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...

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The potential for reuse of iron-rich sludge from waterworks as a replacement for commercial iron salts in wastewater treatment was investigated using acidic and anaerobic dissolution. The acidic dissolution of waterworks sludge both in sulphuric acid and acidic products such as flue gas washing water and commercial iron solution was successful in dissolving the iron from waterworks sludge. The anaerobic dissolution of waterworks sludge due to codigestion with biological sludge (primary and biological activated sludge) resulted in reduction of iron, increase in dissolved iron(II), increase in pH due to the produced alkalinity from dissolution of iron(III)hydroxides from waterworks sludge, lower internal recirculation of phosphate concentration in the reject water and reduced sulphide in the digested liquid. However, recirculation of the produced soluble iron(II) as an iron source for removal of phosphate in the wastewater treatment was limited, because the dissolved iron in the digester liquid was limited by siderite (FeCO 3 ) precipitation. It is concluded that both acidic and anaerobic dissolution of iron-rich waterworks sludge can be achieved at the wastewater treatment plant, and are economically and environmentally more favourable compared to deposition of the waterworks sludge in controlled landfills.

The aim of this article is to present a new biological aerated filter (BAF) for nitrogen removal based on simultaneous nitrification and denitrification. Contrary to the systems which integrate both an aerated and a non-aerated zone to allow complete nitrogen removal in one compact or two different units (pre-denitrification and nitrification), this upflow BAF system is based on the principle of simultaneous nitrification and denitrification since the filter is completely aerated. The denitrification process is possible due to the diffusion effect which dominates biofilm processes. The real time aeration control allows us to maintain a low dissolved oxygen value (0.5 to 3 mg O2/l). In this case, the biofilm will not be fully (or less) penetrated with oxygen and denitrification will be carried out in a large part of the biofilm. Therefore, nitrification and denitrification is running simultaneously in different depths of the biofilm. By using 50% less air this BAF gave the same results (less than 20 mg TN/l) on pilot plant as a classical nitrification and denitrification BAF (Toettrup et al., 1994). Less recirculation was necessary to achieve the same denitrification.

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(2015). Full scale evaluation of combined sewer overflows disinfection using performic acid in a sea-outfall pipe. Chemical Engineering Journal, 270, 133-139. https://doi.org/10.1016Journal, 270, 133-139. https://doi.org/10. /j.cej.2015 AbstractPollution of surface waters with pathogens from combined sewer overflows limits recreational use of surface waters. Large retention basins are a satisfactory solution but they are rarely sufficient for economic or space reasons. Fast disinfection during the overflow is an alternative, but few methods are known and each has problems. This work evaluated for the first time the full-scale disinfection using performic acid by the removal of the two currently regulated indicator bacteria for bathing water quality, E. coli and Enterococcus. Experiments were performed at a sewage bypass through a sea-outfall pipe with a minimum hydraulic retention time of 24 min. The disinfection efficiency in the field was measured by analyzing samples taken before and after the treatment. Samples were also treated with performic acid in the laboratory to measure the disinfection effectiveness and kinetic of degradation of performic acid. Doses of 1-8 ppm of performic acid achieved 1.0-3.5 log removal of E coli and 1.0-2.44 log removal of Enterococcus in the field, but were somewhat higher in laboratory conditions at 1.69-4.38 and 1.0-4.27 log units, respectively. Studies of the degradation of performic acid in collected real samples showed more than 50 % was degraded in 20 min, and mostly degraded by 120 min. Comparison of field and laboratory dosed samples detected that performic acid synthesis didn't start in one event and clogging of the sampler in another event.Overall the tests showed that the treatment was successful but it is indicated that online control could benefit treatments efficiency.

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