Performance of three small-scale wastewater treatment plants. A challenge for possible re use

The study focused on the assessment of the performance of three WWTPs in Greece by the estimation of the microbiological and chemical quality of influent and effluent sewage. Physicochemical parameters were recorded (temperature, pH, COD, BOD, suspended solids, conductivity), and meteorological data were collected (air temperature, rain). Microbiological parameters were analyzed (Escherichia coli, total coliforms, bacteriophages, Salmonella, human adenoviruses, Candida, Pseudallescheria boydii, helminths, parasites Cryptosporidium ssp., and Giardia spp.). Statistically significant correlations among the various aforementioned parameters were investigated, in an attempt to propose appropriate processing performance indicators. Furthermore, the study aimed to assess current joint ministerial decision (JMD) on wastewater reuse, for irrigation purposes; to evaluate its practicability and its potential for public health protection. In the vast majority, outlet samples from all three studied WWTPs were not appropriate for irrigation reuse purposes based on BOD50 and suspended solids limit values, set by the current JMD, for both limited and unrestricted irrigation applications. Reductions for E. coli, total coliforms, and bacteriophages were found to range between 2-3, 1.5-2.5, and 2-4 log(10) values, respectively. Salmonella spp. was detected in outlet sewage samples from Patra (PAT), Arachova (ARH), and Livadeia (LEV), at 23 % (3/13), 33 % (4/12), and 38 % (5/13), respectively. Molds were detected at 92.3 % (12/13), 100 % (13/13), and 91.6 % (11/12), respectively, while Candida was found at 85 % (11/13), 67 % (8/12), and 46 % (6/13). A high prevalence of Pseudallescheria boydii, in outlet samples from all studied WWTPs is an important public health issue, which underlines the need for further studies on this emerging fungal pathogen in wastewater reuse applications. Pseudallescheria boydii was found at 85 % (11/13), 67 % (8/12), and 46 % (6/13), respectively. Helminths were found in both inlet and outlet samples, of all studied WWTPs, at 100 %. Human adenoviruses, were detected at high percentages in outlet samples at 76.9 % (10/13), 92.3 % (12/13), 84.6 % (11/13), respectively, while no influence of UV irradiation was recorded on the entry and exit loads of human adenoviruses. No influence of meteorological parameters was found on the microbiological and chemical parameters, with the exception of a weak positive correlation between environmental temperature and bacteriophages. A moderate positive correlation was found between BOD and suspended solids, bacteriophages, and total coliforms, bacteriophages and E. coli, and bacteriophages and adenoviruses. A significant positive correlation was found between total coliforms and E. coli, COD and BOD, and suspended solids and COD. No correlations were proved between human pathogens and bacterial indicator parameters. Collectively, our findings underlined the unsuitability of the current JMD on wastewater reuse in Greece, or public health protection. The study is expected to support the development of a public health risk assessment model based on quantitative risk assessment on the use of treated wastewater for irrigation purposes in Greece.