Chemical and Biological Treatability Testing of an Industrial Leachate

Remediation efforts are ongoing at the Avtex Fibers Superfund Site in Front Royal, Virginia. As part of the future remediation of several surface impoundments used for viscose waste disposal during plant operation, it may be necessary to extract contaminated leachate and groundwater for ex-situ treatment and discharge to the Shenandoah River. This waste stream contains high concentrations of sulfide (HS-), carbon disulfide (CS2), metals, carbonaceous COD and other contaminants as illustrated in Table 1. The objective of the work was to simulate and optimize the entire treatment system envisioned for this waste stream by conducting a bench-scale continuous flow treatability study. The bench-scale treatment system included preliminary chemical oxidation using un-catalyzed hydrogen peroxide with pH control at 10.5 for selective oxidation of CS2 and HS-, a moving bed biofilm (MBBR) biological treatment process for autotrophic reduced sulfur compound oxidation, pH adjustment with sulfuric acid, and biological treatment using a sequencing batch reactor (SBR) with ferric chloride addition for arsenic and antimony removal. Typical chemical oxidation process effluent contained total sulfide levels from 1-4 mg/L and less than about 30 mg/L total CS2. Free CS2 remained quite low, usually at concentrations less than 1 mg/L and always less than 2 mg/L. The MBBR served to polish remaining HS- and reduced the total CS2 to roughly 12-16 mg/L. COD was typically reduced to less than approximately 500 mg/L. The SBR effluent was characterized by COD and BOD at approximately 300-400 and 40-80 mg/L, respectively, with elevated periods caused by high effluent TSS. Final effluent sulfide concentrations remained low, although some xanthate-bound CS2 remained with total CS2 concentrations averaging about 6 mg/L.

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