United States Environmental Protection Agency EPA/540/F-92/011 October 1992 vvEPA SUPERFUND INNOVATIVE TECHNOLOGY EVALUATION Emerging Technology Bulletin Alternating Current Electrocoagulation Electro-Pure Systems, Inc. Technology Description: Alternating current electrocoagulation (ACE) technology offers an alternative to primary chemical co- agulant or organic polymer addition for breaking stable emulsions and suspensions. The ACE technology is also effective for re- moving certain metals and other soluble pollutants in the polish- ing step of effluent treatment. Traditional chemical coagulant addition generates voluminous, gelatinous sludges which are difficult to dewater and filter slowly. Another disadvantage of chemical coagulation is the high susceptibility to particulate filter shear of the coagulated particulates and emulsion droplets. ACE is- an electrochemical technology for introducing low concentra- tions of a non-toxic polymeric aluminum hydroxide species into aque- ous media. These species neutralize the electrostatic charges on suspended solids and oil droplets thereby inducing accumulation and separation from the aqueous phase. For remediation or effluent treat- ment lower purity aluminum pellets, produced from recycled scrap or beverage cans, can be used. In industrial situations where product purity is a concern, high purity aluminum pellets are required. ACE appreciably enhances the filtration and dewatering rates of solids removed from an effluent. Liquid/liquid and solid/liquid phase separa- tions are achieved with production of sludges that can be filtered more readily than those formed through chemical flocculant addition. The coagulation is induced without adding any soluble species. The sludge produced has a lower contained water content and is more easily dewatered. Separation of the hazardous components from an aque- ous waste with ACE reduces the volume of potentially toxic pollutants requiring special handling and minimizes waste disposal. Significant reductions in total suspended solids of particulate slurries, metal con- centrations, fluorides, and phosphates can also be achieved. See Figure 1 for the ACE basic process flow. The technology can be used to break stable aqueous suspensions containing subimicron-sized particles of up to 10% total solids and stable aqueous emulsions up to 5% oil. Fine-grained products can be recovered using ACE. ACE has been shown to improve the buffering capacity and settling characteristics of sludges. Vent or Treat Gas Aqueous Suspension or Emulsion Control Feed Rate A.C. Coagulator Product Separation Air for Turbulence Figure 1. Alternating current electrocoagulation basic process flow. Printed on Recycled Paper ------- Waste Applicability The ACE technology can be applied to various aqueous-based sus- pensions and emufetons typically generated by contaminated ground- watof, surface runoff, landfill teachate, truck wash, scrubber solutions, tested effluents and extract solutions. Suspensions Include solids such as pigments, days, metallic powdeis, metal ores, and natural colloidal matter, Emulsions Include a variety of solid and liquid contaminants such as peJrateum-based by-products. Reductkxis exceeding 90% in the loadings of aqueous day, latex, and titanium dioxide suspensions have been routinely achieved. Reductions exceeding 80% En the Chemfcat Oxygen Demand (COD) and Total Organic Catbon (TOG) content of diesel fuel-spiked slurries have been aecomplihed ACS has ateo been used for recovery of reusable fine-grained product from Industrial process streams that would have been discharged into the sewer system, and for the extraction of suspended solids from Waste streams which contribute to high biological oxygen demand (BOD) and COD loadings. Use of ACE for municipal wastewater treatment would reduce the quantity of chlorine required to achieve required disinfection levels. Test Results The ACE Technology was tested using two designs of the ACE Separator, (1) a Parallel Electrode unit in which a series of parallel, vertically-oriented aluminum electrodes form a series of monopolar efedrofylic ceils through which the effluent passes, and (2) a Ruidized Bed unit with noa-conductive cylinders equipped with non-consumable metal electrodes between which a turbulent fluidized bed of aluminum altoy peBets Is maintained. The FUdized Bed Unit dissolved aluminum at least one order of magnitude more efficiently than the Parallel Unit. Results reported here are from experiments with the Fluidized Bed ACE Separator. The Emeiging Tecrmofogy/SlTE program research involved testing varfous surrogate wastes prepared from EPAs Synthetic Soil Matrix (SSMJ as stabte aqueous suspensions of si, clay, and topsoil contain- tng efiaseS fuel, metaJs, and a strong surfactant were tested at bench- Bench-scafe experiments were conducted on surrogate wastes pre- pared by mixing 0.2 to 3,0 wt % of the -230 mesh (day and silt) fraction ofthaSSMwihO.Sto 1,5wt%of Number 2 diesel fuel, 0.5 to 0.10 wt % of an emufsifler (nton-IQOX or Alconox soap), and from 10 mg/Lto 100 ttgIL of one or more of the following contaminants: copper, nickel, zinc* Grthophosphafe, or fluoride, The pH of each mixture was adjusted to 5,7, or 9 and the conductivity raised to approximately 1200 uS/cm to 1500 u&em vrtlh NaC! to simulate natural values. Bench-scale results indicated: (1) heating of the waste sluiry during electrocoagulation enhanced phase separation; (2) electrocoagulation produced approxi- mately 83% Jess sludge volume and a 76% improvement in filtration rate when compared to alum (Al,2(SO4)3) treatment; (3) aluminum and stainless steel used as electrode material gave comparable results; and (4) agglomerated particles tend to disaggregate with both in- creased AC current frequency and increased retention time. Pilot-scale experiments of comparative electrocoagulation and alum treatments of a 3% soil slurry containing approximately 50% clays, 1.5% diesel fuel, 0.1% of a strong surfactant and metals (Cu, Cd, Cr, Pb) were conducted. Electrocoagulation produced reductions of total suspended solids (TSS) (222 to 4.5 sng/L), and total organic carbon (TOG) (130-6,6 mg/L). Copper was reduced by 72%, cadmium by 70%, chromium by 92%, and lead by 88%, No appreciable change in total solids (TS) loadings in the supemate resulted from electrocoagulation. Comparative alum additive experiments were also conducted using the same surrogate waste. Alum treatments generally required ap- proximately 30% longer filtration times. ACE Separator treatment reduced the TS and TSS to an equivalent degree and approximately one-quarter the level achieved through alum addition. Better reduc- tions in soluble metal concentrations are achieved with electrocoagulation treatment. Particle size analyses show considerable enhancement in the clay fraction as a resuft of electrocoagulation. The mean sizes of the ACE Separator-treated particulates both in the supernate and the filtrate (188 and 230um respectively;! have increased by a factor of about 85 forthe supernate and approximately 105 for the filtrate, over that in the original slurry (2.2um). For Further Information: EPA Project Manager Naomi Barkley U,S. EPA Risk Reduction Engineering Laboratory 26 West Martin Luther King Drive Cincinnati, OH 45268 (513) 569-7854 Technology Developer Contact: Clifton Farreli Electro Pure Systems, Inc. 10 Hazelwood Drive Amherst, NY 14228 (718)691-2610 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULKRATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/S40fF-92/011 ------- |