本研究之主要目的為探討廢污水在海洋放流時，大腸桿菌在高鹽份濃度水體之自然衰減情形，同時評估不同加氯量與不同的海洋環境條件時，對大腸桿菌消減之影響，所獲得之結果，可以提供各污水處理廠在海洋放流時添加次氯酸鈉濃度之參考依據。
實驗以八里污水處理廠為例，探討放流污水在不同的海水溫度（20℃、25℃、30℃）、不同旳海水鹽度（10%o、20%o、35%o）及控制添加次氯酸鈉加藥量（0ppm、2ppm、3.5ppm、3.8ppm、4ppm、8ppm），對大腸桿菌影響。經由本實驗結果可得知符合法規放流標準之最適添加量，進而分析加藥量來節省操作成本。由八里污水處理廠放流水水質之變化顯示經加氯消毒所得之大腸桿菌數與法規相差甚多，而其他放流水水質分析結果亦顯示大腸桿菌受水質變化而產生差異的可能性不高。
藉由實驗結果計算大腸桿菌衰減速率常數，在設定的三種鹽份濃度下，大腸桿菌的數量在初始的10分鐘內即有明顯的衰減現象，而後趨於平緩，表示大腸桿菌於高濃度鹽份下有明顯衰減比例，呈現35%o＞20%o＞10%o ，這顯示鹽份濃度仍是決定大腸桿菌存活之重要因子，但經過一定時間後大腸桿菌衰減情形會達極限。在另一方面，次氯酸鈉加入後，所有大腸桿菌去除率皆明顯提高，即使高溫下的鹽類影響仍不明顯，表示相較於次氯酸鈉與溫度等環境因子，鹽份濃度並不是大腸桿菌衰減之絶對佔優勢因子。
因此，由實驗結果中得知當鹽份濃度為35%o時，其添加2.0ppm之次氯酸鈉即可符合海洋放流水標準，以目前八里污水處理廠之次氯酸鈉添加量4.0ppm，換言之，一半之次氯酸鈉加藥量，即可達到排放標準，若據此作為操作依據，則應可節省一半之加藥量的費用。

The objective of this study is to examine the depletion ratios of E. coli in variously simulated environmental conditions as wastewater is discharges into the ocean. The appropriately added amount of the disinfectant NaOCl was experimentally determined in order to save the extra operation cost and reduce impact to ocean creatures. The effluent of a primary treatment plant, Bali Wastewater Treatment Plant, is investigated to elucidate the above-mentioned consideration. The obtained result can be a good reference to the other wastewater treatment plants regarding the addition of NaOCl before the ocean disposal.
In this study, the influences of the environmental conditions on E. coli depletion were investigated. The experimental conditions consisted of temperatures (20℃, 25℃ and 30℃); salt concentrations (10%o, 20%o and 35%o), and the different dosage of NaOC1. The experiment is divided into two groups including kinetic depletion rate constant and depletion ratios within 30 minutes. In addition, the wastewater characteristics of Bali Wastewater Treatment Plant were also studied so as to evaluate whether the obtained result can be applied to other wastewater treatment plants or not.
The E. coli numbers in the effluent of Bali Wastewater Treatment Plant are maintained from 240000 to 360000 CFU /ml. The results of the E. coli depletion without NaOCl conditions indicate a dramatically reductive E. coli numbers within the initial 5 minutes under the selected salt concentrations. The increasing temperature and salinity increase E. coli depletion. When the NaOCl is added into the effluent, the depletion rates of the E. coli can fit the Chick’s law. However, the increases in E. coli depletion ratios significantly slow down as the added NaOCl concentration exceeds 2.0ppm. If NaOCl is absent in the effluent, the E. coli numbers will be permitted according to the criteria of wastewater ocean disposal (100000 CFU/ml) under the temperature above 30℃ and salinity above 20%o. For the other environmental conditions, 2.0 ppm of NaOCl is regarded as the best dosage of the disinfectant for the economic cost consideration. To compare the best 2.0ppm dosage with the present 4.0 ppm dosage, the operation cost can be therefore saved from 11 to 18 million dollars /year.

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