Activated Sludge Microorganisms Research Articles

The Aspect of Energetic Uncoupling of Microbial Growth in the Activated Sludge Process - OSA System

A practical application of the concept of uncoupling between catabolism and anabolism during microbial metabolism has been studied in the case of a modified activated sludge system, called OSA (Oxic-Settling-Anaerobic). The OSA system consisted of an oxic completely mixed tank, followed by a settling tank and an anaerobic tank, situated in the returned sludge circuit of the OSA system. The periodic passageway of facultative aerobic activated sludge microorganisms through the anaerobic zone created conditions of uncoupled growth, indicated by ATP stock depletion and resulted in a consecutive reduction of activated sludge production.

The case of both energetic uncoupling and metabolic selection of microorganisms in the OSA activated sludge system

Abstract A modified activated sludge system with anaerobic treatment of returned sludge, named OSA (Oxic‐Settling‐Anaerobic) was studied. The main objective of the research was to create conditions of a physiological stress on microbial growth, resulting in uncoupling of catabolic processes from anabolic ones. This phenomenon, largely described in the literature, is accompanied by energy wastage resulting in biomass yield reduction. The experimental results obtained with a mixed culture (activated sludge) fed on synthetic substrate showed that the anaerobic conditions exerted a kind of selection pressure on microbial metabolism of the activated sludge microorganisms, resulting in metabolic selection of the species being able to favour catabolic pathways. These bacteria, capable of storing polyphosphates under oxic conditions and using them as energy reserves under anaerobic conditions are called poly‐P bacteria. The OSA mixed culture contained about 50 to 60% of these poly‐P bacteria. It has been concluded that the insertion of an anaerobic zone into the returned sludge circuit changed both composition and behaviour of activated sludge microorganisms. The typical phenomena observed in the OSA system were enhanced phosphate removal, reduction of the excess activated sludge production and the suppression of activated sludge filamentous bulking.

Generalists or specialists in activated sludge microorganisms community

The balanced growth model of the bacterial cell was applied to a theoretical description of microorganism community formation in activated sludge treatment. Computer calculations of the model have shown that under the large organic loading the bacterial generalist is displaced by the bacterial specialists from the microorganisms community of activated sludge. Only under the low organic loading can the bacterial generalist settle in an activated sludge composition. Some experimental evidence of such effect is discussed.

Synchronized division of activated sludge microorganisms

Two laboratory continuous activated sludge units were run. One unit was an OSA system with anaerobic stabilization of returned sludge and the other a conventional activated sludge (CAS) system, operated as a control unit. Excess biomass from both systems was used as inoculum for batch experiments in order to study the kinetic behaviour of microorganisms originally grown in oxic-anaerobic conditions. All experiments were carried out with synthetic wastewater. Biomass growth, substrate removal, oxygen uptake and carbon dioxide production were measured using a quadrupole mass spectrometer (Inficon IQ 200) coupled to a 15-1. fermentor (Biolafitte). The results showed that at initial S 0/X 0 ratios higher than 2, cell division occurred, which was demonstrated by an acceleration of substrate removal and biomass growth rates. This division was synchronized (simultaneously occurring cell multiplication) in the case of activated sludge from the OSA unit. The synchronization was induced by periodical exposure of the microorganisms to unfavourable conditions of growth due to starvation under anaerobic conditions. The primary aim of this paper is to point out the existence of synchronized cell division in certain laboratory activated sludge systems and to determine the conditions under which this phenomenon can occur.

Preparation of new support for immobilization of activated sludges

A new support was prepared by the combination of an oxygen enrichment hollow fiber membrane and fibrous support for immobilization of activated sludge microorganisms. A biofilm of activated sludges immobilized and grown on the support were shown to be highly active. It was confirmed that a wastewater treatment method using this new support was efficient for TOC and TN removal.

Biodegradation of 2,4-dichlorophenol by activated sludge microorganisms

Experiments with the degradation of 2,4-dichlorophenol (2,4-DCP) were carried out in completely-mixed systems at constant volumetric loading ( B v) and variable solids retention time (SRT). A mixed substrate consisted of 2,4-DCP (20% of total COD) and methanol (MA, 80% of total COD). The maximum specific rate of 2,4-DCP removal, q max, related to the total biomass in the cultivation system, increased with the decreasing SRT from 0.0118 h −1 at the SRT of 10.8 d up to 0.0783 h −1 at the SRT of 0.6 d. The following values of kinetic constants of microorganisms responsible for the degradation of 2,4-DCP were found (20°C and pH = 7.5): Y COD = 0.37, K s,COD = 0.6 mgl −1, q max = 0.233 h −1, b = 0.036 h −1, μ max = 0.086 h −1 and π x,cr = 0.83 d.

Determination of kinetic constants of activated sludge microorganisms responsible for degradation of xenobiotics

Experiments with the degradation of morpholine (MO), sulphanilic acid (SA), nitrilotriacetic acid (NTA) and methanol (MA) were carried out in completely-mixed systems at constant volumetric loading ( B v) and variable solids retention time (SRT). In the first series, a mixed substrate composed of the above compounds was used (each compound formed 25% of the total COD), in the second, each of the above compounds was used as a sole source of organic carbon and energy. Respirometric studies were carried out with excess biomass in order to determine the following kinetic parameters: yield coefficient ( Y), half-velocity coefficient ( K s), maximum volumetric removal rate ( q v,max) and maximum specific removal rate ( q max). It has been found that both q v,max and q max depend on the SRT of a mixed culture. A method of determining the critical solids retention time, π x,cr, at which q v,max = B v, was developed. The values of π x,cr found were 2.4, 1.5 and 0.62 d in the first series for SA, NTA and MA, respectively, and 3.8, 3.6, 1.3 and 0.52 d in the second series for MO, SA, NTA and MA, respectively. Below π x,cr, there is q v,max < B v, and a tested compound behaves as only partially degradable or nondegradable. Above π x,cr, there is q v,max B v and a system has the potential capability for shock loading treatment. At the minimum solids retention time, π x,min, all microorganisms responsible for the degradation of a given compound are washed out from the cultivation system. The developed method makes it also possible to determine q max, μ max and the decay coefficient, b, of the microorganisms in a mixed culture responsible for the degradation of xenobiotics. The results indicate that the microorganisms responsible for the degradation of the xenobiotics are slow-growing. A kinetic equation based on q v,max and K s was derived and shown to predict well effluent concentrations of the tested compounds at all SRT. None of the tested compounds supported filamentous bulking in completely-mixed reactors under the technological parameters used.

Treatment of Cr(VI)-containing wastewater by addition of powdered activated carbon to the activated sludge process

The effect of powdered activated carbon (PAC) on the removal of hexavalent chromium [Cr(VI)] and chemical oxygen demand (COD) and on oxygen uptake rate (OUR) by activated sludge microorganisms was investigated in batch and continuous flow reactors. The initial adsorption rate of Cr(VI) by PAC was greater than that by activated sludge flocs, and the equilibrium data could be described well by the Freundlich isotherm equation. The addition of PAC was an effective method to allow continuous operation of the biological process in the presence of Cr(VI) and increases in oxygen uptake rate as well as Cr(VI) and COD removal efficiencies were evident. The average COD and Cr(VI) removal efficiencies with PAC addition were 96 and 41%, respectively, while those without PAC addition were 85 and 9%, respectively. The kinetic constants of biological oxidation were determined on the two laboratory scale activated sludge units, one with PAC addition and the other without PAC addition, fed with synthetic wastewater containing Cr(VI). The addition of PAC to the aeration basin increased overall microorganism growth rate and biological removal rate of the substrate.

Growth inhibition of activated sludge microorganisms by chlorophenols and structure-activity relationships and its relation with microbial degradation.

The growth inhibition test method was studied for the hazard evaluation of chemicals to microorganisms which play an important role in an aquatic ecosystem. As a source of microorganisms, standard activated sludge which is distributed from Chemical Inspection and Testing Institute, in Tokyo was used and the degree of growth was measured by a turbidity. On eleven chlorophenols tested, 24 h-EC50 values were correlated with 3 physico-chemical parameters, i.e., n-octanol/water partition coefficient (log Pow), dissociation constant (pKa) and Hammett constant (Σσ). Though the toxicity increases from monochlorophenols to trichlorophenol except for chlorophenols substituted at 2, 6-positions, 2, 3, 4, 6-tetra-and penta-chlorophenol were less toxic than 2, 3-, 3, 5-dichloro-and 2, 3, 4-trichlorophenol. Quantitative structure-activity relationship (QSAR) studies show that partition coefficient, a parameter of lipophilicity, gives the best correlation with 24 h-EC50 values by using square of log Pow. Among the isomers of chlorophenols having the same numbers of chlorine atom, ortho isomer appears to be less toxic than meta and para isomers. With regard to several chlorophenols, 24 h-EC50 values were determined by the respiration inhibition method and ATP measurement method, and compared with 24 h-EC50 values by the growth inhibition method shown above. It is suggested that the respiration inhibition method is less sensitive than the growth inhibition method. Furthermore, a relation ship between toxicity and biodegradability was studied by the performance of microbial degradation test at low concentration where the test chemical did not inhibit the growth of microorganismsand it is suggested a few chlorophenols which are persistent at concentration of 100 mg/l can be degraded at a level of 10 mg/l.

Flow and oxygen transfer in a plunging water jet system using inclined short nozzles and performance characteristics of its system in aerobic treatment of wastewater

For the plunging water jet system using inclined short nozzles, the flow characteristics such as the bubble penetration depth and the gas entrainment rate, which changed depending on the jet velocity, the nozzle diameter, the jet length, and the jet angle were first evaluated in an air-water system. A comparable investigation between our results and those of existing studies used the long nozzles on those characteristics revealed that both the bubble penetration depth and the gas entrainment rate differed depending on the nozzle length; that is, the nozzle-length-to-diameter ratio L(N)/D(N) and that of these characteristics the gas entrainment rate affected considerably by its magnitude and tended to be high when the nozzle of a large L(N)/D(N) ratio was used. It was also confirmed from the oxygen transfer experiments that the transfer efficiency at low jet velocities in the present water jet system was not inferior to the ones of other types of existing aeration systems; that is, the utilization of this jet aeration system to a high rate reactor for wastewater treatment or fermentation was sufficiently possible. The applicability of the plunging jet aeration method to microbial processes was then examined. As a typical example of microbial processes to be tested, the continuous treatment of an organic wastewater using activated sludge microorganisms was carried out, and the performance and related problem when this type of aeration system was applied to such a microbial process were investigated. Experimental results showed that, when viewed from the removal ability of dissolved organic matters, the plunging jet aeration system was capable of treating a wastewater of considerable high loading without the rate of oxygen transfer becoming the biooxydation-rate-limiting factor. Special attention was necessary for the choice of the liquid pump to be employed, however, due to the increased amount of fine suspended solids in the treated water caused by the shearing action between sludge flocks and pump blades.

Inhibition of respiration of activated sludge: Variability and reproducibility of results

AbstractAssessment of the toxicity of chemicals to the respiration of activated sludge microorganisms is a relatively simple and reproducible method when applied to a standard population of bacteria. However, activated sludge is, by nature, a variable commodity, and varying results are often reported. Within‐plant variations can occur from day to day as a result of shifts in the bacterial population, probably caused by changes in the strength of components of the sewage feed. Between‐plant variations can be considerably greater. Factors such as differing operating conditions and presence of industrial waste waters in the sewage can result in differing species composition of the sludge, which, in turn, may account for differing biooxidation rates of components of the waste water and thus different respiration rates. Sludge from different sources, and/or grown under different conditions, may also vary in response to inhibitors, because of varying degrees of reaction of some inhibitors with non‐living sludge components. Therefore, in practice, it has been usual to consider EC50 values from the inhibition of respiration of activated sludge test in terms of order of magnitude. Variations in EC50 results of the ‘ISO’ inhibition of respiration test have been quantified for a number of chemicals, both within and between batches of sludge, and with sludges from different sources. The coefficient of variation of EC50 results within batches of sludge was found to be approximately 9%. Between batch and between source variations were 28–76% depending on the test chemical.

Microbial polymers in the aquatic environment—I: Production by activated sludge microorganisms under different conditions

Soluble waste products of activated sludge microorganisms were prepared under different conditions. After being concentrated by vacuum distillation, the polymers with molecular weights above 10,000 were isolated by dialysis and lyophilization. The lyophilisates, the COD of which amounted to 36–62% of the total COD in the original liquid samples, were hydrolysed with HCl under various conditions. All isolated polymers contained sugars, amino sugars, uronic acids and amino acids, which indicates their heteropolysaccharidic character. They were formed both during growth and during the starvation and decomposition of microorganisms. Biodegradability tests confirmed that the polymers are refractory with the BOD rate constant of 0.03-0.04d −1. The possible reasons for their production are discussed.

Determination of Kinetic Constants of Activated Sludge Microorganisms

A respirometric method for measuring kinetic constants of activated sludge microorganisms by means of a simple respirometer was developed and tested by using two types of mixed culture. It has been found that both the maximum substrate removal rate and the half-velocity coefficient are basically lower with the mixed cultures cultivated in a completely-mixed reactor /filamentous/ than with those cultivated in a selector-type reactor /nonfilamentous/.

Quantitative estimation in cod units of refractory organic compounds produced by activated sludge microorganisms

Data on the amounts of refractory organic compounds produced by activated sludge microorganisms under various conditions of cultivation were collected and treated in order to find the main factors influencing their production. The following systems were compared: batch non-proliferating and proliferating, continuous with high and low mean cell residence time and semicontinuous with separate aerobic sludge stabilization. It has been found that there exists a linear relationship between the refractory microbial products and the initial substrate concentration, both expressed in COD units. Both the slope and intercept of the relationship depend on the mean cell residence time or the observed specific growth rate. Depending on the cultivation conditions, the refractory products can amount to 1–10% of the substrate consumed. It has also been found that the amount of refractory compounds, expressed in COD units, released from 1 g of aerobically decomposed biomass varies from 15 to 25 mg g −1.

Inhibitory effect of refractory organic compounds produced by activated sludge micro-organisms on microbial activity and flocculation

Semicontinuous cultivation of activated sludge micro-organisms was carried out in such a way that all microbial waste products were accumulated in a cultivation medium. It has been found that the microbial waste products in higher concentrations adversely affect the kinetic activity and the flocculating and settling properties of activated sludge micro-organisms. The waste products had the following distribution of molecular weights: 39% below 700, 16% 700–10,000, 35% 10,000–50,000 and 10% above 50,000. Approximately 33% of the fraction with molecular weights above 10,000 were saccharidic polymers.

The effect of acclimatisation on the toxicity of chemicals to activated sludge microorganisms

Legislation controlling the use of new chemicals and concern for environmental protection have resulted in a surge of interest in tests for toxicity to bacteria. Currently used tests for inhibition of respiration, nitrification and growth of sewage bacteria are normally short-term and deliberately use unacclimatised microorganisms. This ‘failsafe’ design is open to criticism, in that safety margins are normally high, taking no account of acclimatisation which may reduce toxicity for continuously discharged chemicals. To investigate the possibility of acclimatisation, activated sludges have been exposed to six organic chemicals for 3 months. Their toxicity (EC 50) was assessed before and after exposure. Results identified only one acclimatised sludge (for pentachlorophenate), although more tolerant bacterial species could also be isolated from the sludges exposed to cetyl trimethyl ammonium bromide and p- benzoquinone. The acclimatisation procedure used generally was not successful in promoting selection of resistant species.

Influence of accumulation capacity of activated sludge microorganisms on kinetics of glucose removal

The kinetics of COD removal in nonproliferating glucose-acclimated activated sludge systems was studied. A general differential equation describing this process involves a rate constant for COD removal due to storing processes (zero order), a rate constant for COD removal due to accumulation processes (first order), and an apparent volumetric accumulation capacity. In their dependence on values of these constants, the courses of COD removal can be linear, nonlinear or combined. The rate constant of accumulation capacity (AC) saturation was found to be independent on the initial concentration of biomass and dependent on the type of cultivation or on the composition of a mixed culture. It varied from 1.8 to 2.6 h −1 with activated sludge cultivated semicontinuously (nonfilamentous) and from 0.8 to 1.0 h −1 with activated sludge cultivated continuously in a completely mixed unit (highly filamentous). It was found that activated sludge microorganisms cultivated semicontinuously possessed an apparent specific AC as high as 600–750 mg g −1, whereas those cultivated continuously in a completely mixed unit had their AC s totally saturated. After a 6-h period of aeration (regeneration) without the presence of an exogenous substrate, the latter microorganisms possessed an apparent specific AC of 174 mg g −1.

Chemico-biological interactions in biological purification system. I. Growth inhibition effect of azo compounds on activated sludge microorganisms.

There are enormous discharge of synthetic organic compounds into the environment by industrial production. These compounds give large influences not only in natural ecosystem but directly in humanlife and industrial production itself. Then it is important for maintenance and development of production to clarify those behaviors in the environment and to reduce those discharge into the environment.

Activated sludge degradation of adipic acid esters.

The biodegradability of three aliphatic adipic acid diesters and a 1,3-butylene glycol adipic acid polyester was determined in acclimated, activated sludge systems. Rapid primary biodegradation from 67 to 99+% was observed at 3- and 13-mg/liter feed levels for di-n-hexyl adipate, di(2-ethylhexyl) adipate, and di(heptyl, nonyl) adipate in 24 h. When acclimated, activated sludge microorganisms were employed as the seed for two carbon dioxide evolution procedures, greater than 75% of the theoretical carbon dioxide was evolved for the three diesters and the polyester in a 35-day test period. The essentially complete biodegradation observed in these studies suggests that these esters would not persist when exposed to similar mixed microbial populations in the environment.