FIXATION OF ELECTROPLATING WASTE SLUDGES
Herman Johannesmeyer, Graduate Student
Mriganka Ghosh, Professor
Civil Engineering Department
University of Missouri
Columbia, Missouri 65211
INTRODUCTION
In the past decade concern for the proper disposal of solid waste has increased tremendously. Particularly, attention has focused on the hazardous component of solid wastes. It is because of the
hazardous component that many strict regulations governing land disposal of solid wastes have been
enacted.
Land disposal is considered by many to be the most objectionable method of hazardous waste disposal. Consequently, many industries have turned to treatment techniques that reduce the toxicity of
these solid wastes prior to burial. These techniques, referred to as solidification/stabilization (fixation) processes, are used to treat industrial sludges that contain hazardous constituents to prevent dissolution or loss of toxic material into the environment. The objective of this study was to investigate
the effectiveness of two fixation techniques, namely silicate-cement fixatio and fly ash-lime fixation,
on an electroplating waste sludge.
WASTE SOURCE
During the 1970's many laws were passed to limit the amount of pollutants discharged by industries. These regulations are called pretreatment regulations and are designed to restrict the amount of
pollutants discharged into Publicly Owned Treatment Works (POTW's). Of the industries affected,
electroplating was one of the first. For many years the solution to pollution was dilution. Pretreatment regulations do not permit this since process effluent limitations are applicable to the treated
effluent prior to dilution with sanitary wastewater, noncontact cooling water, or other non-process
water [1,2].
With the discharge limitations in effect, it was necessary for industries to either reduce the generation of pollutants in the manufacturing processes or remove them from the waste stream with an
onsite wastewater treatment system. The undesirable constituents in electroplating wastewaters are
heavy metals. Excessive heavy metals in a POTW wastewater stream produce detrimental effects on
biological wastewater treatment plants, such as inhibition of biologic treatment operations, accumulation of metals in the digester sludge creating disposal problems, or passing untreated through the system into a natural receiving body of water and producing toxic effects on the aquatic environment
there.
In general, within the electroplating industry, the sources contributing heavy metals to the wastewater loading include: 1) rinse water; 2) intentional process dumps; 3) drips, spills and leaks; 4) process treatment devices (filter cleaning waters or ion exchange regenerant wastewater); 5) ventilation
systems; and 6) accidential spills [3].
The electroplating waste used for this study was obtained from a company in Missouri using electroplating as part of the manufacturing process. The company maintains and operates an industrial
wastewater physical/chemical treatment facility for treating process wastewater before being discharged. A flowchart of the treatment facility is shown in Figure 1. Three waste streams, cyanide,
mixed metal, and acid/alkali are treated separately within the facility. The cyanide stream is chlorinated to oxidize cyanide to carbon dioxide and nitrogen. Metabisulfide is added to the mixed metal
stream to reduce hexavalent chromium, and the acid/alkali stream is combined for pH neutralization.
The streams converge in a header and are treated with lime for hydroxide precipitation of the metals.
A polyelectrolyte is added following the Parshall flume to help settling of metal hydroxide precipitates
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