Long-term formation of microbial products in a sequencing batch reactor

Activated sludge in a sequencing batch reactor (SBR) is subjected to alternating feast-and-famine conditions, which may result in the enhanced production of microbial products: extracellular polymeric substances (EPS), soluble microbial products (SMP), and internal storage products (X_STO). In this work, the long-term formation of these three microbial products by activated sludge in an SBR is investigated using an expanded unified model with a parallel experimental study. We also use the model to compare the impacts in an SBR to those in a continuous-flow activated sludge system. The model captures all experimental trends for all components with solids retention time (SRT) for global steady state and within a cycle. At an SRT of 20 days, the active microorganisms constitute about 28% of the mixed liquor volatile suspended solids (MLVSS); the remaining biomass is comprised of residual inert biomass (X_I) of 40%, EPS of 31%, and X_STO of ∼1%. The active biomass becomes a smaller fraction with the increasing SRT, while the inert biomass becomes increasingly dominant. For soluble components, effluent chemical oxygen demand (COD) is dominated by SMP, which varies to some degree in a cycle, peaking as external substrate becomes depleted. Within the SBR cycle, external substrate (S) declines strongly in the first part of the cycle, and SMP shows a small peak at the time of S depletion. X_STO is the only biomass component that varies significantly during the cycle. It peaks at the time that the input substrate (S) is depleted. Simulation for a continuous-flow activated sludge system and comparison with an SBR reveals that the constant “famine” conditions of the continuous system lead to lower EPS and X_STO, but higher MLVSS and X_I.     

SRT对膜生物反应器出水水质的影响研究

膜生物反应器中ＭＬＶＳＳ为４０００－５０００ｍｇ／Ｌ时,ＣＯＤ的去除率可达９８％左右,ＮＨ３－Ｎ的去除率可达９９％左右。但随ＳＲＴ的继续延长,污泥 度增加,使得内源呼吸加剧和大量微生物死亡,导致上清液的ＣＯＤ上升,ＳＭＰ含量增加,出水ＣＯＤ存在波动性。同时ＳＭＰ的增加会抑制硝作用,ＮＨ３－Ｎ的去除率会略有下降,可维持在９２％左右。     

泥龄在A~2/O法设计和运行中的应用

通过对A2/O系统的分析,提出了按系统的除磷要求计算运行最长泥龄的方法。该方法可在设计和运行中用于对系统的生物除磷能力进行评估,从而指导工艺选择和运行方案设计。文中用计算示例说明了该方法的应用步骤。     

Changes in characteristics of soluble microbial products in membrane bioreactors associated with different solid retention times: Relation to membrane fouling

A membrane bioreactor (MBR) is a promising wastewater treatment technology, but there is a need for efficient control of membrane fouling, which increases operational and maintenance costs. Soluble microbial products (SMP) have been reported to act as major foulants in the operation of MBRs used for wastewater treatment. In this study, SMP in MBRs operated with different sludge retention times (SRTs) were investigated by means of various analytical techniques and their relations to the evolution of membrane fouling were considered. Bench-scale filtration experiments were carried out in a laboratory with synthetic wastewater to eliminate fluctuations that would occur with the use of real wastewater and that would lead to fluctuations in compositions of SMP. Three identical submerged MBRs were operated for about 50 days under the same conditions except for SRT (17, 51 and 102 days). Accumulation of SMP in the MBRs estimated by conventional analytical methods (i.e., the phenol-sulfuric acid method and the Lowry method) was significant in the cases of short SRTs. However, the degrees of membrane fouling in the MBRs were not directly related to the concentrations of SMP in the reactors estimated by the conventional analytical methods. Non-conventional analytical methods such as excitation-emission matrix (EEM) fluorescence spectroscopy revealed that characteristics of SMP in the three reactors considerably differed depending on SRT. Foulants were extracted from the fouled membranes at the end of the operation and were compared with SMP in each MBR. It was clearly shown that characteristics of the foulants were different depending on SRT, and similarities between SMP and the extracted foulants were recognized in each MBR on the basis of results of EEM measurements. However, such similarities were not found on the basis of results obtained by using the conventional methods for analysis of SMP. The results of this study suggest that the use of conventional methods for analysis of SMP is not appropriate for investigation of membrane fouling in MBRs.     

SBR处理村镇生活污水试验研究

研究了用SBR处理系统在不同水力停留时间,不同污泥龄(SRT),不同温度条件下对村镇生活污水的去除有机物、脱氮除磷效果。结果表明,考虑到脱氮除磷效果并兼顾经济的原则,水力停留时间采用6h比较合理,SBR反应器的最适SRT为20d;温度SBR反应器的除磷效果影响较小,SBR反应器更适合处理低温污水。     

短好氧泥龄下A2/O和BAF联合工艺的脱氮除磷特性

采用小试装置,研究了短好氧污泥龄下A2/O和BAF联合工艺处理低C/N和C/P污水时的脱氮除磷特性.结果表明,通过提高A2/O工艺段的厌氧区有机负荷和缺氧区硝酸盐负荷对反硝化聚磷菌（DPAOs）进行选择和强化后,其在聚磷菌（PAOs）中的比例维持在28%左右,工艺具有部分反硝化除磷能力,能够减少脱氮除磷过程中对碳源的总需求量.但在联合工艺中,好氧除磷仍是主要的除磷方式.在A2/O工艺段内,好氧污泥龄在满足好氧PAOs存活的同时,还必须满足抑制硝化细菌生长的要求,且为了保证工艺对磷的整体去除效果,混合液在好氧区的接触时间须大于30 min.此外,以保证缺氧区出水中含有1～4 mg/L的硝态氮为原则来控制BAF出水的回流量,可达到较好的脱氮除磷效果.该联合工艺结合了活性污泥工艺和生物膜工艺的优点,运行稳定,出水水质优良,不仅适合于新建污水处理厂,也特别适合于不能脱氮除磷污水处理厂的技术改造.     

对强化生物除磷机理与工艺认识误区的剖析

结合国际上生物除磷机理与工艺的最新进展,分析了目前我国在污水生物除磷工艺研发和运行中存在的一些认识误区。基于成熟的生物除磷生化代谢机理,指出反硝化除磷菌（DPB）是一种广泛存在于一些强化生物除磷（EBPR）工艺中的聚磷菌（PAOs）,无需特殊培养;对于市政污水,EBPR工艺中出现的聚糖原茵（GAOs）一般不会成为聚磷茵（PAOs／DPB）的竞争者而严重影响系统的除磷功能。针对强化生物除磷工艺的认识误区,指出污泥龄（SRT）是设计的关键参数,在最不利细菌生长的冬季,控制SRT〉12 d即可使EBPR保持较好的硝化与脱氮除磷效果;在污水生物处理除磷工艺选择上,“厌氧池＋氧化沟”只是污水处理升级而演变出的一种被动型工艺,并非最佳的EBPR工艺选择;此外倒置A^2／O工艺由于忽略了聚磷菌所需的进水碳源及DPB的作用,并不一定能改进EBPR的生物除磷效果。     

Anaerobic stabilisation and conversion of biopolymers in primary sludge--effect of temperature and sludge retention time

The effect of sludge retention time (SRT) and process temperature on the hydrolysis, acidification and methanogenesis of primary sludge was investigated in completely stirred tank reactors (CSTRs). The CSTRs were operated to maintain SRTs of 10, 15, 20 and 30 days at process temperatures of 25 degrees C and 35 degrees C. The rates of hydrolysis and the biodegradability of primary sludge were assessed in batch reactors incubated at 15 degrees C, 25 degrees C and 35 degrees C. The results revealed that the major amount of sludge stabilisation occurred between 0 and 10 days at 35 degrees C and 10 and 15 days at 25 degrees C. Hydrolysis was found to be the rate limiting-step of the overall digestion process, for the reactors operated at 35 degrees C and 25 degrees C, except for the reactor operated at 10 days and 25 degrees C. At the latter conditions, methanogenesis was the rate-limiting step of the overall digestion process. Proteins hydrolysis was limited to a maximum value of 39% at 30 days and 35 degrees C due to proteins availability in the form of biomass. The biodegradability of primary sludge was around 60%, and showed no temperature dependency. The hydrolysis of the main biopolymers and overall particulate COD of the primary sludge digested in CSTRs were well described by first-order kinetics, in case hydrolysis was the rate-limiting step. Similarly, the hydrolysis of the overall particulate COD of the primary sludge digested in batch reactors were described by first-order kinetics and revealed strong temperature dependency, which follows Arrhenius equation.     

智慧轨道交通全联网(SRT-IoT)——更广泛的互联互通

以轨道交通行业为背景,以智慧轨道交通(SRT)为对象,研究智慧轨道交通“全联网”(IoT)的基本组成框架和关键技术。将IoT置于下一代Internet背景之中,提出了以“智慧轨道交通骨干通信网”(SRT-BCN)为核心、以“基础接入网-资源网络”为轨道交通信息源和受主网络的“智慧轨道交通全联网(IoT for SRT, SRT-IoT)”的系统组成框架。针对轨道交通行业的特点,进一步将智慧轨道交通基础接入-资源网中与轨道交通有关部分划分为“列车接入-资源网”(TARN)和“地面接入-资源网”(GARN),并分析智慧轨道交通骨干通信网(SRT-BCN)和外围接入/资源网的特点,讨论相关的关键技术。重点讨论了与列车相关的TARN技术,得出需要进一步发展TARN相关网络技术的结论,为实现SRT-IoT更广泛的互联互通奠定研究基础。     

Biohydrogen production from organic solid waste in a sequencing batch reactor: An optimization of the hydraulic and solids retention time

Hydrogen production from organic solids waste was evaluated using a sequencing batch reactor (SBR) under mesophilic conditions, to investigate the effect of the hydraulic retention time (HRT) and solids retention time (SRT) on hydrogen production. The examined HRT and SRT values were from 4.6 to 27 h and 17–102 h, respectively. The results showed high hydrogen production rates (1.86 LH₂/L·d) and a yield of 127.26 mLH₂/gCOD_removed for an SRT of 60 h and an HRT of 16 h. The highest chemical oxygen demand (COD) removal (38.6 ± 6.9%) was also obtained under those conditions. The highest substrate hydrolysis percentage (73.0 ± 11.4%) was obtained at an HRT of 16 h and an SRT of 102 h. A short SRT of 20 h affected hydrogen production, which decreased up to 90%. With an SRT of 20 h and an HRT of 16 h, acetic acid-like fatty acids were mainly obtained. In experiments with a long SRT (60 h), the obtained fatty acid was butyrate. The conversion efficiencies for converting particulate material into fatty acids were 51–47% using a long SRT; a short HRT resulted in percentages of 37–40%. A 3D surface analysis was performed using the maximum hydrogen yield conditions as the central point, showing that the optimal hydrogen production can be obtained with an HRT of 16 h and an SRT of 55 h. Microbial analysis showed the predominance of the Olsenella genus at an HRT< 8 h and the presence of Clostridium at an HRT of 16 h. The HRT is the main parameter leading the community composition in the process.