Optimal sludge retention time for a bench scale MBR treating municipal sewage.

Membrane bioreactors allow for higher sludge concentrations and improved degradation efficiencies with respect to conventional activated sludge. However, in the current practice these systems are often operated under sub-optimal conditions, since so far no precise indications have yet been issued on the optimal operating conditions of MBR for municipal wastewater treatment. This paper reports some results of four years of operation of a bench scale membrane bioreactor where steady state conditions were investigated under different sludge retention times. The whole experimental campaign was oriented towards the investigation of optimal process conditions in terms of COD removal and nitrification, biomass activity and growth, and sludge characteristics. The membrane bioreactor treated real municipal sewage, and four different sludge ages were tested (20, 40, 60, and 80 days) and compared with previous data on complete sludge retention. The results showed that the the biology of the system, as assessed by the oxygen uptake rate, is less affected than the sludge physical parameters. In particular, although the growth yield was observed to dramatically drop for SRT higher than 80 days, the biological activity was maintained under all the tested conditions. These considerations suggest that high SRT are convenient in terms of limited excess sludge production without losses of the treatment capacity. Physical characteristics such as the viscosity and the filterability appear to be negatively affected by prolonged sludge retention times, but their values remain within the ranges normally reported for conventional activated sludge.     

Effect of sludge retention time on characteristics of dynamic membrane in sequencing bioreactors

The characteristics of self-forming dynamic membrane (DM) in sequencing bioreactors under different sludge retention times (SRT) (SRT = 5, 10, 20, 40, 60 days) were studied using a scanning electron microscope, particle sizing distribution and others. The results indicated that the SRT has an evident effect on the characteristics of DM. The content of extracellular polymeric substances and protein decreased with the increase of SRT. The change of polysaccharide was small regardless of SRT. The filtration resistance of the DM was divided into two stages: an initial slowly-rising stage and a fast-rising later stage which were both irrespective of SRT. With the increase of SRT, the filtration resistance increase extent reduced and the running cycle became longer. Compared to the lower SRT, the particle size distribution of mixed liquor and DM has a decreasing trend at higher SRT. The average particle size of DM was larger than that of the mixed liquor irrespective of SRT. The amounts and types of microorganisms on the surface of DM were more abundant as SRT increased. Low SRT produced the DM surface with some Cocci while the high SRT gave the DM dominated with Cocci, Filamentous and Bacillus.     

Impact of sludge retention time on sludge characteristics and microbial community in MBR

In this study, the impact of sludge retention time (SRT) on sludge characteristics and microbial community and the effect on membrane fouling in membrane bioreactor (MBR) was investigated. The results show that MBR with longer SRT has less fouling propensity, in agreement with other studies, despite the fact that the MBR with longer SRT contained higher MLSS and smaller particle size. However, much more soluble microbial products (SMPs) were released in MBR with shorter SRT. More slime on the membrane surface was observed in MBR with shorter SRT while sludge cakes formed on the membrane surface in MBR with longer SRT. The results show that SMP contributes to the severe fouling observed in MBR with shorter SRT, which is in agreement with other studies showing that SMPs were the major foulants in MBR. Under different SRTs of operation, the bacterial community structures of the sludge obtained by use of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) were almost identical, but those on the membrane surface differed substantially. It suggests that, although SRT has impact on sludge characteristics, it doesn't affect the microbial community in the suspension.     

市政污泥好氧发酵前处理工艺比选及工程应用

针对市政污泥好氧发酵技术特点,对其原理、影响因素和优缺点进行了简要说明,并对发酵前处理工艺进行了分析比选.通过与离心机、板框压滤机比较可知,作为一种深度脱水技术,高压带式压滤机较为适用于待发酵污泥的前处理,其优点包括:可与原脱水系统无缝连接、系统占地面积小、建设周期短、能耗和运行费用低、脱水效果好、出泥稳定性高以及可自动操作等.工程应用实践表明,污泥进行深度脱水后再堆肥,减少了堆肥过程中辅料和返混料添加量,节约了项目的运行成本,可缩小项目占地并降低项目投资,对已有项目改造还可增加项目处理量.此外,由于满足园林绿化用泥质标准,该污泥处理厂发酵产物作为园林绿化有机肥进行资源化利用.     

Influence of hydraulic retention time on UASB post-treatment with UF membranes

A pilot UASB reactor coupled with an external ultrafiltration (UF) membrane was operated under three different hydraulic retention times (HRT) for domestic wastewater treatment. The aim was to assess the HRT influence on system performance and fouling. The highest concentrations of COD, total solids, extracellular polymeric substances (EPS) and soluble microbial products (SMP) in UASB effluent and permeate were found when the UASB reactor was operated under the lowest HRT studied (4 hours); although the fulfillment of Mexican Standard for wastewater reclamation was not compromised. This fact could be attributed to the higher shear stress forces inside the UASB reactor when it was operated at low HRT, which promoted the release of biopolymeric substances in its effluent. Besides, the fouling propensity in the UASB effluent was worsened with HRT reduction, by increasing the fouling rate and the specific cake resistance. Based on these results, it is recommended to avoid operating the UASB reactor at low HRTs (less than 4 hours) in order to control SMP and EPS fouling potential. The results presented also suggest that HRT reduction has a detrimental effect on performance and fouling.     

Influence of solid retention time on the rheology of MBR sludge.

The rheological characterization is of crucial importance in sludge management both for biomass dewatering and stabilization purposes and for the definition of design parameters for sludge handling operations. The sludge retention time (SRT) has a significant influence on biomass properties in biological wastewater treatment systems and in particular in membrane bioreactors (MBR). The aim of this work is to compare the rheological behaviour of the biomass in a membrane bioreactor operated under different SRT. A bench scale MBR was operated for four years under the same conditions except for the SRT, that ranged from 20 days to complete sludge retention. The rheological properties were measured over time and the apparent viscosity was correlated with the concentration of solid material under equilibrium conditions. The three models most commonly adopted for rheological simulations were evaluated and compared in terms of their parameters. Steady state average values of these parameters were related to the equilibrium biomass concentration (MLSS). The models were tested to select the one better fitting the experimental data in terms of Mean Root Square Error (MRSE). The relationship between the apparent viscosity and the shear rate, as a function of solid concentration, was determined and proposed.     

The effects of hydraulic retention time and feed COD concentration on the rate of hydrolysis of primary sewage sludge under methanogenic conditions.

A series of completely mixed methanogenic anaerobic digesters have been operated to determine the rate of hydrolysis of primary sewage sludge. The hydraulic retention time was reduced from 60 d to when the system failed (approximately 5 d), while the feed COD concentration was 40, 25, 13 and 2 gCOD/L. A steady state model based on first order kinetics was developed to simulate the hydrolysis rate at each retention time and feed concentration. With the mean value for the hydrolysis rate constant (0.992 +/- 0.492 d(-1)), this model was able to accurately predict the effluent COD for all steady state operating conditions. However, the effluent COD concentration was relatively insensitive to the exact value for this constant. The model provides a framework for analysis of anaerobic digestion experimental data, to enable meaningful comparisons.     

Effect of thermal alkaline pretreatment on the anaerobic digestion of wasted activated sludge

The effect of alkaline pretreatment of waste-activated sludge, using two models to study the sequential hydrolysis rates of suspended (Sanders' surface model) and dissolved (Goel's saturation model) solids, on the mesophilic and thermophilic anaerobic digestion rate is evaluated. The pretreatment, which reduces the size of the solids, increases the reaction rate by increasing the surface area and the specific surface hydrolysis constant (K(SBK)); at thermophilic conditions from 0.45 x 10(-3) kg m(-2) d(-1) for the fresh sludge to 0.74 x 10(-3) kg m(-2) d(-1) for the pretreated sludge and at mesophilic conditions these values are 0.28 x 10(-3) kg m(-2) d(-1) and 0.47 x 10(-3) kg m(-2) d(-1) confirming the usefulness of a pretreatment for solids reduction. But for soluble solids, the thermoalkaline pretreatment decreases the reaction rates by inducing a competitive inhibition on the thermophilic anaerobic digestion rate while in the mesophilic range, a non-competitive inhibition is observed. A mathematical simulation of the consecutive reactions, suspended solids to dissolved solids and to methane in staged anaerobic thermophilic-mesophilic digestion, shows that with 4% suspended solids concentration it is better not to use a thermoalkaline pretreatment because overall solids reduction and total methane production are not as good as without pretreatment.     

城市污水污泥中邻苯二甲酸酯的研究

应用GC/MS对北京城市污泥中的6种邻苯二甲酸酯类环境激素进行了研究。结果表 明,北京城市污泥中邻苯二甲酸酯的总含量(∑PAEs)为20．798-58．245 mg／kg干污泥,其中 DEHP含量最高,约占∑PAEs的90％以上,其余邻苯二甲酸酯类化合物含量较低。影响城市污泥 中邻苯二甲酸酯含量的可能因素包括邻苯二甲酸酯的理化性质、生物降解性能、污水及污泥处理工 艺及污水中邻苯二甲酸酯的来源及含量等。今后应加强对邻苯二甲酸酯迁移转化规律和处理工艺 等方面的研究。     

防止藻类过度繁殖的青草沙水库合理水力停留时间初探

青草沙水库位于长江口长兴岛的西北水域,水量丰富、水质优良,是上海城市供水水源战略转移的重要依托之一.青草沙水库水力停留时间是确定水库运行方式的重要依据,它直接关系到水库水位、泵闸调度及运行成本等.根据水库库形特征,库内外水文水质条件,研究合理水力停留时间,改善水环境,最大限度发挥水库的自净能力,防止藻类大面积繁殖.通过建立水库藻类生长模型,提出青草沙水库满足藻类"水华"控制要求的水力停留时间,在夏季温度较高(>25 ℃)时水库水力停留时间可以取15～18 d,在春秋季温度相对稍低时(<20 ℃)可以取25～30 d.     

Influences of pH and hydraulic retention time on anaerobes converting beer processing wastes into hydrogen.

To convert high-solids organic wastes (3% w./w.) to high-value hydrogen, a full factorial experimental design was employed in planning the experiments for learning the effects of pH and hydraulic retention time (HRT) on the hydrogen production in a chemostat reactor using waste yeast obtained from beer processing wastes. For determining which experimental variable settings affect hydrogen production, predictive polynomial quadratic equation and response surface methodology were employed to determine and explain the conditions required for high-value hydrogen production. Experimental results indicate that a maximum hydrogen production rate of 460 mL/gVSS/d was obtained at pH = 5.8 and HRT = 32 hours. Moreover, hydrogenase targeted RT-PCR results indicate that Clostridium thermocellum and Klebsiella pneumoniae predominated.     

城市固体废弃物持水特性的室内试验

为了对城市固体废弃物的持水特性进行分析,采用非饱和固结仪对6组人工配制的城市固体废弃物试样进行了土水特征曲线测定的室内试验,同时还采用滤纸法量测试样的土水特征曲线,并对试样孔隙大小分布指标λ进行了分析。试验结果表明:试样的进气值很低,为1kPa左右,荷载作用使进气值升高;λ值随着试样初始孔隙比的增加而减小,随着试样有机物质量分数的增加而增加;使用滤纸法测城市固体废弃物的土水特征曲线时,高吸力阶段的值更加合理,更有参考性。     

Effect of 200 days' sludge retention time on performance of a pilot scale submerged membrane bioreactor for high strength industrial wastewater treatment.

A high strength industrial wastewater was treated using a pilot scale submerged membrane bioreactor (MBR) at a sludge retention time (SRT) of 200 d. The MBR was operated at a high sludge concentration of 20 g/L and a low F/M ratio of 0.11 during 300 d of operation. It was found that the MBR could achieve COD and TOC overall removal efficiencies at more than 99 and 98% TN removal. The turbidity of the permeate was consistently in the range of 0.123 to 0.136 NTU and colour254 absorbance readings varied from 0.0912 to 0.0962 a.u. cm(-1). The sludge concentration was inversely proportional to the hydraulic retention time (HRT), yielded excellent organic removal and extremely low sludge production (0.0016 kgVSS/day).     

A study on the role of hydraulic retention time in eutrophication of the Asahi River Dam reservoir

The Asahi River Dam reservoir is one of the important freshwater resources for Okayama City, Japan. The eutrophication of the reservoir has been warned of since the 1980s. In this study, we discuss the relationship between hydraulic retention time and increase of phytoplankton, and the influence of wind-driven currents on the spatial distribution of phytoplankton based on the observations and numerical simulations. Observations were carried out from 1993 to 1995. The numerical simulation of hydraulics in the reservoir was carried out by applying an orthogonal curvilinear finite difference method. Judging from phosphorus and nitrogen concentrations, the water quality of the Asahi River Dam reservoir is usually eutrophic. However, high concentrations of chlorophyll-a are not always observed. The observed dependence of chlorophyll-a concentration on hydraulic retention time is reproduced fairly well by a simple relationship derived from the balance of phytoplankton based on the assumption of complete mixing. The hydraulic retention time is a limiting factor of an increase in phytoplankton in the Asahi River Dam reservoir. It takes a retention time of 2 weeks for the sufficient increase of phytoplankton. The results obtained by the simulations show that the wind-driven currents play an important role in the spatial distribution of phytoplankton.     

我国城镇污泥处理与处置新型技术研究

随着我国城市化进程的不断加快,城市污水的排放量也随之增加,由此产生的大量污泥容易对大气、水体、土壤造成二次污染,使生存环境进一步恶化,生态环境难以修复。在系统总结国内外已有成果的基础上,梳理国内外关于城市污泥处理与处置的新技术,分析污水处理厂污泥处理的关键技术和难点,引进新型污泥处理处置方法,以期为流域水环境综合治理提供理论保障和技术支撑。     

Effect of hydraulic retention time and pH on oxidation of ferrous iron in simulated ferruginous acid mine drainage treatment with inoculation of iron-oxidizing bacteria

The effect of hydraulic retention time(HRT) and pH on the biooxidation of ferrous iron during simulated acid mine drainage(AMD)treatment was investigated.The simulated AMD was highly acidic(pH 2.5),rich in iron(about 1700 mg/L) and copper(about 200 mg/L),and contained high concentrations of sulfate(about 4700 mg/L).The biooxidation of ferrous iron was studied in a laboratory-scale upflow packed bed bioreactor(PBR).The HRT was shortened stepwise from 40 h to 20 h,13 h,and 8 h under the acidic environment at a pH value of 2.2.Then,the influent pH value was changed from 2.2 to 1.2 at a constant suitable HRT.Physiochemical and microbial community structure analyses were performed on water samples and stuffing collected from the bioreactor under different conditions.The results indicate that the efficiency of ferrous iron oxidation gradually decreased with the decrease of HRT,and when the HRT exceeded 13 h,ferrous iron in AMD was almost completely oxidized.In addition,the best efficiency of ferrous iron oxidation was achieved at the influent pH value of 1.8.Microbial community structure analyses show that Leptospirillum is the predominant genus attached in the bioreactor,and low influent pH values are suitable for the growth of Leptospirillum.     

污泥掺烧比例对生活垃圾协同处置的经济影响分析

市政污泥与生活垃圾协同焚烧不仅能够实现污泥减量化、资源化,而且能达成设备共享,是一种具有综合效益的污泥处置方式.针对三类常见的协同处置模式进行对比分析,研究了污泥掺烧比例对焚烧厂污泥综合处置成本的影响.     

干法水泥窑处理市政污泥的运行分析

水泥行业处理固体废弃物是国家发展和改革委员会推广的市政污泥和工业固废的处理途径.根据上海石洞口城市污水处理厂的污泥在上海浦东水泥厂的干法水泥窑中处理的小试数据,对于水泥窑干化焚烧市政污泥的系统进行能量平衡计算,并结合干法水泥窑的特点,分析比较了从水泥生产线不同位置加入污泥的运行安全性和能耗,最终确定加料位置的选择顺序为:生料磨、分解炉、窑尾、冷却机.     

Membrane-coupled anaerobic digestion of municipal sewage sludge.

Membrane-coupled anaerobic digestion utilizes a concept of simultaneous sludge digestion and thickening. Membranes may successfully be applied to eliminate the need for thickening polymers and avoid their likely inhibitory effect on anaerobic biomass. A 550 L completely mixed anaerobic digester was operated under mesophilic conditions (35 degrees C). Two ultrafiltration membrane systems were evaluated for their potential in membrane-coupled anaerobic digestion: vibrating and cross flow. A volatile solids reduction of 590% was achieved at an average mixed liquor suspended solids concentration of 1.8%. The substrate utilization rate was 1.3 d(-1). The vibrating membrane operated at a flux of 1.6-2.0 m3/m2-d and the tubular membrane fluxes in the range 3.4-3.6 m3/m2-d.     

污泥预处理技术的研究现状与前景

介绍当前研究和应用较多的污泥预处理技术.重点对臭氧预处理技术、碱解预处理技术、热预处理技术、微波预处理技术、超声波预处理技术、生物预处理技术和一些联合预处理技术的原理和应用进行了综述,并论述了各种预处理技术的处理效果、影响因素、优缺点及应用前景.指出对于不同预处理技术进行优化组合,能够取得更为显著的效果.