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

Abstract

Microbial metal leaching from sewage sludge (2-9% w/v) was carried out with the iron-oxidizing bacterium Thiobacillus ferrooxidans. Measurements of pH, oxidationreduction potential, and concentration of Fe 2+ indicated that T. ferrooxidans was effective in removing metals from an incubation bath containing less than 5% sludge solids concentration. Specifically, Cu leaching was completely suppressed at a high solids concentration of 9% (w/v). Results indicated that the deactivation of T. ferrooxidans at a high sludge content was mainly due to the presence of inhibiting materials such as organic matter. A mixed culture of sulfur-oxidizing bacteria was obtained by enrichment from anaerobically digested sewage sludge to enhance the efficiency of the microbial leaching process. These bacteria were much more effective in metal leaching than was iron-oxidizing T. ferrooxidans. At 9% (w/v) solids concentration, the leaching efficiencies of Zn and Cu were 78% (2.66 g/kg dry sludge) and 59% (1.36 g/kg dry sludge), respectively. Therefore, when removing heavy metals from the anaerobically digested sewage sludge, the indigenous sulfur-oxidizing bacteria isolated in the current study were more efficient than T. ferrooxidans, especially at high sludge solids concentrations.

Bioleaching of heavy metals from sewage sludge: A review

“…ferroxidans was effective in removing metals from sludge having solids less than 5%. The leaching of Cu was completely stopped at high solids concentration of 9%, whereas the solubilization of Zn decreased from 61% for the sludge having 2% solids to 47% for the sludge having 9% solids (Cho et al, 2002).…”

“…The buffering effect in sludge is due to the presence of basic components such as carbonates (Brombacher et al, 1998). The increase in concentration of the leached metals also results in toxicity that may inhibit the growth of the microorganisms (Cho et al, 2002). Further, the solids content affects the oxidationreduction potential (ORP) of the system.…”

“…In 2 days of batch bioleaching, 47-80% Cu, 42-60% Ni and 40-71% Cd were solubilized . Cho et al (2002) studied batch bioleaching using At. ferrooxidans and reported that high organic matter of the sludge can have inhibitory effect on the bioleaching process, since At.…”

Changes in nutrient profile of soil subjected to bioleaching for removal of heavy metals using Acidithiobacillus thiooxidans

“…ORP increased rapidly between day-6 and day-16 and finally it was 612 mV at the end of the experiment. This may be due to sulfur utilization (oxidation), i.e., as the elemental sulfur is oxidized to soluble sulfate, it leads to decreased concentration of free electrons followed by increase in ORP [25]. In control, no significant increase in ORP was recorded.…”

Effect of the Various Heavy Metals on the Growth and Phosphorus (P) Removal Capacity of the Phosphorus Accumulating Microorganism (Pseudomonas sp.)

“…특히 폐수 중에 함유된 유독성의 크롬, 구리, 납 및 아연 등과 같 은 중금속 이온이 수계에 유출되면 생태계 및 인체에 치명적 인 피해를 줄 수 있기 때문에 중금속이 함유된 폐수의 제거 및 처리를 위한 노력이 다각적으로 이루어지고 있다 (Cho et al, 2002;Ryu et al, 2003). 일반적으로 하수 슬러지의 중 금속 함량은 0.5-2.0%이고, 어떤 경우에는 총 금속 함량이 4.0%에 이르기도 한다 (Blais et al, 1993).…”