Full-scale Activated Sludge Process Research Articles

‘Morphological shifts’ in filamentous bacteria isolated from activated sludge processes

This study aimed at isolating filamentous bacteria from full-scale activated sludge processes and studying them in pure culture. Three cultures were isolated using conventional microbiological techniques. The isolates were positively identified as Gordonia amarae, Thiothrix nivea and Type 1863/Acinetobacter spp., using fluorescent in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probes. However, a ‘morphological shift’ from filamentous to single-cell form was observed in pure culture. The application of fluorescent in situ hybridization (FISH) showed filamentous bacteria to be much more diverse in their ability to adapt to their changing enviroments. Pure culture studies of filamentous bacteria form the basis for application in full-scale activated sludge plants. It therefore remains important that the taxonomic status of filamentous bacteria be determined.

Acinetobacter isolates from different activated sludge processes: characteristics and neural network identification

Acinetobacter species were isolated from various full-scale activated sludge processes based on their abilities to transform an Acinetobacter calcoaceticus BD413 trp E27 auxotroph. Approximately half of the Acinetobacter isolates (149 out of 282 isolates) were able to accumulate polyphosphate, and some used β-hydroxybutyrate as a sole carbon and energy source. Additionally, most of the Acinetobacter isolates were unable to reduce nitrate. These characteristics of Acinetobacter species are desirable for microorganisms responsible for enhanced phosphorus removal in different activated sludge processes. The backpropagation neural network technique was further applied to assign the isolates to distinct Acinetobacter genospecies based on their phenotypic characteristics. In particular, Acinetobacter johnsonii was consistently the major genospecies from different samples obtained from the enhanced phosphorus removal processes or the conventional plant without biological phosphorus removal.

Investigation of an Acetate-Fed Denitrifying Microbial Community by Stable Isotope Probing, Full-Cycle rRNA Analysis, and Fluorescent In Situ Hybridization-Microautoradiography

The acetate-utilizing microbial consortium in a full-scale activated sludge process was investigated without prior enrichment using stable isotope probing (SIP). [13C]acetate was used in SIP to label the DNA of the denitrifiers. The [13C]DNA fraction that was extracted was subjected to a full-cycle rRNA analysis. The dominant 16S rRNA gene phylotypes in the 13C library were closely related to the bacterial families Comamonadaceae and Rhodocyclaceae in the class Betaproteobacteria. Seven oligonucleotide probes for use in fluorescent in situ hybridization (FISH) were designed to specifically target these clones. Application of these probes to the sludge of a continuously fed denitrifying sequencing batch reactor (CFDSBR) operated for 16 days revealed that there was a significant positive correlation between the CFDSBR denitrification rate and the relative abundance of all probe-targeted bacteria in the CFDSBR community. FISH-microautoradiography demonstrated that the DEN581 and DEN124 probe-targeted cells that dominated the CFDSBR were capable of taking up [14C]acetate under anoxic conditions. Initially, DEN444 and DEN1454 probe-targeted bacteria also dominated the CFDSBR biomass, but eventually DEN581 and DEN124 probe-targeted bacteria were the dominant bacterial groups. All probe-targeted bacteria assessed in this study were denitrifiers capable of utilizing acetate as a source of carbon. The rapid increase in the number of organisms positively correlated with the immediate increase in denitrification rates observed by plant operators when acetate is used as an external source of carbon to enhance denitrification. We suggest that the impact of bacteria on activated sludge subjected to intermittent acetate supplementation should be assessed prior to the widespread use of acetate in the wastewater industry to enhance denitrification.

Community survey of ammonia-oxidizing bacteria in full-scale activated sludge processes with different solids retention time

To study the effects of different solids retention time (SRT) on the nitrification activity and community composition of ammonia-oxidizing bacteria (AOB) in two full-scale activated sludge processes during a 5-month period. The AOB community composition was analysed using fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE), and the identified populations were enumerated by quantitative FISH. Potential nitrification rates were determined in batch tests and the in situ rates were calculated from mass balances of nitrogen in the plants. Increased SRT reduced the nitrification activity, but neither the number per mixed liquor suspended solids nor community composition of AOB were affected. Two dominant AOB populations related to Nitrosomonas europaea and Nitrosomonas oligotropha were identified by FISH, whereas only the latter could be detected by DGGE. The effect of a longer SRT on the activity was probably because of physiological changes in the AOB community rather than a change in community composition. Physiological alterations of a stable AOB community are possible and may stabilize activated sludge processes. The commonly used FISH probes designed to target all beta-proteobacterial AOB does not detect certain Nitrosomonas oligotropha populations, leading to an underestimation of AOB if a wider set of probes is not used.

Effect of periodic feeding in sequencing batch reactor on substrate uptake and storage rates by a pure culture of Amaricoccus kaplicensis

A pure culture of Amaricoccus kaplicensis was aerobically cultured at a long culture residence time ( Θ C>12 d), under periodic acetate feeding in a sequencing batch reactor (SBR). The cycle length and, correspondingly, the volumetric organic load rate (vOLR) were varied in the range 4–24 h and 0.76–0.12 g COD l −1 d −1, respectively. The transient response of the microorganism to the acetate spike was investigated throughout batch tests, as a function of SBR cycle length and vOLR. In all tested conditions, a rapid transient response was observed, mainly due to acetate storage in the form of polyhydroxybutyrate, since growth (production of active biomass) played a minor role. Apart from this general trend, the maximum rates under transient conditions increased as the cycle length increased from 4 to 24 h. In the SBR, the longest cycle also caused a decrease in floc size and settleability as well as an increase in the observed yield. The observed effect of SBR operating conditions on the physiological state of cells and their related transient response may have great significance on the performance of full scale activated sludge processes.

Modelling biological phosphorus and nitrogen removal in a full scale activated sludge process

A previously derived metabolically structured model for the biological aerobic and anoxic phosphorus removal was combined with the ASM no. 1 and tested in its capacity to describe a full scale biological nitrogen and phosphorus removal WWTP. The sensitivity of the effluent concentrations and the sludge production towards the stoichiometric and kinetic coefficients, the influent composition, the set-up of the hydraulic model and the flows of air, mixed liquor and return sludge was analysed. This showed that besides a limited number of model parameters (12%) the influent characterisation influenced the model output significant. For calibration of the model only 3 out of the 60 default parameters together with the unknown air input needed to be changed approximately 40% to describe the measurements of soluble components at different places in the full scale WWTP as a function of time. The choice of parameters to calibrate was done on the basis of process and model knowledge rather then on the sensitivity analysis. For the calibration the in-process measurements were much more informative then the effluent measurements.

Acinetobacter isolates from different activated sludge processes: characteristics and neural network identification

Acinetobacter species were isolated from various full-scale activated sludge processes based on their abilities to transform an Acinetobacter calcoaceticus BD413 trp E27 auxotroph. Approximately half of the Acinetobacter isolates (149 out of 282 isolates) were able to accumulate polyphosphate, and some used β-hydroxybutyrate as a sole carbon and energy source. Additionally, most of the Acinetobacter isolates were unable to reduce nitrate. These characteristics of Acinetobacter species are desirable for microorganisms responsible for enhanced phosphorus removal in different activated sludge processes. The backpropagation neural network technique was further applied to assign the isolates to distinct Acinetobacter genospecies based on their phenotypic characteristics. In particular, Acinetobacter johnsonii was consistently the major genospecies from different samples obtained from the enhanced phosphorus removal processes or the conventional plant without biological phosphorus removal.

Correlations of performance for activated sludge using multiple regression with autocorrelation

A method is developed to correlate activated sludge response variables, such as SVI, effluent volatile suspended solids or effluent BOD, with state variables such as F/M ratio, influent BOD, dynamic sludge age, etc. The method is based on multiple linear regression with autocorrelated errors. The method was applied to three data sets from two full-scale activated sludge plants; one a regional municipal utility, the other an industrial facility. Highly statistically significant models were found which could explain 65–82% of the variability in effluent total oxygen demand, 22–60% in effluent volatile suspended solids and 48–88% in sludge volume index. It was only necessary to model up to second order lags. The models were tested for bias using different data sets and produced correlation coefficients between predicted and observed values as high as 0.96. These results show that useful predictive relationships can be developed for full-scale activated sludge processes. The methods could be used to develop a range of automatic process control schemes.

Evaluation of settleability of activated sludge using a sludge settling analyzer

An effective system has been developed to estimate sludge settleability, which consists of an SVI measuring block and a data analyzing block. A settling test using this system was conducted to determine settling characteristics in a full-scale activated sludge process. As a result relations have been discovered between various parameters concerned with sludge settling curves, such as the initial settling velocity (ISV), compression point, the Roberts constant and the sludge volume index (SVI), generally used as sludge settleability.

Studies on dissolved oxygen concentration and sludge retention time affecting the full-scale activated sludge process

We have made a series of experiments on dissolved oxygen (DO) concentration and sludge retention time (SRT) to affect the full-scale activated sludge process. For DO control, a better effluent water quality and a reduced current consumption have been achieved as compared with those in a constant air flow operation. The best control point for the DO control operation is at the outlet side of the aeration tank. For SRT control, effluent COD seems to fluctuate slightly, and is favorably stable when SRT is between 10 and 20 days. It takes about twice as many days as SRT value set up for the total mass of sludge in the process ( M) to be stabilized in case of making set value change as a result of simulation using mathematical models.