Activated Sludge Mixed Liquor Research Articles

Biological control of problematic bacterial populations causing foaming in activated sludge wastewater treatment plants-phage therapy and beyond.

The production of a stable foam on the surfaces of reactors is a global operating problem in activated sludge plants. In many cases, these foams are stabilized by hydrophobic members of the Mycolata, a group of Actinobacteria whose outer membranes contain long-chain hydroxylated mycolic acids. There is currently no single strategy which works for all foams. One attractive approach is to use lytic bacteriophages specific for the foam stabilizing Mycolata population. Such phages are present in activated sludge mixed liquor and can be recovered readily from it. However, no phage has been recovered which lyses Gordonia amarae and Gordonia pseudoamarae, probably the most common foaming Mycolata members. Whole genome sequencing revealed that both G. amarae and G. pseudoamarae from plants around the world are particularly well endowed with genes encoding antiviral defence mechanisms. However, both these populations were lysed rapidly by a parasitic nanobacterium isolated from a plant in Australia. This organism, a member of the Saccharibacteria, was also effective against many other Mycolata, thus providing a potential agent for control of foams stabilized by them.

Linking nitrous oxide emissions to population dynamics of nitrifying and denitrifying prokaryotes in four full-scale wastewater treatment plants

Ammonia-oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and N2O-reducing denitrifiers were measured by quantitative real-time PCR (qPCR) in activated sludge samples from four full-scale wastewater treatment plants (WWTPs) in South Spain, and their abundances were linked to the generation of N2O in the samples using multivariate analysis (Non-metric multidimensional scaling, MDS, and BIO-ENV). The average abundances of AOA remained in similar orders of magnitude in all WWTPs (106 copies amoA/L activated sludge mixed liquor), while significant differences were detected for AOB (105-109copies amoA/L) and N2O-reducers (107-1010copies nosZ/L). Average N2O emissions measured in activated sludge samples ranged from 0.10 ± 0.05 to 6.49 ± 8.89 mg N2O-N/h/L activated sludge, and were strongly correlated with increased abundances of AOB and lower counts of N2O-reducers. A significant contribution of AOA to N2O generation was unlikely, since their abundance correlated negatively to N2O emissions. AOB abundance was favoured by higher NO3− and NO2−concentrations in the activated sludge.

Study on decaying characteristics of activated sludge from a circular plug-flow reactor using response surface methodology

Using pH values, temperature, and dissolved oxygen as the influencing factors, a decaying characteristics experiment of activated sludge was carried out by combining the LIVE/DEAD® Baclight technique with the 2,3,5-triphenyl tetrazolium chloride – dehydrogenase activity determination method. Using batch experiments, a response surface methodology was applied in the experimental design to determine the most important influential factor in the decay of activated sludge. The activated sludge mixed liquor for the experiment was generated in a laboratory-scale circular plug-flow reactor, which has already been approved for an invention patent. The analyzed results revealed that the most important influential factor in sludge activity decay is the pH, followed by temperature and then dissolved oxygen. After the decay experiment, 40.94–90.03% of sludge activity decay is caused by reduced cell activity, and the rest is due to cell death.

Comparison of behaviour and fate of tetrabromobisphenol A (TBBPA) in membrane bioreactors and conventional activated sludge process

Research was completed on the behaviour and fate of tetrabromobisphenol A (TBBPA) in pilot-scale membrane bioreactors and conventional activated sludge (CAS) process at the City of Guelph Wastewater Treatment Plant. Emphasis was on the physicochemical processes, biological transformation and sorption kinetics. Measurement of TBBPA at the environmental level can be challenging, so the main focus of this paper was the development of an analytical method for the nano-level determination of TBBPA. The approach used was gas chromatography-negative ion chemical ionization-mass spectrometry in select ion monitoring mode. For the wastewater matrix studied, the developed method had a low method detection level (MDL) of 2.4 ng/L. The matrix effects for influent and activated sludge mixed liquor were determined to be 36.5 ± 5.9% (n = 10) and 79.2 ± 4.5% (n = 10), respectively. Preliminary results show that the CAS system demonstrates better performance for TBBPA removal, with removal at 83%. This was corroborated by the batch experiments that showed that the synergistic effects of biodegradation and biosorption potentially provide more removal of the TBBPA through the activated sludge process.

Can We Treat Hydraulic Fracturing Flowback with a Conventional Biological Process? The Case of Guar Gum

Hydraulic fracturing of unconventional gas wells utilizes large volumes of water-based fluid to increase formation permeability and, as a result, generates large amounts of wastewater as flowback. This water requires suitable treatment before being reused or discharged into the environment. A principal ingredient of flowback water is guar gum (a gelling agent), which may adversely affect advanced flowback water treatment such as membrane separation. This study demonstrates the potential of an activated sludge mixed liquor to degrade guar under typical flowback conditions (i.e., high concentrations of total dissolved solids (TDS)). Guar was efficiently degraded at a TDS concentration of 1500 mg/L, with more than 90% of the dissolved chemical oxygen demand (CODd) having been removed after 10 h. Increasing the TDS concentration to 45000 mg/L inhibited CODd degradation to 60% removal after 31 h. A high TDS concentration additionally resulted in an increased effluent level of total suspended solids and turbidity; however, these were efficiently reduced using ferric chloride coagulation followed by sedimentation and filtration. Biological reduction of the guar concentration increased the flux of a bench-scale ultrafiltration membrane, demonstrating the potential of the process to treat flowback water prior to membrane separation.

Effect of on-line ultrasound on the properties of activated sludge mixed liquor and the controlling of membrane fouling in SMBR

Membrane fouling is one of the major obstacles for further application of submerged membrane bioreactors (SMBRs). In this study, a bi-frequency on-line ultrasound of 25 kHz and 50 kHz was applied to a laboratory-scale SMBR (SMBR-US) to investigate the alleviating of membrane fouling by ultrasound. Experiments were also carried out in another laboratory-scale SMBR without ultrasound (SMBR-Control). The properties of the activated sludge including mixed liquor suspended solids (MLSS), particle size distribution, viscosity, extracellular polymeric substances (EPS) contents and the total organic carbon (TOC) in supernatant were analyzed. The membrane filtration resistance was then calculated to identify the membrane fouling type in two reactors. During the experiment period, the transmembrane pressure of SMBR-Control system increased very fast compared with the SMBR-US system, indicating a significant mitigating of membrane fouling with on-line ultrasound. The MLSS concentration and mean particle size in SMBR-US system was apparently lower than that of SMBR-Control system, which deduced that the ultrasound can reduce extra sludge production and disintegrate activated sludge flocs in reactors. The mixed liquor viscosity in SMBR-US was consistently lower than that of SMBR-Control system. The MLSS and supernatant TOC played a significant role in membrane filtration of SMBR-Control system, while viscosity had an apparent relationship with the filtration resistance in SMBR-US system. The total membrane filtration resistance in SMBR-US was of 51.85% lower than that of SMBR-Control after 35 days operation, which confirms that the ultrasound has a positive effect on mitigating membrane fouling. The membrane filtration resistance caused by blocking cake layers accounted for 86.63% of the total resistance in SMBR-US system, indicating that the blocking cake layer was the main reason for membrane fouling in SMBR-US system. The resistance caused by blocking cake layers and membrane pore blocks were all relatively high in SMBR-Control system, accounting for 59.26 and 38.18% of the total resistance, respectively, suggesting a higher irreversible membrane pollution in SMBR-Control system.

Monitoring Bacterial Diversity in a full-scale Municipal Wastewater Treatment plant in Dubai by Fluorescence in situ hybridization Technique

In this study, the bacterial diversity in the activated sludge system of a full-scale municipal wastewater treatment plant in Dubai was monitored over a period of one year using ribosomal RNA (rRNA) targeted oligonucleotide probes for a defined phylogenetic group of bacteria by the Fluorescence in situ hybridization (FISH) technique. The largest fraction of the bacterial community in the sludge samples belonged to the gamma-subgroup of proteobacteria (25%) followed by gram positive bacteria of high G+C content(16%), gram positive bacteria with low G+C content (9 %), beta-proteobacteria (8%) and alpha-proteobacteria(5 %) with respect to the population percentages stained by DAPI (4,6-diamino-2-phenylindole).A specific nocardioform actinomycete, simultaneously targeted by both HGC69a and MNP1 probes, was predominantly found throughout the study period in all activated sludge mixed liquor samples. The nocardioform actinomycetes group members were detected in both branched and single cell morphotypes. Most of the previously published genus and species specific probes failed to hybridize to the sludge samples. In conclusion, the overall bacterial community populations detected by the sub-group specific 16S rRNA targeted oligonucleotide probes in FISH technique remained almost constant throughout the period of study irrespective of treatment plant conditions.

Monitoring Microbial Diversity of a Full-Scale Municipal Wastewater Treatment Plant in Dubai

In this study, fluorescence in situhybridization (FISH) technique was employedfor monitoring the microbial community in the activated sludge system of a full-scale municipal wastewater treatment plant in Dubai over a period of one year. A total of 96 activated sludge mixed liquor samples were characterized using ribosomal RNA (16S and 23S rRNA) targeted oligonucleotide probes for defined phylogenetic groups of bacteria. Several filamentous and non-filamentous bacteriawere predominantly found throughout the study period in all activated sludge mixed liquor samples. The bacterial species belonging to High G+C group were detected in both branched and single cell morphotypes. The previously published genus and species specific probes detected several of members belonging to archaea, sulphate reducing bacteria, ammonia-oxidizing bacteria, nitrobacter, nitrospira including halophilic and halotolerantnitrosomonasspp.In conclusion, the overall microbial community populations detected by the sub-group and species specific 16S and 23S rRNA targeted oligonucleotide probes found to be quite diverse and varied seasonally.

Fate and effect of naphthenic acids on oil refinery activated sludge wastewater treatment systems

Naphthenic acids (NAs) are a complex group of alkyl-substituted acyclic, monocyclic and polycyclic carboxylic acids present in oil sands process waters, crude oil, refinery wastewater and petroleum products. Crude oil, desalter brine, influent, activated sludge mixed liquor and effluent refinery samples were received from six United States refineries. The total acid number (TAN) of the six crudes tested ranged from 0.12 to 1.5 mg KOH/g crude oil and correlated to the total NA concentration in the crudes. The total NA concentration in the desalter brine, influent, activated sludge mixed liquor and effluent samples ranged from 4.2 to 40.4, 4.5 to 16.6, 9.6 to 140.3 and 2.8 to 11.6 mg NA/L, respectively. The NAs in all wastewater streams accounted for less than 16% of the total COD, indicating that many other organic compounds are present and that NAs are a minor component in refinery wastewaters. Susceptibility tests showed that none of the activated sludge heterotrophic microcosms was completely inhibited by NAs up to 400 mg/L. Growth inhibition ranging from 10 to 59% was observed in all microcosms at and above 100 mg NA/L. NAs chronically-sorbed to activated sludge mixed liquor biomass and powdered activated carbon (PAC) were recalcitrant and persistent. More than 80% of the total NAs remained in the solid phase at the end of the 10-day desorption period (five successive desorption steps). Throughout a 90-day incubation period, the total NA concentration decreased by 33 and 51% in PAC-free and PAC-containing mixed liquor microcosms, respectively. The lower molecular weight fraction of NAs was preferentially degraded in both mixed liquors. The persistence of the residual, higher molecular weight NAs is likely a combination of molecular recalcitrance and decreased bioavailability when chronically-sorbed to the biomass and/or PAC.

Comparison of polytetrafluoroethylene flat-sheet membranes with different pore sizes in application to submerged membrane bioreactor.

This study focused on phase separation of activated sludge mixed liquor by flat-sheet membranes of polytetrafluoroethylene (PTFE). A 20 liter working volume lab-scale MBR incorporating immersed PTFE flat-sheet membrane modules with different pore sizes (0.3, 0.5 and 1.0 μm) was operated for 19 days treating a synthetic wastewater. The experiment was interrupted twice at days 5 and 13 when the modules were removed and cleaned physically and chemically in sequence. The pure water permeate flux of each membrane module was measured before and after each cleaning step to calculate membrane resistances. Results showed that fouling of membrane modules with 0.3 μm pore size was more rapid than other membrane modules with different pore sizes (0.5 and 1.0 μm). On the other hand, it was not clear whether fouling of the 0.5 μm membrane module was more severe than that of the 1.0 μm membrane module. This was partly because of the membrane condition after chemical cleaning, which seemed to determine the fouling of those modules over the next period. When irreversible resistance (Ri) i.e., differences in membrane resistance before use and after chemical cleaning was high, the transmembrane pressure increased quickly during the next period irrespective of membrane pore size.

PH Adjusting to Reduce Fouling Propensity of Activated Sludge Mixed Liquor in Membrane Bioreactors

The effect of adjusting pH on membrane filterability of activated sludge mixed liquor in membrane bioreactors (MBRs) was studied. The properties of the mixed liquor were analyzed to investigate the mechanisms. The results indicated that moderately adjusting pH was effective to improve the membrane filterability of the mixed liquor. HCl addition provided H+, which reduced the zeta-potential of the colloidal particles. NaOH addition at pH of 8.0–9.0 released some extractable extra-cellular polymeric substances (eEPS) to the supernatant. Re-flocculation occurred. The fouling propensity of the mixed liquor was therefore reduced. Microbial activity was not significantly affected within the pH of 6.0–9.0.

Relationship of protozoan biomass to phosphate and nitrate removal from activated sludge mixed liquor

The relationship between protozoan biomass concentration and phosphate and nitrate removal was investigated in mixed liquor using three different carbon sources as supplements. The study was carried out using three respective initial biomass concentrations in a shaking flask environment. Samples were taken every 24 h to determine phosphate, nitrate, dissolved oxygen and chemical oxygen demand. The results revealed a direct relationship between decreases in nutrient concentrations and increases in cell densities of the isolates. Between 24 and 96 h, the increases in the protozoan density corresponded to a phosphate decreases from initial ranges of 55.42-57.36 mg/L, 50.27-51.17 mg/L and 50.01-50.83 mg/L to final ranges of 2.46-11.90 mg/L, 0.61-11.80 mg/L and 1.29-13.89 mg/L, in the presence of Aspidisca, Trachelophyllum and Peranema, respectively. Nitrate concentrations were observed to decrease from initial ranges of 23.84-25.90 mg/L, 23.94-25.84 mg/L and 26.12-26.54 mg/L to final ranges of 0.11-6.32 mg/L, 0.16-5.60 mg/L and 0.24-9.04 mg/L, respectively. The study had revealed that an increase in cell density of the test isolates produces a corresponding increase in phosphate and nitrate removal.

Estrogen Biodegradation Kinetics and Estrogenic Activity Reduction for Two Biological Wastewater Treatment Methods

Estrogens from anthropogenic and livestock sources are a serious concern for aquatic ecosystems at concentrations less than 1 ng/L Fundamental process parameters to reduce estrogenic activity were investigated for two biotreatment methods: heterotrophic bacterial degradation in municipal activated sludge (AS) and a nitration process that is applicable to high NH4-N wastewaters. Batch tests with estrogen and nitro-estrogen compounds were conducted at nanogram per liter concentrations with mixed liquor from an AS wastewater treatment facility (WWTF) operating at a 3 day solids retention time (SRT) and a membrane bioreactor (MBR) WWTF operating at a 30-40 day SRT. The estrogenic activities of estrone (E1), 17beta-estradiol (E2), and 17alpha-ethinylestradiol (EE2) were reduced 80-97% following nitration. First-order biological degradation rate coefficients (kb) of the nitrated estrogens were 10-50% lower than the parent estrogen compounds. The kb values for EE2 in MBR and AS mixed liquors were similar, 1.67 and 1.63 L/gVSS-day respectively, indicating that the bacteria responsible for EE2 degradation were present at long and short SRTs. The kb values for E1 and E2 were 2 orders of magnitude greater than for EE2. EE2 degradation was 7.5 times faster in the presence of E1 and E2, and no effect was observed with other estrogen mixtures.

Multiple approaches to assess filamentous bacterial growth in activated sludge under different carbon source conditions

To compare molecular and microscopic approaches in determining which filamentous bacteria grow in activated sludge reactors when different carbon sources and different activated sludge mixed liquor inocula are used. Microscopic and molecular (Denaturing Gradient Gel Electrophoresis and Fluorescent In Situ Hybridization) techniques were used to determine which filamentous bacteria became dominant in lab scale reactors treating wastewater composed of different carbon sources. Molecular analysis indicated the presence of Sphaerotilus natans and Thiothrix-related organisms. Microscopy indicated the presence of Nostocoida limicola in some reactors. Sludge volume index increased as filament abundance increased. The detection level of DGGE analysis increased when the abundance levels of the filaments were high. Simultaneous application of traditional and molecular methods was effective, and highlighted the advantages and limitations of each method. Readily biodegradable substances favoured the growth of specific filaments in a mixed liquor environment. The origin of inoculum influenced which specific filamentous bacteria grew. The study shows the potential problems when using particular techniques, and highlights the need for multiple approaches when studying filaments. The study also provides more information on which filaments will grow under different carbon source conditions for a given inoculum.

Nutrient removal from activated sludge mixed liquor by wastewater protozoa in a laboratory scale batch reactor

The aim of the study was to investigate the nutrient removal rate of three wastewater protozoan isolates. The study was carried out in a laboratory-scale batch reactor for a period of 120 h. in a four batch study. Aliquot samples were withdrawn from the reactor every 24 h. for the analysis of phosphate, nitrate, nitrite, ammonia, chemical oxygen demand, dissolved oxygen and pH, using standard methods. The results obtained in the different batches among the three isolates showed PO4 2− removal rate ranging from 0.04 to 0.52 mg-PO4 2−/L/h. while NO3 − nitrate removal rates ranged from 0.08 to 0.16 mg-NO3 −/L /h. Also NO2- and NH3 rates were observed to range between 0.022 and 0.087 mg-NO2 −/L /h. 0.05 and 0.16 mg-NH3 −/L /h, respectively. For the physicochemical parameters, there was no observed COD decrease; rather there was an increase and this was irrespective of isolates and experimental batches. However, dissolved oxygen concentration decreased drastically (below 1 mg/L) at the end of each batch while pH show a decrease after an initial 24 h. period and thereafter increased. This trend was also irrespective of isolates and experimental batches. Overall, the study has been able to show the effect of the test isolates on nutrient removal rates and other physicochemical parameters (COD, DO and pH) in activated sludge mixed liquor.

Protozoan biomass relation to nutrient and chemical oxygen demand removal in activated sludge mixed liquor

The relationship between biomass concentration to nutrient and chemical oxygen demand (COD) removal in mixed liquor supplemented with sodium acetate was investigated, using three protozoan isolates and three different initial biomass concentrations (10(1), 10(2) and 10(3) cells/mL). The study was carried out in a shaking flask environment at a shaking speed of 100 rpm for 96 h at 25 degrees C. Aliquot samples were taken periodically for the determination of phosphate, nitrate, COD and dissolved oxygen, using standard methods. The results revealed remarkable phosphate removal of 82-95% at biomass concentration of 10(3)cells/mL. A high nitrate removal of over 87% was observed at all initial biomass concentration in mixed liquor. There was an observed COD increase of over 50% in mixed liquor in at the end of 96-h incubation and this was irrespective of initial biomass concentration used for inoculation. The study shows the trend in nutrient and COD removal at different biomass concentrations of the test isolates in mixed liquor.

A comparative study of fouling-related properties of sludge from conventional and membrane enhanced biological phosphorus removal processes

The physical and biochemical properties of activated sludge mixed liquor, including floc size distribution, zeta potential, relative hydrophobicity, and bound and unbound (soluble) extracellular polymeric substances (EPS), were examined in this study to evaluate their relationship to membrane fouling. Mixed liquors from a membrane enhanced biological phosphorus removal (MEBPR) process and a conventional enhanced biological phosphorus removal (CEBPR) process were compared. It was found that the floc size distribution and the amount of soluble EPS in the mixed liquor were the most important properties that significantly influenced the fouling propensity of sludge. Contrary to the literature, the content of EPS bound in activated sludge flocs was not found to be directly associated with membrane fouling, and sludge surface properties such as zeta potential and relative hydrophobicity were not closely related to the observed differences in the fouling tendencies of the two types of sludge.

Populations related to Alkanindiges, a novel genus containing obligate alkane degraders, are implicated in biological foaming in activated sludge systems

Activated sludge mixed liquor and biological foam samples were collected from five full-scale municipal wastewater treatment plants in Illinois, all of which were exhibiting biological foaming at the time of sampling. Oligonucleotide probe hybridization consistently measured higher levels of Gammaproteobacteria rRNA in the foam as compared with the mixed liquor for all treatment plants analysed. Cloning and sequencing of 16S rRNA gene amplicons led to the identification of populations which were abundant in each of the treatment plants. These populations were related to the Alkanindiges/Acinetobacter cluster within the Gammaproteobacteria. Further analysis of the 16S rRNA sequences indicated that they clustered in three phylogenetic groups outside the main Alkanindiges/Acinetobacter cluster, suggesting that these groups may represent new taxa. Terminal-restriction fragment length polymorphism analysis showed that these populations were enriched in the foam compared with the underlying mixed liquor similar to the enrichment of the Gammaproteobacteria measured by oligonucleotide probe membrane hybridization. The observed enrichment in foam samples is suggestive of a role for these populations in foam formation or stabilization, and their presence in all treatment plants analysed in this study may be indicative of their widespread abundance in foaming plants.

Mechanism investigation of virus removal in a membrane bioreactor

Virus removal in a membrane bioreactor (MBR) by gravity drain was studied. Coliphage f2 (mean size of 25 nm), which is similar in size to human enteric pathogenic viruses, was selected as a model virus. Two microfiltration membrane modules with pore sizes of 0.22 μm and 0.1 μm were applied to investigate the effects of membrane pore size on the virus rejection. The MBR with these modules could reject virus in a range of 2.6–5.1 logs. The experimental results showed that the mechanisms of virus removal in the MBR involved rejection and inactivation. The virus rejection depended mainly on the dynamic layer on the membrane surface (not membrane itself) because virus rejection by the membrane modules with pore sizes of 0.1 μm and 0.22 μm were similar. The microbial activity and the aeration oxidation were the two important factors for the virus inactivation. It was found that the inactivation of coliphage f2 was much more rapidly in activated sludge mixed liquor than in clean water, and the effect of aeration was significant.

Using inorganic coagulants to control membrane fouling in a submerged membrane bioreactor

Changes of properties (specific filtration resistance, floc size, supernatant TOC and zeta potential) of activated sludge mixed liquor after monomeric and polymeric coagulants [Al2(SO4)3, FeCl3, PAC (polymeric aluminum chloride) and PFS (polymeric ferric sulfate)] addition were studied in this paper. It was found that polymeric coagulants had a better effect on filterability enhancement of mixed liquor than monomeric coagulants. Further research found that the reason was that polymeric coagulants could supply more positive charges for organic particles and sludge flocs, and enhance the functions of charge neutralization, which resulted in higher removal of supernatant organic matter and enlargement of sludge floc size. Thus, polymeric coagulants (PAC, PFS and PAFC) were added in a submerged membrane bioreactor (MBR) and the effect on membrane fouling control was investigated. It was found that polymeric coagulants could control membrane fouling by reducing the initial TMP and the TMP increase rate. Three functions of polymeric coagulants on membrane fouling control were supposed: restraining the formation of gel layer, decelerating the development of foulants and removing stable foulants from the membrane surface. Among the selected coagulants, PFS was the most effective in controlling membrane fouling and the optimal dose was 1.05 mM Fe. If coagulant was added before the MBR was run, a better effect could be obtained.