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This article discusses the pelletising process of ochre and its use for removing phosphate from sewage effluent. It includes lab results, planned work, and the requirements for pellets' physical strength, degradation resistance, size, reactivity, and phosphate capacity.
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Ochre Pelletising and use for phosphate Removal from sewage effluent 2nd February 2005 Jonathan Aumônier
Introduction • Pelletising Process • Lab results – phosphate removal • Micrographs • Windlestone trial • Planned work
Requirements for Pellets • Physical Strength – (Crush and handling) • Resistance to degredation in water • Resistance to degredation through biological activity • Size • Retained Reactivity of Ochre • Retained Phosphate Capacity • High Porosity • No “Film” or “Matrix” Binder System • No Leaching of metals
Extrusion Trial ‘Z’ Blade Mixer-Extruder Cutting Extruded Product Mixer Blades
Pan Pelletising Water & Liquid Binder Powder Feed Pan Angle Θ Product Θ Rotational Speed ω Small Pellets Water & Liquid Binder Powder Feed Large Pellets
Pelletising Equipment Dust Extraction Vibrating Hopper 70cm Diameter Pelletising Pan Variable Speed Helical Feed Screw ASDA Washing-up Bowl
Ochre Sources and use Skinningrove - initial physical test Silwood - MScs - 1st Nafferton Farm trial Acomb - Current lab work - 2/3 of Windlestone pellets - Some to Leitholm Polkemet - 1/3 of windlestone pellets - Leitholm Horden - 1/3 of Leitholm - ESL Nafferton Farm - Stock of pellets
Phosphate remover from solution with varying initial P – after 24 hours P removed (mg/l) Initial P (mg/l) Data from Lawrence Bowden
Rate of phosphate sorption Phosphate load on pellets (mg_P/g) Time (s) Data from Lawrence Bowden
Rapid P Sorption tests Feed Concentration 1 mg/l P Solution Concentration (mg/l P) Residence time (s) Data from Frances Brett
Phosphate removed from solution with varying ionic strength of KCl 100% % Removal 80% Molar strength of solution KCl Data from Lawrence Bowden
Windlestone trial details(Horizontal Flow) • Feed taken from site final effluent • Initial rate 2.7 m3/hr reduced to 0.75 m3/hr • 0.96 m3 of pellets • Contact time 7½min increased to 24 min • Sampled input and output every 25 hr
Windlestone trial details(Vertical Flow) • Feed taken from site final effluent • Flow Rate 0.75 m3/hr • 0.88 m3 of pellets • Mean contact time 90 second (unsaturated flow) • Mean contact time 25 minutes (fully saturated flow) • Sampled input and output every 25 hr
Ochre pellet reaction vessel: Windlestone WWTW – Horizontal Flow Effluent percolates through ochre Inflow Outflow Gravel Images: Jonathan Aumônier Slide: Kate Heal
Final STW Sump at Windlestone Outlet from Trial Inlet for Trial
Results for Windlestone Trial(Horizontal Flow) Feed Phosphate Mg/l P Removal Fraction Date
Windlestone spot resultsResults from samples after maintenance to clear the overflow
Ochre pellet reaction vessel: Windlestone WWTW – Vertical Flow Inlet Pipe From Pump In-line Strainer Inlet Sample Line Spray Bars
Spray Bar Inlet - 0.75 m3/hr 500mm Saturated Zone U Bend Outlet Ochre pellet reaction vessel: Windlestone WWTW – Vertical Flow
Results for Windlestone Trial(Vertical Unsaturated Flow) 0.75 m3/hr mean residence time 90 sec Feed Phosphate Mg/l P Removal Fraction Date Mean Removal 26%
Planned Work • Continue Windlestone trial with saturated flow • More locations • Laboratory tests on ochres and binders • Laboratory continual flow trials