the analytical uncertainty. Overall, it is evident that disinfection efficiency of PAA was more effective in the flocculated and HydroSeparator treated water, but as long as the HydroSeparator was applied efficient disinfection could be achieved by PAA dosing towards preserving bathing water quality.