Land application, biological decontamination, and speciation of metal-laden sewage sludge

Sewage sludge, too often disposed of in landfills, contains high nutrient and organic contents and is now being recycled and beneficially applied to agricultural land worldwide in increasing amounts. Effective industrial pretreatment and monitoring by wastewater treatment facilities can ensure the sludge produced is low in toxic contaminants, both organic and inorganic, and high in nutrients and humus, thus rendering sewage sludge as an effective and cheap alternative to commercial fertilizers. Trace metals are the most significant restraint relative to land application of sludges and can often negate the benefits of land application. Even so, metals in sewage sludge are generally organically bound and therefore less available for plant uptake than the more mobile metal salt impurities found in commercial fertilizers.; This research consisted of three experimental phases including: a laboratory experiment assessing the effect of sludge application on trace metal uptake in specific parts of the Durum wheat plant, a reactor study investigating the feasibility of successfully bioleaching the metal-laden anaerobically digested sewage sludge of the Prague, Czech Republic Central Wastewater Treatment Plant for land application purposes, and an experiment investigating the potential to determine the speciation of metals-in sewage sludges.; Results from the three research phases showed that although the wheat plants were exposed to a large quantity of metals from sludge, plant concentration was generally equivalent to that resulting from fertilizer application; necessary bioleaching bacterial numbers were high and sustainable indicating no adverse affects of the bioleaching bacteria Thiobacillus to organic matter; and elemental speciation (both with and without enhancement) showed that although metals were released by each sequential extraction step, the total release did not account for what was present in the sewage sludge.