Developing an easy-to-apply model for identifying relevant pathogen pathways into surface waters used for recreational purposes

Simulation and engineering demonstration of the advanced treatment of rainy overflow wastewater using a combined system of storage tank-wastewater treatment plant-wetland

We propose a new technology to advanced treat overflow wastewater from a combined sewer system using a storage tank-wastewater treatment plant (STP)-constructed wetland (CW) system. The engineering demonstration (a 7,500 m³ storage tank and a 3,436 m² CW) has been built to treat the combined sewer overflows (CSOs) at the largest combined rainwater/wastewater overflow outlet in the middle reaches of the Xinbaoxiang River, which is the second largest river in the Dianchi Lake Basin. During the rainfall period, CSOs enter the storage tank. After sedimentation purification, the higher concentration CSOs at the bottom enter the STP, and the upper low-concentration CSOs enter CWs, thereby linking the multiple means of treating CSOs and minimizing the impact of CSOs on the STP. During the dry season, CWs can also assist in purification of polluted river water. The supernatant (COD <80 mg/L) and the bottom part water (COD >200 mg/L) of the storage tank were sent to CWs and STP, respectively, for treatment. The project was stably operated over 6 months. The final effluent qualities were 12, 1.79, and 0.18 mg/L for COD, TN, and TP, respectively, which achieved the surface water class V standard. PRACTITIONER POINTS: A combined system of storage tank-wastewater treatment plant-wetland was proposed to advanced treat overflow wastewater of rainy season. The SWMM could calculate the water quality and volume of overflow under different rainfall conditions in the runoff area. The effluent of the engineering demonstration reached the standard of surface water class V.

Reduction of micropollutants and bacteria in a constructed wetland for combined sewer overflow treatment after 7 and 10 years of operation

Repeated investigations on constructed wetlands for the treatment of combined sewer overflows, also named bioretention filters or retention soil filters, are necessary to provide information on their long-term performance. In this study, a sampling campaign was conducted on micropollutants, indicator microorganisms and standard parameters ten years after such filters were in operation and three years after the first investigation; it revealed that the filters lost capacity to remove chemical substances with no or only slow biological degradability. This was the case e.g. for phosphate (decrease from 29 to 11%), diclofenac (67 to 34%) and TCPP (34% to negative reduction). They continued to remove easily degradable parameters such as COD (stable around 75%) stably. The indicator microorganisms Escherichia coli (1.1/0.8 log₁₀), intestinal enterococci (1.3/0.8 log₁₀) and somatic coliphages (0.6/1.0 log₁₀) showed comparably low process variations given the difficulties in sampling and analysing microbial parameters representatively as well as given natural variations in microbial behaviour and growth. Additionally, for bisphenol A, we found a temperature-related difference of removal efficiencies: while in the cold months (winter), the removal was only 53% on average, it increased to 90% in the warm months (summer). As for the long-term prospective of retention soil filters, decision-makers need to identify the most important pollutants in a specific catchment area and adapt the filter design accordingly. If pollutants are targeted that lead to an exhausted filtration capacity, post treatment or the exchange of charged filter material is necessary. However, for easily biologically degradable substances, so far, there is no limit in their use.

Groundwater-Sewer Interaction in Urban Coastal Areas

In this paper, a study of the potential causes of the occurrence of high concentration of Enterococcus Faecalis in surface water within urban areas in dry-weather conditions (DWCs) is presented. Two hypotheses were formulated: (1) undersized sewer system; and (2) groundwater infiltration into damaged sewer pipes. In both cases, more frequent combined sewer overflows (CSOs) may occur discharging untreated sewage into surface water. To evaluate the first hypothesis, a hydraulic model of a sewer was developed assuming a water-tight system. The simulation results show that CSOs never occur in DWCs but a rain event of intensity equal to 1/3 of one-year return period may trigger them. To evaluate the second hypothesis, a model combining sewer failure with groundwater level was developed to identify the sections of damaged sewer below the water table and, therefore, potentially affected by infiltration. The risk of infiltration exceeds 50% in almost half of the entire network even at the lowest calculated water table. Considering 50% of infiltration distributed throughout that part of the network, CSOs can occur also in DWCs.

Combined sewer overflow events and childhood emergency department visits: A case-crossover study

In localities with combined sewer systems, combined sewer overflow (CSO) events frequently occur following high precipitation and can result in the release of untreated sewage and industrial wastewater into surface waters. We hypothesized that either direct contact with or proximity to aerosolized CSO effluent would increase the risk for childhood emergency department (ED) visits for asthma, gastrointestinal (GI) illnesses, and skin and soft tissue infections (SSTIs) in Cincinnati, OH, USA. ED visits for 2010-2014 due to GI diseases, asthma, and SSTIs were extracted from the Cincinnati Children's Hospital Medical Center electronic health records. The location and timing of CSO events were obtained from the Metropolitan Sewer District (MSD) of Greater Cincinnati. ED visits with a residential address within 500m of a CSO site were used in a case-control crossover study with two bi-directional control periods. Conditional logistic regression models were used to estimate the risk of an ED visit associated with a CSO event at lag periods of 0 to 7days. Statistically significant elevated risks for GI-related ED visits was observed two (OR: 1.16 [95% CI 1.04,1.30]) days after CSO events. CSO events were not significantly associated with asthma- or SSTI-related ED visits, but show similar trends. Our findings suggest an increased risk for GI-related ED visits following CSO events among children who reside near CSO sites.

Post-industrial river water quality-Fit for bathing again?

For the Ruhr River, bathing has been prohibited for decades. However, along with significant improvements of the hygienic water quality, there is an increasing demand of using the river for recreational purposes, in particular for bathing. In the "Safe Ruhr" interdisciplinary research project, demands, options and chances for lifting the bathing ban for the Ruhr River were investigated. As being the prominent reason for persisting recreational restrictions, microbiological water quality was in the focus of interest. Not only the faecal indicator organisms (FIOs) as required by the European Bathing Water Directive were considered, but also pathogens such as Salmonella, Pseudomonas aeruginosa, Legionella pneumophila, Campylobacter, Leptospira, enteroviruses and protozoan parasites. In this introductory paper, we firstly relate current recreational desires to historical experiences of river bathing. After recapitulating relevant microbial river contamination sources (predominantly sewage treatment plants, combined sewer overflows, and surface runoffs), we review existing knowledge about the relationships of FIOs and pathogens in rivers designated for recreational purposes, and then trace the evolution, rationale and validity of recreational freshwater quality criteria which are, despite obvious uncertainties, mostly relying on the FIO paradigm. In particular, the representativeness of FIOs is critically discussed. The working programme of Safe Ruhr, aiming at initiating and facilitating a process towards legalisation of Ruhr River bathing, is outlined. Sources of contamination can be technically handled which leaves the actual measures to political decisions. As contaminations are transient, only occasionally exceeding legal limits, a flexible bathing site management, warning bathers of non-safe situations, may amend technical interventions and offer innovative solutions. As a result, a situation-adapted system for lifting of the bathing ban for Ruhr River appears realistic.