Activated Sludge Mixed Liquor Research Articles

Measurement and modelling of ordinary heterotrophic organism active biomass concentrations in anoxic/aerobic activated sludge mixed liquor

Ordinary heterotrophic organism (OHO) active biomass (ZBH) is a key parameter in models for activated sludge systems, which defines quantitatively the kinetic rates of relevant processes. However, ZBH has not been measured directly with consistent success: a simple respirometric batch test has provided varying correspondence between measured and theoretical concentrations. In this paper, the batch test is applied to mixed liquors drawn from well defined anoxic/aerobic parent systems at 10 and 20 d sludge ages, with consistent but poor correspondence between measured and theoretical values. In contrast, aerobic digestion batch tests on the same mixed liquors give good correspondences. It is concluded that the differences between theoretical and batch test measured values are due to the batch test method itself and its interpretation. It is found that the batch test conditions (particularly the substrate/ZBH ratio) influence the kinetic constants derived from the data, and hence the ZBH estimate. Two kinetic models with two competing OHO populations, a fast and a slow grower, are developed and applied to the batch tests and parent systems. The first model is based on kinetic selection only, while the second includes additional metabolic selection. Both models can account for the observations in the batch tests, but the second provides greater consistency between simulations of the parent systems and batch tests.

In situ bioaugmentation of nitrification in the regeneration zone: practical application and experiences at full-scale plants

Nitrification is the rate-limiting process in the design of activated sludge process. It is especially unstable during the winter season (when the temperature of activated sludge mixed liquor drops below 13 degrees C). It is therefore difficult to meet the ammonia effluent standards in winter. The common way to compensate for low nitrification rates at low temperatures is to increase sludge retention time (SRT). However, the increase of SRT is accompanied by negative factors such as elevated sludge concentration, higher sludge loading of secondary clarifiers, formation of unsettleable microflocs, etc. The low performance of nitrification at low temperatures can also be compensated for by enhancing the nitrification population in activated sludge. This paper describes such a method called bioaugmentation of nitrification in situ. This procedure takes place in a so-called regeneration tank, which is situated in the return activated sludge stream. The results of the operation of two wastewater treatment plants with regeneration zones are described in this paper, together with some economic evaluation of the bioaugmentation method.

Molecular characterization of microbial communities in Canadian pulp and paper activated sludge and quantification of a novelThiothrix eikelboomii-like bulking filament

We examined the microbial community structure and quantified the levels of the filamentous bulking organism Thiothrix eikelboomii in samples of activated sludge mixed liquor suspended solids (MLSS) from Canadian pulp and paper mills. Libraries of chaperonin 60 (cpn60) gene sequences were prepared from MLSS total microbial community DNA and each was compared with cpnDB, a reference database of cpn60 sequences (http://cpndb.cbr.nrc.ca) for assignment of taxonomic identities. Sequences similar to but distinct from the type strain of T. eikelboomii AP3 (ATCC 49788T) (approximately 89% identity over 555 bp) were recovered at high frequency from a mill sample that was experiencing bulking problems at the time of sample collection, which corresponded to microscopic observations using fluorescent in situ hybridization with commercially available 16S rDNA-based probes. We enumerated this strain in five mill-derived MLSS samples using real-time quantitative PCR (qPCR) and found that two samples had high levels of the bulking strain (>1012 genomes/g MLSS) and two contained lower but detectable levels of this organism. None of the mill samples contained cpn60 sequences that were identical to the type strain of T. eikelboomii. This technique shows promise for monitoring pulp and paper mill wastewater treatment systems by detecting and enumerating this strain of T. eikelboomii, which may be specific to pulp and paper mill wastewater treatment systems.

Biological Phosphate Uptake and Release: Effect of pH and Magnesium Ions

Enhanced biological phosphorus removal (EBPR) is based on poly-phosphate accumulating organisms' (PAOs) unique features of "luxury" phosphate uptake during aerobic conditions and phosphate release in anaerobic conditions. It is believed that poly-phosphate accumulation is accompanied by the uptake and accumulation of potassium ions (K+) and magnesium ions (Mg2+). The release of phosphate under anaerobic conditions is also accompanied by the release of both cations. The objective of this research was to evaluate the effect of pH and Mg2+ on the biological phosphate uptake and release behavior of activated sludge mixed liquor during aeration and sedimentation. Research results indicate that Mg2+, supplied either by magnesium chloride (MgCl2) or magnesium hydroxide [Mg(OH)2], stimulated phosphate uptake during the aeration period, while pH increase, caused by the application of Mg(OH)2, enhanced phosphate release during the sedimentation period. It is also noted in our experiments with MgCl2 that Mg2+ slightly inhibited anaerobic phosphate release.

활성슬러지 혼합미생물과 Nocardia asteroides에 의한 페놀화합물 분해시 양성자이온의 영향

This study was investigated to evaluate the effect of the sodium ion and pH on toxicity of dinitrophenol at high concentrations (0.41 to 0.54 mM), over a sodium concentration range of 0.1 mM to 107 mM and over a pH range of 5 to 9. The concentration of sodium ions in the activated sludge mixed liquor seemed to have very little effect on dinitrophenol toxicity. However, lack of sodium in the growth media resulted in a reduction of the dinitrophenol degradation rate by bacterial isolate from the activated sludge culture, which has been identified as Nocardia asteroides. Dinitrophenol inhibition was found to be strongly dependent on mixed liquor pH. The dinitrophenol degradation rate was highest in the pH range of 6.95 to 7.84; at pH 5.94 degradation of 75 mg/L dinitrophenol was significantly inhibited; at pH < 5.77, dinitrophenol degradation was completely inhibited after approximately 30% of the dinitrophenol was degraded.

A toxicity testing protocol using a bioluminescent reporter bacterium from activated sludge

A protocol for production, storage, and use of Shock 1 (Shk1) bioreporter cells for toxicity monitoring in wastewater treatment facilities was developed. Shk1 is a bioluminescent toxicity bioreporter for activated sludge previously constructed by the incorporation of lux genes into an activated sludge microorganism. A number of factors affecting Shk1 growth and bioluminescence were examined including the growth medium, tetracycline concentration, storage conditions, and test media. Based on the results of these experiments, a toxicity testing protocol was developed that involved growth of cultures in nutrient broth with tetracycline, storage of cultures at 4 °C, cell activation by reinoculation into nutrient broth, and toxicity testing by cell injection into the test media. Effective use of this approach required standardized time intervals for cell growth, storage, activation and exposure in the test media. Bioluminescence from Shk1 cells was measured in nutrient broth and influent wastewater and activated sludge mixed liquor from a municipal wastewater treatment plant. Using the Shk1 toxicity testing protocol, Zn EC 50 values for bioluminescence in nutrient broth, influent wastewater, and activated sludge mixed liquor were approximately 42, 7, and 32 mg/l, respectively. Zn concentrations as low as 1 mg/l could be detected in influent wastewater. The detection limit in influent wastewater is below the Zn concentrations typically reported to affect the activated sludge process.

Incorporation of inorganic material in anoxic/aerobic-activated sludge system mixed liquor

In the bioreactor of the nitrification denitrification (ND)-activated sludge system, the mixed liquor is made up of organic and inorganic materials. In the current design procedures and simulation models, the influent wastewater characteristics and biological processes that influence the bioreactor mixed liquor organic solids (as volatile suspended solids, VSS, or COD) are explicitly included. However, the mixed liquor total suspended solids (TSS, i.e. organic+inorganic solids) are calculated simply from empirical ratios of VSS/TSS. The TSS concentration is fundamental in the design of secondary settling tanks and waste activated sludge disposal. Clearly, the empirical approach to obtaining an estimate for TSS is not satisfactory within the framework of a fundamentally based model. Accordingly, the incorporation of the inorganic material present in the influent wastewater into ND-activated sludge system mixed liquor was investigated. From an experimental investigation into the distribution of inorganics in the influent, mixed liquor and effluent of a laboratory-scale ND-activated sludge system, it was concluded inter alia that (i) of the total inorganic solids in the influent, only a small fraction (2.8–7.5%) is incorporated into the mixed liquor, (ii) most of the inorganics in the influent (mean 88%) and effluent (mean 98.5%) are in the dissolved form, the balance being particulate, and (iii) the influent and effluent inorganic dissolved solids concentrations are closely equal (mean effluent to influent ratio 100%). Further, a number of models were developed to quantify the mixed liquor inorganic, and, hence, total solids. From an evaluation of these models against the experimental data, it would appear that the best approach to model the incorporation of inorganics into the activated sludge mixed liquor is to follow the concepts and principles used to develop the existing models for organic materials. With this approach, reasonably close correlation between predicted and measured data for mixed liquor and effluent inorganic concentrations were obtained.

Active biomass in activated sludge mixed liquor

The engineering and technology of the activated sludge system are reasonably well established, with systems implemented worldwide for the biological removal of C, N and/or P. Parallel to this development, significant advances have been made in the microbiological and biochemical areas of activated sludge. These advances have been driven by the development of new analytical techniques that allow microorganisms to be studied in situ in the activated sludge environment. However, there has been little cross-linking and overlap between the engineering and technology and microbiology and biochemistry paradigms. In particular, the information from the microbiology and biochemistry has not been integrated into the engineering and technology paradigm, to enable improved system design and optimization. One area that can form a starting point to build bridges between the two paradigm sets, is measurement of active biomass. The current design and simulation models invariably include active biomass for each organism group as fundamental parameters which define quantitatively the kinetic rates of the relevant biological processes. However, these parameters remain purely hypothetical because to date they have not been quantitatively measured; their acceptance is based on the consistency of model predicted results over a wide range of application. This paper describes developments in quantitative measurement of the heterotrophic and autotrophic active biomass concentrations within the engineering and technology paradigm, and the formulation of a multinational project which will attempt to link these measurements and the defined engineering environment to the new microbiological and biochemical analytical techniques. It is hoped that this project will facilitate integration of the two paradigms sets.

Powdered activated carbon‐assisted biotreatment of a chemical synthesis wastewater

AbstractThe effect of powdered activated carbon (PAC) on the biotreatment of an industrial wastewater taken from a chemical plant synthesising drugs for the pharmaceutical sector was studied. Industrial and domestic wastewaters were combined at laboratory scale and the effect of PAC addition was tested in aerobic reactors. The aim of this addition was to decrease inhibitory and non‐biodegradable organics. Two different procedures were applied in testing the effectiveness of PAC. First, PAC was directly added to activated sludge mixed liquor. In the second case, industrial wastewater was first contacted with PAC and then treated biologically. In the evaluation of performance, COD measurements, oxygen uptake rate (OUR) measurements and measurements in the ultraviolet‐visible (UV‐Vis) spectra were taken into consideration. Both direct PAC addition and PAC pretreatment led finally to similar results. In both cases, the concentration of non‐biodegradable matter could be lowered. In particular, the colour of the wastewater was significantly reduced. Direct PAC addition appeared to be more practical and plausible. In any case, PAC addition to activated sludge increased the OUR of the sludge, indicating that inhibition could be decreased. The study also pointed out that in the assessment of PAC performance, the combined evaluation of OUR, spectral parameters and COD would be much more informative than the COD parameter alone.© 2001 Society of Chemical Industry

Formation of density currents in secondary clarifier

Density currents exist in most activated sludge secondary clarifiers, but the causes are controversial. The purpose of this study was investigation of the internal flow regimes to identify and evaluate the principal causes of density currents in secondary clarifiers. This study was part of a project focused on controlling the impact of density currents on the performance of activated sludge secondary clarifiers. A 1:25 scale model of a conceptualized prototype rectangular clarifier was used and was operated by the Froude model law. Experiments were conducted in the laboratory with tap water and in the field with activated sludge mixed liquor. Two inlet baffle, intermediate baffle and effluent weir configurations and three sludge draw-off configurations were used in the experiments. In all cases, one-half of the influent flow was removed through the sludge draw-off ports located in the tank bottom. In each experiment, velocity pattern observations and temperature measurements were made throughout the tank. Observed flow patterns were very similar in the laboratory experiments with tap water and the field experiments with mixed liquor. Temperature-driven density currents formed quickly under all inlet baffle and outlet configurations and were extremely stable. Depth of the density currents was inversely related to the difference between temperatures of the influent and tank contents. A temperature difference as small as 0.2°C resulted in formation of density currents. Moreover, the formation of a density current in the tank was independent of the amount of suspended solids in the entering suspension. Temperature appears to be the primary cause of density currents in secondary clarifiers and the type of density current, surface or bottom, will depend on whether the influent is warmer or cooler than the tank contents. In the field, due to the difference between the air and influent mixed liquor temperature, the formation of density currents in secondary clarifiers appears to be inevitable and little affected by the presence or type of inlet or intermediate baffles.

Effect of Activated Sludge Process and Sludge Storage on Removal of Escherichia coli O157:H7.

An experimental investigation was carried out on removal characteristics of Verotoxin-free Escherichia coli O157: H7 in a batch culture of activated sludge and stored sludge, and then its profiles in a domestic wastewater treatment facility was discussed.Domestic wastewater containing about 104CFU/ml of E. coli O157: H7 was treated by activated sludge (MLSS concentration was about 2, 500 mg/l) at 25°C. E. coli O157: H7 was almost completely removed from the supernatant after 8 hrs, and fecal coliforms and total coliforms were reduced considerably. Although the bacteria in the activated sludge mixed liquor decreased with aeration time, E. coli O157: H7 still survived after 24hrs. E. coli O157: H7 was almost all removed from the stored sludge after 30 days while for fecal coliforms and total coliforms it took up to 150 days for removal.We proposed a case study model for E. coli O157: H7 removal in a middle-scale domestic wastewater treatment facility using the extended aeration process where the bacterial contamination occurs at the level of 104-105CFU/ml. The number of E. coli O157: H7 bacteria declines in the aeration tank during the 24 hr aeration period and is almost completely removed from the resulting biologically treated water. If 0.5% of influent is taken from the sedimentation tank as excess sludge, E. coli O157: H7 survives in this sludge at the level of 102-103CFU/ml. The bacteria in the sedimentary sludge increases by thickening but is almost completely removed during storage over a month.

Factors influencing critical flux in membrane filtration of activated sludge

Membrane filtration of biomass is usually accompanied by significant flux decline due to cake-layer formation and fouling. Crossflow filtration with flux controlled by pumping the permeate can produce stable fluxes if a ‘critical flux’ is not exceeded. Below critical flux the transmembrane pressure is typically very low and increases linearly with imposed flux. Above the critical flux the transmembrane pressure rises rapidly signifying cake-layer formation which is usually accompanied by a continued rise in transmembrane pressure and/or a drop in delivered flux. A range of microfiltration and ultrafiltration membranes with pore sizes from 0.22 to 0.65 µm and molecular weight cut-off of 100 kDa was used. The feed was an activated sludge mixed liquor with concentration in the range of 3–10 g dm−3. The results show that the critical flux depends on feed concentration and crossflow velocity, being higher for higher crossflow velocity or lower feed concentration. Critical flux was also dependent on membrane type, being lower for hydrophobic membranes. Although the transmembrane pressure was higher for the larger pore size membrane, no significant difference in critical flux was observed among different pore size membranes. © 1999 Society of Chemical Industry

Development of a jar testing protocol for chemical phosphorus removal in activated sludge using statistical experimental design

Jar testing is an important tool for the determination of the best chemical dosing regime for a wastewater treatment process. A consistent methodology has been developed for physico-chemico processes such as sedimentation and coagulation. These techniques however, may not be applicable for precipitation processes in a biological system. A jar testing methodology was developed for the chemical removal of phosphorus from activated sludge mixed liquor. In these studies, the optimum conditions for 5 precipitants in activated sludge were determined to compare their relative effectiveness. The precipitants studied were aluminium sulphate, ferrous sulphate, ferric chloride and two aluminium-based polyelectrolyte compounds. Optimisation of this process by a conventional method requires many tests and is time consuming. A 7 factorial design experiment was used firstly to identify the most important variables, followed by a statistical “hill climbing technique” to determine the optimum conditions for a specific chemical precipitant. Using only 20 tests per chemical (not including repeats), good phosphorus removal efficiencies (ranging from 87.8–96.6%) were produced for all of the precipitants.

Acetate Limitation and Nitrite Accumulation during Denitrification

Nitrite accumulated in denitrifying activated sludge mixed liquor when the carbon and electron source, acetate, was limited. If acetate was added to obtain a carbon-to-nitrogen (C:N) ratio in the range of 2:1 to 3:1, nitrate was completely consumed at the same rate with no nitrite accumulation, indicating that nitrate concentration controlled the respiration rate as long as sufficient substrate was present. However, when acetate was reduced to a C:N ratio of 1:1, while nitrate continued to be consumed, >50% of the initial nitrate-nitrogen accumulated as nitrite and 29% persisted as nitrite throughout an endogenous denitrification period of 8–9 h. While nitrite accumulated during acetate-limited denitrification, the specific nitrate reduction rate increased significantly compared with the rate when excess acetate was provided as follows: 0.034 mg-NO3-N/mg-mixed liquid volatile suspended solids/h versus 0.023 mg-NO3-N/mg-mixed liquid volatile suspended solids/h, respectively. This may be explained by nitrat...

Characterization of filamentous foaming in activated sludge systems using oligonucleotide hybridization probes and antibody probes

A quantitative method was developed for estimating Gordona mass in activated sludge foam and mixed liquor samples. The technique involves in situ hybridization with a genus-specific fluorescently labeled oligonucleotide probe calibrated on pure cultures of Gordona. The immunofluorescent technique of Hernandez et al. was modified to allow staining with fluorescently labeled antibody and hybridization probes. The results of this technique were compared to those from membrane hybridization studies using radioactively-labeled oligonucleotide probes. Quantitative membrane hybridizations, in situ hybridizations, and antibody staining resulted in significantly different levels of Gordona in activated sludge foam, activated sludge mixed liquor, return activated sludge, and anaerobic digester sludge. Simultaneous staining with labeled antibodies and oligonucleotide probes provide a definitive identification for Gordona, and represents a new approach for in situ studies of this organism's role in foaming.

A national survey of activated sludge separation problems in the Czech Republic: filaments, floc characteristics and activated sludge metabolic properties

The extent of activated sludge separation problems associated with excessive growth of filamentous microorganisms has increased recently in the Czech Republic. Most of the activated sludge plants in the country were contacted by mail with a questionnaire, the aim of which was to obtain the basic technological data on the plants and on the nature and intensity of activated sludge separation problems. Selected activated sludge plants were visited at different periods of the year and samples of activated sludge mixed liquor and foam were collected for microscopic examination and kinetic batch tests. It was found that good settling properties were associated more with good quality activated sludge flocs than with the absence of filaments. On the other hand, a very high abundance of filaments always resulted in bulking or foaming. The most common filamentous microorganisms in activated sludge mixed liquors were M. parvicella, N. limicola and Types 0092, 0041 and 0803 while the foams were mostly dominated by M. parvicella, NALOs (GALOs) and N. limicola. Seasonal shifts in filamentous population diversity were also observed. M. parvicella, Type 0092, N. limicola, Type 0803 and Type 0041 were dominant in both conventional and biological nutrient removal activated sludge plants whereas the other Eikelboom's types of filaments dominated mostly in conventional activated sludge plants. The ability of foams to denitrify depended on the dominating filamentous microorganism and type of substrate.

Heterotrophic active biomass component of activated sludge mixed liquor

In the current steady state design and kinetic simulation models for activated sludge systems, the heterotrophic active biomass (XH) is a key parameter. However, this parameter remains hypothetical within the structure of the models; it has not been measured directly, primarily due to the lack of suitable simple experimental techniques. In this paper a simple batch test procedure is used to quantify XH in mixed liquor samples drawn from a well-defined parent anoxic/aerobic activated sludge system operated at sludge ages 12d and 20d. The measured XH concentrations are in close agreement with those calculated theoretically for the parent system at 12d sludge age, but are about 1/2 the theoretical values for the system at 20d sludge age. While the good correspondence at 12d sludge age provides substantive direct evidence supporting both the models and the experimental method, reasons for the poor correspondence at 20d sludge age need to be found.

Characterization of filamentous foaming in activated sludge systems using oligonucleotide hybridization probes and antibody probes

A quantitative method was developed for estimating Gordona mass in activated sludge foam and mixed liquor samples. The technique involves in situ hybridization with a genus-specific fluorescently labeled oligonucleotide probe calibrated on pure cultures of Gordona. The immunofluorescent technique of Hernandez et al. was modified to allow staining with fluorescently labeled antibody and hybridization probes. The results of this technique were compared to those from membrane hybridization studies using radioactively-labeled oligonuelcotide probes. Quantitative membrane hybridizations, in situ hybridizations, and antibody staining resulted in significantly different levels of Gordona in activated sludge foam, activated sludge mixed liquor, return activated sludge, and anaerobic digester sludge. Simultaneous staining with labeled antibodies and oligonucleolide probes provide a definitive identification for Gordona, and represents a new approach for in situ studies of this organism's role to foaming.

A national survey of activated sludge separation problems in The Czech republic: Filaments, floc characteristics and activated sludge metabolic properties

The extent of activated sludge separation problems associated with excessive growth of filamentous microorganisms has increased recently in the Czech Republic. Most of the activated sludge plants in the country were contacted by mail with a questionnaire, the aim of which was to obtain the basic technological data on the plants and on the nature and intensity of activated sludge separation problems. Selected activated sludge plants were visited at different periods of the year and samples of activated sludge mixed liquor and foam were collected for microscopic examination and kinetic batch tests. It was found that good settling properties were associated more with good quality activated sludge flocs than with the absence of filaments. On the other hand, a very high abundance of filaments always resulted in bulking or foaming. The most common tilamentous microorganisms in activated sludge mixed liquors were M. parvicella, N. limicola and Types 0092,0041 and 0803 while the foams were mostly dominated by M. parvicella, NALOs (GALOs) and N. limicola. Seasonal shifts in filamentous population diversity were also observed. M. parvicella, Type 0092, N. limicola, Type 0803 and Type 0041 were dominant in both conventional and biological nutrient removal activated sludge plants whereas the other Eikelboom's types of filaments dominated mostly in conventional activated sludge plants. The ability of foams to denitrify depended on the dominating tilamentous microorganism and type of substrate.

Heterotrophic active biomass component of activated sludge mixed liquor

In the current steady state design and kinetic simulation models for activated sludge systems, the heterotrophic active biomass (XH) is a key parameter. However, this parameter remains hypothetical within the structure of the models; it has not been measured directly, primarily due to the lack of suitable simple experimental techniques. In this paper a simple batch test procedure is used to quantify XH in mixed liquor samples drawn from a well-defined parent anoxic/aerobic activated sludge system operated at sludge ages 12d and 20d. The measured XH concentrations are in close agreement with those calculated theoretically for the parent system at 12d sludge age, but are about 1/2 the theoretical values for the system at 20d sludge age. While the good correspondence at 12d sludge age provides substantive direct evidence supporting both the models and the experimental method, reasons for the poor correspondence at 20d sludge age need to be found.