Simultaneous saccharification and co‐fermentation of paper sludge to ethanol by Saccharomyces cerevisiae RWB222. Part II: Investigation of discrepancies between predicted and observed performance at high solids concentration
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Abstract:
The simultaneous saccharification and co-fermentation (SSCF) kinetic model described in the companion paper can predict batch and fed batch fermentations well at solids concentrations up to 62.4 g/L cellulose paper sludge but not in batch fermentation at 82.0 g/L cellulose paper sludge. Four hypotheses for the discrepancy between observation and model prediction at high solids concentration were examined: ethanol inhibition, enzyme deactivation, inhibition by non-metabolizable compounds present in paper sludge, and mass transfer limitation. The results show that mass transfer limitation was responsible for the discrepancy between model and experimental data. The model can predict the value of high paper sludge SSCF in the fermentation period with no mass transfer limitation. The model predicted that maximum ethanol production of fed-batch fermentation was achieved when it was run as close to batch mode as possible with the initial solids loading below the mass transfer limitation threshold. A method for measuring final enzyme activity at the end of fermentation was also developed in this study.Keywords:
Volatile suspended solids
Enzymatic Hydrolysis
Ethanol Fermentation
The causes of the appreciable increase of dimethyl disulfide (DMDS)-forming bacteria in abnormally conditioned activated sludge were investigated. The strains II-Ab-43 (Corynebacterium) and III-Ab-5 (Pseudomonas), which were isolated from abnormally conditioned activated sludge under high biochemical oxygen demand (BOD) loading, were used to find suitable environmental conditions for DMDS formation and for growth. Both strains formed DMDS at high concentrations and grew well in culture medium with weak alkalinity and a high content of BOD substances, at 20-30°C. Activated sludge was cultured at the BOD load of 0.55 kg-BOD/m3·d at various pHs from 6.0 to 9.5. The state of activated sludge was normal at pH 6.0-8.5, but abnormal at pH 9.5. The DMDS-forming ability of the mixed liquor was constant at low values at pH 6.0-8.5, but increased distinctly at pH 9.5. With an increase of BOD load to 5.5 kg-BOD/m3·d at pH 9.5, the state of activated sludge deteriorated and the DMDS-forming ability rose further. In the aeration tanks of night soil treatment plants, DMDS was detected under conditions of weak alkalinity (pH 8.4-9.1) and high BOD of the influent (BOD 501-5540 mg/l). These results agreed with those obtained in the laboratory. The effluent parameters (BOD, chemical oxygen demand (COD), suspended solids (SS)) from settling tanks in which DMDS was detected in the aeration tanks had higher values than those in cases where DMDS was not detected. It became clear that environmental conditions of weak alkalinity and high BOD, due to abnormally conditioned activated sludge, were suitable for the growth of DMDS-forming bacteria, and DMDS was consequently detected in the aeration tank. It appears that DMDS could be a useful index for evaluating the state of activated sludge.
Alkalinity
Volatile suspended solids
Biochemical oxygen demand
Total suspended solids
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Activated sludge that had been grown on a completely soluble wastewater in a pilot plant was subjected to aerobic digestion in batch, lab-scale reactors. During the course of digestion, destruction of nonvolatile solids occured so that is was preferable to express the kinetics of digestion upon the loss of total suspended solids rather than volatile suspended solids. The first-order rate constant for the destruction of degradable suspended solids was found to be unaffected by the solids retention time (SRT) at which the activated sludge had been grown, whereas the nondegradable fraction of the activated sludge was found to increase as the SRT increased.
Volatile suspended solids
Aerobic digestion
Digestion
Total dissolved solids
Fraction (chemistry)
Total suspended solids
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Catalase activity of mixed liquor suspended solids of aeration tank of activated sludge plants in Milwaukee, WI, was measured in sonicated samples. Catalase activity varied in the samples of mixed liquor suspended solids collected from the head and end of the aeration tanks; in return activated sludge; and in waste activated sludge. Catalase activity decreased in mixed liquor suspended solids, on prolonged aeration (8 days), in the absence of added sewage. Volatile suspended solids and catalase activity seemed to bear a relationship.
Volatile suspended solids
Sewage sludge
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Many attempts have been made to find simple and reliable methods for determining the activity of activated sludge. The most simple method is a measure of mixed liquor suspended solids (MLSS) or mixed liquor volatile suspended solids (MLVSS). Neither of these measurements, however, measures the cell activity but only the cell weight, and they do not dis tinguish between living and dead cells. More specific methods for measuring the active cell mass have been used by several workers, methods ranging from stan dard plate counts to the measuring of the cell constituents present only in living cells. A review of these works is presented in a paper by Weddle and Jenkins.1 None of these methods is simple or suitable for serial analysis. In the same paper, Weddle and Jenkins stated that a significant measure of the activity of activated sludge is the rate of substrate removal. In aerobic systems, such as in the activated sludge process, the substrate is removed by biological oxydation, with oxygen as the final electron acceptor. The rate of substrate re moval may, therefore, be equivalent to the oxygen uptake rate (OUR). The OUR is an extensively used measure for the activity of activated sludge in research laboratories. The OUR can be measured by the manometric technique of Warburg, but because this technique requires special equipment and skilled technicians, it has been used little in controlling wastewater treatment plants. The development of the oxygen electrodes has made measuring OUR much easier and time-saving, and it is surprising that the use of oxygen electrodes in measuring OUR in activated sludge plants has not totally replaced other methods. If a method for measuring the activity of activated sludge is to serve as a practical controlling measurement, it must express the total oxygen uptake capacity for well-conditioned, unpoi soned sludge, as well as for sludge which has been influenced by components toxic to the microorganisms in the sludge. Furthermore, a method which is to be widely used in treatment plants must be simple to carry out and must not need expensive equipment. This work is an attempt to develop such a method.
Volatile suspended solids
Methylene blue
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Abstract Correlation between dehydrogenase activity, oxygen uptake, viable cell counts and volatile suspended solids in activated sludge has been examined with reference to their applicability as measures of viability in models of the activated‐sludge process. It was concluded that volatile suspended solids is in general a satisfactory viability parameter.
Volatile suspended solids
Viability assay
Total suspended solids
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Respirometry
Volatile suspended solids
Total suspended solids
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Ethanol Fermentation
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In this study, the effect of static magnetic fields (SMFs) on improving the performance of activated sludge process to enhance the higher rate of microbial growth biomass and improve sludge settling characteristics in real operation conditions of wastewater treatment plants has been investigated. The effect of SMFs (15 mT), hydraulic retention time, SRT, aeration time on mixed liquor suspended solids (MLSS) concentrations, mixed liquor volatile suspended solids (MLVSS) concentrations, α-factor, and pH in the complete-mix activated sludge (CMAS) process during 30 days of the operation, were evaluated.There were not any differences between the concentration of MLSS in the case (2148.8 ± 235.6 mg/L) and control (2260.1 ± 296.0 mg/L) samples, however, the mean concentration of MLVSS in the case (1463.4 ± 419.2 mg/L) was more than the control samples (1244.1 ± 295.5 mg/L). Changes of the concentration of MLVSS over time, follow the first and second-order reaction with and without exposure of SMFs respectively. Moreover, the slope of the line and, the mean of α-factor in the case samples were 6.255 and, - 0.001 higher than the control samples, respectively. Changes in pH in both groups of the reactors were not observed. The size of the sluge flocs (1.28 µm) and, the spectra of amid I' (1440 cm-1) and II' (1650 cm-1) areas related to hydrogenase bond in the case samples were higher than the control samples.SMFs have a potential to being considered as an alternative method to stimulate the microbial growth rate in the aeration reactors and produce bioflocs with the higher density in the second clarifiers.
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In this study, the performance of wastewater treatment plant located at sector I-9 Islamabad, Pakistan, was evaluated. This full scale domestic wastewater treatment plant is based on conventional activated sludge process. The parameters which were monitored regularly included total suspended solids (TSS), mixed liquor suspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS), biological oxygen demand (BOD), and chemical oxygen demand (COD). It was found that the biological degradation efficiency of the plant was below the desired levels in terms of COD and BOD. Also the plant operators were not maintaining consistent sludge retention time (SRT). Abrupt discharge of MLSS through the Surplus Activated sludge (SAS) pump was the main reason for the low MLSS in the aeration tank and consequently low treatment performance. In this study the SRT was optimized based on desired MLSS concentration between 3,000–3,500 mg/L and required performance in terms of BOD, COD and TSS. This study revealed that SRT is a very important operational parameter and its knowledge and correct implementation by the plant operators should be mandatory.
Volatile suspended solids
Biochemical oxygen demand
Total suspended solids
Wastewater quality indicators
Total dissolved solids
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In a slaughterhouse's full-scale extended aeration activated sludge wastewater treatment plant (WWTP), operating under complete solids retention time, the evolution of mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) concentration, food to micro-organisms ratio (F/M) and substrate utilization rate (SUR) were studied for over a year. Biomass growth phases in correlation to sludge biological and morphological characteristics were studied. Three distinguished growth phases were observed during the 425 days of monitoring. The imposed operational conditions led the process to extended biomass starvation conditions, minimum F/M, minimum SUR and predator species growth. MLSS and MLVSS reached a stabilization phase (plateau phase) where almost zero sludge accumulation was observed. The concept of degradation of the considered non-biodegradable particulate compounds in influent and in biomass (cell debris) was also studied. Comparison of evolution of observed sludge yields (Yobs) in the WWTP with Yobs predictions by activated sludge models verified the degradation concept for the considered non-biodegradable compounds. Control of the sedimentation process was achieved, by predicting the solids loading rate critical point using state point analysis and stirred/unstirred settling velocity tests and by applying a high return activated sludge rate. The nitrogen gas related sedimentation problems were taken into consideration.
Volatile suspended solids
Sedimentation
Settling
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