中温下UASB反应器的启动

利用四个相同的UASB反应器做平行对比试验，R1，R2和R3利用浓缩池污泥作为接种污泥，R4利用化粪池污泥作为接种污泥，研究了两种不同接种污泥一浓缩池污泥、化粪池污泥在UASB启动阶段的差别和Al^3＋，Ca^2＋在UASB启动阶段对污泥颗粒化进程的影响。     

污泥气循环UASB反应器的启动及循环时间的研究

试验研究了常温条件下污泥气循环UASB反应器对低浓度城市生活污水的处理效率及污泥气循环方式对处理效率的影响.结果表明：在常温条件下,该反应器CODCr容积负荷可达到5.0 kg/（m3·d）,运行稳定、出水清澈,CODCr去除率可达80％以上;同时,研究表明污泥气循环时间对UASB反应器的稳定运行有着重要的影响.     

The roles of calcium in sludge granulation during UASB reactor start-up

Six upflow anaerobic sludge blanket (UASB) reactors were concurrently operated for 146 d to examine the effects of calcium on the sludge granulation process during start-up. Introduction of Ca2+ at concentrations from 150 to 300 mg/l enhanced the biomass accumulation and granulation process. The calcium concentration in the granules was nearly proportional to the calcium concentration in the feed, and calcium carbonate was the main calcium precipitate in the granules. The specific activity of granules decreased with increasing influent calcium concentration. The optimum calcium concentration for the granulation was from 150 to 300 mg/l. The addition of low-concentration calcium to the UASB reactors appeared to enhance the three steps of sludge granulation: adsorption, adhesion and multiplication, but it did not lead to a different proliferation of predominant microorganisms in the granules.     

Performance of high-loaded ANAMMOX UASB reactors containing granular sludge

The performance of high-loaded anaerobic ammonium oxidizing (ANAMMOX) upflow anaerobic sludge bed (UASB) reactors was investigated. Two ANAMMOX reactors (R1 with and R2 without effluent recycling, respectively) were fed with relatively low nitrite concentration of 240 mg-N L⁻¹ with subsequent progressive increase in the nitrogen loading rate (NLR) by shortening the hydraulic retention time (HRT) till the end of the experiment. A super high-rate performance with nitrogen removal rate (NRR) of 74.3-76.7 kg-N m⁻³ day⁻¹ was accomplished in the lab-scale ANAMMOX UASB reactors, which was 3 times of the highest reported value. The biomass concentrations in the reactors were as high as 42.0-57.7 g-VSS L⁻¹ with the specific ANAMMOX activity (SAA) approaching to 5.6 kg-N kg-VSS⁻¹ day⁻¹. The high SAA and high biomass concentration were regarded as the key factors for the super high-rate performance. ANAMMOX granules were observed in the reactors with settling velocities of 73-88 m h⁻¹. The ANAMMOX granules were found to contain a plenty of extracellular polymers (ECPs) such as 71.8-112.1 mg g-VSS⁻¹ of polysaccharides (PS) and 164.4-298.2 mg g-VSS⁻¹ of proteins (PN). High content of hemachrome (6.8-10.3 μmol g-VSS⁻¹) was detected in the ANAMMOX granules, which is supposed to be attributed to their unique carmine color.     

Accelerated start-up and enhanced granulation in upflow anaerobic sludge blanket reactors

In the present study, the effects of a cationic polymer on reactor start-up and granule development were evaluated. A control reactor R1 was operated without adding polymer, while the other five reactors designated R2, R3, R4, R5 and R6 were operated with different polymer concentrations of 20, 40, 80, 160 and 320 mg/L, respectively. Experimental results demonstrated that adding the polymer at a concentration of 80 mg/L markedly accelerated the start-up time. The time required to reach stable treatment at an organic loading rate (OLR) of 4 g COD/L.d was reduced by approximately 50% in R4 as compared with the control reactor. The same reactor with 80 mg/L polymer was able to achieve an OLR of 12 g COD/L.d after 59 days of operation, while R1, R2, R3, R5 and R6 achieved the same loading rate at much longer period of 104, 80, 69, 63 and 69 days, respectively. Comparing with the control reactor, the start-up time of R4 was shortened markedly by about 43% at this OLR, while other reactors also recorded varying degree of shortening. Monitoring on granule development showed that the granule formation was accelerated by 30% from the use of the appropriate dosage of polymer. Subsequent granules characterization indicated that the granules developed in R4 with 80 mg/L polymer exhibited the best settleability, strength and methanogenic activity at all OLRs. The organic loading capacities of reactors were also increased by the polymer addition. The maximum organic loading of the control reactor was 24 g COD/L.d, while the polymer-assisted reactor added with 80 mg/L polymer attained a markedly increased organic loading of 40 g COD/L.d. The laboratory results obtained demonstrated that adding the cationic polymer could result in shortening of start-up time and enhancement of granulation, which in turn lead to improvement in organics removal efficiency and loading capacity of the UASB system.     

Dispersion and treatment performance analysis of an UASB reactor under different hydraulic loading rates

Mixing and transport phenomena affect the efficiency of all bioreactor configurations. An even mixing pattern at the macro-level is desirable to provide good conditions for substrate transport to, and from, the microbial aggregates. The state of segregation of particulate material in the reactor is also important. The production of biogas in anaerobic reactors is another factor that affects mixing intensity and hence the interactions between the liquid, solid and gaseous phases. The CSTR model with some degree of short-circuiting, dead zones and bypassing flows seems to describe the overall hydrodynamics of UASBs. However, few data are available in the literature for full-scale reactors that relate process performance to mixing characteristics. Dispersion studies using LiCl were done for four hydraulic loading rates on a full-scale UASB treating domestic wastewater in Ginebra, Valle del Cauca, southwest Colombia. COD, TSS, and Settleable Solids were used to evaluate the performance of organic matter removal. The UASB showed a complete mixing pattern for hydraulic loading rates close to the design value (i.e. Q = 10-13l s(-1) and HRT=8-6 h). Gross mixing distortions and localised stagnant zones, short-circuiting and bypass flows were found in the sludge bed and blanket zones for both extreme conditions (underloading and overloading). The liquid volume contained below the gas-liquid-solid separator was found to contribute to the overall stagnant volume, particularly when the reactor was underloaded. The removal of organic matter showed a log-linear correlation with the dispersion number.     

Rheological and fractal characteristics of granular sludge in an upflow anaerobic reactor

The rheological and fractal characteristics of the granular sludge in an upflow anaerobic sludge blanket (UASB) reactor were investigated in this study. The influences of sludge concentration and temperature on the rheological properties of the granular sludge were evaluated, and the Bingham model was adopted to describe its rheology. In addition, image analysis was used to determine the sludge fractal dimension. The results indicate that the UASB granular sludge showed a shear-thinning behavior. The relationships between the limiting viscosity and the sludge concentration, as well as the limiting viscosity and temperature could be respectively modeled using an exponential equation and Arrhenius equation well. The Bingham model was able to adequately describe the rheology of the granular sludge. The fractal dimension of the granular sludge, 2.79+/-0.03, was larger than that of some other aggregates, suggesting that the granular sludge were more compact and denser. Furthermore, the relationship between rheological and fractal properties of the granular sludge could be properly described with the model proposed by Shih et al. [1990. Scaling behavior of the elastic properties of colloidal. Phys. Rev. A 42, 4772-4779].     

Dynamic and distribution of ammonia-oxidizing bacteria communities during sludge granulation in an anaerobic-aerobic sequencing batch reactor

The structure dynamic of ammonia-oxidizing bacteria (AOB) community and the distribution of AOB and nitrite-oxidizing bacteria (NOB) in granular sludge from an anaerobic-aerobic sequencing batch reactor (SBR) were investigated. A combination of process studies, molecular biotechniques and microscale techniques were employed to identify and characterize these organisms. The AOB community structure in granules was substantially different from that of the initial pattern of the inoculants sludge. Along with granules formation, the AOB diversity declined due to the selection pressure imposed by process conditions. Denaturing gradient gel electrophoresis (DGGE) and sequencing results demonstrated that most of Nitrosomonas in the inoculating sludge were remained because of their ability to rapidly adapt to the settling-washing out action. Furthermore, DGGE analysis revealed that larger granules benefit more AOB species surviving in the reactor. In the SBR were various size granules coexisted, granule diameter affected the distribution range of AOB and NOB. Small and medium granules (d < 0.6 mm) cannot restrict oxygen mass transfer in all spaces of the sludge. Larger granules (d > 0.9 mm) can result in smaller aerobic volume fraction and inhibition of NOB growth. All these observations provide support to future studies on the mechanisms responsible for the AOB in granules systems.     

改良UASB反应器处理海藻酸钠废水的试验研究

本试验采用改良UASB反应器在常温条件下现场处理海藻酸钠废水,试验历时94 d,在絮状污泥为主条件下,容积负荷6.0 kgCOD/(m3.d)时,COD去除率达到85%,出水pH 6.8左右,VFA稳定在400 mg/L左右,设备运行稳定.试验结果表明,常温下利用改良UASB处理海带渣废水是可行的.     

Effect of feeding pattern and storage on the sludge settleability under aerobic conditions

The selection of filamentous bacteria is often assumed to be associated with specific microbial properties such as growth rate, substrate uptake rate, substrate affinity and potential for substrate storage. In this study we aimed to verify some of these factors. Sequencing batch reactor (SBR) systems were used to scale-down aerobic activated sludge systems with an aerobic selector. Adding acetate in different aerobic feeding periods allowed us to simulate a variable relative size of aerobic selector with different bulk liquid substrate concentrations. The experiments showed that as expected, the aerobic fill time ratio (FTR(ox)) and the corresponding feast period, which can be assumed similar to contact time in an aerobic selector, had a strong effect on the sludge settleability. Promoting a strong substrate gradient in the SBR (FTR(ox)<5.4%) resulted in good sludge settleability (SVI<120mLg(-1)). Whenever acetate was added in a limiting rate (FTR(ox)>6.2%), a condition in which the acetate concentration in the reactor was always very low, the sludge settleability decreased (SVI>150mLg(-1)). Sludge settleability could be improved by changing the feeding strategy to a pulse feed. The maximum specific acetate uptake rate and poly beta-hydroxybutyrate (PHB) production rate of bad settling sludge, including bulking sludge, was similar to well-settling sludge, which is not in accordance with the general assumptions that well settling sludge have a higher maximal substrate uptake rate and better storage capacities. An alternative hypothesis for the development of filamentous structures in biological flocs has been formulated. It is hypothesized that bulking sludge originates from the presence of substrate gradients in sludge aggregates. Whereas at low bulk liquid substrate concentration filamentous bacteria give easier access to the substrate at the outside of the flocs and thereby proliferate, at high bulk liquid substrate concentration there is no substrate advantage for filamentous organisms and smooth bacterial structures predominate. In this hypothesis there is no need for an intrinsic difference in kinetic parameters between floc and filamentous bacteria. Where presence of filamentous bacteria is related to process conditions, the presence of a specific filament is likely due to presence of a specific limiting substrate.     

Effect of specific gas loading rate on thermophilic (55 degrees C) acidifying (pH 6) and sulfate reducing granular sludge reactors

The effect of the specific gas loading rate on the acidifying, sulfate reducing and sulfur removal capacity of thermophilic (55 degrees C; pH 6.0) granular sludge bed reactors treating partly acidified wastewater was investigated. A comparison was made between a regular UASB reactor and a UASB reactor continuously sparged with N(2) at a specific gas loading rate of 30 m(3)m(-2)d(-1). Both UASB reactors (upflow velocity 1.0 mh(-1), hydraulic retention time about 5h) were fed a synthetic wastewater containing starch, sucrose, lactate, propionate and acetate and a low sulfate concentration (COD/SO(4)(2-) ratio of 10) at volumetric organic loading rates (OLR) ranging from 4.0 to 49.8 gCODl(-1) reactord(-1). Immediately after imposing an OLR of 25 gCODl(-1) reactord(-1), the acidification and sulfate reduction efficiency dropped to 80% and 30%, respectively, in the UASB reactor. Both efficiencies recovered slowly to 100% during the course of the experiment. In the N(2) sparged reactor, both the acidification and sulfate reduction efficiency remained 100% following the OLR increase to 25 gCODl(-1) reactord(-1). However, the sulfate reduction efficiency gradually decreased to about 20% at the end of the experiment. The biogas (CO(2) and CH(4)) production rate in the UASB was very low, i.e. <3l biogasl(-1) reactorday(-1), resulting in negligible amounts (<20%) of H(2)S stripped from the reactor liquid. The total H(2)S concentration of the N(2) sparged UASB reactor effluent was always below 25 mgl(-1), but incomplete sulfate reduction kept the maximal H(2)S stripping efficiency below 70%.     

内循环UASB处理酒精废水及其颗粒污泥特性

针对传统UASB反应器在启动时颗粒污泥形成缓慢的问题,采用内循环UASB反应器作为厌氧单元对酒精废水进行处理。其以低负荷启动,启动完成后容积负荷为7.9 kg/(m3.d),对COD的去除率可达80%,整个试验阶段对NH3-N的平均去除率为16.38%。扫描电镜显示颗粒污泥中的优势菌开始为短杆菌,随着培养时间的延长则出现了球菌;而现有UASB反应器中颗粒污泥的优势菌为丝状菌。对沼气成分进行分析,CH4含量最高为81.61%,N2含量则随着颗粒污泥培养时间的延长由3.68%增加至18.59%。     

Removal of micropollutants from urban wastewater using a UASB reactor coupled to a MBR at different organic loading rates

This study examines the removal of micropollutants (MPs) in a hybrid process that combines anaerobic and aerobic redox conditions under different Organic Loading Rates (OLRs).

A laboratory-scale pilot-plant composed of an Upflow Anaerobic Sludge Blanket reactor (UASB) combined with a membrane bioreactor (MBR) was operated. Six MPs were analyzed: the hormones estrone, 17-α-ethinyl estradiol and 17-β-estradiol, the plasticizer bisphenol A and the pharmaceuticals carbamazepine and diclofenac. In order to study its influence on removal efficiencies, the system was operated at three different OLRs: high (0.67 ± 0.15 kg COD/m³ d), medium (0.37 ± 0.06 kg COD/m³ d) and low (0.11 ± 0.02 kg COD/m³ d).

The results demonstrated the synergistic effects due to the double biological treatment, with removal rates above 90% for the hormones and the plasticizer. Pharmaceuticals were the most resistant compounds, being only partially removed in the liquid phase. Removal rates of the MPs were higher at high OLR of the influent.     

Performance comparison of a pilot-scale UASB and DHS system and activated sludge process for the treatment of municipal wastewater

This study compares the performance of a pilot-scale combination of UASB and DHS system to that of activated sludge process (ASP) for the treatment of municipal sewage. Both systems were operated in parallel with the same sewage as influent. The study was conducted for more than 300 days, which revealed that organic removal efficiency of UASB+DHS system was comparable to that of ASP. Unfiltered BOD removal by both systems was more than 90%. However, UASB+DHS system outperformed ASP for pathogen removal. In addition, volume of excess sludge production from UASB+DHS was 15 times smaller than that from ASP. Moreover, unlike ASP, there is no requirement of aeration for the operation of UASB+DHS system, which makes it an economical treatment system. Considering the above observations, it was concluded that UASB+DHS system can be a cost-effective and viable option for the treatment of municipal sewage over ASP, especially for low-income countries.     

Anaerobic biodegradability and treatment of grey water in upflow anaerobic sludge blanket (UASB) reactor

Feasibility of grey water treatment in an upflow anaerobic sludge blanket (UASB) reactor operated at different hydraulic retention time (HRT) of 16, 10 and 6h and controlled temperature of 30 degrees C was investigated. Moreover, the maximum anaerobic biodegradability without inoculum addition and maximum removal of chemical oxygen demand (COD) fractions in grey water were determined in batch experiments. High values of maximum anaerobic biodegradability (76%) and maximum COD removal in the UASB reactor (84%) were achieved. The results showed that the colloidal COD had the highest maximum anaerobic biodegradability (86%) and the suspended and dissolved COD had similar maximum anaerobic biodegradability of 70%. Furthermore, the results of the UASB reactor demonstrated that a total COD removal of 52-64% was obtained at HRT between 6 and 16 h. The UASB reactor removed 22-30% and 15-21% of total nitrogen and total phosphorous in the grey water, respectively, mainly due to the removal of particulate nutrients. The characteristics of the sludge in the UASB reactor confirmed that the reactor had a stable performance. The minimum sludge residence time and the maximum specific methanogenic activity of the sludge ranged between 27 and 93 days and 0.18 and 0.28 kg COD/(kg VS d).     

Effect of extended idle conditions on structure and activity of granular activated sludge

In industry and in tourist areas, periods exist during which no or only very little sewage is produced, and the wastewater treatment facilities have to be set into an idle phase over several days and even weeks. When wastewater is generated again and delivered to the treatment plant, the microorganisms in the activated sludge plant may have lost activity, and the activated sludge flocs may have disintegrated. From previous observation, it is assumed that granular activated sludge is more resistant against long-term storage than activated sludge flocs. Experiments using a laboratory-scale sequencing batch reactor (SBR) were conducted to study the impacts of a 7-weeks anaerobic idle time on structural integrity and metabolic activity of granular activated sludge, and the time required to regain the former operational status of the plant. Oxygen consumption rate (OCR) was used as an indicator to evaluate the metabolic activity of the sludge. The results revealed that the size, color and sedimentation characteristics of the granular sludge did hardly change during the storage period. Sludge activity, however, dropped to values as low as 0.17 mg min(-1)L(-1). After restarting the reactor, the OCR increased within 1 day to a level of 0.57 mg min(-1)L(-1), kept rising at a linear rate in the following days, and reached after 1 week, a value of 5.74 mg min(-1)L(-1) typical for the former activity status. These results imply that granular activated sludge can be stored for a considerably long period of time, and brought into service again relatively quickly. After an idle period of 7 weeks, it took less than a week to regain full capacity of the SBR.     

Behavior of inorganic elements during sludge ozonation and their effects on sludge solubilization

The behavior of inorganic elements (including phosphorus, nitrogen, and metals) during sludge ozonation was investigated using batch tests and the effects of metals on sludge solubilization were elucidated. A decrease of ∼50% in the ratio of sludge solubilization was found to relate to a high iron content 80-120 mgFe/gSS than that of 4.7-7.4 mgFe/gSS. During sludge ozonation, the pH decreased from 7 to 5, which resulted in the dissolution of chemically precipitated metals and phosphorus. Based on experimental results and thermodynamic calculation, phosphate precipitated by iron and aluminum was more difficult to release while that by calcium released with decrease in pH. The release of barium, manganese, and chrome did not exceed 10% and was much lower than COD solubilization; however, that of nickel, copper, and zinc was similar to COD solubilization. The ratio of nitrogen solubilization was 1.2 times higher than that of COD solubilization (R² = 0.85). Of the total nitrogen solubilized, 80% was organic nitrogen. Because of their high accumulation potential and negative effect on sludge solubilization, high levels of iron and aluminum in both sewage and sludge should be considered carefully for the application of the advanced sewage treatment process with sludge ozonation and phosphorus crystallization.     

Sedimentation behaviour of sludge particles in a biogas tower reactor and the function of a hydrostatically pressurized sedimenter

It was found that anaerobic sludge particles contain gas bubbles. Due to the compressibility of the bubbles, which are entrapped in the sludge agglomerates, a pressure-dependent sedimentation characteristic of the sludge particles was found and mathematically described. Enhanced hydrostatic pressure results in a considerable increase of the settling velocity of sludge particles. On this basis the concept of a hydrostatically pressurized sedimenter is presented and its performance analyzed. Due to the hydrostatical pressurization of the sedimenter the produced gas is kept in the liquid phase until the liquid phase is saturated. To avoid a degassing of the liquid which results in the undesired release of gas bubbles a maximum liquid dwell time in the sedimenter must not be exceeded.     

The contribution of biotic and abiotic processes during azo dye reduction in anaerobic sludge

Azo dye reduction results from a combination of biotic and abiotic processes during the anaerobic treatment of dye containing effluents. Biotic processes are due to enzymatic reactions whereas the chemical reaction is due to sulfide. In this research, the relative impact of the different azo dye reduction mechanisms was determined by investigating the reduction of Acid Orange 7 (AO7) and Reactive Red 2 (RR2) under different conditions. Reduction rates of two azo dyes were compared in batch assays over a range of sulphide concentrations in the presence of living or inactivated anaerobic granular sludge. Biological dye reduction followed zero order kinetics and chemical dye reduction followed second-order rate kinetics as a function of sulfide and dye concentration. Chemical reduction of the dyes was greatly stimulated in the presence of autoclaved sludge: whereas chemical dye reduction was not affected by living or gamma-irradiated-sludge. Presumably redox-mediating enzyme cofactors released by cell lysis contributed to the stimulatory effect. This hypothesis was confirmed in assays evaluating the chemical reduction of AO7 utilizing riboflavin, representative of the heat stable redox-mediating moieties of common occurring flavin enzyme cofactors. Sulfate influenced dye reduction in accordance to biogenic sulfide formation from sulfate reduction. In assays lacking sulfur compounds, dye reduction only readily occurred in the presence of living granular sludge, demonstrating the importance of enzymatic mechanisms. Both chemical and biological mechanisms of dye reduction were greatly stimulated by the addition of the redox-mediating compound, anthraquinone-disulfonate. Based on an analysis of the kinetics and demonstration in lab-scale upward-flow anaerobic sludge bed reactors, the relative importance of chemical dye reduction mechanisms in high rate anaerobic bioreactors was shown to be small due to the high biomass levels in the reactors.     

Biological hydrolysis and acidification of sludge under anaerobic conditions: the effect of sludge type and origin on the production and composition of volatile fatty acids

New wastewater treatment processes resulting in considerably reduced sludge production and more effective treatment are needed. This is due to the more stringent legislations controlling discharges of wastewater treatment plants (WWTPs) and existing problems such as high sludge production. In this study, the feasibility of implementing biological hydrolysis and acidification process on different types of municipal sludge was investigated by batch and semi-continuous experiments. The municipal sludge originated from six major treatment plants located in Denmark were used. The results showed that fermentation of primary sludge produced the highest amount of volatile fatty acids (VFAs) and generated significantly higher COD- and VFA-yields compared to the other sludge types regardless of which WWTP the sludge originated from. Fermentation of activated and primary sludge resulted in 1.9-5.6% and 8.1-12.6% COD-yields, soluble COD (SCOD)/total COD (TCOD), in batch experiments, respectively. The COD-yields for primary, activated and mixed sludge were 19.1%, 6.5% and 21.37%, respectively, in semi-continuous experiments operated at solids retention time (SRT) of 5d and temperature of 37 degrees C. The benefit of fermentation for full-scale application was roughly estimated based on the experiments performed in semi-continuous reactors. The results revealed that even though the VFA production of primary sludge was higher compared to activated sludge, substantial amounts of VFA could be produced by fermentation of activated sludge due to the substantially higher production of activated sludge in WWTPs.