Biological processes: The effects of initial pH, percentage inoculum and nutrient enrichment on the solubilization of sediment bound metals

Abstract

Abstract. Biological solubilization of metals in highly contaminated sediments (Lachine Canal, Montreal, P.Q., Canada) was tested in 500 mL batches. The biological process uses the leaching capacity of Thiobacilli. Batch experiments were performed to determine the influence of initial pH, the percentage of inoculum, and the addition of nitrogen and phosphate on the efficiency of the process. Similar metal recoveries were obtained at either of the initial pH values (pH 4.0 and pH 4.5). The addition of 20% inoculum (v/v) appears to result in acceptable yields over a short time period (24-48 hours). Solubilization of Cu is strongly correlated with the presence of bacteria (r 2 increase with time up to 0.90 after 53h). In the case of Zn (within first 6 hours) and Pb Cat the beginning), the chemical environment appears to be the main factor controlling solubilization of these elements (r 2 up to 0.99). The addition of nutrients had no affect on the production of Thiobacilli, but the addition of NH4 reduced the solubilization of Zn, Pb (r 2 up to 0.90) and at the beginning, the solubilization of Cu (r2=0.67). While the addition of PO43-diminished the solubilization of Zn, Pb and Cu (r 2 up to 0.96). Upon addition of substrate (FeSO4.7H20), the growth of Thiobacilli already present in the sediments is favored. The application of this process to sediments appears feasible, as Zn and Cu levels were at acceptable levels following treatment. Further studies are necessary to improve the removal of Pb.

Effect of Solids Concentration on Bacterial Leaching of Heavy Metals from Sewage Sludge

“…The sulfur-oxidizing ability of the mixed cultures isolated in this study was quantitatively evaluated by determining the SO 4 2-concentration formed in the MW medium during the enrichment. The SO 4 2-concentration was measured by ion chromatography (Waters 510) with a conductivity detector (Waters 420) and an IC-PakAnion column (4.6 mm φ × 50 mm L, Waters).…”

“…Most of the studies in microbial leaching have employed Thiobacillus ferrooxidans [2][3][4]11,15 or sulfur-oxidizing bacteria. 5,6,[12][13][14] The mixed cultures of T. ferrooxidans and T. thiooxidans have also been examined with or without an addition of alternative energy sources such as Fe (II) and elemental sulfur.…”

“…1 Several methods have been studied for leaching heavy metals from sewage sludge, [2][3][4][5][6][7] and they can be broken down into two categories: chemical leaching [8][9][10] and microbial leaching. [2][3][4][5][6][7][11][12][13][14][15] The chemical leaching method generally involves the use of mineral acids, such as H 2 SO 4 and HCl, at pH 1.5-2.0. 1 The solubilization of heavy metals has been greatly enhanced by heating during the treatment process.…”

“…15 However, a literature survey reveals that most of the studies on the microbial leaching of heavy metals have employed sewage sludge obtained directly from a digestion reactor in wastewater treatment facilities. [2][3][4][5][6][7]14,15 This sewage sludge has a low solids content, less than 4% (w/v). In general, the solids concentration for anaerobically digested sewage sludge has been 1.3-1.8% (w/v), and even for thickened sludge, the solids concentration has beeñ 3.8% (w/v).…”

Transformation of heavy metals from sewage sludge during bioleaching

“…Compared with other runs, pH of PS has a faster decrease in first three days, which may be due to the existence of a large number of inorganic components in PS [16]. The pH in OS and SS decrease at the similar rate, which indicates that anaerobic or aerobic treatment forbio-sludge does not significantly affect acidification process of bioleaching.…”