添加Fe(Ⅲ)抑制厭氧生物腐蝕之研究

Abstract

本研究目的為利用添加電子接受者Fe3+於一硫還原菌優勢存在環境中之方法，藉此分析反應槽在此情形下之水質、菌相及腐蝕度之變化，並探討此環境下鐵片腐蝕之影響。 根據水質分析結果顯示，添加Fe3+於一硫還原反應為優勢電子接受者程序中，當水體中總有機碳量足夠時，鐵還原反應及硫還原反應同時存在進行，且並沒有相互抑制情形發生；而當水體中總有機碳量缺乏時，則可以發現硫還原反應及鐵還原反應互相影響；另外Fe3+供應者型態之不同亦影響鐵還原菌之鐵還原能力，由水質分析結果發現檸檬酸鐵較氯化鐵易受鐵還原菌所利用。 根據菌相及腐蝕度分析結果顯示，當添加檸檬酸鐵後，菌相中明顯出現具鐵還原能力之化學異營菌E.coli k12菌株，且為優勢菌種；而改以氯化鐵作為三價鐵供給者後，則發現硫還原菌在水體中之比例則上升，因此推論三價鐵型態亦影響菌相之變化。添加Fe3+以後發現水體腐蝕電流下降許多，且與水中溶解性硫化物濃度具有正相關，表示水中硫化物濃度越低，造成金屬腐蝕之影響亦隨之降低，故添加Fe3+的確對腐蝕抑制具有效果。但由鐵片重量法腐蝕分析顯示，鐵片之放置位置不同造成腐蝕度皆有差異，主要推測與鐵片上生物膜及添加Fe3+後進流基質pH值之變化有相當關係，但由一僅鐵還原菌存在之環境下作鐵片重量腐蝕分析顯示，當水體中優勢存在鐵還原菌環境下，鐵片之腐蝕度是明顯低於含硫還原菌優勢存在之環境下，因此證實利用鐵還原反應來抑制腐蝕是具有效果之方法。

This study is to investigate the effects for adding Fe(Ⅲ) in an SRB-enriched anaerobic bioreactor, which caused the variations of the water quality, microbial communities and corrosion rates. The influence of the mild steel in this situation is also evaluated. The results suggest that addition of Fe(Ⅲ) compound to the reactor in which sulfate was the predominant terminal electron-acceptor, when the concentrations of total organic compound (TOC) are excess, sulfate reducing process and iron reducing process occur simultaneously. When TOC are limited in that anaerobic bioreactor, sulfate reducing process and iron reducing process were compete with each other. The magnitude of reduction for Fe(Ⅲ) is depended on the kinds of the Fe(Ⅲ)-contained compounds. The results suggest that ferric citrate is more available than ferric chloride for iron-reducing bacteria (IRB) under these conditions. While the ferric citrate was added to the reactor, the E.coli k12 which possessed the iron-reduced ability is occurred and become the predominant bacteria. However when the Fe(Ⅲ) source is replaced by FeCl3 ,the percentage of SRB is increased among the microbial community. It infers that the variations of microbial communities were influenced by the various Fe(Ⅲ) forms. After adding Fe(Ⅲ), it was suggest that corrosion currents decreased and was positive proportion to dissolvable sulfide concentration in the reactor. It shows that the corrosion rates of mild steel coupons and the dissolved sulfide concentration were decreased, so it was effective for inhibiting SRB-induced corrosion. But the results of weight loss tests show that the corrosion rates of iron coupons were not agree the results on the Tafel tests. It inferred that the weight-loss was mainly related with both the biofilm formed on the mild steel and the pH of the influent substrate. The results of weight-loss tests show that the coupon corrosion under the condition which IRB predominant was less than under the condition which SRB predominant. It suggested that the iron reducing reaction can be an effective method for inhibiting SRB-induced biocorrosion.