41    CHARACTERIZATION OF TREATMENT RESIDUES FROM
HAZARDOUS WASTE TREATMENT, STORAGE, AND
DISPOSAL FACILITIES
Barry D. Kaplan, Senior Engineer
Metcalf & Eddy, lnc
Wakefield, Massachusetts 01888
INTRODUCTION
The RCRA Hazardous and Solid Waste Amendments of 1984 mandate that a ban on land disposal
of hazardous wastes be considered. EPA is required to evaluate alternative technologies for each
waste category and to establish treatment standards for banned wastes based on the lowest level
achieved by a best demonstrated available technology (BDAT). As part of the program to develop this
information, field evaluation of alternative technologies for treating or destroying wastes that have
been listed for priority action were conducted. The primary focus of this study was to evaluate the
treatability of metal-bearing and solvent (F001-F005) wastes. This paper presents information on
existing technologies being applied to the treatment of these wastes, the effectiveness of these processes, and the environmental impacts of these processes in terms of residues and emissions.
FACILITY A
Process Description
Facility A is a commercial off-site treatment facility accepting aqueous wastes generated by the
electroplating industry, as well as other metal finishing operations. Table I summarizes ihe types of
waste streams treated during the sample episode including their SIC code and RCRA waste code.
The liquid treatment process, depicted in Figure 1, entails four basic processes: cyanide oxidation,
hexavalent chromium reduction, metals precipitation, and solids separation. The cyanide oxidation
process uses a waste sodium hypochlorite solution to oxidize cyanide in a single-stage batch reactor.
The waste used during the sampling episode was a scrubber solution from the production of chlorinated chemicals (RCRA Waste Code D003). Typically, few incoming wastes necessitate treatment for
cyanide.
Hexavalent chromium is reduced to trivalent chromium in a single-stage batch reactor, using iron-
bearing (ferrous) waste acid as the reducing agent. The waste used during the sampling episode was a
waste picking acid from the metal processing industry (RCRA Waste Code K062). The chromium
reduction is accomplished under alkaline conditions in order to minimize corrosion of equipment and
eliminate the potential emission of by-product gases (e.g. NO-,, CU) that could be generated under
acidic reaction conditions. Upon successful reduction of the hexavalent chromium, the waste is then
precipitated similar to all other treatment batches.
The chemical precipitation process entails addition of bolh a lime slurry, to initially precipitate the
heavy metals as their insoluble hydroxides, and a soluble sulfide waste to precipitate any remaining
dissolved metals. The sulfide polishing reagent was a by-product scrubber solution from ihe production of a sulfurized esler (RCRA Waste Code D003). The contents of the reactor are pumped lo one of
two precoat vacuum filters for solids separation. Perlite. a volcanic ash, is currently used as a precoat
although diatomaceous earth has been used in the past. The filtrate from the precoal filter is discharged to the municipal sewer system. The solids scraped from the filter are conveyed to segregated
bulk containers. Samples from each container are subjected to the 24-hour EP toxicity test to ensure it
is nonhazardous prior to transport to a final disposal site.
409