The Application of Cross-flow Microfiltration Technology to the Concentration of Sewage Works Sludge Streams

A LOCALLY DEVELOPED cross-flow microfiltration process using woven fabric tubes was used to concentrate waste activated sludge and anaerobic digested sludge from a conventional sewage works.
Results showed that waste activated sludge could be concentrated from 5 to 50 g/l total solids. The permeate quality was good (0 to 50 mg/l suspended solids), but deteriorated both with time and increasing feed solids concentration.
A cross-flow microfilter was coupled to a pilot scale anaerobic digester and the digester solids were increased from 26 to 55 g/l total solids. The organic loading to the digester was increased from 1.8 to 3.1 kg volatile solids per m³ per day. The solids retention time was held constant at 26 days, while the liquid retention time was decreased from 26 to 14 days. The permeate quality was significantly better than the supernatant liquor from a comparable digester (suspended solids 122 and 570 mg/l, respectively).
Data obtained from the cross-flow microfiltration of waste activated sludge was used to regress for the constants in a mathematical model of steady-state flux.     

The Application of a Newly Developed Tubular Filter Press to the Dewatering of a Waterworks Sludge

THE PROTOTYPE OF a tubular configured filter press has been installed at a local water treatment plant. The prototype unit dewaters the polyelectrolyte/Bentonite slurry resulting from the treatment of 30 Ml/d of surface water to a spadable cake. In this process a slurry is fed under pressure into a self-supporting array of porous fabric tubes; the liquid in the slurry filters through the tube walls while the slurry solids are deposited as a thin layer on the internal walls of the tubes. After a relatively thin cake has been formed, it is dislodged from the tube walls by means of a roller cleaning device. The cake is transported out of the tubes and deposited on a perforated conveyor belt where it is drained and conveyed to a collection hopper. The plant is fully automated and has been operating successfully since January 1987.