Bacterial Leaching of Heavy Metals From Anaerobically Digested Sewage Sludge

Abstract

Spreading of sewage sludges on agricultural land is an attractive sludge management option because it combines beneficial reuse and disposal at the same time. However, it is important to reduce the metal content in the sludge in order to minimize the health hazard associated with metal uptake by plants and its subsequent accumulation in the food chain. Treatment of sludge with acid for metal removal is not practical because a large amount of acid is required. Typically 0.5 to 0.8 g of H2SO4/g dry weight of sludge will be required to achieve over 70% removal of cadmium (Cd), zinc (Zn) and nickel (Ni). Lead (Pb) and copper (Cu) are not significantly removed. A biological process called bacterial leaching, which has been used commercially for extracting copper and uranium from low grade ores, was reviewed and its potential for removing heavy metals from anaerobically digested sewage sludge was investigated. Leaching experiments were conducted and the results showed that about 80 to 90% removal of cadmium, zinc and nickel, and 60 to 70% removal of copper were possible. The acid requirement was significantly reduced because only 0.15 g of H2SO4/g dry weight of sludge was needed.

Bioleaching of cadmium and nickel from synthetic sediments by Acidithiobacillus ferrooxidans

“…Only 30% solubilization was achieved in the acid-leaching reactor even after 4 days. The results are comparable with Ni solubilization data, 70% solubilization of Ni after 8 days, obtained from anaerobically digested sewage sludge by Wong and Henry (1983). However, Blais et al (1992b) observed only 40% Ni solubilization from municipal sludge with an iron-oxidizing mixed culture during 10 days of microbial leaching.…”

“…However, Blais et al (1992b) observed only 40% Ni solubilization from municipal sludge with an iron-oxidizing mixed culture during 10 days of microbial leaching. Both Wong and Henry (1983) and Blais et al (1992b) reported significantly higher cadmium solubilization (80%) than Ni solubilization from the same sludge samples. Mercier et al (1996) reported that microbial leaching processes were capable of solubilizing 80% Cd, 73% Cu, and 90% Cu from heavily contaminated sediments.…”

“…Moreover, microbial leaching has been successfully applied to anaerobically digested municipal sludges (Wong & Henry 1984;Tyagi & Couillard 1989;Ravishankar et al 1994) and contaminated sediments (Mercier et al 1996;Seidel et al 1998;Chen & Lin, 2001;Tsai et al 2003). One of the principal microorganisms involved in bioleaching is Acidithiobacillus ferroxidans (formerly Thiobacillus ferrooxidans) (Kelly & Wood 2000;Kinzler et al 2003), a chemoautotrophic bacterium which can grow by oxidizing both reduced sulfur compounds and ferrous iron in a pH range of 1.5-3 (Torma & Itzkovitch 1976;Wong & Henry 1983). The mechanism of bioleaching was thought to be either a direct bacterial attack on sulfide minerals (equation (1)) or an indirect attack by the products of microbial metabolism (equations (2)-(4) (Hutchins et al 1986):…”

Phytotoxicity and speciation of copper, zinc and lead during the aerobic composting of sewage sludge

“…It has been reported that total content of metals in sewage sludge was about 0.5-4% (on a dry weight basis) [5]. However, heavy metals associated with different fractions had different impacts on the environment [6] and their phytotoxicity would connect to some forms rather than the total concentration of metals [7].…”

Fractionation study in bioleached metallurgy wastes using six-step sequential extraction

“…There are many efforts to recover valuable elements from industrial wastes and to decrease potential risk of environmental contamination. One of the recently applied methods is bioleaching (the solubilization of metals from solid substrates either directly by the metabolism of leaching bacteria or indirectly by the products of their metabolism [4]) Bioleaching is a simple, economical and effective process for metal solubilization from industrial wastes or biosolids [1][2][3]. Metal solubilization from solid wastes or other solids is achieved through the activity of some chemolithotrophic bacteria for example autotrophic or heterotrophic bacteria.…”