運用電透析技術現地去除地下水中硝酸鹽氮之研究

The Study of In-Situ Nitrate Removal from Groundwater Using Electro-Dialysis

近年來，地下水中硝酸鹽氮濃度高已經引起全球的關注。目前已有多種技術被普遍用來去除原水中硝酸鹽氮。本研究選用中部某淨水場之地下水水源做為原水來源，以電透析之試驗，探討對硝酸鹽氮之去除效能、產水品質及電量消耗成本分析。實驗結果顯示，施加電壓提高，可增加硝酸鹽氮之去除效率，電壓範圍值30V至60V時，其反應時間約30秒，硝酸鹽之去除效率即可達為52.50%至63.34%。當流速自2L/min增加至5L/min，外加電壓60V下，發現去除率從63.34%下降44.17%。本研究採用電透析技術之中的「倒極式電透析試驗（Electro Dialysis Reversal，EDR）」，此技術運轉時間長，消耗的電能穩定，於本試驗中發現增加電壓10V，則多耗0.1度電且處理1m^3水量，平均產水1噸約耗3度電；原水的硝酸鹽氮濃度為11.7mg/L～17.1mg/L之範圍，電壓10V～60V之硝酸鹽氮去除率為30.89%～66.9%。考量用電成本與硝酸鹽之去除，電透析進行倒極試驗下，其最佳操作電壓為35V，此時處理1m^3水的耗電量約3.05度，可得45%之硝酸鹽去除率。將電透析所產生之濃縮水進行水耕種植加以回收利用，結果顯示，藉由水耕種植可降低水中硝酸鹽氮之濃度，確定此法是可行的且無需添加其他營養液即可耕種。

In recent years, high nitrate concentration in groundwater has gained global attention. There are a several technologies that are commonly utilized in the removal of nitrate from raw water. Raw water was obtained from a groundwater monitoring well from central region of waterworks in Taiwan. In the ED study, nitrate removal efficiency was examined, the water quality of the product effluent was analyzed and power cost analysis was determined. The results show that increasing the voltage applied causes an increase in the nitrate removal efficiency. Within the voltage range of 30 to 60V, about 52.50% to 63.34% of nitrate removal efficiency was obtained in shorter reaction time of 30s. Under an applied voltage of 60V, the removal rate was observed to decrease from 63.34% to 44.17% as flow rate was increased from 2 L/min to 5 L/min.Electricity consumption was observed to be stable, where a voltage increase of 10 V corresponds to a 0.1 kWh consumption of electricity. The electricity utilized in one treatment cycle of EDR is an average of 3 kWh. A removal efficiency of 30.89% to 66.90% would utilize a voltage in the range of 10 to 60 V, when the nitrate concentration about 11.7mg/L to 17.1mg/L. Using a voltage of 35 V, one ton of power is consumed of 3.05 degree that provides a 55% residual nitrate and 45% nitrate removal. Hydroponic cultivation method was utilized in the treatment of nitrate from wastewater, where nitrate was absorbed using hydroponic vegetables. The uptake of nitrate could also serve as a fertilizer in the growth of hydroponic vegetables.