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.     

The EC Bathing Water Directive: a Sampling Problem

The relatively frequent observation, during periods of onshore drift, of a surface line of convergence in nearshore coastal waters may have significant implications for the sampling procedure used for monitoring compliance with the EC Bathing Water Directive. A simple theory is developed for predicting the formation of the convergence line, and a possible alternative sampling method is suggested.     

Potential Impacts of Climatic Change and of Sea-Level Rise on the Yields of Aquifer, River and Reservoir Sources

Using regional statistics of daily rainfall, a simple water-balance model was employed to generate runoff sequences with which to simulate the yield/storage behaviour of reservoirs in south-east England, in north-west England, and North Wales. Similarly sequences of recharge to an unconfined aquifer in eastern England were the basis of deriving its yield/storage behaviour. Then, taking scenarios of the year 2030 rainfall and evaporation, provided by the University of East Anglia's Climatic Research Unit, reductions in yield were calculated to be 5–15% below present-day values. For direct supply reservoirs, greater percentage reductions in yield were found to apply to the south-east region, as compared to the north-west. The results from the aquifer example are interpreted on a novel basis which allows an immediate comparison with the surface reservoir examples.
Coastal sea-water intrusion was modelled for three common geological conditions (i) the Grimsby Chalk (confined), (ii) the Brighton Chalk (unconfined), and (hi) the Otter Valley Sandstone (unconfined). In all three cases the effect of a possible 0.6 m rise in mean sea level was shown to have only a marginal effect on sustainable yields, which reduced by about 1.5%.
Estuarine fresh-salt water interfaces are important to the abstraction regime of freshwater intakes in the lower reaches of rivers. The effect of a 0.6-m sea-level rise on the saline interface location at high tide was evaluated by hydrodynamic computational models. Only a minor inland shin of the interface was found, less man 800 m in the Thames tideway and less than 500 m in the Lune estuary. The Severn estuary is exceptional in having its saline interface move 3.5 km landwards for the same 0.6-m rise in mean sea level.     

Validation of building energy evaluation techniques

The application of building energy evaluation techniques in design is discussed and the present position with regard to the validation of dynamic thermal computer models is reviewed with particular reference to ongoing Building Research Establishment/Science and Engineering Research Council research.     

Use of Mixing Zone to Derive a Toxicity Test Consent Condition

This paper describes how the Clyde River Purification Board (the regulatory authority) and Bee-cham Pharmaceuticals (the identified discharger) agreed and adopted a novel means of controlling a pharmaceutical plant effluent which is discharged to Irvine Bay, Scotland. Control was achieved by means of a consent (licence) condition requiring compliance with a laboratory test of acute toxicity, which was added to the more orthodox conditions already imposed upon the discharge. The new condition was derived using the concept, explicit in the environmental quality objective/environmental quality standard approach to pollution control, of an allowable mixing zone around the outfall. The derivation and validation of the condition necessitated laboratory and field bioassay, current measurements and dye releases, and the use of a plume development model.     

Clinical evaluation of infrared autorefractors for use in contact lens over refraction

We examined the ability of autorefractors to provide an accurate means of contact lens over-refraction measurement. Over-refraction measures, performed using six commercially available automated infrared autorefractors and retinoscopy, were compared with subjective refraction. A total of 40 contact lens wearers (20 soft lens wearers and 20 rigid gas permeable (RGP) lens wearers) participated in the study. All six autorefractors were able to provide over-refraction measures in all subjects. Data analysis revealed differences in autorefractor performance between the two types of contact lens wearer with greater accuracy and lower variability being found in the soft lens wearing subjects compared with the RGP group. The level of agreement between retinoscopy and subjective over-refraction results was lower in soft lens wear and higher in RGP wear than the levels found between the autorefractor and subjective over-refraction measures. We conclude that autorefractors provide a useful means of measuring contact lens over-refraction in soft lens wearers. Over-refraction results should be treated more cautiously in RGP wearers.     

Plumbosolvency Control in Soft Waters

Experience of plumbosolvency control in the soft waters of north-west England is presented, and expectations for complying with the new lead standards are indicated. The influence of natural organic matter on the solubility of lead is highlighted - in particular its importance in the setting of target pH values in phosphated waters. An analysis of a large quantity of regulatory lead-compliance data confirms the benefit of the introduction of phosphate. At a distribution zone level, the impact and benefit of a change in plumbosolvency conditions on regulatory data are demonstrated using a non-parametric statistical technique. To assist in the operational management of plumbosolvency conditions, a number of performance metrics have been developed; these quantify (in a simple way), the quantity, variability and delivery of phosphate, and pH. The expected benefit from plumbosolvency control has been assessed in several ways, indicating that reasonable compliance against 25 μg/l might be achievable, but against 10 μg/l this is more questionable.     

Water Quality Implications of an Observed Trend of Rainfall and Runoff

The catchment of the upper Clyde estuary has experienced a significant and steady increase of rainfall over the past twenty years. The corresponding increase of runoff has had a positive impact on the water quality both of the individual rivers and of the estuary. Examples are provided to show that approximately one third of some observed improvements are attributable to the additional dilution. It is emphasized that comparisons of water quality data, either by region or by period, should allow for climate variability.     

Activity theory and critical incident recall as a pedagogical approach for using online knowledge-building communities in schools

Networked computers provide an important opportunity for schools to extend learning by engaging students in online interactions which supplement their offline learning. These communities of learners can be understood using activity theory as a unifying framework. This leads to a novel pedagogy in which records of online interactions provide the stimulus for subsequent offline discussions.