BACKGROUND: Pathogenic microorganisms at the effluents of treatment plants entail a potential risk to public health. Enteric viruses such as adenoviruses (AdVs) and enteroviruses (EVs) are responsible for many waterborne diseases. Wastewater treatment methods eliminate successfully the load of indicators but other pathogens such as viruses have been detected in high concentrations at the effluents of wastewater plants. In this perspective, two constructed wetlands (CWs) systems (S1 and S2) were employed and fed with primary wastewater. S1 consists of a free water surface (FWS) wetland and a horizontal subsurface flow (HSSF) wetland working in series, while S2 consists only of the HSSF. Also, both systems included a sand filter (SF) after the HSSF.RESULTS: Results showed that these low-cost systems are capable of eliminating effectively the bacterial indictors (total coliforms, Escherichia coli, Enterococci) achieving removal rates of almost 99% for S1 (3.2-4 Log units) and 89-98% for S2 (1.9-2.7 Log units). Regarding viruses, AdVs, EVs and phages were detected at all sampling points and during all seasons, and they were only partly removed in S1 and/or S2. For example, the virus load was decreased by 2.5 Log units for AdVs and 3.4 Log units for EVs in the case of S1, while the respective values were 4.3 and 1.9 Log units for S2. CONCLUSIONS: Generally, CWs eliminated successfully the bacterial load, while the remaining virus load was significant, thus strengthening the argument that viruses could be a reliable indicator for fecal contamination.

The occurrence of emerging organic contaminants (EOCs) in wastewaters and the inability of the conventional wastewater treatments plants to deal with them have been pointed out several times over the last few years. As a result, remnants of those compounds released into the aquatic environment present a potential risk for public health. Constructed wetlands (CWs) have been proposed as environmentally friendly, low-cost alternative systems with satisfactory results for different types of contaminants. This study aimed to evaluate the efficiency of a CW system, planted with the halophyte Juncus acutus, to eliminate bisphenol A (BPA) and two antibiotics, namely ciprofloxacin (CIP) and sulfamethoxazole (SMX) under different operating conditions. The behavior of Escherichia coli and enterococcal populations in terms of changes in their resistance profile for the selected antibiotics and the abundance of two resistance genes (qnrA and sul1) were also examined. BPA and CIP were significantly removed by the CW, with an overall removal of 76.2% and 93.9% respectively and with the plants playing a vital role. In contrast, SMX was not significantly eliminated. Moreover, fluctuations in the antibiotic resistance profile of bacteria were observed. Treatment processes affected the response of the two selected bacterial indicators, depending on the conditions employed in each case. Furthermore, increased levels of resistance genes were monitored in the system effluent. This study indicates that CWs, as tertiary wastewater treatment systems, may demonstrate high removal rates for some but not all EOCs. This implies that each EOC identified in the feed stream should be tested assiduously by analyzing the final effluents before their reuse or discharge into water bodies.

BACKGROUNDHospital wastewater (HWW) charges wastewater treatment plants (WWTPs) with a mixture of contaminants such as pharmaceutically active compounds (PhACs) and pathogenic bacteria. This matrix is considered highly toxic to the ecosystem and organisms, and it may induce the development of antibiotic resistant bacteria (ARB) and the transfer of antibiotic resistance genes (ARGs) within microbial communities. Conventional WWTPs cannot treat HWW effectively, because they have not been designed to confront this challenge. Therefore, this study investigated the applicability of photocatalysis to purify HWW, regarding its ecotoxicity and the removal rates of targeted substances, selected pathogenic bacteria and specific ARGs.RESULTSThe HWW samples showed high toxicity towards the bioindicator Daphnia magna population, while they also contained significant levels of ARB and ARGs. Upon application of the photocatalytic treatment, the pharmaceutical concentrations decreased at a rate of >80% and the removal rates of the examined bacteria (Escherichia coli, Enterococci, Klebsiella sp. and Staphylococcus sp.) were >80%. Importantly, the bacteria remaining after photocatalysis were sensitive to the tested antibiotics. Conversely, the examined ARGs were present in high concentrations before and after photocatalytic treatment. For example, the concentrations of the selected genes, namely ampC, sul2, tetA and qnrA, in the effluents were from 104 to 106 gene copies L−1.CONCLUSIONSPhotocatalysis may be a promising treatment technique for the elimination of PhACs and pathogenic bacteria from HWW. Moreover, it proved capable of altering the antibiotic resistance profile of the bacteria surviving after treatment, making them sensitive to certain antibiotic compounds. However, the main concern regarding public health protection remains, as the presence of ARGs in effluents in considerable concentrations may induce antibiotic resistance in bacterial communities of aquatic environments. © 2023 Society of Chemical Industry (SCI).