Model-based analysis on growth of activated sludge in a sequencing batch reactor

A mathematical model is developed to describe the growth of multiple microbial species such as heterotrophs and autotrophs in activated sludge system. Performance of a lab-scale sequencing batch reactor involving storage process is used to evaluate the model. Results show that the model is appropriate for predicting the fate of major model components, i.e., chemical oxygen demand, storage polymers (X _STO), volatile suspended solid (VSS), ammonia, and oxygen uptake rate (OUR). The influence of sludge retention time (SRT) on reactor performance is analyzed by model simulation. The biomass components require different time periods from one to four times of SRT to reach steady state. At an SRT of 20 days, the active bacteria (autotrophs and heterotrophs) constitute about 57% of the VSS; the remaining biomass is not active. The model established demonstrates its capacity of simulating the reactor performance and getting insight in autotrophic and heterotrophic growth in complex activated sludge systems.     

Characterization of microbial traits associated with glyphosate biodegradation in industrial activated sludge

Summary The microorganisms from two industrial (I1, I2) activated sludges that treat glyphosate (N-phosphonomethyl glycine) wastes and one domestic (D1) sludge were enumerated by microscopic examination and by the use of eight selective media. I1 and I2 had higher total counts but fewer pseudomonads and no yeasts. The enumerations correlated directly with traditional biological performance measurements. A total of 393 microbial strains were isolated from the sludges to correlate the occurrence and relationship of glyphosate-degrading activity (GDA) to 155 biochemical and morphological characteristics. Each activated sludge contained unique bacterial populations with the microbes treating industrial wastes, capable of utilizing a wide range of carbohydrates. Numerical taxonomy (arithmetic average linkage) using simple matching and Jaccard coefficients confirmed that there were five (D1), three (I1), and 12 (I2) clusters. GDA was found in only a small portion of the industrial clusters and did not correlate with any other characteristic tested, even though the GDA strains had a large phenotypic diversity. This suggests that GDA is not a universal trait and its expression requires enrichment through specific selective pressures.     

Production of an extracellular polysaccharide byAgrobacterium sp DS3 NRRL B-14297 isolated from soil

A bacterium isolated from soil and identified asAgrobacterium sp produced a water-soluble extracellular polysaccharide capable of producing highly viscous solutions. Gas chromatographic analysis revealed a sugar composition of glucose, galactose and mannose in the molar ratio of 7.52.41, together with 3.7% (w/w) pyruvic acid. Methylation analyses showed the presence of (13)-, (14)- and (16)-linked glucose, (13)- and (14, 16)-linked galactose and a small portion of (13)-linked mannose residues. Succinic acid was not present. The molecular weight of the polysaccharide was estimated by light scattering to be 2×10⁶ Da. The viscosity of solutions containing the polysaccharide remained constant from pH 3 to 11, and decreased by 50% when heated from 5 to 55°C. Maximum yield of the polysaccharide, 20 g L^–1, was reached in 48 h at 30°C incubation.     

Polyphosphate kinase genes from full-scale activated sludge plants

The performance of enhanced biological phosphorus removal (EBPR) wastewater treatment processes depends on the presence of bacteria that accumulate large quantities of polyphosphate. One such group of bacteria has been identified and named Candidatus Accumulibacter phosphatis. Accumulibacter-like bacteria are abundant in many EBPR plants, but not much is known about their community or population ecology. In this study, we used the polyphosphate kinase gene (ppk1) as a high-resolution genetic marker to study population structure in activated sludge. Ppk1 genes were amplified from samples collected from full-scale wastewater treatment plants of different configurations. Clone libraries were constructed using primers targeting highly conserved regions of ppk1, to retrieve these genes from activated sludge plants that did, and did not, perform EBPR. Comparative sequence analysis revealed that ppk1 fragments were retrieved from organisms affiliated with the Accumulibacter cluster from EBPR plants but not from a plant that did not perform EBPR. A new set of more specific primers was designed and validated to amplify a 1,100 bp ppk1 fragment from Accumulibacter-like bacteria. Our results suggest that the Accumulibacter cluster has finer-scale architecture than previously revealed by 16S ribosomal RNA-based analyses. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Biodegradation of wastewater pollutants by activated sludge encapsulated inside calcium-alginate beads in a tubular packed bed reactor

The wastewater treatment plants produce large quantities of biomass (sludge) that require about one-third of the total inversion and operation plant costs for their treatment. By the microorganisms immobilization it is possible to handle high cell concentration in the reactor, increasing its efficiency, reducing the loss of biomass and the wash out is avoided. Moreover, there is no cell growth then the sludge production is reduced. In this study, the COD removal and VSS variation were modeled in a tubular reactor with activated sludge immobilized in Ca-alginate. Moreover, two aspects that are commonly not considered in the performance of the actual reactors of this kind were introduced; the performance in non-steady state and the dispersion effect. The model was calibrated with an actual wastewater taken out from a Mexican wastewater treatment plant. The results of the performance of the tubular bioreactor at different scenarios (i.e., different residence time and VSS in the reactor) are presented. With longer residence times and higher VSS concentration in the Ca-alginate beads in the tubular bioreactor it is possible to increase the time operation of the bioreactor and to treat higher volumes of wastewater. During the process, the sludge generation was drastically reduced and it is possible to remove nitrogen form the wastewater making this process more attractive.     

Model-based design of different fedbatch strategies for phenol degradation in acclimatized activated sludge cultures

Microbial degradation of phenol was studied using batch and fedbatch cultures of acclimatized activated sludge under a wide range of phenol (0-793 mg l⁻¹) and biomass (0.74-6.7 g l⁻¹) initial concentrations. As cell growth continued after total phenol removal, the production and later consumption of a main metabolic intermediate was considered the step governing the biodegradation kinetics. A model that takes explicitly into account the kinetics of the intermediate was developed by introducing a specific growth rate model associated with its consumption and the incorporation of a dual-substrate inhibitory effect on phenol degradation. Biomass growth and phenol removal were adequately predicted in all the cultures. Moreover, the model-based design of the fedbatch feeding strategies allowed driving separately the phenol degradation under substrate-limitation and substrate-inhibition modes. A sensitivity analysis was also performed in order to establish the importance of the parameters in the accuracy of model predictions.     

Biodegradation of naphthalene in the oil refinery wastewater by enriched activated sludge

The main purpose of this paper is to study naphthalene (NAP) biodegradation by acclimated activated sludge, employing the culture-enrichment method in a continuous flow bioreactor of the wastewater treatment process. The effects of various COD loadings and influent flow rates of an artificial wastewater containing 15 mg l⁻¹ NAP on the biodegradation rates of the activated sludge will be investigated, in order to determine the biodegradation kinetics and minimum mean cell residence time of the activated sludge. From the experimental results, it was found that the resulting enriched activated sludge follows the growth rate of the Monod type and can biodegrade those COD and NAP loadings in the influents efficiently, and its bio-treatment efficiency on NAPs increases with the decrease of influent flow rate. The sludge volume index (SVI) of the resulting enriched activated sludge meets the design value required by the convectional activated sludge process for the treatment of wastewater.     

Modeling the acclimation of activated sludge to a xenobiotic

This work established a mathematical model that formulated degrader formation by conversion of indigenous microbial cells. Degrader conversion is attributed to genetic induction whose force is dependent on the strength of acclimating xenobiotic and the amount of indigenous cells. After successful conversion, which requires an amount of time proportionate to the lag, degraders grow on the xenobiotic substrate. This model formulated the lag and degrader formation with the sigmoid function and degrader growth with the Haldane kinetics. The model so completed accurately simulates the degradation and biomass courses during acclimation and degradation of a xenobiotic by indigenous activated sludge, wherein the factors relating to the acclimation process are given values. The model serves the need for a rational representation of microbial acclimation to a xenobiotic.     

Nitrite effect on nitrous oxide emission from denitrifying activated sludge

Laboratory-scale experiments were conducted to examine the N₂O emission during the denitrification process. For each of the 6 runs carried out, synthetic effluent was fed in a 10 l batch mixed liquor to investigate the effect of nitrite on N₂O emission and Helium was continuously bubbled through the reactor at constant rate (0.12 l/min) to favour N₂O transfer and detection. An increasing COD/NO₃⁻-N influent ratio from 3 to 7 was firstly applied (runs 1–3). Secondly, NO₂⁻ pulse additions were performed during run 4 and 5 (10 and 20 mg N/l, respectively). Finally, the reactor was fed with influent containing both NO₂⁻ and NO₃⁻. We showed that N₂O emission was detected shortly after NO₂⁻ accumulation, few minutes after the substrate feeding. The highest emission occurred at the lower COD/NO₃⁻-N ratio (=3) and at the higher NO₂⁻ addition (20 mg N/l). In addition, the higher nitrogen conversion to N₂O gas (14.4%) was obtained with an influent containing initially both NO₂⁻ and NO₃⁻. Our results suggest a direct effect of the NO₂⁻ concentration on the N₂O emission. We have also confirmed the inhibitory effect of NO₂⁻ concentration on N₂O reduction.     

Oily sludge degradation by bacteria from Ankleshwar, India

Three bacterial strains, Bacillus sp. SV9, Acinetobacter sp. SV4 and Pseudomonas sp., SV17 from contaminated soil in Ankleshwar, India were tested for their ability to degrade the complex mixture of petroleum hydrocarbons (such as alkanes, aromatics, resins and asphaltenes), sediments, heavy metals and water known as oily sludge. Gravimetric analysis showed that Bacillus sp. SV9 degraded approx. 59% of the oily sludge in 5 days at 30 °C whereas Acinetobacter sp. SV4 and Pseudomonas sp. SV17 degraded 37% and 35%. Capillary gas chromatographic analysis revealed that after 5 days the Bacillus strain was able to degrade oily sludge components of chain length C₁₂–C₃₀ and aromatics more effectively than the other two strains. Maximum drop in surface tension (from 70 to 28.4 mN/m) was accompanied by maximum biosurfactant production (6.7 g l⁻¹) in Bacillus sp. SV9 after 72 h, these results collectively indicating that this bacterial strain has considerable potential for bioremediation of oily sludge.     

Toxic effects of toluene on the growth of activated sludge bacteria

Two bacteria were isolated from the activated sludge sample of a wastewater treatment plant in Dublin by enrichment culture technique with toluene as the sole source of carbon and energy. They were identified as Aeromonas caviae (To-4) and Pseudomonas putida (To-5). The growth of these bacteria depended on the manner in which toluene was supplied. In general, growth was better when toluene was supplied in the vapour phase. When toluene was added directly to the growth medium it was found to be toxic to the organisms but the toxic effect could be alleviated in the presence of other carbon sources and by the acclimation of the cells. The growth of To-4 on toluene has never been previously reported.     

Biodegradation by activated sludge and toxicity of tetracycline into a semi-industrial membrane bioreactor

Much attention has been devoted recently to the fate of pharmaceutically active compounds such as tetracycline antibiotics in soil and water. Tetracycline (TC) biodegradability by activated sludge derived from membrane bioreactor (MBR) treating swine wastewater via CO₂-evolution was evaluated by means of modified Sturm test, which was also used to evaluate its toxicity on carbon degradation. The impact of tetracycline on a semi-industrial MBR process was also examined and confronted to lab-scale experiments. After tetracycline injection in the pilot, no disturbance was detected on the elimination of organic matters and ammonium (nitrification), reaching after injection 88% and 99% respectively; only denitrification was slightly affected. Confirming the ruggedness and the superiority of membrane bioreactors over conventional bioreactors, no toxicity was observed at the considered level of TC in the pilot (20 mg TOC L⁻¹), while at lab-scale sodium benzoate biodegradation was completely inhibited from 10 mg TOC L⁻¹ TC. The origin of the activated sludge showed a significant impact on the performances, since the ultimate biodegradation was in the range −50% to −53% for TC concentrations in the range 10–20 mg TOC L⁻¹ with conventional bioreactor sludge and increased to 18% for 40 mg TOC L⁻¹ of TC with activated sludge derived from the MBR pilot. This confirmed the higher resistance of activated sludge arising from membrane bioreactor.     

Effect of addition of one carbon source on the operation of sequencing batch reactor in order to remove nitrogen and COD from poultry wastewater

The effect of carbon source addition on the operation of a sequencing batch reactor in order to remove nitrogen and COD of poultry wastewater was studied. The reactor was constructed with a glass tube having a volume of 7 l and a jacket for temperature control. The reactor bottom consisted of a conical porous stone in order to promote liquor aeration and agitation. Initial conditions and operation strategies were adjusted to improve the final effluent quality. According to the attained experimental results, it was verified that nitrification and denitrification can occur simultaneously in aerated culture, contrary the observation of some authors.     

Mathematical modeling of aerobic granular sludge: A review

Aerobic granulation may play an important role in the field of wastewater treatment due to the advantages of aerobic granules compared to the conventional sludge flocs, such as denser structure, better settleability and ensured solid-effluent separation, higher biomass concentration, and greater ability to withstand shock loadings, which is promising for a full-scale implementation. As an aid for this implementation, mathematical modeling would be an invaluable tool. In this paper, the existing mathematical models available in literature concerning aerobic granule systems are reviewed, including the modeling of the dynamic facets of the aerobic granulation process, the mass transfer and detachment in aerobic granules, the granule-based sequencing batch reactor, the fate of microbial products in granules, and the multi-scale modeling of aerobic granular sludge. An overview of the parameters used in the aerobic granular modeling approaches is also presented. Our growing knowledge on mathematical modeling of aerobic granule might facilitate the engineering and optimization of aerobic granular sludge technology as one of the most promising techniques in the biological wastewater treatment.     

Molecular insight into activated sludge producing polyhydroxyalkanoates under aerobic–anaerobic conditions

One of the options enabling more economic production of polyhydroxyalkanoates compared to pure cultures is the application of mixed cultures. The use of a microbial community in a sequencing batch reactor has a few advantages: a simple process control, no necessity for sterile processing, and possibilities of using cheap substrates as a source of carbon. Nevertheless, while cultivation methods to achieve high PHAs biomass concentration and high productivity in wild and recombinant strains are defined, knowledge about the cultivation strategy for PHAs production by mixed culture and species composition of bacterial communities is still very limited. The main object of this study was to characterize on the molecular level the composition and activity of PHAs producing microorganism in activated sludge cultivated under oxygen limitation conditions. PHAs producers were detected using a PCR technique and the created PHA synthase gene library was analyzed by DNA sequencing. The obtained results indicate that PHAs-producers belonged to Pseudomonas sp., and possessed genes coding for mcl-PHA synthase. The kinetics of mcl-PHA synthase expression was relatively estimated using real-time PCR technology at several timepoints. Performed quantitative and qualitative analysis of total bacterial activity showed that there were differences in total activity during the process but differential expression of various groups of microorganisms examined by using DGGE was not observed.     

Isolation of rhodoquinone-containing chemoorganotrophic bacteria from activated sludge

Abstract Several strains of Gram-negative aerobic chemoheterotrophic bacteria which produced rhodoquinone were isolated from activated sludge. All isolates contained a rhodoquinone with eight isoprene units as a major component in addition to the corresponding homologue of ubiquinone. The isolates seemed to make up a single taxon because of their homogeneity in phenotypic and chemotaxonomic properties, but could not be allocated to any known taxa of Gram-negative bacteria.     

Polymerase chain reaction analysis of transgenic plants contaminated byAgrobacterium

Agrobacterium-mediated genetic transformation is a method of choice for the development of transgenic plants. The presence of latentAgrobacterium that multiplies in the plant tissue in spite of antibiotic application confounds the results obtained by polymerase chain reaction (PCR) analysis of putative transgenic plants. The presence ofAgrobacterium can be confirmed by amplification of eitherAgrobacterium chromosomal genes or genes present out of transfer DNA (T-DNA) in the binary vector. However, the transgenic nature ofAgrobacterium-contaminated transgenic plants cannot be confirmed by PCR. Here we report a simple protocol for PCR analysis ofAgrobacterium-contaminated transgenic plants. This protocol is based on denaturation and renaturation of DNA. The contaminating plasmid vector becomes double-stranded after renaturation and is cut by a restriction enzyme having site(s) within the PCR amplicon. As a result, amplification by PCR is not possible. The genomic DNA with a few copies of the transgene remains single-stranded and unaffected by the restriction enzyme, leading to amplification by PCR. This protocol has been successfully tested with 4 different binary vectors and 3Agrobacterium tumefaciens strains: EHA105, LBA4404, and GV3101.     

Modeling chlorophenols degradation in sequencing batch reactors with instantaneous feed-effect of 2,4-DCP presence on 4-CP degradation kinetics

Two instantaneously fed sequencing batch reactors (SBRs), one receiving 4-chlorophenol (4-CP) (SBR4) only and one receiving mixture of 4-CP and 2,4-dichlorophenol (2,4-DCP) (SBRM), were operated with increasing chlorophenols concentrations in the feed. Complete degradation of chlorophenols and high-Chemical oxygen demand (COD) removal efficiencies were observed throughout the reactors operation. Only a fraction of biomass (competent biomass) was thought to be responsible for the degradation of chlorophenols due to required unique metabolic pathways. Haldane model developed based on competent biomass concentration fitted reasonably well to the experimental data at different feed chlorophenols concentrations. The presence of 2,4-DCP competitively inhibited 4-CP degradation and its degradation began only after complete removal of 2,4-DCP. Based on the experimental results, the 4-CP degrader’s fraction in SBRM was estimated to be higher than that in SBR4 since 2,4-DCP degraders were also capable of degrading 4-CP due to similarity in the degradation pathways of both compounds.     

Active heterotrophic biomass and sludge retention time (SRT) as determining factors for biodegradation kinetics of pharmaceuticals in activated sludge

The present study investigates the biodegradation of pharmaceutically active compounds (PhACs) by active biomass in activated sludge. Active heterotrophs (X_bh) which are known to govern COD removal are suggested as a determining factor for biological PhAC removal as well. Biodegradation kinetics of five polar PhACs were determined in activated sludge of two wastewater treatment plants which differed in size, layout and sludge retention time (SRT).Results showed that active fractions of the total suspended solids (TSS) differed significantly between the two sludges, indicating that TSS does not reveal information about heterotrophic activity. Furthermore, PhAC removal was significantly faster in the presence of high numbers of heterotrophs and a low SRT. Pseudo first-order kinetics were modified to include X_bh and used to describe decreasing PhAC elimination with increasing SRT.     

Substrate specificity of a long-chain alkylamine-degrading <Emphasis Type="Italic">Pseudomonas</Emphasis> sp isolated from activated sludge

A bacterium strain BERT, which utilizes primary long-chain alkylamines as nitrogen, carbon and energy source, was isolated from activated sludge. This rod-shaped motile, Gram-negative strain was identified as a Pseudomonas sp. The substrate spectrum of this Pseudomonas strain BERT includes primary alkylamines with alkyl chains ranging from C₃ to C₁₈, and dodecyl-1,3-diaminopropane. Amines with alkyl chains ranging from 8 to 14 carbons were the preferred substrates. Growth on dodecanal, dodecanoic acid and acetic acid and simultaneous adaptation studies indicated that this bacterium initiates degradation through a C_alkyl–N cleavage. The cleavage of alkylamines to the respective alkanals in Pseudomonas strain BERT is mediated by a PMS-dependent alkylamine dehydrogenase. This alkylamine dehydrogenase produces stoichiometric amounts of ammonium from octylamine. The PMS-dependent alkylamine was found to oxidize a broad range of long-chain alkylamines. PMS-dependent long-chain aldehyde dehydrogenase activity was also detected in cell-free extract of Pseudomonas strain BERT grown on octylamine. The proposed pathway for the oxidation of alkylamine in strain BERT proceeds from alkylamine to alkanal, and then to the fatty acid.