Development and Implementation of a Novel Sulfur Removal Process from H2S Containing Wastewaters.

A novel process for removing sulfur from wastewater containing dissolved sulfide has been developed and implemented in a membrane bioreactor (MBR) process treating anaerobically pretreated industrial (pulp and paper) wastewater at the Gippsland Water Factory. Controlled oxygen addition to the first bioreactor zone (constituting 27.7% of the total bioreactor volume) to create oxygen-limiting conditions, followed by oxygen-sufficient conditions in the remaining zones of the bioreactor, provide the necessary conditions. Dissolved sulfide is oxidized to elemental sulfur in the first zone, and the accumulated sulfur is retained in the bioreactor mixed liquor suspended solids (MLSS) in the remaining zones. Accumulated sulfur is removed from the process in the waste activated sludge (WAS). Oxidation of dissolved sulfide to elemental sulfur reduces the associated process oxygen requirement by 75% compared to oxidation to sulfate. Microscopic examinations confirm that biological accumulation of elemental sulfur occurs. Process performance was analyzed during a nearly 2-year commissioning and optimization period. Addition of air in proportion to the process influent dissolved sulfide loading proved the most effective process control approach, followed by the maintenance of dissolved oxygen concentrations of 1.0 and 1.5 mg/L in the two downstream bioreactor zones. Sufficient oxygen is added for the stoichiometric conversion of dissolved sulfide to elemental sulfur. Enhanced biological phosphorus removal also occurred under these conditions, thereby simplifying supplemental phosphorus addition. These operating conditions also appear to lead to low and stable capillary suction time values for the MBR mixed liquor.

Diagnosis of dissolved organic matter removal by GAC treatment in biologically treated papermill effluents using advanced organic characterisation techniques.

Granular activated carbon (GAC) exhaustion rates on pulp and paper effluent from South East Australia were found to be a factor of three higher (3.62cf. 1.47kgm(-3)) on Kraft mills compared to mills using Thermomechanical pulping supplemented by Recycled Fibre (TMP/RCF). Biological waste treatment at both mills resulted in a final effluent COD of 240mgL(-1). The dissolved organic carbon (DOC) was only 1.2 times higher in the Kraft effluent (70 vs. 58mgL(-1)), however, GAC treatment of Kraft and TMP/RCF effluent was largely different on the DOC persisted after biological treatment. The molecular mass (636 vs. 534gmol(-1)) and aromaticity (5.35 vs. 4.67Lmg(-1)m(-1)) of humic substances (HS) were slightly higher in the Kraft effluent. The HS aromaticity was decreased by a factor of 1.0Lmg(-1)m(-1) in both Kraft and TMP/RCF effluent. The molecular mass of the Kraft effluent increased by 50gmol(-1) while the molecular mass of the TMP/RCF effluent was essentially unchanged after GAC treatment; the DOC removal efficiency of the GAC on Kraft effluent was biased towards the low molecular weight humic compounds. The rapid adsorption of this fraction, coupled with the slightly higher aromaticity of the humic components resulted in early breakthrough on the Kraft effluent. Fluorescence excitation-emission matrix analysis of the each GAC treated effluent indicated that the refractory components were higher molecular weight humics on the Kraft effluent and protein-like compounds on the TMP/RCF effluent. Although the GAC exhaustion rates are too high for an effective DOC removal option for biologically treated pulp and paper mill effluents, the study indicates that advanced organic characterisation techniques can be used to diagnose GAC performance on complex effluents with comparable bulk DOC and COD loads.