Effect of sludge flocs on the aeration performance of suction-impellers

The authors have investigated a special aspect of the transfer of oxygen: the aeration performance of small-scale suction-impellers in a suspension of activated sludge floes and a performance comparison with clear water. The principle of the impellers is, that in order to disperse air bubbles into the aforementioned liquids, all that we need do is a simple stirring. Due to the impellers the authors could not show a reduction of the oxygen transfer coefficient in the presence of sludge flocs. Former comparative studies of oxygen transfer, using a fixed orifice, did show a reduction in the presence of sludge flocs. Therefore, it seems probable that the effect of activated sludge flocs on the transfer coefficient is linked with the manner in which air is dispersed, i.e., depends on whether an orifice is fixed or moved. The experimental results allow presumption that by developing a high intensity of shear near the location where air bubbles are produced, we are able to minimize the effect of sludge flocs on the process of bubble formation.     

Enhancement of the activated sludge process by activated carbon produced from surplus biological sludge

Surplus biological sludge from wastewater treatment operations was converted into activated carbon and then added to the aerated vessel of an activated sludge process treating phenol and glucose. The addition of activated carbon, either sludge-based or commercial, enhanced phenol removal from 58 to 98.7% and from 87 to 93% for COD with feed concentrations of 100 mg phenol l^–1 and 2500 mg COD l^–1. No differences were found between the activated sludge-activated carbon bench scale continuous reactors operating with either commercial or sludge-based activated carbon in spite of the higher adsorption capacity of the former.     

Ruthenium red adsorption method for measurement of extracellular polysaccharides in sludge flocs

A nondestructive method of measuring extracellular polysaccharides (ECP) in activated sludge floes using Ruthenium Red dye adsorption was developed at the Environmental Engineering Laboratory at the University of Colorado at Boulder. The effects of pH, buffer solution, dye concentration, sludge mass, temperature, and incubation time on dye adsorption was determined. Ruthenium Red dye adsorption to bacterial floes was found to fit a Brunauer-Emmett-Teller (BET) isotherm model. Of the other environmental conditions in the system, pH was found to have the strongest effect on dye adsorption to bacterial flocs. The amount of extra cellular polysaccharides (ECP) measured by Ruthenium Red adsorption was compared with extracellular polysaccharides measured by two chemical extraction methods. Of all methods considered Ruthenium Red dye adsorption measured the highest amount of extracellular polysaccharide with the lowest amount of bacterial cell disruption. Thus, Ruthenium Red dye adsorption was more effective than extraction procedures for measurement of extracellular polysaccharides in activated sludge flocs.     

Neural network analysis of the diffusional limitations in activated sludge flocs

This work deals with the development of a comprehensive but simplified version of floc model for the activated sludge process. The rate expression of the type used by the IAWPRC Task Group was employed in this study to represent the reaction kinetics inside the floc matrix. The intraparticle mass transport was then incorporated to account for the effects of the diffusional limitations. Solution to the floc model was obtained by orthogonal collocation technique. Since the actual reactions are not only related to the sludge floc size and the bulk characteristics but are also associated with the floc size distribution, the concept of overall effectiveness factor was therefore used. Evaluation of overall effectiveness factors using neural network analysis was carried out and potential control strategies were discussed.     

Planning the purification process of active cDNA in expression cloning strategies

In principle, it is possible to clone the gene for any receptor that can be expressed in the Xenopus laevis frog oocyte and assayed electrophysiologically (E. S. Levitan, 1988, TINS 11, 41-43). Repeated fractionation of a lambda vector cDNA library made from mRNA which encodes the receptor protein will eventually lead to a single cDNA clone. This strategy poses the question as to how large should a lambda vector cDNA aliquot be at any fractionation stage in order that one may be relatively certain that the aliquot contains the clone of interest, and how many times should the fractionation be repeated in order that one isolate the single clone of interest? The purification of active cDNA is an iterative process. At each fractionation stage we specify the probability of at least one active cDNA in the total aliquot to be high. The required size of the aliquot taken depends upon this specified probability and the additional probability of selecting at random an individual cDNA which is active. We require an estimate of the latter probability for the initial stage. For subsequent stages Baye's estimators of these probabilities are used in the formula for calculating the aliquot size at each stage. We show how to perform this calculation when there is equal amplification of the active and remaining sequences and when the active sequence has a non-representative (unequal) amplification. When equal amplification holds a relatively simple formula is provided for calculating the expected number of stages needed in the process. When unequal amplification holds there is no simple calculation for this quantity and the entire sequence of calculations leading to termination of the process must be performed. In either case the minimum lambda vector amplification (growth) factor required at each stage to yield an adequate amount of cDNA for analysis is calculable.     

Kinetics for activated sludge process design: Experiment application to straw paper wastewater treatment

Degradation kinetics for the treatment of straw paper wastewater in an activated sludge process have been studied and a kinetic model has been derived for both batch and continuous experiments. These two methods are reasonably equivalent only when rather low concentrations of substrate are involved. In other cases batch and continuous results are quite different. Both models, however, show a dependence upon concentration corresponding to that which is typical of multicomponent substrate degradation. The kinetic model derived from continuous tests appears to be more suitable for designing industrial processes in that it avoids oversizing of the aeration unit.     

Practical application of aqueous two-phase partition to process development for the recovery of biological products

The practical application of aqueous two-phase systems (ATPS) to process development has been exploited for several years for the recovery of biological products. Unfortunately, this has not resulted in an extensive presence of the technique in commercial processes. Some of the main identified reasons for such situation involve the full understanding of the mechanism governing phase formation and the behaviour of solute partitioning in ATPS processes, the cost of phase forming polymers and the necessary extended time to understand the technique for process development. In this review paper, some of the practical disadvantages attributed to ATPS are addressed. The practical approach exploited to design ATPS processes, the application to achieve process integration, the increasing use for the recovery of high-value products and the recent development of alternative low cost ATPS, are discussed. It is proposed that the potential trend in the application of ATPS processes for the recovery of biological products will involve the recovery of high-value bio-particulate products with medical applications. This proposed trend in the application of ATPS will address the urgent need to rapidly and economically bring new biopharmaceutical products to market using scaleable and efficient bioprocess technology.     

Coupling purification and in situ immobilization process of monoclonal antibodies to clenbuterol for immunosensor application

Clenbuterol (CL), which promotes the growth of muscular tissue and the reduction of body fat in pigs and cattle, has been confirmed to be a potential hazard to human health. In this study, a monoclonal antibody to clenbuterol (CL mAb) from a hybridoma culture supernatant was purified by an aqueous two-phase system (ATPS) at different polyethylene glycol (PEG) concentrations, PEG molecular weights, pH values, and NaCl concentrations. Then the CL mAb was immobilized in situ by directly adding polystyrene microspheres (PSMSs) into a PEG phase containing CL mAb. Using the immobilized antibody, an immunosensor was constructed to detect the CL residues in pork samples. The results showed that using an ATPS composed of 15% (w/w) PEG6000, 15% (w/w) phosphate, and 15% (w/w) NaCl at pH 8.0, the partition coefficient was 7.24, the activity recovery was 87.86%, and the purification fold was 2.88. The PEG–CL mAb–PSMS retained approximately 98% of its initial activity after 30-ml phosphate buffer (PBS) washings. After 30 days of storage, the CL mAb–PSMS lost nearly 75% of its activity, whereas the PEG–CL mAb–PSMS retained as much as 95% of its initial activity. Furthermore, the constructed immunosensor obtained recoveries of 90.5 to 102.6% when applied to pork samples spiked with CL.     

Inhibiting effect of textile wastewater on the activity of sludge from the biological treatment process of the activated sludge plant

Textile industry represents an important source of toxic substances rejected in environment. Indeed, effluent of these industries contains dyes and chemicals. They are rejected in environment without any treatment. The aim of this work is to evaluate ecotoxicological effect of industrial textile effluents on the sludge harvested from activated sludge treatment plant of Marrakech city (Morocco). For this, we are interested in determining the inhibition condition that corresponds to 50% decrease of bacterial activity in sludge. Obtained results showed that inhibition percentage of bacterial activity depends narrowly on contact time and on added effluent volume, until a limit concentration where there is no degradation of substratum. In fact, substratum degradation speed shows about 65 times decrease when 80% (v/v) of textile wastewater is added, in comparison with the controlled one. Consequently the inhibition constant (Ki) that corresponds to 50% of bacterial inhibition activity is estimated to 0.65 mg l^?1 of dye. These studies confirm a real ecotoxicological risk of these effluents. Therefore, a treatment is mandatory before their rejection in environment.     

Selection of optimum biological sludge for zinc removal from wastewater by a biosorption process

Summary Biosorption of zinc by sludge micro-organisms obtained from different steps of a conventional SWT plant has been studied. The best types of activated sludge for the process were found to be thickened, anaerobic and dewatered sludge giving up to 90–98% of metal elimination when working at initial zinc concentration lower than 50 mg/l. A relationship between pH and conditional stability constant has been found.     

Strategy for minimization of excess sludge production from the activated sludge process

Increased attention has been given to minimization of sludge production from activated sludge process since environmental regulations are being more and more stringent in relation to excess sludge disposal. In a biological process, the more organic carbon utilized in carbon dioxide production, the fewer sludge produced, and vice versa. This paper, therefore, reviews strategies developed for minimization of excess sludge production, such as oxic-settling-anaerobic process, high dissolved oxygen process, uncoupler-containing activated sludge process, ozonation-combined activated sludge process, control of sludge retention time and biodegradation of sludge in membrane-assisted reactor. In these modified activated sludge processes, excess sludge production can be reduced by 20-100% without significant effect on process efficiency and stability. It is expected that this paper would be helpful for researchers and engineers to develop novel and efficient operation strategy to minimize sludge production from biological systems.     

Excess sludge reduction by biological way: from experimental experience to a real full scale application

The aim of this study was to investigate the ability of a biological process applied in the sludge line and based on the alternation of oxic and anoxic phases, to minimize the waste sludge production. After some tests in pilot scale, the process was applied in a real municipal wastewater treatment plant of 35,000 PE trying out one setting of working experimental conditions. A rate of the recycle flow was conditioned in a treatment basin, maintaining an HRT of 10 days. The control device operated for the 50% of time in the ORP range between -400 and -200 mV, and for the 50% in the ORP range between -200 and +50 mV. The mass balance defined an actual observed growth yield equal to 0.09 kgTVSkgCODr(-1), and the heterotrophic yield values, assessed by batch tests, seemed to be a suitable marker for the sludge reduction and for the energy uncoupling.     

The application of constant recycle solids concentration in activated sludge process.

The applicability of the model derived by Ramanathan and Gaudy (Biotechnol. Bioeng., 11, 207, (1969)) for completely mixed activated sludge treatment holding the recycle solids concentration as a system constant was investigated using an actual industrial organic wastewater. Short-term experiments were conducted at various dilution rates (1/8, 1/6, 1/4, 1/2, 1/1.5 hr-1) for two recycle solids concentration values (5000 and 7000 mg/liter). The influent substrate concentration was maintained at 1000 mg/liter COD and the hydraulic recycle ratio- alpha, was kept at 0.3. It was found that for bottling plant (Pepsi Cola) wastewaters, a steady state with respect to reactor biological solids and effluent COD, at different dilution rates, could be attained, lending experimental evidence to the assumption that a steady state could be reached in developing the model and also affecting the applicability of the model in industrial organic wastewater. The reactor biological solids and effluent COD calculated from the model closely agreed with the observed values at dilution rates lower than 0.5 hr-1. Operation at dilution rates higher than 0.5 hr-1 will washout the biological solids from the reactor and the recycle substrate concentration will be apparent if the concentration of XR were not increased.     

A multidimensional birth process and its application to some problems in the dynamics of biological populations

This paper is a sequel to a paper by the author entitled “Restricted Transition Probabilities and Their Applications to Some Problems in the Dynamics of Biological Populations” (Bull. Math. Biophysics, 1966,28, 315–331). The paper is divided into two parts. In part one some aspects of the maximum size attained by the population during a finite time interval are studied for the case the stochastic process underlying the evolution of the population is a birth process. Two interesting by-products emerge from the study presented in part one; namely a combinatorial method of finding solutions to the Kolmogorov differential equations in special cases, and secondly, a set of criteria for the optimum allocation of genotypes in the host population of a host-pathogen system. The optimum allocation of genotypes in the host population is a problem of practical importance in controlling plant pathogens. In part two the theory of restricted transition probabilities developed in the companion paper is applied in finding the distribution of the time to the appearance of the first mutation for the case of a two dimensional birth process. The distribution of the time to the appearance of the first mutation is of importance in understanding the role mutation plays in the evolution of a population, particularly in the pathogen population of a host-pathogen system. The research reported in this paper was supported by the United States Atomic Energy Commission, Division of Biology and Medicine Project AT(45-1)-1729.     

Biomimetic-dye affinity adsorbents for enzyme purification: application to the one-step purification of Candida boidinii formate dehydrogenase

Formate dehydrogenase (FDH, EC 1.2.1.2) was purified from Candida boidinii cells in a single step by biomimetic-dye affinity chromatography. For this purpose, seven' biomimetic analogues of the monochlorotriazine dye, Cibacron(R) Blue 3GA (CB3GA), and parent dichloro-triazine dye, Vilmafix((R)) Blue A-R (VBAR), bearing a car-boxylated structure as their terminal biomimetic moiety, were immobilized on crosslinked agarose gel, Ultrogel((R)) A6R. The corresponding new biomimetic-dye adsorbents, along with nonbiomimetic adsorbents bearing CB3GA and VBAR, were evaluated for their ability to purify FDH from extracts obtained after press-disintegration of C. boidinii cells. Optimal conditions for maximizing specific activity of FDH in starting extracts (1.8 U/mg) were realized when cell growth was performed on 4% methanol, and press disintegration proceeded in four consecutive passages before the homogenate was left to stand for 1 h (4 degrees C). When compared to nonbiomimetic adsorbents, biomimetic adsorbents exhibited higher purifying ability. Furthermore, one immobilized biomimetic dye, bearing as its terminal biomimetic moiety mercap-topyruvic acid linked on the chlorotriazine ring (BM6), displayed the highest purifying ability. Adsorption equilibrium data which were obtained for the BM6 adsorbent in a batch system corresponded well to the Langmuir isotherm and, in addition, breakthrough curves were taken for protein and FDH adsorption in a fixed bed of BM6 adsorbent. The dissociation constant ( K(D)) of the complex between immobilized BM6 and FDH was found to equal 0.05 muM. Adsorbent BM6 was employed in the purification of FDH from a 18-L culture of C. boidinii in a single step (60% overall yield of FDH). The purified FDH afforded a single-band on sodium dodecyl sulphate poly-acrylamide gel electrophoresis, and a specific activity of 7,0 U/mg (30 degrees C). (c) 1995 John Wiley & Sons, Inc.     

A non-structured pseudo-homogeneous model for the activated sludge process

The conventional activated sludge process has been in use for many years for treating wastewater. In this paper a non-structured pseudo-homogeneous model was developed to describe the process. Volume changes as well as the external resistance between the forming flocs and substrate were considered in the model. The kinetic model together with the values of parameters were obtained from the literature. A retention time of 12 hr was found to give over 95% removal of the substrate from the wastewater. Floc diameter, retention time, fraction of biomass recycled, substrate and biomass feed concentration were found to be important factors in the overall efficiency of the treatment process.