Evaluation of the operation of Wheeler filters ：A case study of Tanding water treatment plant

[[abstract]]近年來台灣環境變遷，原水水質劇變、濁度不斷飆高，考驗著淨水場的淨水處理能力。惠勒式快濾池是台灣地區早期(1960~1970)廣泛使用於自來水淨水場，做為淨水處理流程中後段最重要的物理處理單元，過濾去除水中大部分濁度物質與微生物，再經過加氯消毒後，即可獲得乾淨安全衛生之飲用水，故快濾池的處理效率極為重要。本研究探討的主要課題是如何提昇惠勒式快濾池的處理效率，從快濾池相關設施體檢及維護標準和快濾池各項操作參數評估兩方面著手，在不影響正常供水下，選定潭頂淨水場第2號快濾池進行實場試驗，使其達到最佳操作，並建立快濾池標準操作程序。 快濾池相關設施體檢作業部份，進行濾池及濾料表面目測觀察檢視、濾料取樣及分析、濾層膠羽貯留分析、支撐礫石高程及濾砂深度量測繪圖、反沖洗濾料膨脹率試驗及反沖洗濾池目測觀察檢視等項目之實場檢查、試驗作業，以瞭解及診斷目標快濾池的健康狀況，針對快濾池所發現的問題，進行後續的改善和維護工作，以確保快濾池正常運作，進而提升快濾池過濾效能，並參酌淨水場操作人力、能力及實際需求，建立快濾池體檢標準作業程序及頻率和快濾池相關設施儀器、設備保養維護作業程序及校正頻率。 快濾池操作程序作業部份，進行快濾池過濾程序(降速過濾和定濾率過濾)、反沖洗流率控制及初期過濾濾率控制等實驗，將實驗成果進行分析、評選。快濾池過濾程序實驗成果，針對過濾操作性、濾程、水頭損失、過濾速度、過濾水濁度、過濾總水量及濁度去除率等各項參數進行評選，選出定濾率過濾程序為最佳快濾池過濾程序。反沖洗流率控制實驗成果，以濾料膨脹率及反沖洗時間兩項參數進行評選，選出TypeⅠ(反沖洗流率閥門第1段開度13 ％、延遲時間30 sec、第2段開度65 ％ ) 為最佳反沖洗流率控制程序。初期過濾濾率控制等實驗成果，以初期過濾水濁度、初期過濾水濁度上升時間及操作分段等三項參數進行評選，選出Type G (第1段濾率3000 CMD 延遲30 min 後，第2段濾率為分配流量11000 CMD ) 為最佳初期過濾濾率控制程序。最後依據實驗所獲得最佳快濾池各項操作參數，建立快濾池標準操作程序，提供淨水場辦理快濾池自動化操作，撰寫電腦圖控軟體製作時參考，以減少人為操作失誤，有效提升淨水處理效能。[[abstract]]Recently environmental changes in Taiwan such as aggravated raw water quality and turbidity increase cause tough challenges to water treatment plants Wheeler filter one major unit of drinking water treatment process has been used in water treatment plants since early sixties because it can remove turbidity and microorganism effectively which is very important for safe drinking water This study focused on how to improve the efficiency of an aged Wheeler filter by improving its operation and maintenance procedures and to propose a standard operating procedure (SOP) for its optimal operation No 2 Wheeler filter in Tanding water treatment plant was chosen for the case study Several tests were performed to examine and diagnose the rapid filter for further improvement including surface observation of the filter sampling and analysis of the filter media floc retention analysis gravel mapping and media depths measurement as well as bed expansion and observation during backwash Meanwhile a SOP for the examination and maintenance of Wheeler filters was proposed including test items and frequency as well as calibration frequency of examination facilities For the optimization of a rapid filter filtration tests (including declining rate of filtration and constant rate of filtration) control of backwash flow rate and early filtration rate were perfomed The data of filtration tests were evaluated according to the following criteria: feasibility of operation period of filtration head loss turbidity and flow rate of filtrate as the rejection ratio of turbidity and constant rate of filtration was found to be more effective than declining rate of filtration The data of backwash flow rate tests were evaluated according to the criteria of filter media expansion and backwash time and Type Ⅰ(the first valve 13 % open retention time 30 sec second valve 65 % open) was the optimal procedure among the 6 tested senarios The data of early filtration rate tests were evaluated according to the criteria of turbidity of filtrate; the time before the raise of turbidity in filtrate and the stages of operation Type G (the first filtration rate 3000 CMD retention time 30 min second filtration rate 11 000 CMD) was the optimal procedure among the 8 tested scenarios Finally a SOP for the optimization of Wheeler filters was proposed by comprehending the optimal operating procedures and an automated control program was formulated to reduce artificial control error and optimize the performance of Wheeler filter