Temperature modeling in activated sludge systems: a case study.

A model of temperature dynamics was developed as part of a general model of activated-sludge reactors. Transport of heat was described by the one-dimensional, advection-dispersion equation, with a source term based on a theoretical heat balance over the reactor. The model was compared to several reference models, including a tanks-in-series model and the dispersion model with heat components neglecting biochemical-energy inputs and other activated-sludge, heat-balance terms. All the models were tested under steady-state and dynamic conditions at a full-scale facility, the Rock Creek wastewater treatment plant in Hillsboro, Oregon, using meteorological data from a station located 16 km from the plant. The dispersion model and tanks-in-series model matched in situ temperature data with absolute-mean errors less than 0.1 degrees C. Neglecting biochemical-heat-energy inputs in the activated-sludge reactor underestimated temperatures by up to 0.5 degrees C. The biochemical-heat-energy inputs accounted for 30 to 40% of the total heat flux throughout the year.     

NaCl盐度对耐盐活性污泥沉降性能及脱氮的影响

针对海水冲厕工程的实施,采用序批式活性污泥反应器(SBR)处理实际含盐生活污水,考察了盐度对耐盐活性污泥沉降性能及脱氮效能的影响。研究发现,经过长期盐度驯化后的污泥系统也会出现丝状菌污泥膨胀。在经过10 g/L盐度长期驯化的污泥系统中,污泥容积指数(SVI)随着盐度的升高而降低,盐度升高使丝状菌减少,污泥絮体变小变密实。但是,盐度降低时会引发更严重的污泥膨胀,导致污泥流失。对脱氮性能的研究表明,硝化菌的耐盐能力较强。当盐度由10 g/L改变为0、5、15、20 g/L时,氨氮去除率依然可以维持在99%以上。但亚硝酸盐积累率无论是盐度升高或降低时都升高,这表明驯化后污泥中的亚硝酸氧化菌(NOB)对盐度变化的耐受能力比氨氧化菌(AOB)弱,无论盐度升高或降低都会对其产生较大的影响。     

Assessing microbial communities for a metabolic profile similar to activated sludge.

To search for reliable testing inocula alternatives to activated sludge cultures, several model microbial consortia were compared with activated sludge populations for their functional diversity. The evaluation of the metabolic potential of these mixed inocula was performed using the Biolog EcoPlates and GN and GP MicroPlates (Biolog, Inc., Hayward, California). The community-level physiological profiles (CLPPs) obtained for model communities and activated sludge samples were analyzed by principal component analysis and hierarchic clustering methods, to evaluate the ability of Biolog plates to distinguish among the different microbial communities. The effect of different inocula preparation methodologies on the community structure was also studied. The CLPPs obtained with EcoPlates and GN MicroPlates showed that EcoPlates are suitable to screen communities with a metabolic profile similar to activated sludge. New, well-defined, standardized, and safe inocula presenting the same metabolic community profile as activated sludge were selected and can be tested as surrogate cultures in activated-sludge-based bioassays.     

Effects of sludge properties on the thickening and dewatering of waste activated sludge.

The thickening and dewatering of waste activated sludge, from a pilot-scale submerged membrane bioreactor and two bench-scale, complete-mix activated sludge reactors (high-shear and low-shear aeration) treating the same municipal primary effluent, were investigated. Solids settling and compaction were measured using the diluted sludge volume index (DSVI) analysis and a batch centrifugation analysis, respectively. Elevated levels of filamentous microorganisms resulted in higher DSVI values and lower centrifuged pellet concentration. Elevated levels of nocardioform bacteria resulted in lower solids float concentrations, and higher colloidal material reduced solids recovery in batch flotation experiments. Sludge filterability, measured as time-to-filter, was shown to be a function of extracelluar polymeric substances and colloidal material, where higher levels of either reduced sludge filterability. Additional research is necessary to confirm these results using full- or demonstration-scale thickening and dewatering units.     

Tetracycline as a selector for resistant bacteria in activated sludge

Tetracycline, one of the most widely used antibiotics, is excreted into wastewater after consumption by humans and animals. The focus of this research was to evaluate the fate of tetracycline resistant bacteria in the activated sludge process as a function of tetracycline loading. The studies were conducted with aerobic biological sequencing batch reactors (SBRs). When comparing 250 microgl(-1) tetracycline fed SBRs with parallel SBRs having a background influent wastewater tetracycline concentration of approximately 1 microgl(-1), tetracycline fed reactors were found to have increased concentrations and production rates of tetracycline resistant bacteria, higher net growth rates of resistant bacteria, and higher percentages of tetracycline resistant bacteria, which were amplified by increase in organic loading and growth rates.     

Simultaneous nitrification-denitrification and clarification in a pseudoliquified activated sludge system.

This paper describes results from a pilot study of a novel wastewater treatment technology, which incorporates nutrient removal and solids separation to a single step. The pseudoliquified activated sludge process pilot system was tested on grit removal effluent at flowrates of 29.4 to 54.7 m3/d, three different solid residence times (SRT) (15, 37, and 57 days), and over a temperature range of 12 to 28 degrees C. Despite wide fluctuations in the influent characteristics, the system performed reliably and consistently with respect to organics and total suspended solids (TSS) removals, achieving biochemical oxygen demand (BOD) and TSS reductions of > 96% and approximately 90%, respectively, with BOD5 and TSS concentrations as low as 3 mg/L. Although the system achieved average effluent ammonia concentrations of 2.7 to 3.2 mg/L, nitrification efficiency appeared to be hampered at low temperatures (< 15 degrees C). The system achieved tertiary effluent quality with denitrification efficiencies of 90 and 91% total nitrogen removal efficiency at a total hydraulic retention time of 4.8 hours and an SRT of 12 to 17 days. With ferric chloride addition, effluent phosphorous concentrations of 0.5 to 0.8 mg/L were achieved. Furthermore, because of operation at high biomass concentrations and relatively long biological SRTs, sludge yields were over 50% below typical values for activated sludge plants. The process was modeled using activated sludge model No. 2, as a two-stage system comprised an aerobic activated sludge system followed by an anoxic system. Model predictions for soluble BOD, ammonia, nitrates, and orthophosphates agreed well with experimental data.     

Immobilized-cell-augmented activated sludge process for treating wastewater containing hazardous compounds.

A novel bioaugmentation scheme called immobilized-cell-augmented activated sludge (ICAAS) was developed. Offline enricher reactors were used to maintain immobilized acclimated cells applied to augment completely mixed activated sludge (CMAS) treating a pentachlorophenol (PCP) pulse loading. Cellulose triacetate (CA) and powder activated carbon (PAC) combined with CA (PAC + CA) were the two media types used for entrapping the PCP-degrading culture. With ICAAS at 5% by volume augmentation, PCP removal of 73.1 and 75.1% via biodegradation, volatilization, and adsorption onto suspended cells, entrapped cells, and media was achieved for the systems with CA and PAC + CA media, respectively, while PCP removal in a control CMAS, which had a comparable level of combined PCP adsorption onto suspended cells and volatilization as the ICAAS, was 48.7%. Results further showed that the immobilized cells retained their PCP-degrading ability when they were fed with the inducer (PCP) once every 20 days.     

活性污泥1号模型废水特性的测定研究

废水的水质特性是活性污泥数学模型研究和应用的重要方面。采用呼吸计量法及常规化学分析法对污水处理厂的废水特性进行了测定,通过研究发现,污水处理厂的曝气沉砂池出水中SS占总COD的比例平均为10．49％;Xs占总COD的比例平均为14．24％;S1占总COD的比例平均为5．52％。初沉池出水中Ss占总COD的平均比例为9．62％;Xs占总COD的比例平均为16．97％;S1占总COD的比例平均为11．38％。     

The effect of wastewater cations on activated sludge characteristics: effects of aluminum and iron in floc.

Wastewater samples collected from seven wastewater treatment plants (WWTPs) were characterized to assess the impacts of wastewater cations on the activated sludge process. The cations included in this study were sodium (Na+), potassium, ammonium, calcium, magnesium, aluminum (Al), and iron (Fe). Among the selected cations, Al and Fe were of most interest to this study because their role in bioflocculation has not been extensively studied and remains largely unknown. The data showed that WWTPs contained highly varying concentrations of Na+, Al, and Fe in the wastewater and that these cations were responsible for differences between WWTPs as to sludge dewatering rates and effluent quality. In general, a high influent Na+ concentration caused poor sludge dewatering and effluent characteristics. However, when sufficient Al and Fe were present in floc, the deleterious effects of Na+ were offset. The data associated with Al further revealed that waste activated sludge with low Al contained high concentrations of soluble and colloidal biopolymer (protein + polysaccharide), resulting in a high effluent chemical oxygen demand, high conditioning chemical requirements, and poor sludge dewatering properties. These results suggest that Al will improve activated sludge effluent quality by scavenging organic compounds from solution and binding them to floc.     

剩余活性污泥好氧消化优势菌株筛选及污泥稳定化效果分析

为了促进污水处理厂剩余污泥好氧消化效率,缩短污泥稳定化时间,筛选得到R3、R16、R19等3株对污泥好氧消化促进效果较为明显的优势菌种,通过16S rRNA基因序列分析表明,R3、R16、R19分别属于Bacillus sp.、Pseudomonas sp.和Bacillus sp.。研究结果表明：投加R3、R16、R19菌株,分别于第9天、第10天、第9天污泥达到消化稳定化状态,TOC降解率达到40%,比对照组分别提前了4、3、4 d,与对照组稳定化完成时的SVI相比,SVI值较对照组分别降低了14.1%、9.0%和11.1%。当消化反应进行到第13天时,投加R3、R16、R19菌株,MLSS降解率较对照组分别提高了7.1%、3.3%和8.2%。此外,投加优势菌株不同程度地加快了TOC、硝酸盐氮和氨氮在消化液中的积累,并且有利于磷的溶出。     

Filamentous scum bacteria in activated sludge plants: detection and identification quality by conventional activated sludge microscopy versus fluorescence in situ hybridization.

Detection of filamentous bacteria morphotypes involved in scum formation in activated sludge wastewater treatment plants by conventional sludge microscopy is often doomed to fail because of morphological and taxonomical variations. The aim of this study is to compare detection, identification, and quantification quality of filamentous "scum bacteria" found by conventional activated sludge microscopy and fluorescence in situ hybridization (FISH). In the case of filamentous Microthrix parvicella and Eikelboom morphotypes 1863 and 1851, conventional activated sludge microscopy and FISH results correspond well. In contrast, conventional activated sludge microscopy overlooks nocardioform actinomycete and type 1863 single cells. On the other hand, FISH underestimates filamentous nocardioform actinomycetes and morphotypes 0041/0675 or 0092 because of insufficient cell wall permeability or because of their taxonomic variability, with a resulting inadequacy of previously published probes. Nostocoida limicola morphotype results are still inconclusive because of low bacteria numbers being available in situ and the enormous taxonomic variability within this group.     

Heavy metal removal by activated sludge: influence of Nocardia amarae.

The goal of this research was to examine the metal binding capacity of Nocardia amarae cells and to assess the influence of Nocardia cells on the overall metal binding capacity of activated sludge. Metal sorption capacities of the pure Nocardia cells and activated sludge biomass containing various levels of added Nocardia pure cultures were determined by a series of batch experiments. Batch sorption isotherms for nickel (Ni), copper (Cu), and cadmium (Cd) showed that the pure culture of N. amarae exhibited significantly higher metal sorption capacity than the activated sludge biomass obtained from Wilmington Wastewater Treatment Plant (Wilmington, DE). Surface area of biomass estimated by a dye technique showed that pure N. amarae cells growing at stationary phase have substantially more specific surface area than that of activated sludge from Wilmington Treatment Plant. A two-fold difference in specific surface area indicated that the higher metal sorption capacity of Nocardia cells may be due to the higher specific surface area. The metal sorption capacity of activated sludge increased proportionally with the amount of Nocardia cells present in the mixed liquor. This increase was attributed to the greater specific surface area of the mixed liquor samples containing greater amounts of Nocardia cells.     

Development of a new model for batch sedimentation and application to secondary settling tanks design.

Assuming that settling takes place in two zones (a constant rate zone and a variable rate zone), a model using four parameters accounting for the nature of the water-suspension system has been proposed for describing batch sedimentation processes. The sludge volume index (SVI) has been expressed in terms of these parameters. Some disadvantages of the SVI application as a design parameter have been pointed out, and it has been shown that a relationship between zone settling velocity and sludge concentration is more consistent for describing the settling behavior and for design of settling tanks. The permissible overflow rate has been related to the technological parameters of secondary settling tank by simple working equations. The graphical representations of these equations could be used to optimize the design and operation of secondary settling tanks.     

Behaviour of bacterial extracellular polymeric substances from activated sludge: a review

Extracellular Polymeric Substances (EPS) are the predominant constituents of activated sludge and dramatically affect its properties. As EPS constitute as much as 50–90% of the solid phase of sludge, the use of EPS may bring a great reduction in sludge volume and mass, which have been great environmental interest. In this paper, results of over 60 publications related to structure, composition, storing condition, extraction and characteristics of EPS and their influences on behaviours of EPS is analysed. Possible application of EPS in heavy metal contamination is also discussed, together with a brief consideration of possible research interests.     

Modeling depth filtration of activated sludge effluent using a compressible medium filter.

A new filter, using a compressible-filter medium, has been evaluated for the filtration of secondary effluent. The ability to adjust the properties of the filter medium by altering the degree of the medium compression is a significant departure from conventional depth-filtration technology. Unlike conventional filters, it is possible to optimize the performance of the compressible-medium filter (CMF) by adjusting the medium properties (i.e., collector size, porosity, and depth) to respond to the variations in influent quality. Because existing filter models cannot be used to predict the performance of the CMF, a new predictive model has been developed to describe the filtration performance of the CMF and the effect of medium-compression ratio. The model accounts for the fact that the properties of the filter medium change with time and depth. The model, developed for heterodisperse suspensions and variable influent total suspended solids concentrations, can be used to predict all possible phases of filtration (i.e., ripening, constant removal, and breakthrough). A hyperbolic-type, second-order, nonlinear, partial-differential equation was derived to model the CMF. The equation was solved using the finite-difference numerical method. The accuracy of the numerical method was tested by a sensitivity analysis and a convergence test. The model is first-order accurate with respect to medium depth and time. Field data were obtained for the filtration of settled secondary effluent using a CMF with a capacity of 1200 m3/d. Model predictions were compared with observed performance from filter runs conducted at medium-compression ratios between 15 and 40% and filtration rates from 410 to 820 L/m2 min. The difference between the observed and the predicted values was found to be within 0 to 15%.     

硝化速率法用于活性污泥活性测试的研究

以城市污水厂回流污泥中的硝化细菌(氨氧化细菌和亚硝酸盐氧化细菌)为受试生物,HgCl2为标准毒性物质,通过对两组实验--氨氧化速率实验(NH 4-N→NO-2-N)和亚硝酸盐氧化速率实验(NO-2-N→NO-3-N)的研究表明,氨氧化细菌对HgCl2的灵敏度(IC50=0.034 mmol/L)明显高于亚硝酸盐氧化细菌(IC50=0.20 mmol/L).氨氧化速率法测试活性污泥活性时,使用NH 4-N或NO-X-N指标需要120 min或更长的时间,但使用NO-2-N指标仅需30 min就可完成测试,而且结果重现性要比NH 4-N和NO-X-N好,其变异系数CV为5.9 %.     

Inocula from activated sludge for ready biodegradability testing: homogenization by preconditioning

The use of activated sludge as inoculum source in ready biodegradability tests (RBT) suffers from several drawbacks related to the heterogeneity of these communities. In this work, the ability of a 7-day aeration period in a mineral medium to homogenize the characteristics of various activated sludges, as suggested by some RBT, was studied. The biodegradation potential of three activated sludge supernatants obtained from different wastewater treatment plants was assessed in terms of cultivable cell density, dehydrogenasic activity and a profile of hydrolytic enzymes. After the preconditioning, the homogenization of these characteristics in the supernatants was observed, as well as a decrease. When preconditioned inocula were used in acetate RBT, the biodegradation kinetics were homogenized. However, some preconditioned supernatants lost their ability to degrade an easily-assimilable xenobiotic compound (aniline) during the observation period, showing the effect of inoculum preconditioning on the behavior of complex bacterial communities, specialist populations (e.g. aniline degraders) being more sensitive than generalist populations (e.g. acetate degraders). These results show that preconditioning cannot be an optional inoculum pretreatment in RBT, and emphasize the importance of further studies focusing on inoculum homogenization.     

Immobilized cell augmented activated sludge process for enhanced nitrogen removal from wastewater.

The immobilized cell augmented activated sludge (ICAAS) system combines a cell immobilization technique and an offline enricher-reactor for the bioaugmentation of the activated sludge system to improve treatment performances. In this study, enhanced nitrogen removal using ICAAS was investigated. Laboratory-scale, offline, batch enricher-reactors were used to maintain nitrification and denitrification activities of coimmobilized nitrifiers and denitrifiers used to augment a laboratory-scale completely mixed activated sludge system (CMAS) treating synthetic wastewater. Cellulose triacetate was the media used to entrap nitrifiers and denitrifiers at a 2:1 mass ratio. The ICAAS augmented with the coimmobilized cells between 5 and 20% by volume gained 24 +/- 5% higher nitrogen removal than a control CMAS, which provided nitrogen removal of 28 +/- 7%. The ICAAS scheme is a viable alternative for upgrading existing activated sludge systems to gain better nitrogen removal. .     

Mechanism of effective nocardioform foam control measures for non-selector activated sludge systems.

Solids retention time (SRT), biological scum trapping and recycle, and the dynamic equilibrium between Nocardioform populations in the foam and the mixed liquor are the controlling factors in activated sludge foaming events caused by Nocardioform bacteria. For the operating modes described in this paper, a cured mixed liquor foaming condition (filament counts of approximately 10(5) intersections/g volatile suspended solids) was only achieved when SRT control, selective wasting, and polymer addition were in effect. Solids retention time control, with the SRT remaining below 1.5 days, and selective wasting will cure a severely foaming mixed liquor, but effects will only be observed after 3 or 4 months after implementation. The combined wastage of Nocardioform bacteria from selective wasting and SRT control can ensure long-term foam control to the operation of a pure-oxygen activated sludge system with foam-trapping features. An SRT of 0.3 days will result in the complete washout of Nocardioform bacteria from the activated sludge system, which can then operate at an SRT of 3 days free of Nocardioform. Polymer addition to mixed liquor is only effective for foam control when a large portion of the system biomass exists as a heavy layer of foam above the mixed liquor.     

超声预处理对剩余污泥酶活性的影响

为了研究不同工况下超声波预处理对剩余污泥酶活性变化的影响,对剩余污泥进行不同输入能量、频率的超声预处理,测定了预处理后污泥蛋白酶和脱氢酶的变化规律。结果表明：1）超声预处理在低能量输入条件下对污泥蛋白酶和脱氢酶活性存在促进作用,而随着超声能量的进一步增加,酶活性逐渐降低直至出现抑制现象;2）超声频率对污泥酶活性影响较为显著,其中20 kHz超声频率对蛋白酶和脱氢酶活性的促进效果最高,其次分别为25和33 kHz;3）当输入能量高于8 000 kJ·（kg TS）-1后,25和33 kHz频率超声预处理对污泥蛋白酶和脱氢酶活性存在抑制效应,引起该现象的原因分析可能是高频超声空化现象及伴随的热化学效应引起的生物酶失活导致的。