Nutrient release from integrated constructed wetlands sediment receiving farmyard run‐off and domestic wastewater

Constructed wetland sediments are frequently contaminated with nitrogen and phosphorus. There is a risk that accumulated pollutants can either be remobilised or reach the groundwater. Five identical mesocosms, which were filled with subsoil collected from full‐scale integrated constructed wetland (the first cell receives the most contaminated influent), were set up to examine nutrient removal within sediment layers. The results indicated that accumulated nutrients leached out into inflow water and that the sediment capacity of nutrient retention decreased as the wetlands aged. Furthermore, the mesocosm planted with Phragmites australis achieved better treatment results compared with the one planted with Agrostis stolonifera. The risk of contamination to groundwater does not exist because none of the treated water reached the bottom outlet during the study period. Both the bentonite (clay) and biogeochemical processes taking place within sediments proved to be efficient in preventing polluted water from infiltrating into lower lying soils.     

Combined permeable pavement and photocatalytic titanium dioxide oxidation system for urban run‐off treatment and disinfection

Permeable pavement systems (PPS) are frequently associated with high removal efficiencies for water quality parameters. Their effluent can, therefore, be recycled, for example, for sprinkling onto gardens. Nevertheless, some stakeholders fear that potentially pathogenic organisms within the treated run‐off could be too high, and therefore they request disinfection before recycling. The aim of this paper is, therefore, to assess the efficiency of a batch flow combined titanium dioxide (TiO₂) and ultraviolet (UV) light photocatalytic reactor in removing water‐borne microbial contaminants from the effluent of PPS. Combined TiO₂ and UV photocatalytic reaction times between 80 and 100 min were required for the complete removal of Escherichia coli, total coliforms and faecal Streptococci, which had mean initial counts of 1.5 × 10⁷, 4.4 × 10⁶ and 6.9 × 10⁵ colony‐forming units (CFU) per 100 mL, respectively. In comparison, UV disinfection alone resulted in insignificant microbial removal. Suspended TiO₂ powder was more effective than small immobilised TiO₂ crystals.     

Using an acoustic Doppler current profiler in a small river

Some practical and theoretical concepts related to the use of an acoustic Doppler current profiler (ADCP) in a small river are examined. The importance of understating the limitations of the measurement equipment and a system for locating the exact position of the ADCP are discussed. Details of a new measurement protocol which is suitable for small rivers are presented. Small samples of data measured in the River Blackwater are used to illustrate the concepts outlined in the paper. It is concluded that ADCPs can be successfully used in small rivers provided sufficient care is taken over their deployment and subsequent data analysis. However, in some cases it is acknowledged that additional modifications to the ADCP may need to be undertaken as illustrated in the paper.     

An improved understanding of canal hydraulics and flood risk from breach failures

British Waterways (BW) is the largest navigation authority in the UK, managing a network of 3200 km of inland waterway. Central to this function is the management of a complex water supply system, where water is transferred for resource management, to maintain navigation and for sale to third parties. The navigations also provide land drainage, with 30% of the English and Welsh catchments draining, into the network. Understanding the hydraulic mechanisms present is essential to manage the risks to infrastructure, land, property and personnel. This paper describes studies that have reduced the uncertainty of the hydraulic appraisals of canals. A programme of primary research included site surveys, hydraulic trials and modelling. Hydraulic roughnesses for a range of canal channel types were derived and the impact of structures was quantified. The paper then applies these findings to investigate a recent canal breach. Importantly, in terms of the hydraulic appraisal, pound water levels and flows were automatically monitored throughout the event. The breach was modelled via an innovative dual weir approach. The modelled water level drawdown compared very closely with that measured. In conclusion, this paper illustrates the major steps forward that BW has made in developing the understanding of canal hydraulics and breach failures. This paper is of interest to consultants, researchers and other workers who study canal hydraulics and flood risk throughout the UK and overseas.     

Influence of anaerobic digestion on the carbon footprint of various sewage sludge treatment options

This paper describes the results of a model set up to determine carbon footprints for sludge treatment solutions with and without standard or advanced anaerobic digestion. Complete and 'gate' (up to the point the sludge leaves the sewage works gate) footprints were calculated. The lowest carbon footprints corresponded with advanced digestion options, which reduced downstream energy and transport (hence carbon) requirements regardless of the endpoint of the sludge. The lowest complete carbon footprint solution coincided with advanced digestion, followed by drying with energy recovery. However, this option had the highest gate carbon footprint. In terms of gate carbon footprint, land application of an advanced digested sludge cake had the smallest footprint, followed by land application of dried pellets and finally incineration.     

Fate of endocrine-disrupting chemicals in percolating domestic wastewater effluent

Septic tanks and other on-site systems are a common means of disposing domestic wastewater effluent in Ireland. In assessing site suitability, subsoils below the percolation trench have an important role in attenuating pollutants and hence in protecting groundwater. As part of an investigation into the hydraulic performance of treatment systems at four sites in Ireland with different subsoil characteristics, a series of samples were analysed for endocrine-disrupting chemicals (EDCs), including oestrogens, surfactants and organic oxygen compounds. EDCs were found at all four sites, but only at low concentrations (often below those at which their presence could be confirmed) and generally only in samples known to be percolating effluent. Further research should target oestrogen compounds, as these appear to be present in higher concentrations than the other EDCs and also have greater potency.     

MEMBRANE BIOREACTORS AND CONSTRUCTED WETLANDS FOR TREATMENT OF RENDERING PLANT WASTEWATER

The performance of a novel industrial membrane bioreactor (MBR) comprising denitrification, nitrification and ultrafiltration for the secondary treatment of primary treated animal rendering wastewater has been compared with an experimental, low-cost and novel vertical-flow constructed wetland planted with Typha latifolia L. (Reedmace or Broad-leaved Cattail). The process wastewater followed pre-treatment by dissolved air flotation (DAF). The mean DAF effluent gave highly variable chemical oxygen demand (COD) and ammonia concentrations of 5816 (standard deviation (SD): 3005.0) and 614 (SD: 268.7) mg/l, respectively. The mean MBR effluent for COD and ammonia was 37 and 86 mg/l, respectively. The mean treatment performance of the constructed wetland for COD, ammonia and suspended solids was 205, 67 and 57 mg/l, respectively.     

Learning from the extreme River Tyne flood in January 2005

Extreme floods often demonstrate unanticipated characteristics that pose problems for management and response. The floods on the Tyne and Eden in January 2005 provided numerous examples of such unexpected response. This paper describes characteristics of storm rainfall and runoff generation on the River Tyne catchment, flood effects and damage. Unusual aspects of hydrological behaviour are highlighted as a basis for assessing what lessons can be learned for flood risk management. These include problems associated with coincidence of extreme wind speeds and rainfall, the retarding influence of floodplain storage on flood wave travel time in extreme flows, the influence of critical storm duration on the severity of the resulting flood on headwaters and main river, and the variety of mechanisms of flood occurrence. The occurrence of such an extreme flood provides the opportunity to validate and enhance the review process of the Environment Agency's flood zone maps.     

A review of catchment management in the new context of drinking water safety plans

By managing a catchment effectively, the range and amount of contaminants entering waters used for public water supply can be reduced, with resultant benefits for both water companies and consumers. Consequently, catchment management is increasingly being recognised as being at the heart of the water environment. An overview of current and previous catchment management initiatives is given, along with the European Landscape Convention, which could be used as a vehicle for the implementation of a national catchment management strategy. The adoption of the drinking water safety plan approach is strongly advocated by the World Health Organisation, and effective catchment management underpins this approach. Effective management of our catchments will also make a significant contribution to meeting our obligations under the Water Framework Directive, by helping to address the serious issue of diffuse pollution from agriculture.