湖山淨水場聚氯化鋁及氯化鐵混凝最適加藥及其對清水殘餘鋁含量之影響

Abstract

一般初設淨水場需依原水濁度建立混凝劑最適加藥曲線，才可進行淨水場的操作。近年來環保署已公告淨水場清水鋁含量之管制規定，依飲用水水質標準，未來淨水場清水鋁含量將管制到0.2 mg/L as Al，而台灣許多淨水場其清水殘餘鋁超過此法規標準限值。本研究在降低殘餘鋁的前提下，評估最適合湖山淨水場的混凝劑，以南幹渠、清水溪為湖山淨水場原水自102年7月至103年4月共採樣10次，並以瓶杯試驗決定PACl、FeCl3兩種混凝劑的最適藥量，以及評估PACl搭配硫酸以減少殘餘鋁含量的加藥方式。 研究結果顯示，南幹渠、清水溪原水中顆粒含鋁、鐵含量隨原水濁度增加而增加，但顆粒錳僅微量存在水中且與原水濁度變化無明顯相關。使用PACl作為混凝劑時，南幹渠及清水溪原水混沉後上澄液過濾水殘餘鋁超過飲用水水質標準限值(0.2 mg/L as Al)之比例超過40%。改採PACl搭配硫酸加藥方式，每噸水最少須添加2.5 mL濃硫酸(98%)條件下，過濾水總鋁量可小於0.2 mg/L as Al。然而，使用FeCl3為混凝劑時，過濾水無溶解性鐵、鋁以及色度等問題。另外，PACl混凝劑搭配加酸之方式可有效降低水中溶解鋁量。在不同原水濁度下(3000 NTU以下)，隨原水濁度增加，FeCl3混凝劑最適加藥量較PACl混凝劑少，加藥成本也較PACl混凝劑搭配硫酸所需之成本低。

It is required to establish the curve of optimal coagulant dosage with turbidity of raw water for the operation of new waterworks. Recently, the limit of residual aluminum in the finished water from water treatment plant (WTP) has been officially announced by environmental prevention agency (EPA). It has been proven that the total Al in the finished water from a lot of water treatment plant in Taiwan exceeds the limit (0.2 mg/L as Al) of drinking water quality standard. This study aims to evaluate the optimal chemicals for the reduction of residual Al in the finished water of Hushan WTP. Two kinds of raw water samples (Nangan River and Qingshui River) for Hushan WTP were collected for ten times to determine the optimal dosage of coagulant (PACl and FeCl3) with jar tests. In addition, the addition of acid coupled with PACl coagulation was carried out to evaluate the reduction of residual Al. The results showed that the quantity of particulate aluminum and iron increases with increasing the turbidity of raw water, but the quantity of particulate manganese is insensitive to turbidity. For Nanganr and Qingshui River, the ratio of residual Al in the filtrate exceeding the limit (0.2 mg/L as Al) of drinking water quality standard is over 40%. For PACl coagulation with the addition of sulfate (98%) at the condition of 2.5 mL per ton water, the residual Al of filtrate is less than 0.2 mg/L as Al. However, the dissolved Al and Fe in the filtrate is comply with the limit of standard without apparent color. The residual dissolved Al can be effectively reduced by PACl coagulation with the addition of acid. Below 3000 NTU, the increase in the optimal dosage for FeCl3 coagulation with increasing turbidity of raw water is less than that for PACl coagulation.