30    TREATING ELECTROPLATING WASTEWATER
USING AN ANAEROBIC FILTER
M. J. Gundry, Project Engineer
Simcoe Engineering Group Limited
Pickering, Ontario, L1V 1A1
J. G. Henry, Professor
D. Prasad, Microbiologist
Department of Civil Engineering
University of Toronto
Toronto, Ontario, M5S 1A4
INTRODUCTION
Electroplating industries are the major contributors of metals to municipal sewers.1 Pretreatment
of electroplating wastewaters is essential to reduce their impact on wastewater treatment plants.
Metals are removed from electroplating wastewaters using physicochemical processes such as chemical precipitation, ion exchange, reverse osmosis, evaporation, electrodialysis and electrolytic recovery.2 These technologies are effective in removing metals, but require chemical additions (chemical
precipitation and ion exchange) or energy inputs (reverse osmosis, electrodialysis and electrolytic
recovery) in excess of that required for pumping.
Removal of heavy metals can also be accomplished in biological wastewater treatment systems
(aerobic and anaerobic) by the adsorption of metal ions on the biomass and/or by biologically
mediated precipitation.
Extracellular polymers produced by microorganisms have been found to adsorb cations.3,4 Cell wall
proteins and lipids contain anionic ligands (phosphoryl, carboxyl and hydroxyl groups) which can
also adsorb cations.5 It has been observed that Pb, Zn, and Cu have a high affinity for biosorption,
while nickel has a low affinity for biosorption.3,6,7,8
Biological reactions involved in metal precipitation include both methane-producing bacteria
(MPB) and sulfate-reducing bacteria (SRB) which produce, respectively, carbonates and sulfides as
shown below:
CH3COO- + H20 ^   CH4 + HCOj- (1)
CHjCOO" + S04f™   HS + 2HCO3- (2)
Bicarbonate (HCO3) and carbonate (C032) can precipitate metals as metal carbonates. Hydrogen
sulfide reacts with metals to form insoluble metal sulfides.
Dissimilatory SRB such as Desulfovibrio, Desulfotomaculum, and Desulfobacter use sulfate
(S042") as an electron acceptor during the anaerobic degradation of organics.9 During this process,
S04 is reduced to S2". The S2" is then available to precipitate metals as metal sulfides. Anaerobic
filters utilizing sulfate reducing bacteria, have been studied for the removal of metals from acid mine
drainage, landfill leachate and other wastes.10,11
This study deals with the use of an anaerobic filter to remove metals from a nickel electroplating
wastewater. Rinse waters from acid type plating baths, comprising the largest waste load from
electroplating industries, are laden with heavy metals and sulfates.12 Since most of these constituents
are in soluble form, these plating wastewaters are ideal for treatment by an anaerobic filter, provided
these wastes are supplemented with suitable organic and inorganic nutrients. These nutrients can be
supplied by raw sewage, which, in addition to being nutritionally balanced, is inexpensive and readily
available in the vicinity of electroplating industries.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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