| 摘要: | 近年畜牧業發展快速，使臺灣農業生產值大幅提升，而畜牧糞尿處理，過往是以廢水方式管制，業者為降低成本，將未處理之廢水排至河川，導致環境逐漸惡化；環保署制定「畜牧糞尿肥分利用策略」以改善生態污染問題，利用經厭氧發酵而成沼渣為農田肥料使用，可增加土壤肥分外，對環境亦可減輕負擔。
本研究以沼渣為肥料施於土壤中，探討施用沼渣對土壤及滲出水的重金屬成份影響分析，以盆栽進行模擬實驗，並以化肥做對照，實驗後分析土壤的基本性質，再以微波王水消化法與Tessier序列萃取法進行土壤及滲出水之重金屬總量及組態分析，藉此評估生態風險。
研究結果顯示，使用不同肥料後，土壤酸鹼值(pH值)均有下降，但沼渣含有豐富的腐植質及微量養分元素等，使有機質相較於化學肥料含量較高，但沼渣本身水溶性鹽類較多，導致施用沼渣後土壤導電度(EC)上升。
添加沼渣之土壤重金屬濃度方面，銅與鋅濃度增加量較多，分別是銅13mg/kg、鋅55.7mg/kg；土壤滲出水平均重金屬濃度，分別為銅0.41mg/kg、鋅0.65 mg/kg，鉛、鉻、鎳及鎘重金屬濃度皆小於0.1 mg/kg；以Tessier序列萃取分析土壤重金屬組態，施用沼渣後，鉛、鋅、鎳主要為殘留態及鐵錳氧化態存在；鉻、鎘主要比例為殘留態；銅則以有機態、殘留態存在；以組態特性評估結果，鉛、鋅、鎳重金屬以鐵錳氧化態存在時，在較低的氧化還原電位下，易使鐵錳氧化物產生溶解現象，導致重金屬被釋出，鉻、鎘主要為殘留態，對生態較無影響，但須注意鎘在土壤中之累積；銅重金屬以有機態存在於環境時，屬於易釋出且具生物有效性之型態，所以帶來的潛在環境風險較高。
經重金屬總量分析，重金屬銅、鋅在施用後累積總量分別為銅0.04 mg/kg、鋅0.09 mg/kg，其餘金屬皆小於0.01 mg/kg，質量平衡結果呈現，沼渣中之銅及鋅分別有98.57 %及99.05 %比例將持續積累於農田土壤；以沼渣肥料進行施肥，評估重金屬累積之超標年限，經計算結果，重金屬銅超標年限約為148年，重金屬鋅約為242年，與過往國內實際使用沼渣施肥之評估年限約銅為190年、鋅為82年相當，可以推測沼渣施用在短期內較無重金屬的污染風險，長期使用則需要週期性檢測，以確保應用於農田的安全性。
經重金屬總量分析，重金屬銅、鋅在施用後累積總量分別為銅0.04 mg/kg、鋅0.09 mg/kg，其餘金屬皆小於0.01 mg/kg，質量平衡結果呈現，沼渣中之銅及鋅分別有98.57 %及99.05 %比例將持續積累於農田土壤；以沼渣肥料進行施肥，評估重金屬累積之超標年限，經計算結果，重金屬銅超標年限約為148年，重金屬鋅約為242年，與過往國內實際使用沼渣施肥之評估年限約銅為190年、鋅為82年相當，可以推測沼渣施用在短期內較無重金屬的污染風險，長期使用則需要週期性檢測，以確保應用於農田的安全性。
;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. |
