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水资源短缺与能源危机推动了水处理技术的革新。在“双碳”背景下,传统的以能耗换水质的水处理技术已无法满足可持续发展的要求[1]。开发以能源再生-资源回收为目的的新技术,降低水处理过程中的碳排放,对于实现我国的“双碳”目标有着重要意义[2]。与传统的好氧生物处理技术相比,厌氧生物处理技术能够在废水处理过程中实现资源回收和能源再生,在水处理中具有广阔的应用前景[3-4]。近年来厌氧生物处理技术开始逐步应用于低浓度废水(如市政污水)的处理,但有机物含量低时厌氧微生物生长缓慢,且低产气量较难实现泥水混合液的充分搅拌,导致有机物的去除转化效果不理想,从而限制了厌氧技术在低浓度废水处理中的应用[5]。厌氧膜生物反应器(anaerobic membrane bioreactors, AnMBR)采用厌氧处理与膜分离相结合的方式,将水力停留时间(hydraulic retention time, HRT)和污泥龄(sludge retention time, SRT)分开[6],有效弥补了传统厌氧生物处理技术存在的弊端,具有生物量大、出水水质高以及能耗低等优点[7],是实现低浓度废水厌氧生物处理的理想技术。
已有很多研究报道了AnMBR用于处理低浓度废水时可以实现较好的有机物去除和产甲烷性能,但运行过程中存在着膜污染的问题,常需要通过沼气循环、混合液回流等方式增大体系混合程度来减轻膜污染。另一方面,AnMBR出水中含有较多的溶解性甲烷(dissolved methane, DCH4),甲烷是一种温室气体,DCH4解吸后[8](释放到大气)会造成能量流失和温室效应。现有研究[9-11]表明,AnMBR出水DCH4的质量浓度为8.8~19.1 mg·L–1,因此,而流失的甲烷占总甲烷产量的23%~88%。在较多研究中,测得DCH4的浓度经常高于亨利定律计算的理论值,即AnMBR出水的DCH4往往是过饱和的[12],其过饱和度即相比于理论DCH4的倍数为1.3~4.1倍[9,13]。已有部分研究通过外置气体分离器[14-17]对AnMBR出水DCH4进行回收并取得了较好的效果,但上述过程存在着能量消耗、占地增加和工艺流程长等问题。甲烷的液-气传质会显著改变甲烷的溶解程度,其传质系数[10,18]主要受反应器运行条件(如负荷、混合效率、温度)的影响,在不同工况下AnMBR出水DCH4的过饱和度具有较大的差异[19]。YEO等[10]在采用混合液循环的AnMBR中研究结果表明,随着负荷提升产气速率不断增大,有利于解除甲烷气-液传质的限制,从而降低了DCH4的过饱和度。研究不同工况对AnMBR中甲烷气-液分配特征的影响,有望通过反应器运行方式的调控,实现原位降低DCH4的浓度。为此,本研究针对AnMBR出水存在DCH4过饱和问题,基于AnMBR的低浓度废水处理过程,探究了不同负荷和混合方式对有机物去除和DCH4的影响。揭示上述过程甲烷气-液传质系数的变化规律并阐明AnMBR中甲烷的气-液分配特征,进一步用于指导反应系统运行,以期为降低AnMBR的碳排放量和能耗提供参考。
负荷与混合方式对厌氧膜生物反应器中甲烷气-液分配特征的影响
Effects of load and mixing mode on methane gas-liquid distribution characteristics in anaerobic membrane bioreactors
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摘要: 厌氧膜生物反应器(anaerobic membrane bioreactors, AnMBR)出水普遍存在过饱和的溶解性甲烷(dissolved methane, DCH4),易造成能量流失和温室效应,阐明AnMBR中甲烷气-液分配特征对提高甲烷回收率具有重要意义。为此,本文研究了负荷和混合方式对AnMBR中甲烷气-液分配特征的影响。结果表明,在35 oC,负荷为0.6~1.8 kg·(m3·d)–1的条件下,AnMBR实现了较好的有机物去除效果(COD去除率>90%),运行过程DCH4均处于过饱和状态(过饱和度为1.3~2.1),随着负荷的提升DCH4浓度升高,过饱和度有所下降;相比于循环混合,在浪式脉冲混合条件下的甲烷传质系数(KLa)更大,其中DCH4浓度、过饱和度及DCH4占进水COD的比例均较低。AnMBR大部分进水COD转化为甲烷,主要以气态形式存在 (50.2%~60.0%)。浪式脉冲混合时反应器总能耗比循环混合降低了85.9%~88.0%,提升负荷有利于实现AnMBR处理废水过程的能量平衡。
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关键词:
- 厌氧膜生物反应器 (AnMBR) /
- 溶解性甲烷 /
- 负荷 /
- 混合方式 /
- 传质系数
Abstract: Dissolved methane (DCH4) is commonly found in the effluent of anaerobic membrane bioreactor (AnMBR), thus easily causing energy loss and greenhouse effect. Understanding the characteristics of methane gas-liquid distribution is crucial to improve the methane recovery in AnMBR. This study investigates the effects of load and mixing mode on the methane gas-liquid distribution in AnMBR. The results showed that the AnMBR achieved favorable organic removal (COD removal >90%) at 35 oC and 0.6~1.8 kg·(m3·d)–1 load, but DCH4 remained oversaturated (oversaturation ratio of 1.3~2.1) throughout operation. As the load was elevated, DCH4 concentrations also increased while the oversaturation ratios decreased. Wave-pulse mixing mode, with higher methane transfer coefficient (KLa), resulted in lower DCH4 concentration, oversaturation ratio and the proportion of DCH4 to influent COD compared with cyclic mixing mode. Most of the influent COD was converted to methane in gaseous form (50.2%~60.0%). The total energy consumption of reactor under wave-pulse mixing mode was 85.9%~88.0% lower than that of cyclic mixing mode. Elevating load is prone to achieve a net energy balance during AnMBR wastewater treatment.-
Key words:
- anaerobic membrane bioreactors (AnMBR) /
- dissolved methane /
- load /
- mixing mode /
- transfer coefficient
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表 1 不同阶段的运行条件
Table 1. Operation conditions of different phases
阶段 负荷/(kg·(m3·d)–1) 进水COD/(mg·L–1) 混合方式 A1 0.6 500 循环 A2 0.6 500 浪式脉冲 B1 1.2 1 000 循环 B2 1.2 1 000 浪式脉冲 C1 1.8 1 500 循环 C2 1.8 1 500 浪式脉冲 -
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