Modeling the formation of soluble microbial products(SMP) in drinking water biofiltration

Both a theoretical and an empirical model were developed for predicting the formation of soluble microbial products （SMP） during drinking water biofiltration. Four pilot-scale biofilters with ceramsite as the medium were fed with different acetate loadings for the determination of SMP formation. Using numerically simulated and measured parameters, the theoretical model was developed according to the substrate and biomass balance. The results of this model matched the measured data better for higher SMP formation but did not fit well when SMP formation was lower. In order to better simulate the reality and overcome the difficulties of measuring the kinetic parameters, a simpler empirical model was also developed. In this model, SMP formation was expressed as a function of fed organic loadings and the depth of the medium, and a much better fit was obtained.

Effects of operational factors on soluble microbial products in a carrier anaerobic baffled reactor treating dilute wastewater

The effects of feed strength, hydraulic residence time （HRT）, and operational temperatures on soluble microbial product （SMP） production were investigated, to gain insights into the production mechanism. A carrier anaerobic baffled reactor （CABR） treating dilute wastewater was operated under a wide range of operational conditions, namely, feed strengths of 300-600 mg/L, HRTs of 9- 18 h, and temperatures of 10-28℃. Generally, SMP production increased with increasing feed strength and decreasing temperature. At high temperature （28℃）, SMP production increased with decreasing HRT. As the temperature was decreased to 18 and 10℃, the SMP production was at its peak for 12 h HRT. Therefore, temperature could be an important determinant of SMP production along with HRT. A higher SMP to soluble chemical oxygen demand （SCOD） ratio was found at high temperature and long HRT because of complete volatile fatty acid degradation. SMP accounted for 50%-75% of the SCOD in the last chamber of the CABR. As a secondary metabolite, some SMP could be consumed at lower feed strength.

Insights into membrane fouling implicated by physical adsorption of soluble microbial products onto D3520 resin

Membrane fouling is a major problem in membrane bioreactors(MBRs).In this study,membrane fouling caused by membrane rejection and adsorption was study.Filtration tests indicated that membrane rejected SMP,causing membrane pore blockage and then forming a gel layer.Batch adsorption experiments showed that adsorption of SMP onto PVDF membrane was a spontaneous physical adsorption process.Meanwhile,the absolute valueΔG of adsorption of SMP onto D3520 was higher than that of adsorption of SMP onto PVDF membrane,so SMP preferentially adsorbed onto D3520 rather than PVDF membrane.Thus,the effect of ARs on reducing the SMP concentration was investigated.It was found that,6 g of D3520 was suitable for adsorption of SMP.This physical adsorption involved external film diffusion,intra-particle diffusion,and surface adsorption.The Redlich–Peterson isotherm model performed best in terms of describing this equilibrium data.The mechanism of membrane fouling mitigation was verified by MBR simulation system.A case study of AR–MBR system was conducted.The results showed that addition of D3520 can effectively alleviate the development of membrane fouling.

Insight into the interaction between trimethoprim and soluble microbial products produced from biological wastewater treatment processes

Soluble microbial products(SMPs),dissolved organic matter excreted by activated sludge,can interact with antibiotics in wastewater and natural water bodies.Interactions between SMPs and antibiotics can influence antibiotic migration,transformation,and toxicity but the mechanisms involved in such interactions are not fully understood.In this study,integrated spectroscopy approaches were used to investigate the mechanisms involved in interactions between SMPs and a representative antibiotic,trimethoprim(TMP),which has a low biodegradation rate and has been detected in wastewater.The results of liquid chromatography-organic carbon detection-organic nitrogen detection indicated that the SMPs used in the study contained 15% biopolymers and 28% humic-like substances(based on the total dissolved organic carbon concentration)so would have contained sites that could interact with TMP.A linear relationship of fluorescent intensities of tryptophan protein-like substances in SMP was observed(R^(2)>0.99),indicating that the fluorescence enhancement between SMP and TMP occurred.Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that carboxyl,carbonyl,and hydroxyl groups were the main functional groups involved in the interactions.The electrostatic andπ-πinteractions were discovered by the UV-vis spectra and 1H nuclear magnetic resonance spectra.Structural representations of the interactions between representative SMP subcomponents and TMP were calculated using density functional theory,and the results confirmed the conclusions drawn from the 1H nuclear magnetic resonance spectra.The results help characterize SMP–TMP complexes and will help understand antibiotic transformations in wastewater treatment plants and aquatic environments.

Photodegradation of soluble microbial products(SMPs) from membrane bioreactor by GO-COOH/TiO2/Ag

This study aimed to explore a new degradation method-photocatalysis technology to polish membrane bioreactor(MBR) effluent, using 2,6-di-tert-butylphenol(2,6-DTBP) as a model soluble microbial product(SMP).2,6-DTBP is one of the predominant SMPs in MBR effluent, which is refractory and difficult to biodegrade.This study developed a novel carboxylated graphene oxide/titanium dioxide/silver(GO-COOH/TiO2/Ag) nanocomposite to photodegrade 2,6-DTBP.GO-COOH/TiO2/Ag was successfully synthesized, using L-cysteine as the linker bonding TiO2/Ag to GO-COOH.The structural, morphological and optical properties of the GO-COOH/TiO2/Ag nanocomposite were characterized using various techniques.Owing to synergistic effects, the GO-COOH/TiO2/Ag nanocomposite exhibited enhanced photocatalytic degradation performance under solar light irradiation when compared to TiO2, Ag and GO-COOH.To remove 25 mg/L 2,6-DTBP, the reaction time for GOCOOH/TiO2/Ag was only 30 min, faster than the 90 min required for pure TiO2 or Ag.In addition, the 200 mg/L GO-COOH/TiO2/Ag nanocomposite aqueous solution showed the best performance under solar light, with 99% removal of 2,6-DTBP.This enhanced capability is likely due to the surface plasmon resonance(SPR) effect contributed by Ag nanoparticles(NPs) doped onto the TiO2.In addition, GO-COOH had a high effective surface area, which assisted in degrading the 2,6-DTBP through improved adsorption.The stability study showed that the photocatalytic activity of the GO-COOH/TiO2/Ag was stable enough for recycling multiple times.The effective degradation performance and excellent stability demonstrates that the GO-COOH/TiO2/Ag nanocomposite can be a promising photocatalyst in the field of effluent SMP photodegradation, which solves the problem of the difficult biodegradation of highly toxic 2,6-DTBP.

The effect of continuous Ni(Ⅱ) exposure on the organic degradation and soluble microbial product(SMP) formation in two-phase anaerobic reactor

A two-phase anaerobic reactor fed with glucose substrate（3 g chemical oxygen demand（COD）/L） was used to investigate the effects of toxic metals on the degradation of organics and the soluble microbial product（SMP） formation. Low concentrations of Ni（II）（5 and10 mg/L） promoted the acid phase, whereas high concentrations（15, 20, and 25 mg/L）exhibited an inhibitory effect on, but did not alter the fermentative method, which mainly involved the fermentation of propionic acid. The methanogenic microorganism exhibited a strong capability adapting constantly increased Ni（II） levels. The acid phase was an accumulation stage of SMP. In the absence of Ni（II）, the high-molecular-weight material in the effluent SMP mainly contained polysaccharide, tryptophan, and casein. Methanogens metabolized most of the polysaccharide, the whole tryptophan content, and part of the casein, leading to the presence of humic acid and protein in effluent. After Ni（II） dosage, the protein and polysaccharide of the acid phase increased, and tryptophan changed, while casein remained stable. More protein than polysaccharide was produced, suggesting the prominent function of protein when addressing the negative effect of toxic metals. The analysis of DNA confirmed the change of bacterial activity.

Potential acute effects of suspended aluminum nitride (AlN) nanoparticles on soluble microbial products (SMP) of activated sludge

The study aims to identify the potential acute effects of suspended aluminum nitride（Al N）nanoparticles（NPs） on soluble microbial products（SMP） of activated sludge.Cultured activated sludge loaded with 1,10,50,100,150 and 200 mg/L of Al N NPs were carried out in this study.As results showed,Al N NPs had a highly inverse proportionality to bacterial dehydrogenase and OUR,indicating its direct toxicity to the activated sludge viability.The toxicity of Al N NPs was mainly due to the nano-scale of Al N NPs.In SMP,Al N NPs led to the decrease of polysaccharide and humic compounds,but had slight effects on protein.The decrease of tryptophan-like substances in SMP indicated the inhibition of Al N NPs on the bacterial metabolism.Additionally,Al N NPs reduced obviously the molecular weight of SMP,which might be due to the nano-scale of Al N.

Importance of nutrient availability for soluble microbial products formation during a famine period of activated sludge:Evidence from multiple analyses

Much remains unknown about compositional variations in soluble microbial products(SMP)with the shift of the substrate condition from a feast to a famine phase in biological treatment systems.This study demonstrated that the formation of SMP could be suppressed by up to 75%during the famine phase with the addition of essential nutrients.In contrast,presence of electron acceptor did not play any significant role during the stress condition,showing the similar amounts of SMP(r=0.98,p<0.05)formation between the bioreactors supplied with air and N2.The SMP formed in the famine phase was more biorefractory in the famine versus the feast phase with a linear correlation shown between the production and their aromatic structures in the composition(R^2>0.95).The fluorescence excitation-emission matrix coupled with parallel factor analysis(EEM-PARAFAC)revealed the presence of four different fluorescent components,including two protein-like(C1 and C4),fulvic-like(C2),and humic-like(C3)components,in the SMP and bEPS formed at different conditions.Both C1 and C4 showed increasing trends(R^2>0.95)with the length of starvation in the bioreactors without essential nutrients.Nutrient availability was found to be a key factor to quench the production of large-sized biopolymers.This study provides a wealth of information on operation conditions of activated sludge treatment systems to minimize large sized SMP molecules(particularly proteins),which typically exert many environmental concerns to effluent organic matter quality.

Removal of anaerobic soluble microbial products in a biological activated carbon reactor

The soluble microbial products （SMP） in the biological treatment effluent are generally of great amount and are poorly biodegradable. Focusing on the biodegradation of anaerobic SMP, the biological activated carbon （BAC） was introduced into the anaerobic system. The experiments were conducted in two identical lab-scale up-flow anaerobic sludge blanket （UASB） reactors. The high strength organics were degraded in the first UASB reactor （UASB1） and the second UASB （UASB2, i.e., BAC） functioned as a polishing step to remove SMP produced in UASB1. The results showed that 90% of the SMP could be removed before granular activated carbon was saturated. After the saturation, the SMP removal decreased to 60% on the average. Analysis of granular activated carbon adsorption revealed that the main role of SMP removal in BAC reactor was biodegradation. A strain of SMP-degrading bacteria, which was found highly similar to Klebsiella sp., was isolated, enriched and inoculated back to the BAC reactor. When the influent chemical oxygen demand （COD） was 10,000 mg/L and the organic loading rate achieved 10 kg COD/（m 3 ·day）, the effluent from the BAC reactor could meet the discharge standard without further treatment. Anaerobic BAC reactor inoculated with the isolated Klebsiella was proved to be an effective, cheap and easy technical treatment approach for the removal of SMP in the treatment of easily-degradable wastewater with COD lower than 10,000 mg/L.

Evaluation of factors influencing soluble microbial product in submerged MBR through hybrid ASM model

In this study,a mathematical model was established to predict the formation of the soluble microbial product(SMP)in a submerged membrane bioreactor.The developed model was calibrated under the reference condition.Simulation results were in good agreement with the measured results under the reference condition.The calibrated model was then used in the scenario studies to evaluate the effect of three chosen operating parameters:hydraulic retention time(HRT),dissolved oxygen concentration,and sludge retention time(SRT).Simulation results revealed that the SMP dominated the soluble organic substances in the supernatant.The scenario studies also revealed that the HRT can be decreased to 1 h without deteriorating the effluent quality;dissolved oxygen concentration in the reactor can be kept at 2–3 mg/L to maintain the effluent quality,reduce the content of SMP,and minimize operating costs;the optimal SRT can be controlled to 10–15 d to achieve complete nitrification process,less membrane fouling potential,and acceptable organic removal efficiency.

膜-生物反应器污泥缺氧反硝化过程中SMP的形成

在不同C/N比下,研究了膜-生物反应器在缺氧状态下溶解性微生物产物（SMP）的形成规律.结果表明,不同C/N比的反硝化过程,随着底物的降解,SMP都呈现不同程度的累积,且高C/N比下的合成量（9~10mgCOD/gVSS）高于低C/N比下的合成量（3~4mgCOD/gVSS）.从SMP的组分来看,不同C/N比下糖类的代谢规律相似,蛋白质则随着C/N比的升高其含量占SMP总量的比例增加,成为膜污染潜在的主要贡献者.随着反硝化过程的进行,体系中亚硝酸盐的累积对SMP的形成没有影响.

膜生物反应器中贫营养条件下SMP的产出研究

文章为考察膜生物反应器微生物在贫营养条件下,溶解性微生物产物(SMP)的产出规律和特性,为优化MBR反应器的运行、延缓膜污染提供理论依据。对天津大学游泳馆MBR系统中的污泥混合液进行贫营养实验。研究表明贫营养条件下SMP产出可以分为两个阶段:EPS溶解产生SMP阶段和死亡细胞胞内物质溶出产生SMP阶段。伴随营养物质的匮乏,SMP中大分子物质所占比例显著增加,从第3天的20.2%(占TOC总量的比例),到第8天上升为39.2%,从而会加剧膜污染,并且不同阶段产生的SMP都可以刺激微生物提高对基质的降解速率,SMP浓度与污泥的比好氧速率呈正相关关系。

SMP形成与降解机制分析及其对MBR膜过滤的影响

以膜生物反应器(membrane bioreactor,MBR)中活性污泥为研究对象,考察了溶解性微生物代谢产物(soluble microbial product,SMP)的形成及降解机制,并探讨了SMP对膜过滤的影响。实验结果表明,在基质存在时反应器内的SMP主要以基质利用相关型产物(utilization associated products,UAP)为主;当基质耗尽后,生物生长相关型产物(biomass associated product,BAP)浓度增加;内源呼吸过程中BAP的产出主要来源于松散胞外聚合物(loosely bound EPS,LB)的水解;通过傅里叶变换红外光谱(FTIR)检测表明,UAP主要由多聚糖和蛋白质组成,而BAP主要是多聚糖和腐殖酸;与UAP相比,膜对BAP截留效果较好,最佳的水力停留时间(hydraulic retention time,HRT)时MBR出水同时包含UAP及BAP,BAP浓度与膜过滤阻力呈显著正相关。

盐度冲击下MBR污泥SMP和EPS的三维荧光光谱解析

利用三维荧光(EEM)技术研究了不同盐度冲击下膜-生物反应器(MBR)污泥微生物溶解性产物(SMP)和胞外聚合物(EPS)的变化规律,分析不同盐度冲击下MBR污泥SMP和EPS的EEM图谱.结果表明,当冲击盐度大于2.5g/L时,SMP的EEM图谱中色氨酸荧光峰B(270nm,350nm)、类胡敏酸荧光峰C(375,475nm)、类富里酸荧光峰D(260,460nm)以及EPS的EEM图谱中色氨酸荧光峰B的荧光强度随冲击盐度的提升而增加,EPS的EEM图谱中类胡敏酸C峰的荧光强度则随冲击盐度的提升而下降.用平行因子分析(PARAFAC)方法确定EEM图谱中存在的4个组分,分别为类蛋白质组分C1(230/280,350nm),类胡敏酸组分C2(290/310,380nm)、C3(290/360,460nm)和C4(270/340,440nm);当冲击盐度大于2.5g/L时,SMP中C1、C3和C4组分的荧光强度与冲击盐度呈正相关,而EPS中C3和C4组分的荧光强度分别与冲击盐度呈正相关和负相关,其相关系数均≥0.90;SMP中类蛋白质荧光组分和类胡敏酸组分的荧光强度之和分别与测定的蛋白质含量和胡敏酸含量呈明显的正相关性,相关系数均>0.93,可作为荧光组分强度定量计算的依据,而EPS中此相关性并不明显.

不同污泥龄下MBR内SMP对膜污染的影响

采用3套膜生物反应器(MBR)研究不同污泥龄下溶解性微生物产物(SMP)对膜污染的影响。结果表明,随着污泥龄的延长,上清液中SMP的质量浓度逐渐降低,SMP中多糖和蛋白质含量与总SMP的变化趋势相同,也逐渐降低。高分子组分及疏水性有机组分占总SMP比例逐渐升高。而膜污染层中SMP的变化与上清液中SMP存在差异性。通过对上清液及膜污染层中SMP与膜污染速率进行相关性分析,结果表明上清液中SMP含量及性质与膜污染速率相关性不显著,而膜污染层中SMP质量浓度、多糖、高分子组分以及疏水性酸性组分对膜污染有显著影响。

MBR中SMP与污泥特性之间的相关性

以模拟生活污水为研究对象,在膜通量恒定的条件下,考察了MBR(Membrane Bioreac-tor)内SMP(Soluble Microbial Product)的积累与污泥特性之间的相关性.结果表明,SMP可以被微生物降解,SMP的浓度在反应器中呈先增加后降低.最终趋于稳定的变化趋势,并最终达到其产生—降解的动态平衡.反应器运行初期,絮状污泥的VSS/SS、污泥比基质降解速率、OUR和SVI迅速下降,分别由初始的0.913、0.72 kg/(kg.d)、6.78 mg/(g.d)和108降至第24天的0.72、0.187 kg/(kg.d)、3.74 mg/(g.h)和43,之后缓慢上升,至第40天左右时基本趋于稳定,但均低于初始值.MBR中SMP的积累与污泥特性密切相关,SMP的积累降低了污泥的沉降性能和单位质量污泥的微生物含量及其代谢活性,在膜的截留作用下,系统对污染物的总体去除率未因此而受到影响,系统运行稳定.

模拟废水高温厌氧消化出水中SMP的特性研究

为考察废水高温厌氧消化出水中溶解性微生物产物(SMP)的特性,采用高温厌氧序批式反应器处理葡萄糖模拟废水,运用尺寸排除色谱(SEC)分离厌氧消化出水溶解性有机物(DOM),结合溶解性有机碳(DOC)、UV254吸光度和三维荧光光谱分析方法,对不同分离组分进行了定性和定量研究.结果表明,SMP在出水DOM(356mg/L,以DOC计)中占90.8%,其在高分子量(MW)(10k^100kDa)、中等MW(1k^10kDa)和低MW(<1kDa)内的含量分别为46.8%、45.4%和7.8%.高MW内的SMP比中等、低MW内的SMP有更高的芳香度.废水高温厌氧消化出水中SMP的荧光物质以高的酪氨酸类物质含量,低的富里酸和腐殖酸类物质含量为主要特征.低MW区域的SMP主要包括酪氨酸类物质,而富里酸和腐殖酸类物质主要集中于中等MW区域,色氨酸类和微生物副产物类物质在各MW区域内均有分布.高、中等MW区域(不含630Da<MW<4kDa部分)内的荧光物质组成并无显著差异,但色氨酸和微生物副产物类物质的结构形态则产生了变化.

MBR反应器中SMP的研究

膜生物反应器(MBR)在水处理领域的应用已引起人们的广泛关注。然而膜污染已成为制约MBR反应器广泛应用的主要障碍,其中溶解性微生物产物(SMP)又是影响膜污染的重要因素。为此,介绍了MBR反应器的膜污染成因与SMP膜污染机理,综述了近年来国内外关于SMP的成因及其对膜污染影响的研究进展,并对SMP的研究模型进行了总结,最后提出了SMP膜污染的防治措施,以利于MBR反应器的推广应用。

MBR处理城市垃圾渗滤液中溶解性微生物产物(SMP)的影响分析

研究以好氧膜生物反应器(MBR)处理城市垃圾渗滤液,以膜截留的有机物量的变化间接反映SMP在反应器中的积累情况,以及其对污泥活性和污泥混合液过滤性能的影响,结果表明,随着进水垃圾渗滤液可生化性由0.60降至0.28,MBR中被膜截留的有机物浓度由226.4 mg/L增加至504.0 mg/L,积累程度加剧,并会抑制污泥脱氢酶活性,对反应器中混合液过滤性能有负面影响。

MBR中SMP的累积及其对反应器运行的影响

研究了膜生物反应器(MBR)中溶解性微生物产物(SMP)的累积及其对反应器运行的影响。试验结果表明:在MBR稳定运行的情况下,多糖是SMP的主要成分。而且,MBR内的SMP浓度高于普通活性污泥处理工艺(CAS),这是源于MBR中微滤膜对于部分分子量较大污泥EPS的截留作用。MBR中SMP的积累会对污泥的MLVSS/MLSS和脱氢酶活性产生不利影响,抑制生物代谢活性。稳定情况下,蛋白质和多糖的含量总和分别约占出水和混合液上清液TOC的95%和64%,由此可知SMP是出水和混合液上清液中污染物中的重要组成部分。