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.     

Extensions to modeling aerobic carbon degradation using combined respirometric-titrimetric measurements in view of activated sludge model calibration

Recently a model was introduced to interpret the respirometric (OUR) -titrimetric (Hp) data obtained from aerobic oxidation of different carbon sources in view of calibration of Activated Sludge Model No.1 (ASM1). The model requires, among others, the carbon dioxide transfer rate (CTR) to be relatively constant during aerobic experiments. As CTR is an inherently nonlinear process, this assumption may not hold for certain experimental conditions. Hence, we extended the model to describe the nonlinear CTR behavior. A simple calibration procedure of the CO2 model was developed only using titrimetric data. The identifiable parameter subset of this model when using titrimetric data only contained the first equilibrium constant of the CO2 dissociation, pK1, the initial aqueous CO2 concentration, C(Tinit) and the nitrogen content of biomass, i(NBM). The extended model was then successfully applied to interpret typical data obtained from respirometric-titrimetric measurements with a nonlinear CO2 stripping process. The parameter estimation results using titrimetric data were consistent with the results estimated using respirometric data (OUR) alone or combined OUR and Hp data, thereby supporting the validity of the dynamic CO2 model and its calibration approach. The increased range of applicability and accurate utilization of the titrimetric data are expected to contribute particularly to the improvement of calibration of ASM models using batch experiments.     

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.     

Activated sludge response to emulsified lipid loading

The possible adverse effects of natural fats and oils (lipids) upon biological wastewater treatment systems have been the subject of much speculation and some disagreement. This study addressed the specific question of possible effects of emulsified lipids upon activated sludge process performance. Lipid form and fatty acid composition were determined on wastewater samples. Experimental studies employing bench scale activated sludge units indicated that effluent quality is either not significantly different or occasionally is better than that from sucrose supplemented control plants receiving comparable organic loading (F/M > 0.80). Furthermore, emulsified lipids clearly do not exhibit an inhibitory effect on either the specific soluble substrate utilization rate or the mixed liquor oxygen consumption rate.However, effluent quality parameters were found to be dependent upon unit lipid loading to a highly significant degree. As well, unit lipid loading (g lipid g⁻¹ MLSS-day) provided a better explanation of effluent quality than either the food to microorganism ratio or the mixed liquor lipid burden (g lipid extracted from MLSS g⁻¹ MLSS). The findings of this study indicate the conditions where lipid overloading occurs. This data provides a basis for controlling emulsified lipid loading to the activated sludge process which should apply to plants which receive high lipid loading such as those encountered in industrial wastewater treatment applications.     

Respirometric measurements on activated sludge

The parameters required to describe the metabolism of activated-sludge according to the equations of Michaelis and Menten or Monod can be determined by simple batch experiments. For the sake of clarity one should distinguish between “long-run” batch experiments with a period of unlimited growth, like the BOD determination, and “short-run” experiments with a very small relative cell growth. In this paper the possibilities of a simple short-term oxygen demand test are examined. This method is expected to be applied in practice for process control, viz. continuous monitoring of influent BOD, measuring the concentration of viable sludge bacteria and for measuring toxicity.     

Microbial viability measurements and activated sludge kinetics

A laboratory study was performed to evaluate the influence of microbial viability information on a widely used steady-state kinetic model of slurry-type biological wastewater treatment processes. Adenosine triphosphate (ATP), determined by the luciferin-luciferase firefly lantern extract method using a liquid scintillation spectrometer to measure light emission, was used as the indicator of microbial viability. It was found that the microbial viability of activated sludge mixed liquor volatile suspended solids (MLVSS) exhibits a functional relationship with biological solids retention time (θ_c), i.e., being essentially 100% at low values of 0_c and decreasing to a nearly constant value at the higher values of 0_c, typical of activated sludge process operation. Values of the model coefficients were also affected by the microbial viability of the MLVSS.Based on mass balance considerations and ATP measurements, it is proposed that the MLVSS of an activated sludge system treating a soluble organic waste can be divided into the following three fractions: (I) active or viable microbial solids, (2) inert microbial debris solids, and (3) nonviable biodegradable microbial solids. Implications of viability information in design and operation are discussed.     

Critical operational parameters for zero sludge production in biological wastewater treatment processes combined with sludge disintegration

Mathematical models were developed to elucidate the relationships among process control parameters and the effect of these parameters on the performance of anoxic/oxic biological wastewater processes combined with sludge disintegrators (A/O-SD). The model equations were also applied for analyses of activated sludge processes hybrid with sludge disintegrators (AS-SD). Solubilization ratio of sludge in the sludge disintegrator, alpha, hardly affected sludge reduction efficiencies if the biomass was completely destructed to smaller particulates. On the other hand, conversion efficiency of non-biodegradable particulates to biodegradable particulates, beta, significantly affected sludge reduction efficiencies because beta was directly related to the accumulation of non-biodegradable particulates in bioreactors. When 30% of sludge in the oxic tank was disintegrated everyday and beta was 0.5, sludge reduction was expected to be 78% and 69% for the A/O-SD and AS-SD processes, respectively. Under this condition, the sludge disintegration number (SDN), which is the amount of sludge disintegrated divided by the reduced sludge, was calculated to be around 4. Due to the sludge disintegration, live biomass concentration decreased while other non-biodegradable particulates concentration increased. As a consequence, the real F/M ratio was expected to be much higher than the apparent F/M. The effluent COD was maintained almost constant for the range of sludge disintegration rate considered in this study. Nitrogen removal efficiencies of the A/O-SD process was hardly affected by the sludge disintegration until daily sludge disintegration reaches 40% of sludge in the oxic tank. Above this level of sludge disintegration, autotrophic biomass concentration decreases overly and TKN in the effluent increases abruptly in both the A/O-SD and AS-SD processes. Overall, the trends of sludge reduction and effluent quality according to operation parameters matched well with experimental results found in literatures.     

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.     

A new technique for monitoring alum sludge conditioning

A technique based on measurements of fluctuations in the intensity of light transmitted through a flowing sludge suspension was used to evaluate polymer performance in alum sludge conditioning. The ratio of the r.m.s. of the fluctuations to the average transmitted light intensity exhibits a well-defined response, usually a substantial increase, to sludge particle aggregation. This aggregation reflects the improvement in sludge filterability as also indicated by concurrent CST measurements. Five polymers, cationic, anionic and nonionic were used in conditioning the sludge. Tests were conducted using a mixer set at 700 rpm with a corresponding velocity gradient of 1900 s⁻¹. The technique was shown to give a very rapid convenient indication of the conditioning effect of polymeric flocculants. It could be very easily adapted to online applications.     

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.     

Experimental study on ionic soil stabilizer combined with vacuum preloading to solidify sludge

Bulletin of Engineering Geology and the Environment - As one of the main means of non-destructive testing, ultrasonic waves&nbsp;can effectively detect damage inside rock, which provides an...     

多尺度监测手段结合三维建模技术应用于边坡变形监测

本文通过沿海港口地区岩质边坡的监测工作,将三维扫描技术与多尺度监测手段相结合,建立了边坡变形的多尺度监测系统,为边坡的稳定性和安全提供了保障。     

Activated sludge exopolymers: separation and identification using size exclusion chromatography and infrared micro-spectroscopy

Extracellular polymeric substances were extracted from activated sludge using a resin exchange method and analyzed. The separation and identification of EPS were carried out by size exclusion chromatography and Fourier transform infrared micro-spectroscopy. Chromatograms of extracted EPS exhibited seven peaks. Proteins varying in molecular weights from 670 to 45 kDa were present in all the peaks. Polysaccharides corresponding to molecular weights of approximately 1 and approximately 0.5 kDa were present in only three peaks. Strong association of polysaccharides and proteins was observed. Infrared results revealed the presence of one type of polysaccharide and two types of proteins (A and B). Proteins differed mainly in the length of their associated alkyl chains and in the ratio of ester/acidic functionalities.     

污泥联合不同有机质对厌氧发酵产酸的影响

研究了城市有机垃圾的三种主要成分(碳水化合物,蛋白质,脂质)与市政污泥联合厌氧发酵产酸的过程,试验结果表明,蛋白类有机质能大幅提高厌氧发酵效率,其后期产酸量达到14.52 g/L,挥发酸产率43.47%,分别比污泥单独厌氧发酵提高218%和59%;污泥联合脂质厌氧发酵产酸量最低,仅为单独厌氧发酵产酸量的39%。     

Novel insights into sludge dewaterability by fluorescence excitation-emission matrix combined with parallel factor analysis

Sludge dewatering is of major interest in sludge volume reduction and handling properties improvement. Here we report an approach of fluorescence excitation-emission matrix (EEM) combined with parallel factor (PARAFAC) analysis to elucidate the factors that influence sludge dewaterability. Sludge flocs from 11 full-scale wastewater treatment plants were collected to stratify into different extracellular polymeric substances (EPS) fractions and then to characterize their fluorescence EEMs. Both the normalized capillary suction time (CST) and specific resistance to filtration (SRF) were applied to determine sludge dewaterability. The results showed that fluorescence EEMs of tightly bound fractions were not affected by the wastewater sources. In contrast, fluorescence EEMs of loosely bound fractions were affected by the wastewater sources. All the fluorescence EEMs could be successfully decomposed into a six-component model by PARAFAC analysis. Both normalized CST and SRF were significantly correlated with component 1 [excitation/emission (Ex/Em) = (220, 275)/350] in the supernatant fraction, with components 5 [Ex/Em = (230, 280)/430] and 6 [Ex/Em = (250, 360)/460] in the slime and LB-EPS fraction. These results reveal that except for proteins-like substances (component 1), sludge dewaterability is also affected by humic acid-like and fulvic acid-like substances (components 5 and 6) in the slime and LB-EPS fractions. Furthermore, this paper presents a promising and facile approach (i.e., EEM-PARAFAC) for investigating sludge dewaterability.     

A combined approach for a better understanding of wastewater treatment plants operation: statistical analysis of monitoring database and sludge physico-chemical characterization

Biological wastewater treatment plants (WWTP) are complex systems to assess. Many parameters are recorded daily in WWTP to monitor and control the treatment process, providing huge amounts of registered data. A combined approach of extracting information from the WWTP databases by statistical methods and from the sludge physico-chemical characterization was used here for a better understanding of the WWTP operation. The monitored parameters were analysed by multivariate statistical methods: Principal Components Analysis and multiple partial linear regression. The WWTP operational conditions determine the sludge characteristics. The bacterial activity of the sludge in terms of extra-cellular polymeric substances (EPS) production was assessed using size exclusion chromatography and the internal structure of sludge flocs was observed by confocal laser scanning microscopy. The diagnosis of three paper mill WWTP enabled the identification of an important EPS production, the presence of the nitrification process and the presence of PO₄³⁻ nutrient in WWTP-A. These three main characteristics of WWTP-A were related with a systematically good sludge settling. In WWTP-B and C with bad settling, the bacterial activity was weak.     

Activated sludge treatment of abattoir wastewater—II : Influence of dissolved oxygen concentration

Performance of laboratory scale completely mixed activated sludge reactors fed with abattoir wastewater was measured at different dissolved oxygen (DO) concentrations. Degradation of fat present in the influent was inhibited at DO concentrations below about 0.5 mg l⁻¹, leading to sludges with high fat content which settled poorly due to excessive numbers of filamentous microorganisms. Fat was degraded rapidly at higher DO concentrations (up to 4.0 mg l⁻¹) and the sludge contained few filamentous microorganisms, a low fat content and settled readily. However, effluent quality was highest at low DO concentrations due to lower levels of soluble breakdown products from the fat.When wastewater was fed intermittently at constant aeration rate, sludge with a low fat content and good settleability resulted, even though the DO concentration was about 0.2 mg l⁻¹ for more than 30% of the time. Effluent quality was also high. Thus it is concluded that for full-scale abattoir treatment plants where wastewater flow is intermittent, DO concentration may be low during periods of high loading without adversely affecting effluent quality or sludge settleability.     

Variation of sludge volume index with activated sludge characteristics

Activated sludge samples from 2 laboratory units and 12 sewage treatment plants were examined to determine the effect of filamentous microorganisms, floc size and suspended solids concentration on SVI. An attempt was also made to correlate SVI to zone settling velocity. At a suspended solids concentration range of 700–4800 mg 1⁻¹ there was no effect of filamentous microorganisms at filament length concentrations below 10⁷μm (mg SS)⁻¹. However, when it was over 10⁷ μm (mg SS)⁻¹ SVI increased sharply with increasing concentrations of filamentous microorganisms.At all suspended solids concentrations examined SVI varied with floc size at filament length concentrations below 10 μm (mg SS)⁻¹. But, at filament length concentrations higher than this level, no effect of floc size on SVI was observed.The effect of suspended solids concentration on SVI was examined at different levels of filament lengths. It was found that the shape of SVI-suspended solids concentration curve varied with the level of filament lengths. A well defined relationship was found between SVI and zone settling velocity at all suspended solids concentrations examined.