EVALUATION OF LOW COST DISSOLVED AIR FLOTATION PRIMARY SOLIDS REMOVAL PROCESS TO IMPROVE PERFORMANCE OF WORLD扴 LARGEST SUBMERGED BIOLOGICAL CONTACTOR PLANT AT FLEETWOOD, ENGLAND

摘要

Detailed investigations were carried out at the world抯 largest Submerged BiologicalContactor (SBC) wastewater treatment plant to ascertain the exact causes of a severehydrogen sulphide and unstable final effluent problem. The detailed investigationsdemonstrated the root cause was organic overloading of the SBC plant resulting in thedevelopment of an undesirable, thick, sulphide generating bioflim with infestation fromsulphide oxidising filaments, Thiothrix and Beggiatoa. Successful reduction of thebiosolids sulphide release was carried out by a combination of operational alterationsand chemical dosing. The requirement for advanced primary solids removal washighlighted leading to the pilot testing of Dissolved Air Flotation in place ofconventional sedimentation. The DAF pilot showed Total Biochemical Oxygen Demandreductions of 50 % without the use of chemicals, but showed the process is vulnerableto changes in influent conditions. Preliminary optimisation of the DAF pilot highlightedthe importance of upstream preparation of the influent through adequate flocculation.The DAF pilot allowed full scale costing to be carried out and demonstrated a capitalsaving of ?million ($9.6 million USD) on comparison with conventional primarysettlement.