Activated sludge respirometric measurements

Respirometric measurements of activated sludge were shown to be a valuable source of information with respect to the kinetics of substrate bio-oxidation. Two new techniques were elaborated which used an oxygen probe to enable determination of different rates of oxygen consumption. It would appear possible to determine the biochemical oxygen demand of a given substrate based on short period oxygen consumption measurements. The two techniques applied have shown consistency, both in evaluation of oxygen consumption rates as an operational parameter at an activated sludge treatment plant and in determination of substrate biochemical oxygen demand rate. The respirometric measurement, as shown can also be used to evaluate the biomass yield coefficient.     

Random response to stochastic floor loading

In order to model random structural responses to floor loads, floor load-effects are modelled with regard to the randomness of the loads and of the influence functions relating loads to load-effects. The floor loading is represented by a stochastic process model, and influence functions are represented as random functions of distributed structural stiffnesses. Approximate expressions are obtained for the means and variances of floor-load-effects and related equivalent uniformly distributed loads. These expressions involve load parameters, stiffness parameters and influence factors derived from influence functions. Influence factors for deflections of several floor systems are tabulated and the practical application of the results is illustrated with calculations for the means and variances of the long-term deflections of two reinforced-concrete floor slabs. The proposed model is distinguished from a well-known load-effect model by its ability to account for the response randomness due to local fluctuations of stiffness. This ability is useful in modelling deflections and other load effects which might be significantly affected by random stiffness fluctuations.     

Activated sludge monitoring with combined respirometric-titrimetric measurements

A short review of different respirometric methods is presented, and advantages and disadvantages of different principles are discussed. In this study a combined respirometric-titrimetric set-up was applied to monitor the degradation processes during batch experiments with activated sludge. The respirometer consists of an open aerated vessel and a closed non-aerated respiration chamber. It is operated with two oxygen probes resulting in two sources of information on the oxygen uptake rate; both collected at a high frequency. The respirometer is combined with a titrimetric unit that keeps the pH of the activated sludge sample at a constant value through the addition of acid and/or base. The cumulative amount of added acid and base serves as a complementary information source on the degradation processes. Interpretation of respirometric data resulting from validation experiments (additions of acetate and urea as ammonium source) showed that the set-up provided reliable data. Data interpretation was approached in two ways: (1) via a basic calculation procedure, in which the oxygen uptake rates were obtained by an oxygen mass balance over the respiration chamber, and (2) via a model-based procedure in which substrate transport was included for a more accurate data interpretation. Simulation examples showed that the presence of substrate transport in the model may be crucial for a correct data interpretation, since experimental conditions (e.g. low flow rate) and/or the biodegradation kinetic parameters (e.g. high Ks) may otherwise lead to data interpretation errors. Earlier studies already pointed out that titrimetric data can be related to nitrification, and this was also confirmed in this study. However, in addition, it was shown here for experiments with acetate that the amount of acid dosed was clearly related to the amount of acetate degraded. This indicates that the titrimetric data can be used to study the carbon source degradation. For the titrimetric data in this study, a model-based analysis was however only applied for the nitrification process. For an experiment with ammonium, it was illustrated that the estimation of biodegradation kinetics on a combined respirometric-titrimetric data set significantly improves confidence intervals of the parameters compared to the parameter estimation based on respirometric or titrimetric data separately.     

Activated sludge deflocculation under temperature upshifts from 30 to 45 degrees C

Twelve independent batch experiments (<9h) with fresh municipal activated sludge were conducted to assess the occurrence and the mechanisms of deflocculation under a temperature shift from 30 to 45 degrees C. In each experiment, a transient reactor (2 L) was subjected to the temperature shift and a control reactor was operated at a constant temperature of 30 degrees C. The occurrence of deflocculation was demonstrated by the increase in turbidity and in the concentrations of biopolymers in the sludge supernatant from the transient reactor. The maximum levels of proteins in the supernatants ranged from 53 to 81 mg/L, for DNA from 34 to 36 mg/L, for humic compounds from 20 to 40 mg/L, and for carbohydrates from 21 to 31 mg/L. All the biopolymer concentrations in the control reactor remained below 5-10 mg/L. The release of biopolymers was accompanied by an increase in sludge supernatant conductivity (16-32% increase, up to 1.20 mS/cm), soluble chemical oxygen demand (from 129 to 440 mg/L), total suspended solids (>25 mg/L up to 128 mg/L), and a decrease in the mixed liquor volatile suspended solids (up to 11%). The temperature shift was also found to inhibit microbial metabolism by reducing the sludge biomass substrate removal capacity, as measured by oxygen-uptake rates. The temperature shift had a marginal effect causing sludge lysis (as an increase in beta-galactosidase activity) and had no significant impact on sludge viability (live/dead ratio of bacterial cells). It was concluded that sludge deflocculation under a temperature shift from 30 to 45 degrees C involves the solubilisation of extracellular polymeric substances from the flocs and likely also floc fragmentation. In addition, sludge deflocculation and the inhibition of microbial metabolism explain the poor treatment performance observed in previous continuous reactors under similar temperature shifts.     

Response of dissolved oxygen to changes in influent organic loading to activated sludge systems

The major objective of this investigation was to examine the response of the activated sludge process to transient organic loadings and to evaluate the applicability of dissolved oxygen (DO) concentration and oxygen uptake rate as process control variables.A modified laboratory-scale activated sludge unit was used to continuously measure the ambient dissolved oxygen level. The change of the dissolved oxygen concentration responded to variations in the influent composition of the wastewater. First, the system was maintained at steady-state and system variables were measured for soluble TOC, MLVSS and oxygen uptake rate. The organic shock loading was induced by increasing or decreasing the baseline feeding of TOC concentration. As soon as a transient loading occurred the DO levels in the system were continuously monitored with the DO analyzer.A simplified material balance equation for dissolved oxygen in the system was developed and the dynamic behavior of oxygen uptake rate was examined. It was demonstrated that under transient conditions the changes in the dissolved oxygen concentration reflected the variations in the exogenous respiration rate of the biomass in the system due to fluctuations in the influent waste characteristics. Based upon the rapid response to the shock loading and the correlation of the change in the DO level to the magnitude of the shock loading, the two variables (DO concentration and oxygen uptake rate) generated from this biological monitor showed potential as a control variable for the activated sludge process.     

Activated sludge treatment of slaughterhouse wastes with protein recovery

The feasibility of applying activated sludge processes to slaughterhouse effluents with the object of resource recovery as well as treatment was examined on a laboratory scale. Optimizing the food: micro-organism (F:M) ratio for maximum biomass production resulted in a fourfold reduction of the respiratory oxygen requirement when compared with a conventionally loaded activated sludge system. Maximum biomass was produced with only a slight reduction in COD removal efficiency compared with the classical system, and the release of plant nutrients was much lower. Approximately 70% of the feed COD could be recovered as biomass having a crude protein content of 50–55% of dry weight. Amino acid analyses of the recovered protein indicated that it had nutritional value and was deficient only in sulphur amino acids. A first order economic analysis suggests that the optimized treatment/recovery process could be self supporting from the sale of recovered biomass.     

Control of activated sludge filamentous bulking—III. Effect of sludge loading

Previous experiments have indicated a possibility of controlling the filamentous bulking of activated sludge by cultivating a mixed culture in a system with the plug flow pattern or in a system with a selector. These experiments, however, were conducted at approximately constant sludge load [0·3–0·4 kg BOD₅(kg MLVSS day)⁻¹] and sludge age (4·5–5·0 days) so that the results obtained had only a limited validity. Further experiments were, therefore, carried out in order to find if the previous findings hold also for activated sludge systems with high sludge loads and low sludge ages.The experiments were conducted on four activated sludge systems with different flow patterns: two of them as complete-mixing reactors and the other two as reactors with the plug flow pattern, having dispersion numbers of 0·08 and 0·07. A mixture of starch and peptone was used as the substrate. All systems were operated at sludge ages 2 and 3 days and at sludge loads from 0·5 to 2·3 kg BOD₅(kg MLVSS day)⁻¹.It was found that at sludge loads above 0·5 kg kg⁻¹ day⁻¹ mixed cultures developed in the systems with the plug flow pattern possessed high values of the SVI and contained high portions of filamentous microorganisms. This was found in spite of sufficiently high concentration gradients of the substrate along these systems. It means that plug flow and, consequently, the concentration gradient of the substrate along the activated sludge system may not be the only factor in controlling the selection of microorganisms in a mixed culture. An additional factor must exert an influence on the population dynamics and selection of microorganisms in mixed cultures at high sludge loads and low sludge ages.The experiments have confirmed findings of others that values of the SVI depend on the sludge load. However, different trends of dependence were observed in the systems with different flow patterns. While in the complete-mixing systems the SVI decreased with increasing sludge loading in the systems with the plug flow pattern it increased.A greater phosphorus demand was observed in plug flow systems than in those with complete mixing.     

Activated sludge treatment of abattoir wastewater—I : Influence of sludge age and feeding pattern

As part of a study to provide data for the design of abattoir activated sludge plants laboratory-scale completely mixed reactors were fed with abattoir wastewater, continuously and intermittently using an 8 h feed, 16 h starvation pattern. The standard biokinetic coefficients and the effluent concentrations of COD. TKN and phosphorus were measured for the continuously fed reactors at sludge ages of 5, 10 and 20 days. Sludge settleability and filterability were also measured.Values obtained for the biokinetic coefficients Y and k_d were within the range of values reported for other substrates but k was lower and k_x higher. Effluent TKN and phosphorus concentrations were low at the three sludge ages, but the COD concentration was high at sludge ages of 5 and 10 days. In contrast to the data reported for many other wastewaters the effect of sludge age on the SVI was small. Intermittent feeding was tested at a single sludge age of 10 days. It produced an effluent and sludge with better and more stable characteristics than those from the continuously fed reactor at the same sludge age.     

Tall building configuration effects on their response to earthquake loading

This paper studies and analyzes the response and behavior of regular and irregular building structures in earthquake zones. The non-linear dynamic response of tall buildings structures were obtained using five simulated models, which were subjected to UBC code dynamic and static equivalent earthquake loads. The maximum response of the structural models were computed and analyzed in order to verify the effects of building configuration on drift results. Drift results agreed with codes recommendations regarding building configuration and showed that regular buildings performance in resisting earthquake forces is better than that of irregular buildings.     

扭转轴在强动载荷作用下的动力响应

从小变形理论出发,建立了受分布载荷的圆轴扭转问题的冲击动力响应的控制方程,探讨了响应过程中的饱和冲量矩现象,发现了对于高载范围内的脉冲载荷相应于最大变形的饱和冲量矩的现象。     

Influence of process loading intensity on sludge clarification and thickening characteristics

The separation of microbial mass in an activated sludge system depends on the formation of large settleable sludge flocs. Microbial cells agglomerate into small clumps and subsequently into sludge flocs by a natural bioflocculation process. The resulting biological mass may exist as individual cells, small aggregates, or large flocs in the aeration basin effluent. In the secondary clarifier, only large flocs are separated by sedimentation while individual cells and small aggregates are washed out as effluent suspended solids.

In the present study, the separation of sludge by sedimentation was shown to be closely related to the surface roughness of the resulting flocs. Normal sludges were observed to have relatively smooth surfaces while filamentous and zoogloeal bulking sludges were noted to have rough and diffused surfaces. The filamentous growths and the non-filamentous protuberances on the bulking sludge surface serve to increase the frictional drag between the moving solid and the liquid. This contributes to a lower settling velocity and associated dewatering rate of bulking sludges.

Conversely, the quantity of non-settleable solids was shown to be related to the quantity of extracellular biopolymers excreted by the microorganisms. The quantity of biopolymers produced decreased for higher Process Loading Intensity or lower sludge age levels thereby resulting in poor aggregation of cells into clumps and subsequently into flocs. This contributes to low clarification efficiencies of the activated sludge process.     

Dynamic response of nitrifying activated sludge batch culture to increased chloride concentration

Dynamic response of nitrifying activated sludge batch cultures to increased chloride concentration was studied in this paper, which focused upon the changes in the specific nitrification rate (SNR) and nitrifier population when the chloride level was gradually or stepwise increased to 30,000 mg Cl L-1. The dominant species of ammonia-oxidizers and nitriteoxidizers in the population were examined by Fluorescent in situ hybridization technique with 16S rRNA-targeted oligonucleotide probes. It was found that neither chloride increasing approaches affected the SNR of the batch cultures before the chloride concentration exceeded 10,000 mg Cl L-1, after which the stepwise increase approach reduced the SNR more significantly than the gradual increase approach. From 10,000 to 18,000 mg Cl L-1 a down-and-up pattern of the SNR variation appeared in both approaches, which was associated with the change in the dominant species of ammonia-oxidizers from non-saline-resistant species such as Nitrosomonas europaea-lineage and Nitrosomonas eutropha to saline-resistant species, such as the Nitrosococcus mobilis-lineage. Nitrobacter was the only dominant species when the chloride concentration was below 10,000 mg Cl L-1, where no nitrite-oxidizers survived. Therefore, the 10,000 mg Cl L-1 chloride level is a critical level for the shift of the nitrifier population in the nitrifying activated sludge batch cultures.     

有机负荷对污泥减量HA-A/A-MCO工艺吸放磷的影响

开发了一种具有同步除磷脱氮和污泥减量功能的HA-A/A-MCO工艺,分析了该工艺的方法及流程,并对其进行了试验研究,通过静态试验发现,当负荷增加至一定程度,有机物不再是磷释放的限制性因子,HA-A/A-MCO系统厌氧释磷的临界有机负荷为0.141 g COD/（g MLSS.d）,单位污泥最大可释放贮磷量为5.7 mg P/g MLSS。     

爆炸作用下夹层玻璃幕墙动力响应试验研究

为研究夹层玻璃在爆炸作用下的动力响应特征,对四边简支夹层玻璃面板进行了爆炸作用试验研究。试验按3个爆炸等级进行,研究了夹层玻璃面板在不同爆炸当量下的动力响应特征和破坏形态。试验表明：爆炸作用后冲击波的超压迅速升至峰值,并在数十毫秒内逐渐衰减,夹层玻璃的位移和应力随爆炸等级的增加而增大;在爆炸作用下,玻璃面板开始碎裂时裂纹在中心处呈环状,并由中心向四周均匀扩散,整个裂纹呈放射状展开,随着爆炸等级的增加,最终呈撕裂状破坏,钢化玻璃破碎为颗粒附着在PVB胶层上,没有发生飞溅。同时运用LS-DYNA有限元分析软件对试验模型进行了数值分析,分析所得玻璃面板的中心点最大位移与试验结果差别为38.7%,最大应力与试验结果的差别为20%,所得破坏模式与试验结果相吻合,表明数值模拟方法可靠。     

Nonlinear response of masonry wall structures subjected to cyclic and dynamic loading

The assessment of the dynamic or seismic performance of complex structures often requires the integration in the time domain of the structural equation of motion in the frame of a nonlinear analysis. Although sophisticated methods have been developed for the nonlinear analysis of masonry wall structures, including the macro- and micro-modeling approaches, these require large computational effort still limiting the extent and complexity of the structures analyzed. This paper presents an alternative method based on the Generalized Matrix Formulation for masonry skeletal structures and load bearing wall systems, which has been proved as an efficient formulation for the analysis of the strength capacity of these kinds of structures (Roca et al. (2005) [17]). The basic formulation has been complemented with a uniaxial cyclic constitutive model for masonry and a time integration scheme. The ability of the resulting approach to predict the nonlinear dynamic response of masonry structures is shown through its application to the time domain analysis of an experimental scale masonry building with available experimental results on its dynamic response.     

Microbial population dynamics during aerobic sludge granulation at different organic loading rates

Laboratory experiments were carried out to investigate the evolution of the bacterial community during aerobic sludge granulation. The experiments were conducted in three 2.4L sequencing batch reactors (SBRs) that were seeded with activated sludge and fed with glucose-based synthetic wastewater. Three different influent organic concentrations were introduced into the three SBRs, R1, R2 and R3, resulting in chemical oxygen demand (COD) loading rates of 1.5 (R1), 3.0 (R2) and 4.5 (R3)kg/m(3)d, respectively. Changes in bacterial diversity throughout the granulation process were monitored and analysed using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) techniques. The experimental results demonstrate that glucose-fed aerobic granules could be formed without significant presence of filamentous bacteria. Granules formed at different loading rates had different morphology, structural properties and bacterial species. A higher loading rate resulted in faster formation of larger and loose granules, while a lower loading rate resulted in slower formation of smaller and more tightly packed granules. The biomass underwent a dynamic transformation in terms of bacterial species richness and dominance during the granulation process. The reactor with the highest substrate loading rate had the lowest species diversity, while the reactor with the lowest substrate loading rate had the highest species diversity. Different dominant species of beta- and gamma-Proteobacteria and Flavobacterium within the granule communities from the three different SBRs were confirmed by analysis of 16S rDNA sequences of the PCR products separated by DGGE. It is apparent that a few common bacterial species play an important role in the formation and growth of aerobic granules and help sustain the granular sludge structure in the bioreactors.     

Dynamic response and reliability analysis of tall buildings subject to wind loading

This paper explores the wind stochastic field from a new viewpoint of stochastic Fourier spectrum (SFS). The basic random parameters of the wind stochastic field, the roughness length z₀ and the mean wind velocity at 10 m height U₁₀, as well as their probability density functions (PDF), are obtained. It provides opportunities to use probability density evolution method (PDEM), which had been proved to be of high accuracy and efficiency, in computing the dynamic response and reliability of tall buildings subject to the wind loading. Principals and corresponding numerical solving algorithm of the PDEM are first presented. Then, the adopted model of the wind stochastic field is described briefly. The simulation method of the fluctuating wind velocity based on the SFS is introduced. Finally, as an example of the application of the PDEM, a 20-storey frame subject to wind loading is investigated in detail. The responses, including the mean value and the standard deviation, and the reliabilities of the frame are evaluated by the PDEM. The results demonstrate that the PDEM is applicable and efficient in the dynamic response and reliability analysis of wind-excited tall building.     

Drained and undrained response of deep tunnels subjected to far-field shear loading

An analytical solution for a rectangular opening in an infinite elastic medium subjected to far-field shear stresses has been derived for drained and undrained loading conditions. A number of numerical simulations has been conducted to determine the distortion of a rectangular structure in an infinite elastic medium under far-field shear stresses also for drained and undrained conditions and when there is full slip or no slip at the ground–structure interface. The results show that the shape of the opening has a minor influence on the structure’s deformations and that full-slip conditions result in lower deformations. Undrained conditions tend to reduce distortions when the structure is more flexible than the ground, but tend to increase them for stiffer structures. A comparison between results obtained for a rectangular lined opening and for a circular lined opening are presented, and show that deformations of a rectangular structure with no-slip can be estimated from equations derived for a circular opening with an incompressible liner and also with no-slip. The effects of flexibility, slip condition at the interface, and drained or undrained loading are different for circular tunnels than for rectangular tunnels.