| dc.description.abstract | In recent years, the livestock farming industry has been developing rapidly and is an important part of Taiwan′s agricultural production. However, in the past, the policy for the treatment of livestock waste and urine was to treat the digestate as waste water. In order to improve river pollution problem and rural air quality, the EPA is promoting the ＂Livestock Manure and Urine Fertilisation Strategy＂. The biogas residue is used as farmland fertilizer.
In this study, digestate was applied as fertilizer to the soil to investigate the effects of digestate application on the composition and environmental impact of heavy metals in soil and leachate. The potential environmental risks were evaluated.
The results of the study showed that the pH value of the soil decreased slightly after the application of digestate because the digestate was rich in humus and micronutrients, which made the organic content higher than that of the chemical fertilizer group, but the digestive had more water-soluble salts, which led to an increase in soil conductivity (EC) after the application of digestate.
In terms of heavy metal concentrations in the soil, the concentrations of copper and zinc increased more, at 0.65 mg/kg for copper and 1.36 mg/kg for zinc respectively, while the concentrations of lead, chromium, nickel and cadmium were all less than 0.1 mg/kg.
The Tessier sequence extraction analysis showed that after application of digestate, lead, zinc and chromium were mainly in the residual state and ferromanganese oxidation; nickel and cadmium were mainly in the residual state; and copper was in the organic and residual state.
As a result of the configuration assessment, the presence of lead, zinc and chromium heavy metals in the ferromanganese oxide state tends to cause dissolution of ferromanganese oxides at low redox potentials, resulting in the release of heavy metals
Cadmium and nickel are mainly in residual form and have no impact on the ecology, while copper and heavy metals in organic form are easily released and biologically effective when present in the environment, thus posing a higher potential environmental risk.
The total heavy metal analysis showed that the total accumulation of copper and zinc in the soil was 0.04 mg/kg for copper and 0.09 mg/kg for zinc respectively.The assessment of the exceedance of the cumulative age limit for heavy metals using digestate fertilizer was calculated to be about 148 years for heavy metal copper and 242 years for heavy metal zinc, which is comparable to the assessment of 190 years for copper and 82 years for zinc for the actual use of digestate fertilizer in other stndy in the past .It can be assumed that the application of digestate will be less risky in the short term in terms of heavy metal contamination, while long-term use will require periodic testing to ensure the safety of the application on farmland. | en_US |