PHYSICOCHEMICAL AND BIOLOGICAL TREATMENT OF A CONCENTRATED INDUSTRIAL LEACHATE FROM AGED PROCESS WASTE AT A VISCOSE RAYON PRODUCTION FACILITY

Viscose Rayon process waste was disposed of in open surface impoundments and resulted in the formation of a concentrated leachate, which is now associated with a semi-solid, cellulose-based waste material. Since the alkaline leachate is a presumed source for a groundwater plume extending down-gradient from the surface impoundments, the leachate “source” may require extraction and treatment as a component of the remedial action. This work represents a preliminary experimental evaluation to develop treatment concepts for discharging the leachate to a surface water receiving stream. The contaminants of concern for the leachate include high levels of carbon disulfide (CS2) and hydrogen sulfide (H2S), as well as heavy metals such as arsenic, antimony, and zinc. The leachate also contains high levels of dissolved silica and soluble cellulose xanthate, which is stable at high pH but degrades to form insoluble cellulose and CS2 at neutral and acidic pH. Due to the cellulose and reduced sulfur compounds, the leachate is characterized by a BOD and COD of about 5,000 and 14,000 mg/L, respectively. Neutralization of pH 10.2-10.3 leachate samples to pH 6-7 caused the precipitation of cellulose and amorphous silica and the volatilization of H2S and CS2. This process alone provided approximately 60% BOD and COD removal. It is expected that gas phase treatment will be required to manage H2S and CS2 emissions, however oxidant addition prior to neutralization could significantly reduce the emission rate. The effluent from the leachate neutralization process should be readily amenable to aerobic biological treatment.