Urban wastewater system management and risk assessment under catastrophic antiviral pandemic conditions

There are considerable concerns that wastewater treatment processes will be unable to effectively remove elevated antiviral Oseltamivir carboxylate (OC) concentrations during a pandemic wave and that toxic exposures might result in urban receiving waters. A risk management framework for the wastewater system under such catastrophic stress conditions is outlined with the main focus being on the protection of critical functions, services and workforce operations. A generic risk assessment approach for predicting OC removal rates in sewage treatment works (STWr) and receiving surface water concentrations (PECSW) is examined. The wide range of predicted daily concentrations values varying between 20 and– 10310µg L-1 d-1 resulting from the application of the modelling approach and this confers little confidence in the risk methodology and argues that toxicological risk for OC pandemics remains insufficiently characterised. The operation of STW unit treatment process however, would appear to be relatively robust under predicted pandemic stress conditions in terms of functional performance although system management difficulties might predicate optimal removal rates

The role of stormwater in the urban water cycle

The potential contributions of impermeable surface water discharges to urban water resource management strategies are considered through the development and analysis of an urban water cycle (UWC) study approach. The structure, outputs and benefits of a UWC study are described and a test application of the methodological approach is made to the Eastside development area within the city of Birmingham, UK. Water demand and usage rates for the proposed 170ha regeneration area are quantified and potentially significant savings identified assuming re-use of stormwater runoff which would considerably facilitate a more sustainable future urban water cycle strategy

Urban surface water pollution problems arising from misconnections

The impacts of misconnections on the organic and nutrient loadings to surface waters are assessed using specific household appliance data for two urban sub-catchments located in the London metropolitan region and the city of Swansea. Potential loadings of biochemical oxygen demand (BOD), soluble reactive phosphorus (PO4-P) and ammoniacal nitrogen (NH4-N) due to misconnections are calculated for three different scenarios based on the measured daily flows from specific appliances and either measured daily pollutant concentrations or average pollutant concentrations for relevant greywater and black water sources obtained from an extensive review of the literature. Downstream receiving water concentrations, together with the associated uncertainties, are predicted from derived misconnection discharge concentrations and compared to existing freshwater standards for comparable river types. Consideration of dilution ratios indicates that these would need to be of the order of 50–100:1 to maintain high water quality with respect to BOD and NH4-N following typical misconnection discharges but only poor quality for PO4-P is likely to be achievable. The main pollutant loading contributions to misconnections arise from toilets (NH4-N and BOD), kitchen sinks (BOD and PO4-P) washing machines (PO4-P and BOD) and, to a lesser extent, dishwashers (PO4-P). By completely eliminating toilet misconnections and ensuring misconnections from all other appliances do not exceed 2%, the potential pollution problems due to BOD and NH4-N discharges would be alleviated but this would not be the case for PO4-P. In the event of a treatment option being preferred to solve the misconnection problem, it is shown that for an area the size of metropolitan Greater London, a sewage treatment plant with a Population Equivalent value approaching 900,000would be required to efficiently remove BOD and NH4-N to safely dischargeable levels but such a plant is unlikely to have the capacity to deal satisfactorily with incoming PO4-P loads from misconnections

Protection of the water environment using balancing facilities.

A monitoring programme of water quality was carried out during wet and dry weather conditions in two balancing ponds adjacent to the A34 Newbury By-pass. The ponds were constructed to treat and store stormwater runoff. Pond B was a vegetated pond planted with Phragmites australis and Pond F/G was a constructed wetland with a sub-surface flow system and P. australis at the inlet and, initially, Typha latifolia at the outlet although this was later replaced by Phragmites. There was little difference between the pollutant removal performances of both ponds although Pond F/G was sometimes more efficient in removing nickel and nitrate and zinc during the summer. Recommendations are made for the design, construction, operation and maintenance and future monitoring of wetlands for highway runoff treatment

Constructed wetlands and links with sustainable drainage systems.

The potential of constructed wetlands with sustainable drainage systems in urban catchments is reviewed. Data from wetland systems used to treat domestic wastewaters were not directly applicable to stormwater treatment due to the differences in inflow regimes and pollutant loading. Urban wetland performance, costs, design, retrofitting, operation and maintenance are considered. The role of urban wetlands in wildlife and landscape enhancement and the benefits to the community are discussed. The implementation of sustainable drainage systems and catchment planning along with decision support systems are reviewed. Constructed wetlands offered considerable potential for the control and treatment of urban stormwater runoff. Recommendations are made for future work

Behaviour of selected emerging pollutants in stormwater best management practices (BMPs)

A range of emerging pollutants (EPs) are now being considered for regulatory designation as potentially hazardous or as priority substances. These EPs occur ubiquitously in urban receiving waters and have both point and non-point sources. The occurrence and likely sources of four selected EPs (diclofenac, perfluoro-octane sulphonic acid; PFOS, hexabromocyclododecane; HBCD and dichlorvos; DDVP) found in urban surface water discharges are discussed with reference to extreme events and CSO discharges. A unit operating process (UoP) methodology is utilised to evaluate primary BMP removal mechanisms and the susceptibility of the individual EPs to be removed by these processes based on their physico-chemical properties. Despite the prevailing low level concentrations encountered in urban runoff, the methodology provides a scientifically underpinned screening framework to identify the most appropriate BMP controls for the pollutant(s) under consideration. True source control approaches such as direct infiltration, green roofs, rain gardens and porous paving would appear to the moist effective management measures

Assessing the impact of Swales on receiving water quality

Swales are one type of sustainable drainage system (SuDS) which contribute to the management of water quality in receiving waterbodies. Using a semi-quantitative approach, an impact assessment procedure is applied to the residual water quality that is carried forward to surface waters and groundwaters following treatment within a swale. Both volumetric and pollutant distributions are considered as stormwater passes through the swale system. The pollutant pathways followed by TSS, nitrate, chloride, metals (Cd, Cu, Pb, Zn) and polyaromatic hydrocarbons (PAHs) are determined for a swale receiving highway runoff. For TSS, metals and PAHs between 20% and 29% of the total mean influent pollutant load is predicted to be directed to infiltration through the underlying soils compared to between 4% and 16% of chloride and nitrate. Although surface water impacts are deemed possible, the discharges of swales to groundwaters are assessed to represent a negligible impact for effectively maintained systems

Development of a qualitative approach to assessing risks associated with the use of treated wastewater in agricultural irrigation

The European Commission’s draft regulation for minimum requirements for water reuse in agriculture addresses microbial and basic water quality parameters but does not consider the potential impacts of chemicals of emerging concern (CECs) on human and environmental health. Because insufficient data prevents the quantitative characterisation of risks posed by CECs in treated wastewater (TWW), this paper presents a framework, which combines data and expert judgement to assess likelihood of occurrence and magnitude of impact. An increasing relative scale is applied where numeric values are pre-defined to represent comparative levels of importance. Subsequently, an overall assessment of the level of risk is characterised by multiplying together allocated scores, to obtain a single discrete overall score per CEC. Guidelines to support implementation of the framework as far as soil (the initial receiving compartment and pathway to further protected targets) are developed and applied. The approach is demonstrated through its application to clarithromycin, where results indicate that – under the considered scenario - there is limited possibility of its occurrence in soil in a bioavailable form. The role of a qualitative risk assessment approach is considered and the opportunity for its outputs to inform future research agendas described

Risk prioritisation of stormwater pollutant sources

This paper describes the development of a pollutant risk prioritisation methodology for the comparative assessment of stormwater pollutants discharged from differing land use types and activities. Guidelines are presented which evaluate available data with respect to ‘likelihood of occurrence’ and ‘severity of impact’. The use of the developed approach is demonstrated through its application to total suspended solids, biochemical oxygen demand, lead and cadmium. The proposed benchmarking scheme represents a transparent and auditable mechanism to support the synthesis of data from a variety of sources and is sufficiently flexible to incorporate the use of chemical, physical and/or ecological data sets. Practitioners involved in developing and implementing pollutant mitigation programmes are assisted in two key ways. Firstly through enabling the risks to receiving waters from diffuse pollution on a source-by-source and/or pollutant-by-pollutant basis at a catchment scale to be comparatively assessed and prioritised. Secondly, the methodology informs the selection of appropriate diffuse pollution control strategies