Characteristics and Reuse Potential as Fertilizer Based on Heavy Metal Concentrations in Domestic Wastewater Biosolids (Taiwan)

Abstract

Use of biosolid as fertilizer, soil conditioner and soil additive has been promoted in the US, Europe and Japan for some time. However, heavy metals of high concentrations contained in the sewage biosolid may through plant absorption and food chain seriously affect human health and contaminate the soil if the sludge is used directly as fertilizer or soil conditioner. Numerous studies have been conducted on the correlation between biosolid heavy contents and bioavailability. In Taiwan, there is no integral data on concentrations and characteristics of heavy metals contained in biosolids that supports the re-use of biosolid as fertilizer. Hence, the feasibility of re-using biosolid has not be implemented and promoted. In this research, six representative wastewater treatment plants in Taiwan have been selected for collecting biosolid samples in order to understand the concentrations and characteristics of heavy metals contained in biosolids so that the feasibility of re-using these biosolids can then be evaluated. The analysis results reveal that the biosolids collected from the six wastewater treatment sludge contains Cd has the greatest concentration differences among sample collected from different wastewater treatment plants with 130.6 % difference followed by As (90.2 % difference), and Ni (71.3 % difference). Cadmium contained in Fu-Tien wastewater treatment plant sludge has the greatest difference at different sample times with 58.7% difference; nickel is the next with 47.2 % difference. When the distribution of metal bond fraction is concerned, copper, lead, cadmium and zinc show little difference; copper exists primarily in organic bond fraction, lead in residual fraction, cadmium in residual fraction and organic bond fraction, zinc in Fe/Mn-oxide bond fraction. When reused as fertilizer, the biosolid that contains cadmium, nickel and zinc could exceed the limitations. It can be rinsed in 1 M HCl solution to effective reduce its heavy metal contents to meet the minimum standards for reuse as fertilizer in soil.