February 15-18, 2009 Washington State Convention Center Seattle ...

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A COMPARISON OF TWO ALUMINUM BASED COAGULANTS FOR PHOSPHORUS
PRECIPITATION AND SUSPENDED SOLIDS REMOVAL USING INCLINED BELT FILTER
TECHNOLOGY TO DEWATER RECIRCULATING AQUACULTURE EFFLUENT
Mark J. Sharrer, Kata Rishel and Steven T. Summerfelt
Conservation Fund Freshwater Institute
1098 Turner Road
Shepherdstown, WV 25443 USA
m.sharrer@freshwaterinstitute.org
Aquaculture production methods typically produce a high volume fish farm effluent that contains low concentrations of organic
material and nutrients that can result in adverse affects on a receiving water body. Effective removal of particulate and dissolved
fractions of these pollutants is necessary to adhere to state and federal regulatory guidelines and for proper overall fish farm
management. Efficient collection of particulate waste products is evident in recirculating aquaculture systems (RAS) technology.
Backwashing and flushing of mechanical filters and gravity settling units results in a small volume of waste concentrated
effluent relative to the entire recirculating volume. When further wastewater treatment is desired, this reduction in volume
increases treatment efficiency and reduces cost of on-site treatment options.
Inclined belt filter technology for wastewater treatment utilizes polymer / coagulant amendments to aggregate solids and precipitate
dissolved phosphorus, separating these constituents from final discharge. The purpose of this research was to flocculate
fish culture wastewater with a polymer and compare the phosphorus adsorption capacity and optimal dosing requirements of
either aluminum chloride (AlCl 3 ) or aluminum sulfate (Alum) prior to inclined belt filter dewatering. A series of bench-scale jar
tests applying each coagulant (without polymer) determined the most effective dose based upon total suspended solids (TSS)
and dissolved reactive (DRP) phosphorus concentrations in jar supernatant. A subsequent series of jar tests determined the
optimal combination of polymer dose and previously determined coagulant (AlCl 3 and Alum) doses.
Based upon the jar test analyses, four flocculant/coagulant doses were compared utilizing an inclined belt filter operated at the
Conservation Fund Freshwater Institute for solids dewatering from commercial scale recirculating rainbow trout (Oncorhynchus
mykiss) production. Chemical amendment treatments applied were 1) 10 mg/L polymer (control), 2) 10 mg/L polymer +
290 mg/L AlCl 3 , 3) 10 mg/L polymer + 50 mg/L Alum, and 4) 10 mg/L polymer + 146 mg/L AlCl 3 (stoichiometric equivalent
of 50 mg/L Alum). Results indicate that filtrate TSS removal was >98.8 when applying any coagulant in combination with the
polymer. Further, DRP removal was most efficient applying AlCl 3 at 290 mg/L (95.9%) in combination with the polymer.
Table 1. Percent removal of key water quality parameters at each treatment