Abstract
The paper presents the results of research on the use of ultrafiltration, using membranes of 200 and 400 kDa separation, for disinfection of municipal treated wastewater. The research was conducted on a fractional technical scale using real municipal treated wastewater from two large wastewater treatment plants treating most of the wastewater over the one-million polycentric Gdańsk agglomeration (1.2 million inhabitants). UF 200 kDa and UF 400 kDa processes enabled further improvement of the physical and chemical parameters of treated wastewater. Total phosphorus (to below 0.2 mg/L–UF 200 kDa, 0.13 mg/L–UF 400 kDa) and turbid substances (to below 0.2 mg/L, both membranes) were removed in the highest degree. COD was reduced efficiently (to below 25.6 mgO2/L–UF 200 kDa, 26.8 mgO2/L–UF 400 kDa), while total nitrogen was removed to a small extent (to 7.12 mg/L–UF 200 kDa and 5.7 mg/L–UF 400 kDa. Based on the reduction of indicator bacteria; fecal coliforms including E. coli (FC) and fecal enterococci (FE) it was found that the ultrafiltration is an effective method of disinfection. Not much indicator bacterial were observed in the permeate after processes (UF 200 kDa; FC—5 CFU/L; FE—1 CFU/L and UF 400 kDa; FC—70 CFU/L; FE—10 CFU/L. However, microscopic analysis of prokaryotic cells and virus particles showed their presence after the application of both membrane types; TCN 3.0 × 102 cells/mL–UF 200 kDa, 5.0 × 103 cells/mL–UF 400 kDa, VP 1.0 × 105/mL. The presence of potentially pathogenic, highly infectious virus particles means that ultrafiltration cannot be considered a sufficient disinfection method for treated wastewater diverted for reuse or discharged from high load wastewater treatment plants to recreational areas. For full microbiological safety it would be advisable to apply an additional disinfection method (e.g., ozonation).
Highlights
The significant microbiological contamination of treated wastewater, shown in numerous works [1,2,3,4] draws the attention of sewage treatment plant operators to the disinfection processes [5,6,7,8,9,10,11]
Other research conducted on a model [17] and technical scale [18,19,20] indicate a positive selection of bacteria which show the features of multi-resistance, by wastewater treatment processes with the activated sludge method
The aim of this study is to evaluate the effectiveness of ultrafiltration processes in the disinfection of treated municipal wastewater, carried out under technical and operational conditions, and to assess the impact of these processes on the physico-chemical properties of treated wastewater discharged to surface waters
Summary
The significant microbiological contamination of treated wastewater, shown in numerous works [1,2,3,4] draws the attention of sewage treatment plant operators to the disinfection processes [5,6,7,8,9,10,11]. Other research conducted on a model [17] and technical scale [18,19,20] indicate a positive selection of bacteria which show the features of multi-resistance, by wastewater treatment processes with the activated sludge method. Another significant threat are pathogenic viruses, commonly found in raw and treated sewage [21,22,23] as well as in the environment receiving wastewater or other pollutants of fecal origin [23,24]. Their removal is important in the context of the epidemiological threat associated with the current Covid-19 pandemic [25,26,27], as well as dissemination of other viral diseases [23,24,28]
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