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Relationship between sludge settleability and membrane fouling in a membrane bioreactor

SUN Yujiao, WANG Yong, HUANG Xia

《环境科学与工程前沿（英文）》 2007年第1卷第2期页码 221-225 doi: 10.1007/s11783-007-0038-9

摘要： The evolution of activated sludge settleability and its relationship to membrane fouling in a submerged membrane bioreactor were studied at a lab-scale equipment fed with synthetic wastewater. It was found that sludge volume index (SVI) gradually increased and the sludge settleability was reduced, which was caused by the propagation of filamentous bacteria. With increasing SVI, the average increasing rate of trans-membrane pressure increased, the stable filtration period was shortened, and the two stages (smooth stage and accelerating stage) of the trans-membrane pressure were more obvious. At the same time, the increasing rate of trans-membrane pressure at the smooth stage decreased and the rate at the accelerating stage increased with SVI, respectively. The observation by using scanning electronic microscopes showed the cake layer with loose structure and large thickness formed on the membrane surface due to the appearance of filamentous bacteria and high SVI in sludge. Influence of the sludge settleability on the trans-membrane pressure was related to the structure and thickness of the cake layer on the membrane.

关键词： Influence bioreactor activated filamentous lab-scale equipment

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Structure and formation of anoxic granular sludge —A string-bag hypothesis

Binbin WANG,Dangcong PENG,Xinyan ZHANG,Xiaochang WANG

《环境科学与工程前沿（英文）》 2016年第10卷第2期页码 311-318 doi: 10.1007/s11783-014-0748-8

摘要： Anoxic granular sludge was developed in a laboratory-scale sequencing batch reactor which was fed with sodium acetate and sodium nitrate as electron donor and accepter. The sludge in the reactor was almost granulated after approximately 90 days of cultivation. In the present study, a detailed examination of surface morphology and internal structure of anoxic granular sludge was conducted using scanning electron microscope. It showed that the bacteria inside the granules had a uniform, coccus-like shape. By contrast, filamentous bacteria were predominant outside the granules. These bacteria were woven and had wrapped the coccus bacteria together to form granules. The small amounts of DO in the liquid bulk promoted the growth of filamentous bacteria on the surface of the granules. A string-bag hypothesis was proposed to elucidate the structure and formation of the anoxic granular sludge. It suggested that micro-aeration could be a method to promote granulation in practical anoxic treatment systems.

关键词： granulation sequencing batch reactor anoxic sludge scanning electron microscope filamentous bacteria

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Formation of coke in thermal cracking of jet fuel under supercritical conditions

ZHU Yuhong, YU Caixiang, LI Zimu, MI Zhentao, ZHANG Xiangwen

《化学科学与工程前沿（英文）》 2008年第2卷第1期页码 17-21 doi: 10.1007/s11705-008-0024-1

摘要： Continuous-flow reactor experiments were carried out to study coke formation from thermal cracking of home-made jet fuel RP-3 under supercritical conditions. The mechanism and precursor of coke forming were analyzed. The starting cracking temperature of RP-3 fuel was determined to be 471.8°C by differential scanning calorimetry (DSC). Temperature-programmed oxidation and scanning electron microscopy (SEM) characterizations of the stressed tubes showed that there are three different coke species including chemisorbed carbon, amorphous carbon and filamentous coke in the solid deposits. More than 90% of coke deposits are carried away by the supercritical fluid, which has strong capabilities of extraction for coke deposits and their precursors. There were 17.1 wt-% of iron and 11.1 wt-% of chromium found on the coke surface detected by energy dispersive spectroscopy (EDS) which suggests carburetion on alloy. RP-3 fuel and its cracking liquids were analyzed by GC-MS,which showed that the content of alkyl benzene and alkyl naphthalene increased evidently in cracking liquids.

关键词： dispersive spectroscopy different extraction calorimetry filamentous

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Control of sludge settleability and nitrogen removal under low dissolved oxygen condition

Zhaoxu PENG, Yongzhen PENG, Zhenbo YU, Xuliang LIU, Xiaoling LI, Randeng WANG

《环境科学与工程前沿（英文）》 2012年第6卷第6期页码 884-891 doi: 10.1007/s11783-012-0408-9

摘要： Low dissolved oxygen (DO) is an energy-saving condition in activated sludge process. To investigate the possible application of limited filamentous bulking (LFB) in sequencing batch reactor (SBR), two lab-scale SBRs were used to treat synthetic domestic wastewater and real municipal wastewater, respectively. The results showed that prolonging low DO aeration duration and setting pre-anoxic (anaerobic) phase were effective strategies to induce and inhibit filamentous sludge bulking, respectively. According to the sludge settleability, LFB could be maintained steadily by adjusting operation patterns. Filamentous bacteria content and sludge volume index (SVI) were likely correlated. SVI fluctuated dramatically within a few cycles when around 200 mL·g , where altering operation pattern could change sludge settleability in spite of the unstable status of activated sludge system. Energy consumption by aeration reduced under low DO LFB condition, whereas the nitrification performance deteriorated. However, short-cut nitrification and simultaneous nitrification denitrification (SND) were prone to take place under such conditions. When the cycle time kept constant, the anoxic (anaerobic) to aerobic time ratio was determining factor to the SND efficiency. Similarity keeping aerobic time as constant, the variation trends of SND efficiency and specific SND rate were uniform. SBR is a promising reactor to apply the LFB process in practice.

关键词： limited filamentous bulking sequencing batch reactor sludge settleability sludge volume index simultaneous nitrification denitrification

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Cultivation of aerobic granular sludge in a conventional, continuous flow, completely mixed activated sludge system

Xi CHEN,Linjiang YUAN,Wenjuan LU,Yuyou LI,Pei LIU,Kun NIE

《环境科学与工程前沿（英文）》 2015年第9卷第2期页码 324-333 doi: 10.1007/s11783-014-0627-3

摘要： Aerobic granules were formed in a conventional, continuous flow, completely mixed activated sludge system (CMAS). The reactor was inoculated with seed sludge containing few filaments and fed with synthetic municipal wastewater. The settling time of the sludge and the average dissolved oxygen (DO) of the reactor were 2 h and 4.2 mg·L , respectively. The reactor was agitated by a stirrer, with a speed of 250 r·min , to ensure good mixing．The granular sludge had good settleability, and the sludge volume index (SVI) was between 50 and 90 mL·g . The laser particle analyzer showed the diameter of the granules to be between 0.18 and 1.25 mm. A scanning electron microscope (SEM) investigation revealed the predominance of sphere-like and rod-like bacteria, and only few filaments grew in the granules. The microbial community structure of the granules was also analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Sequencing analysis indicated the dominant species were α, β, and γ- , , and . The data from the study suggested that aerobic granules could form, if provided with sufficient number of filaments and high shear force. It was also observed that a high height-to-diameter ratio of the reactor and short settling time were not essential for the formation of aerobic granular sludge.

关键词： aerobic granular sludge completely mixed activated sludge system (CMAS) continuous flow shear force filamentous bacteria polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE)