Gömeç Ciğdem Yangin
Environmental Engineering Department, Faculty of Civil Engineering, Istanbul Technical University, Maslak, Istanbul, Turkey.
J Environ Sci Health A Tox Hazard Subst Environ Eng. 2006;41(6):1117-27. doi: 10.1080/10934520600620519.
Anaerobic digestion of the primary sludge with or without scum addition and the role of pH were evaluated in four completely stirred tank reactors (CSTR) operated as batch systems at 35 degrees C (mesophilic). For investigating the scum influence, two CSTRs were only fed with the primary sludge (PS) whereas the other CSTRs were composed of the primary sludge with 15% scum (PS+Scum). The pH in two reactors was fixed at 6.5, whereas the pH in the other two reactors was left to be operated at their original values for evaluating the retardation in biodegradation rates at low pH values. Since scum is generally produced at most primary settling tanks and given into the anaerobic digesters, the behavior of the CSTR was examined with or without scum addition. The results indicated that scum addition favoured low pH levels and led to retardation in methanogenesis. Besides, pH control enhanced the biodegradation rates and led to methanogenesis to perform at shorter digestion times in the reactors. The destructions of TSS and VSS were better when the pH was controlled. When only primary sludge was used as the substrate, the reactors with or without pH control removed VSS with a corresponding production of VFAs and soluble COD. However, their productions ceased earlier and the complete VFAs consumption occurred 4 days earlier in the reactors with pH control. In the reactors consisting of PS+Scum, soluble COD productions continued during 4 days of digestion. However, soluble COD remained constant and almost no VFAs consumption occurred during the whole operation period without pH control whereas VFAs were consumed completely after around 11 days in the reactor with pH control. Overall, scum addition caused methanogenesis to perform at longer operation periods when the pH was controlled and kept above 6.5. When the pH was not controlled, scum favoured acidic conditions and did not allow methanogenesis to start due to the fact that methanogens could not perform well at low pH levels.
在四个作为间歇系统运行的完全搅拌釜式反应器（CSTR）中，于35摄氏度（中温）下评估了添加或不添加浮渣时初级污泥的厌氧消化以及pH值的作用。为研究浮渣的影响，两个CSTR仅投喂初级污泥（PS），而其他CSTR则由含15%浮渣的初级污泥（PS + 浮渣）组成。两个反应器中的pH值固定在6.5，而另外两个反应器的pH值则保持在其原始值，以评估低pH值下生物降解速率的延迟情况。由于浮渣通常在大多数初级沉淀池产生并进入厌氧消化器，因此研究了添加或不添加浮渣时CSTR的行为。结果表明，添加浮渣有利于低pH水平并导致甲烷生成延迟。此外，pH控制提高了生物降解速率，并使甲烷生成在反应器中更短的消化时间内进行。当pH得到控制时，总悬浮固体（TSS）和挥发性悬浮固体（VSS）的分解效果更好。当仅使用初级污泥作为底物时，有或没有pH控制的反应器去除VSS并相应产生挥发性脂肪酸（VFAs）和可溶性化学需氧量（COD）。然而，它们的产生更早停止，并且在有pH控制的反应器中，VFAs的完全消耗提前4天发生。在由PS + 浮渣组成的反应器中，可溶性COD在4天的消化过程中持续产生。然而，在没有pH控制的整个运行期间，可溶性COD保持恒定，几乎没有VFAs消耗，而在有pH控制的反应器中，VFAs在大约11天后被完全消耗。总体而言，当pH得到控制并保持在6.5以上时，添加浮渣会导致甲烷生成在更长的运行期内进行。当pH未得到控制时，浮渣有利于酸性条件，并且由于产甲烷菌在低pH水平下不能良好发挥作用，不允许甲烷生成开始。
