Water-Recycling Technologies in the UK

Urban water recycling in the form of rain, grey or black water is becoming an important element of demand-management practice in the UK, and appropriate technology allows the use of three different water sources for similar applications. The level of pollution in the water source and the application to which it is being recycled, dictate the level of technology which is used. This paper describes current water re-use practices in the UK (in terms of water source, technology scale, type and efficiency) and examines five case studies. Of more than 150 schemes identified, most are rainwater-collection systems and these are generally sited in rural areas. There are various single-house greywater recycling sites, many of which are part of water company or Environment Agency monitoring programmes. Larger-scale schemes employ both natural and hi-tech treatment options. Operationally successful schemes utilise appropriate technology for the end-use, although the economic benefits of many of the schemes are poor.     

ADAPTING LOW-FLOW FREQUENCY ANALYSIS FOR USE WITH SHORT-PERIOD RECORDS

Low-flow frequency analysis techniques are robust only where the flow record is relatively long and the flow regime is known to be stationary over time. If applied to short-period flow records. low-flow frequency analysis can give poor or misleading results. This paper examines the effectiveness of data-transfer methods for improving the characterisation of low-flow frequency relationships for gauged sites with flow records of less than fifteen years.
Two transfer methods were considered. In each case the sequence of annual minimum flows from an analogue catchment was used to provide extra information about the sequence of flows at the site of interest. Transposing the standardised probability distribution function of annual minima between analogue sites worked where their flow records were highly correlated. However, better results were obtained where recurrence intervals for observations at the subject site were estimated from recurrence intervals for the same years in the analogue record.     

BIOFILM FORMATION IN GRANULAR-BED FILTERS

A high microbiological quality of drinking water must be ensured to protect public health. The filtration techniques that are used in treating drinking water play an important role; however, a biofilm can form on granular-media filters and the accumulated bacteria can slough off and enter the filtered water.
The aim of this research was to examine (a) the potential for biofilm formation and detachment from filter sand, and (b) the effect of different backwash regimes on biofilm removal. During the operation of the filter, bacteria became attached to the sand media, particularly in the top 30 mm of the filter bed. A water-only backwash at 20% and 40% bed expansion demonstrated poor removal of biofilm throughout the depth of the bed. Collapse-pulsing is a more efficient method and results in a reduction in the number of bacteria in the filtered water.     

An Assessment of Water Demand Management Options from a Systems Approach

A systems approach is used to model the urban water and wastewater system. Scenarios are developed for the implementation of a range of water demand management measures, including (a) leakage reduction, (b) the increasing use of water metering, (c) the replacement of standard WCs by low-flow WCs, and (d) the introduction of greywater recycling systems. These measures are assessed according to the water saving, cost per unit of water saved, and other indicators of the relative contribution to the sustainability of the system. Preliminary assessments of selected environmental costs and benefits are also included.     

Considerations for Recycling Sewage Effluent in the UK

Technical, environmental, legislative and institutional considerations in relation to effluent re-use are described, with specific reference to experiences gained through the development of a scheme to augment Essex and Suffolk Water's Hanningfield reservoir with effluent from Chelmsford sewage-treatment works. Effluent standards are driven by a number of EU directives associated with protection of fisheries, recreational water quality, eutrophication and nitrate control for designated sensitive areas, and surface-water abstraction. The selection of the most appropriate strategy for re-use needs to consider public perception issues, in addition to technical feasibility and environmental concerns.     

Evaluation of a Pilot-Scale Bioscrubber for the Removal of Hydrogen Sulphide

This technical note describes an investigation on the feasibility of using treated wastewater to support the operation of a fixed-film bioscrubber for H₂S removal. A laboratory-scale fixed-film bioscrubber was assembled using Thiobacillus bacteria which were isolated from a sample of raw sludge, cultured in the laboratory, and immobilised onto the scrubber's plastic packing media by an immersion method.     

Benefits of Flow Data for Flood-Protection Design

Stream gauging data play a vital role in the planning of flood mitigation strategies. A study of the value of stream flow data for the design of levee systems shows that the availability of a reasonable sample of pertinent data can be worth many times the cost of collecting that data.     

Mapping Turbidity, Surface Temperature and Water Circulation Patterns with the Aid of Satellite Imagery

Water turbidity, surface temperature and circulation of Barton and Wroxham Broads, two of the Norfolk Broads, were studied using one reflective (TM1) and the thermal (TM6) TM band. The results indicated that the through-flowing path of the River Ant in Barton Broad is the major influence on the distribution of these parameters. In Wroxham Broad, both turbidity and surface temperature displayed a uniform distribution. This could be explained by the absence of a predominant direction of flow.     

CONSTRUCTED WETLANDS FOR MINEWATER TREATMENT: PERFORMANCE AND SUSTAINABILITY

Wetlands were constructed between 1995 and 1999 to treat discharges from abandoned coalmines in the Pelenna Valley, South Wales. This was one of the first and most comprehensive demonstrations of passive minewater treatment technology in Europe, incorporating aerobic and anaerobic cells, including 'reducing and alkalinity-producing systems. The wetlands were monitored to assess their performance and longevity and were found to remove 82-96% of the incoming iron, with no decline in treatment performance over the monitoring period to 2002. Oxidation was found to be the dominant iron-removal process, even in vertical-flow cells which were designed to utilise anaerobic processes. Factors limiting the longevity of iron-removal processes were identified. maintenance requirements were highlighted and life-span predictions were calculated for the systems. The wetlands were shown to be an effective and low maintenance (but not maintenance-free) method of treating net-acidic and net-alkaline minewater.     

The Affordability of Water in an African Town

This paper examines (a) the ability of consumers in a typical medium-sized African town to pay for a piped water supply, and (b) the implications for the financial viability of the local water undertaking. It demonstrates that, at present, people are paying about 10% of their income for water, and this appears to be near their limit of affordability. However, it is shown that it is possible for the water company to improve its revenue, whilst maintaining its present tariffs, by providing more private connections. Furthermore, the aim of improving water-company revenues is compatible with providing improved services to its urban customers.