Heavy metals extraction from anaerobically digested sludge

Abstract

This paper reports on the chemical extraction efficiency in the removal of heavy metals from sludge from an activated-sludge system, which receives as influent both industrial and municipal wastewater. Utilizing a series of chemical extractants in a sequential order comprised the first phase of the research, called sequential chemical extraction (SCE). The work started with the well-known Tessier method followed by Veeken and by Sims and Kline SCE schemes. Afterwards, modified versions of Tessier and Veeken schemes were applied. The second phase, named chemical extraction using pH progressive changes, concerns an alternative to the extraction process. Four acids were tested: nitric, hydrochloric, oxalic and citric and the pH values as well as the time were varied. Some conclusions reveal that although modifying Tessier and Veeken schemes provides more consistent results, SCE is still an imperfect method regarding specificity and selectivity. Besides, it is not advisable to apply one SCE scheme developed for one specific situation to another one, once the accurateness of the method depends on several factors such as sort of material and chemicals, contact time, temperature, etc. The extraction efficiency increases using nitric or hydrochloric acids at low pH values, promoting high extraction efficiency level.

The Possibility of Organo-Mineral Fertilizer Production from Sewage Sludge

“…The first one is to control individual sources of heavy metals discharges, the second one is connected with controlling diffuse sources (using lead-free gasoline, copper-free tap water transport systems) and the third one is the removal of heavy metals from sewage sludge. The process of heavy metals removal from sewage sludge consists of four steps: solubilization of heavy metals by changing the pH and oxidation-reduction potential, separating the liquid including mobilized metals, chemical precipitation of heavy metals, and removal from leachate [39].…”

Novel sludge treatment technology enhances toxic metal removal, pathogen reduction, sludge digestibility and dewaterability

“…For most of the metals, the organically bound fraction usually makes up a fairly large component (Babel and del Mundo Dacera, 2006, Daskalakis et al, 2013, Lake et al, 1984, Marchioretto, 2003, Wang et al, 2005, which agrees with the fact that extracellular polymeric substances (EPS) are an important sink for toxic metals in sludge (Brown and Lester, 1979, Liu et al, 2001, Tian et al, 2006. Another important metal fraction is the inorganically bound, particularly sulfide and carbonate precipitates.…”

“…With a series of chemical agents extracting in a specific sequence, metals in different forms will be solubilised step by step (Marchloretto et al, 2002). There are several SCE procedures to fractionate metals in sludge samples using different extracting agents, which separate metals into various fractions (Filgueiras et al, 2002, Lake et al, 1984, Sims and Kline, 1991, Tessier et al, 1979, Ure et al, 1993.…”

“…The best metal removal process achieved about 80% Cu and 100% Zn solubilisation with citric acid at pH 1.5. Marchioretto (2003) investigate the acid leaching efficiency of organic acids and inorganic acids. The results showed that at pH 3 and pH 4, citric acid had the best metal leaching performance, which is again likely caused by the complexing properties of citrate anion.…”

“…The expense for nitrite dosing would be much lower than other metal removal strategies, such as H 2 O 2 , where the required final concentration of H 2 O 2 is higher than 10 g/kg dry solids (Beauchesne et al, 2007, Dewil et al, 2007, Ito et al, 2008. To avoid possible negative consequences from the sulfate addition into sludge, hydrochloric acid could be used for acidification, considering that hydrochloric and sulfuric acids have comparable metal leaching performances (Marchioretto, 2003) and both are commonly used inorganic acids.…”