Filtration of secondary effluent using FilterClear, a four-media filtration process
Hoyland, G.1, Huo, C.1 and McLean, I.2, 1Bluewater Bio, UK, 2FilterClear, UK
(free)
Abstract FilterClear™ is a depth filtration process which uses four different granular media with a wide overall particle size range. The purpose of this paper is to describe an investigation into the performance of FilterClear treating (i) secondary effluents, both humus effluent and activated sludge effluent, and (ii) effluent directly from percolating filters.
The investigation was undertaken at Cambridge Sewage Treatment Plant, UK, over four months in 2012. Two different filters were used in the investigation. The Phase 1 filter had a ‘perforated pipe and gravel’ base, and the Phase 2 filter a floor with distribution nozzles. Activated sludge effluent was filtered only in Phase 1. The two phases comprised a total of 16 scenarios covering the three influents and range of loading velocities from 9.3 m/h to 31.2 m/h.
The following table summarises the performance obtained when filtering humus effluent and activated sludge effluent: Scenarios Influent Parameter TSS concentration (mg/l) Solids removal Influent Effluent (%) 1.1 to 1.4 Humus effluent 95 percentile 25.8 7.4 – Average 18.1 4.5 74.8 1.8 to 1.10 Activated sludge effluent 95 percentile 26.6 4.8 – Average 18.6 3.0 83.8 2.1 to 2.3, 2.5 and 2.6 Humus effluent 95 percentile 37.0 8.2 – Average 22.5 4.7 79.1 In all cases, performance was excellent, and no discernible correlation was obtained between loading velocity and filtration efficacy. When treating percolating filter effluent, solids removal averaged 92% in both phases, and, in Phase 2, the 95 percentile effluent TSS concentration was only 8.0 mg/l, in spite of the high concentration of the FilterClear influent. With regard to average BOD values of FilterClear effluents, they were consistently less, by about 1 mg/l, than the average TSS concentrations, for both filtered humus effluent and activated sludge effluent. Thus, FilterClear effluents had low BOD values as well as low TSS concentrations.
Keywords filtration, granular, sand, magnetite, activated, humus, quality
Introduction Quality standards imposed on treated effluents from waste water treatment plants in the UK are becoming more stringent; for example, a 95 percentile standard of 10 mg/l or less for TSS concentration and BOD is now common. Tertiary filtration is a cost effective process for reducing TSS concentrations of secondary effluents and concomitantly the concentration of BOD and of other parameters. FilterClear is a granular filtration process with a wide range of applications, from seawater and brackish water pre-treatment in membrane RO systems to tertiary treatment of secondary effluents. The purpose of this paper is to describe an investigation into the performance of FilterClear treating (i) secondary effluents, both humus effluent and activated sludge effluent, and (ii) effluent directly from percolating filters. Filtration of percolating filter effluent may be used as emergency treatment. The investigation was undertaken at Cambridge WwTP, UK, for four months from February to May 2012. Anglian Water’s framework partner, @one Alliance, managed the investigation, including the operation and monitoring of the FilterClear equipment. FilterClear Technology
