Cleanup of sewage sludge spiked with Cd, Cu, and Zn: Sludge quality and distribution of metals in the "soil-plant-water" system.

Corn was grown under greenhouse conditions in the presence of uncleaned versus cleaned municipal sewage sludge to assess the effectiveness of a chemical leaching process that uses an inorganic acid and strong oxidants to clean biosolids (i.e., to remove metals without reducing their agronomic potential). Specifically, our study analyzed physicochemical sludge from the Montreal (MSL) wastewater treatment plant (WTP) and biological sludge from the Becancour (BSL) WTP. Both biosolids were spiked with individual metals (dry weight basis): Cd (100 mg kg-1), Cu (3000 mg kg-1), and Zn (5000 mg kg-1), or their mixture. MSL biosolid enrichment led to the solubilization of added metals and removed 84-88% of Cd, 78-79% of Cu, and 79-81% of Zn. Similarly, BSL biosolid enrichment resulted in the removal of 86-88% of Cd, 80-81% of Cu, and 88-89% of Zn. The fractional distribution of metals varied between biosolids depending on their production process, stabilization, and initial metal concentration. In the MSL biosolids, only Cu partitioning was influenced by spiking, cleanup, and washing. The three metals (Cd, Cu, and Zn) occurred either in their crystalline phase or were linked to Fe oxide, organic matter, or carbonate. In the BSL biosolids, the metals that were not in their crystalline phase were only associated with Fe oxide. This study demonstrated that 99% of Cd and Cu and 97% of Zn contents remained in the soil; however, biosolid cleanup generally decreased metal concentrations in plants, leachate, and/or soil.

Decontamination of sludge by the METIX-AC process. Part II: effects on maize growth and bioaccumulation of metals.

Given the fact that, according to our knowledge, no study has compared the agro-environmental use of decontaminated with non-decontaminated sludge, a greenhouse experiment was carried out to test the growth of maize (Zea mays L., G-4011 Hybrid) and bioaccumulation of metals in the presence of four different sludges (MUC, QUC, BEC and DAI), before and after their decontamination by a novel process (METIX-AC). Data showed that decontaminated sludge ameliorated plant growth and biomass production, and decreased bioaccumulation of metals, more than control soil, inorganic chemical fertilization, or conventional non-decontaminated sludge. Since chemicals used by the METIX-AC process contained S and Fe, decontaminated sludge introduced large amounts of these elements, while the overall presence of metals was reduced. Often, sludge dose also affected maize growth and bioaccumulation of metals. Overall, no toxicity to plants was noticed and bioaccumulation and transfer of many metals remained below the limits reported in the literature.

Decontamination of sludge by the METIX-AC process. Part I: effects on sludge quality and leaching of chemicals.

Sludge decontamination removes metals, and then generates biosolids that can be safely recycled in agriculture. The research currently presented is probably one of the initial comparison of the agro-environmental impact of decontaminated versus non-decontaminated sludge. Four different sludge were tested at two rates (80 and 160 kg/ha N), before and after their decontamination by a new process (METIX-AC), and subsequently compared to non-amended and inorganically fertilized soil, for maize cultivation under greenhouse conditions. Results presented in this paper reveal that the METIX-AC process very successfully extracted several metals from sludge (e.g., up to 87%, 72% and 66%, respectively for Cd, Cu and Zn), while preserving satisfactory levels of nutrients (e.g., less than 7% of lost TKN). The proposed process was, however, inefficient for extracting Cr and Pb. The mechanisms of metal removal from sludge and their leaching into drainage water are discussed. Decontaminated sludge ameliorated the water holding capacity of soil, reduced the total quantities of leachates, and produced drainage water of an acceptable quality. Yet, leaching of N-compounds was not significantly (Pr