Hydrolysed Cellulose Material as Sulfate Reduction Electron Donor to Treat Metal- and Sulfate Containing Waste Water

Abstract

The amenability of hydrolysed cellulose material to low cost sulfate reduction electron donor was examined with fluidized bed reactor (FBR) treating synthetic mine waste water. The studied cellulose material was dried Phalaris arundinacea reed, which was acid hydrolysed (1.5 w/w % H2SO4, 7 w/w % solids) at 120oC to hydrolyse polymeric materials to biodegradable monomers. The FBR was operated at 35oC, and ethanol has previously been used as the electron donor. FBR was fed with synthetic waste water (pH 4.5) containing soluble fraction of Phalaris arundinacea hydrolysate, metals (Fe and Zn) and sulfate. The switch of the electron donor from ethanol to hydrolysate was successful. The acidic influent was neutralized in the FBR by the alkalinity produced in the oxidation of Phalaris arundinacea hydrolysate. The main oxidation product of the soluble hydrolysate was acetate, which accumulated in the FBR during overloading. The percent sulfate reduction remained in the range of 40-95 %. The highest obtained hydrogen sulfide production was 0.91 g L-1d-1 at a hydraulic retention time (HRT) of 9 h, while highest sulfate reduction was 8.4 g L-1d-1 (HRT 8 h). Iron and zinc precipitated in the FBR, and highest metal precipitation rates were 1.14 g Fe L-1 d-1 and 30 mg Zn L-1d-1 (HRT 8 h). The electron donor load was measured as soluble chemical oxygen demand (CODs), and highest CODs removal rate was 2.13 g L-1d-1 (HRT 9 h) and CODs percent oxidation 92 % (HRT 10 h). Soluble Phalaris arundinacea hydrolysate was found to be a suitable electron donor for sulfate reducing FBR and mine waste water treatment. The soluble fraction of Phalaris arundinacea hydrolysate was used very efficiently by sulfate-reducing bacteria (SRB). Additionally, batch bottle assays showed that SRB-enrichment also used solid, dried Phalaris arundinacea as electron donor for sulfate reduction (total sulfide yield 340 mg L-1 in 14 days). The results of sulfate reduction and iron precipitation are shown in figures 1 A-B.