Advances in Water Treatment and Enviromental Management

RIBBLE ESTUARY WATER QUALITY IMPROVEMENTS 249but that their effects did not extend into the bathing waters. In view of this the investigationsinto the most appropriate method of reducing bacterial loads to the estuary, to achieve bathingwater compliance, concentrated on dealing with the contributions from Preston and Fairhaven.Because of the various constraints imposed by the existing land use around the estuary theavailable options could be narrowed down to:a sea outfall for flows from Fairhaven or Fairhaven and Preston together;treatment of Fairhaven and Preston flows separately and discharge via the existingoutfalls;transfer flows from Fairhaven to Preston for combined treatment with a dischargevia the existing Preston outfall.Figure 3. Effects of the present storm discharges from Southport on bacterialconcentrations. Dispersion model simulations, E. coli concentrations greater than2 000 per 100 ml: a Southport STW, b Southport Combined Sewer Overflows.In considering possible locations for long sea outfalls there was only one possible site, situatedto the north of Lytham, where it would be feasible to site a headworks within a reasonabledistance of water sufficiently deep to provide adequate initial dilution of the effluent. Evenfrom this position an outfall of around 6.5 km would be required to reach water with a lowwater depth greater than 10 m.The probable effects of variations of these schemes were compared with the assumption that3DWF would be discharged. Investigations of the effects of dealing with flows of around 6DWFwere left until the modelling of the effects of storm discharges with 3DWF receiving treatmenthad been examined. Removal of the Preston and Fairhaven flows from the estuary to a longsea outfall resulted in a dramatic improvement in the bacteriological quality in the bathingwaters off Lytham, but produced an area of high bacteriological contamination off the FyldeCoast near to a number of identified bathing areas. Even the discharge of flows from Fairhavenalone resulted in a relatively large area of high bacterial numbers near to these sensitive highamenity waters.The effects of treating the Fairhaven and Preston flows, either separately, or together at thepresent Preston STW site, depend on the assumptions made about the degree of bacterialremoval. The bacterial load from Preston is so large in relation the volume of the receivingwaters that it is necessary to reduce bacterial concentrations by 99 per cent before the effectson the Lytham bathing waters become acceptable (Figure 4). If Fairhaven flows are treatedseparately and discharged on the ebb a bacterial reduction of between 90 and 95 per centwould be required.