[Characteristics of Heavy Metals in Chicken Manure Organic Fertilizers in the Huang-Huai-Hai Region and related Environmental Risk Assessment]

One hundred and twenty types of chicken manure organic fertilizer samples were collected from five provinces and two cities in the Huang-Huai-Hai region, to investigate heavy metal content, fractionation, and environmental risk through toxicity characteristic leaching procedures. Results showed that content of heavy metals in chicken manure organic fertilizer varied greatly, in the order of Zn > Cu > Pb > As > Cd. When compared with the standard for organic manure, ratios of Cd, As, and Pb exceeded the standard by 6.7%, 47.05%, and 14.28%, respectively. Moreover, the content of heavy metals varied significantly in different provinces. Cd and Zn in organic manure fertilizers were mainly Fe and Mn oxide-bound fractions, accounting for 37.3% and 43.79%, respectively. However, the proportion of residual fractions of Pb, organically-bound fractions of Cu, and exchangeable forms of As were higher. Contents of TCLP-Zn,-Cu,-Cd,-Pb and-As in organic manure were 41.11, 33.3, 0.07, 1.25, and 0.21 mg·kg^-1, respectively. The number of samples in which Zn and Pb in organic manure exceeded the standard was 6 and 5, respectively, with these mainly obtained from Hebei and Jiangsu provinces. There was a significant correlation between total content of Zn, Cu, Cd, and As in organic manure and content of TCLP (P<0.05). Based on an annual manure application rate of chicken manure of 15 t·hm^-2, safe application of chicken manure is in the order of Henan > Tianjin > Anhui=Shandong=Jiangsu > Hebei > Beijin.

Solidification and Biotoxicity Assessment of Thermally Treated Municipal Solid Waste Incineration (MSWI) Fly Ash

In the present work, thermal treatment was used to stabilize municipal solid waste incineration (MSWI) fly ash, which was considered hazardous waste. Toxicity characteristic leaching procedure (TCLP) results indicated that, after the thermal process, the leaching concentrations of Pb, Cu, and Zn decreased from 8.08 to 0.16 mg/L, 0.12 to 0.017 mg/L and 0.39 to 0.1 mg/L, respectively, which well met the limits in GB5085.3-2007 and GB16689-2008. Thermal treatment showed a negative effect on the leachability of Cr with concentrations increasing from 0.1 to 1.28 mg/L; nevertheless, it was still under the limitations. XRD analysis suggested that, after thermal treatments, CaO was newly generated. CaO was a main contribution to higher Cr leaching concentrations owing to the formation of Cr (VI)—compounds such as CaCrO₄. SEM/EDS tests revealed that particle adhesion, agglomeration, and grain growth happened during the thermal process and thus diminished the leachability of Pb, Cu, and Zn, but these processes had no significant influence on the leaching of Cr. A microbial assay demonstrated that all thermally treated samples yet possessed strong bactericidal activity according to optical density (OD) test results. Among all samples, the OD value of raw fly ash (RFA) was lowest followed by FA700-10, FA900-10, and FA1100-10 in an increasing order, which indicated that the sequence of the biotoxicity for these samples was RFA > FA700-10 > FA900-10 > FA1100-10. This preliminary study indicated that, apart from TCLP criteria, the biotoxicity assessment was indispensable for evaluating the effect of thermal treatment for MSWI fly ash.

Cellular Mutagenicity and Heavy Metal Concentrations of Leachates Extracted from the Fly and Bottom Ash Derived from Municipal Solid Waste Incineration

Two incinerators in Taiwan have recently attempted to reuse the fly and bottom ash that they produce, but the mutagenicity of these types of ash has not yet been assessed. Therefore, we evaluated the mutagenicity of the ash with the Ames mutagenicity assay using the TA98, TA100, and TA1535 bacterial strains. We obtained three leachates from three leachants of varying pH values using the toxicity characteristic leaching procedure test recommended by the Taiwan Environmental Protection Agency (Taiwan EPA). We then performed the Ames assay on the harvested leachates. To evaluate the possible relationship between the presence of heavy metals and mutagenicity, the concentrations of five heavy metals (Cd, Cr, Cu, Pb, and Zn) in the leachates were also determined. The concentrations of Cd and Cr in the most acidic leachate from the precipitator fly ash and the Cd concentration in the most acidic leachate from the boiler fly ash exceeded the recommended limits. Notably, none of the nine leachates extracted from the boiler, precipitator, or bottom ashes displayed mutagenic activity. This data partially affirms the safety of the fly and bottom ash produced by certain incinerators. Therefore, the biotoxicity of leachates from recycled ash should be routinely monitored before reusing the ash.