Performance Of Activated Sludge Process Research Articles

Metagenomics and metatranscriptomics suggest pathways of 3-chloroaniline degradation in wastewater reactors

Biological wastewater treatment systems are often affected by shifts in influent quality, including the input of toxic chemicals. Yet the mechanisms underlying the adaptation of activated sludge process performance are rarely studied in a controlled and replicated experimental setting, particularly when challenged with a sustained toxin input. Three replicate bench-scale bioreactors were subjected to a chemical disturbance in the form of 3-chloroaniline (3-CA) over 132 days, after an acclimation period of 58 days, while three control reactors received no 3-CA input. Ammonia oxidation was initially affected by 3-CA. Within three weeks of the experiment, microbial communities in all three treatment reactors adapted to biologically degrade 3-CA resulting in partial ammonia oxidation recovery. Combining process and microbial community data from amplicon sequencing with potential functions gleaned from assembled metagenomics and metatranscriptomics data, two putative degradation pathways for 3-CA were identified. The first pathway, determined from metagenomics data, involves a benzoate dioxygenase and subsequent meta-cleavage of the aromatic ring. The second, determined from intensive short-term sampling for gene expression data in tandem with 3-CA degradation, involves a phenol monooxygenase followed by ortho-cleavage of the aromatic ring. The relative abundances of amplicon sequence variants associated with the genera Gemmatimonas, OLB8, and Taibaiella correlated significantly with 3-CA degradation. Metagenome-assembled genome data also showed the genus OLB8 to be differentially enriched in treatment reactors, making it a strong candidate as 3-CA degrader. Using replicated reactors, this study has demonstrated the impact of a sustained stress on the activated sludge process. The unique and novel features of this study include the identification of putative pathways and potential degraders of 3-CA using long-term and short-term sampling in tandem with multiple methods in a controlled and replicated experiment.

Effect of polystyrene nanoplastics on the activated sludge process performance and biomass characteristics. A laboratory study with a sequencing batch reactor

The fate and presence of nanoplastics in wastewater treatment systems is a topic of increasing interest. Furthermore, challenges related to their quantification and identification have made it difficult to set up experimental conditions and compare results between studies. In this study, the effect of 100 nm polystyrene nanoplastics on activated sludge was evaluated. A concentration of 2 μg/L was used to continuously feed a sequencing batch reactor (SBR-NPs). Under the experimental conditions used in this study, no changes were observed in the process performance of the SBR-NPs compared to the reactor used as a control. Neither nitrification nor organic matter removal efficiency, which was 96% for both SBRs, were affected by the presence of 100 nm polystyrene nanoplastics, which suggests that the tested nanoplastics were not sufficiently toxic to the biomass. Although no significant differences in the relative abundances of predominant phyla between SBR-Control and SBR-NPs were observed, a slight shift in the relative abundance of Patescibacteria (1.5 ± 0.6% and 3.7 ± 0.8% in SBR-Control and SBR-NPs, respectively, at the end of the test) occurred. The higher abundance of this phylum in SBR-NPs compared to SBR-Control may suggest that these bacteria have some sensitivity to the presence of 100 nm polystyrene nanoplastics. Furthermore, even with the absence of nitrification inhibition, it was observed stagnation of the growth of Nitrotoga bacteria in SBR-NPs, which also suggests that the polystyrene nanoplastics could have an inhibitory effect on these cells and an impact on nitrification in the long term.

Influence of bisphenol A occurrence in wastewaters on biomass characteristics and activated sludge process performance.

In this work, the influence of bisphenol A (BPA) on biological wastewater treatment was studied. For it, two sequencing batch reactors (SBRs) were operated for three months. Both SBRs were fed with synthetic wastewater (SW), adding 1mg·L-1 of BPA into the feed of reactor SBR-BPA, while the other one operated without BPA as a control reactor (SBR-B). In addition, batch experiments were performed with adapted and non-adapted activated sludge, simulating the reaction step of SBR-BPA, to determine the pathways for BPA removal. Results of batch experiments showed that adsorption and biodegradation were the only significant BPA removal routes. BPA removal by biodegradation was more efficient when adapted biomass was used in the tests (32.2% and 8.2% with adapted and non-adapted biomass, respectively), while BPA adsorption removal route was similar in both types of activated sludge (around 40%). Regarding the SBRs experiments, after 16days no BPA concentration was detected in SBR-BPA effluent. In the adaptation process, SBR-BPA biomass was more sensitive to low temperatures resulting in higher effluent turbidity, COD and soluble microbial products concentrations than in SBR-B. However, once temperature increased, adapted biomass from SBR-BPA presented higher activity than SBR-B biomass, showing higher values of sludge production, microbial hydrolytic enzymatic activities and specific dynamic respiration rate. The bacterial community study revealed the increase of abundance of Proteobacteria (especially Thiothrix species) and Actinobacteria (especially Nocardioides species) phyla at the expense of Bacteroidetes and Chloroflexi phyla in SBR-BPA during its operation.

Suitability of Sludge Biotic Index (SBI), Sludge Index (SI) and filamentous bacteria analysis for assessing activated sludge process performance: the case of piggery slaughterhouse wastewater.

Piggery slaughterhouse wastewater poses serious issues in terms of disposal feasibility and environmental impact, due to its huge organic load and variability. It is commonly treated by means of activated sludge processes, whose performance, in case of municipal wastewater, can be monitored by means of specific analyses, such as Sludge Biotic Index (SBI), Sludge Index (SI) and floc and filamentous bacteria observation. Therefore, this paper was aimed at assessing the applicability of these techniques to piggery slaughterhouse sewage. A plant located in Northern Italy was monitored for 1year. Physical, chemical and operation parameters were measured; the activated sludge community (ciliates, flagellates, amoebae and small metazoa) was analysed for calculating SBI and SI. Floc and filamentous bacteria were examined and described accordingly with internationally adopted criteria. The results showed the full applicability of the studied techniques for optimizing the operation of a piggery slaughterhouse wastewater treatment plant.

Process Improvement by Application of Membrane Bioreactors

Membrane bioreactors (MBR) – combinations of common bioreactors and membrane separation units for biomass retention – offer new possibilities for bioprocesses and wastewater treatment according to the particular goal and demands of the process. MBRs combine the benefits of high biomass concentrations to increase removal rates or volumetric productivity with the possibility to run a continuous process at controlled biomass retention e.g., by individual control of hydraulic and biomass residence times, production or degradation kinetics as well as biocoenosis composition can be optimized beyond chemostat or common activated sludge process performance. Although several practical experiences and data are already available for design and operation of MBR processes there is still considerable optimization potential. In MBRs, bioreactor and membrane filtration cannot be regarded as individual unit operations as they interact in a number of ways. Therefore, MBRs need to be considered as hybrid reactors. In this paper, some of the biology–membrane interactions are exemplarily discussed and data from different research and technical aspects including maintenance kinetics, membrane fouling, and rheology are presented.

The immunochemical detection of stress proteins in activated sludge exposed to toxic chemicals

The heat shock protein, GroEL, was found to be induced in activated sludge cultures exposed to perturbations of chemicals (cadmium, pentachlorophenol, and acetone) or heat stress. In laboratory activated sludge reactors, GroEL was rapidly induced (within minutes) in the presence of 5 mg/l or greater total cadmium. At 5 mg/l cadmium, however, moderate to insignificant changes in activated sludge process performance indicators [effluent suspended solids concentration, chemical oxygen demand (COD) removal, and specific oxygen uptake rate] were observed. As total cadmium concentrations increased above 5 mg/l, there was a significant and consistent increase in effluent volatile suspended solids concentrations from activated sludge sequencing batch reactors relative to unstressed controls. These results indicate that stress proteins may serve as sensitive and rapid indicators of mixed liquor toxicity which can adversely impact treatment process performance, but that GroEL may not be a good candidate protein for this purpose.

Activated sludge process performance using a multistage tower aeration tank

This study's objective was to clarify both experimentally and theoretically whether a vertical multistage tower aeration tank system is advantageous as compared with a completely mixed system, particularly with respect to purification efficiency, sludge settleability, and excess sludge production. In comparing the two systems: (1) purification efficiency in the multistage tower aeration system with partial fluid mixing with a large Peclet number was higher than in a corresponding completely mixed system for all applied organic loadings; (2) the multistage tower aeration system had some definite advantages with respect to sludge settleability and excess sludge production; (3) the activated sludge system's higher performance with partial fluid mixing was shown quantitatively with the axial dispersion model in conjunction with growth kinetics which involved rapid uptake such as biosorption and subsequent oxidative biodegradation processes of organic substances.

A model for evaluation of activated sludge process performance

A model for evaluation of activated sludge process performance

The Response of Activated Sludge Process to Hazardous Organic Wastes

The response of a laboratory-scale activated sludge unit to diethyl phthalate, dimethyl phthalate, 2,4-dinitrophenol, 2,4-dimethylphenol and 4-nitrophenol was examined. The system tolerated phthalate esters well and the acclimation was quick. The response of the system to stepwise increasing concentrations of other hazardous compounds was observed as increasing effluent COD and solids losses from the system due to changing settling characteristics of the sludge. It was concluded that: (1) Diethyl phthalate and dimethyl phthalate do not affect activated sludge process performance, and their removal rates (measured in terms of COD) are high (95 percent or better). (2) High concentrations (in excess of 900 mg/L) of phthalate esters are tolerated well by activated sludge, and acclimation to each step increase requires just a few days. (3) Acclimation to 2,4-dinitrophenol is slower, and approximately 8 mg/L of this compound is enough to upset system performance temporarily. (4) Activated sludge is also a viable process (in terms of COD removal) for wastes containing 2,4-dimethylphenol in addition to phthalate esters and 2,4-dinitrophenol. (5) Activated sludge may not tolerate hazardous organic wastes well if the wastewater composition is complex. (6) Acclimation of activated sludge process to a particular organic compound (4-nitrophenol in this study) will improve the response of the system to a shock load by the same compound.

The Effect of Activated Carbon Pore Structure on Activated Sludge Process Performance

The Effect of Activated Carbon Pore Structure on Activated Sludge Process Performance

Activated sludge response to emulsified lipid loading

The possible adverse effects of natural fats and oils (lipids) upon biological wastewater treatment systems have been the subject of much speculation and some disagreement. This study addressed the specific question of possible effects of emulsified lipids upon activated sludge process performance. Lipid form and fatty acid composition were determined on wastewater samples. Experimental studies employing bench scale activated sludge units indicated that effluent quality is either not significantly different or occasionally is better than that from sucrose supplemented control plants receiving comparable organic loading (F/M > 0.80). Furthermore, emulsified lipids clearly do not exhibit an inhibitory effect on either the specific soluble substrate utilization rate or the mixed liquor oxygen consumption rate. However, effluent quality parameters were found to be dependent upon unit lipid loading to a highly significant degree. As well, unit lipid loading (g lipid g −1 MLSS-day) provided a better explanation of effluent quality than either the food to microorganism ratio or the mixed liquor lipid burden (g lipid extracted from MLSS g −1 MLSS). The findings of this study indicate the conditions where lipid overloading occurs. This data provides a basis for controlling emulsified lipid loading to the activated sludge process which should apply to plants which receive high lipid loading such as those encountered in industrial wastewater treatment applications.

Optimal periodic control of activated sludge processes: II. comparison with conventional control for structured sludge kinetics

Earlier computational studies of optimal periodic operation of wastewater treatment plants are extended to include comparisons with classical control performance and to consider a structured sludge kinetics model. For two quite different examples, periodic control reduces effluent BOD and/or its variability relative to conventional control. Furthermore, the optimal periodic control for structured sludge kinetics can be substantially different from the Monod/decay sludge kinetics result, illustrating the importance of accurate identification of sludge kinetics for optimizing activated sludge process performance.

The effect of inorganic salts on the activated sludge process performance

The effect of inorganic salts such as sodium chloride and sodium sulfate on the performance of the activated sludge process was examined. When proper acclimation procedures were followed, the adverse effects of salts on the process were minimized. One of the parameters monitored, effluent suspended solids, had very low values (less than 10 mg l −1) up to an inflow sodium chloride concentration of about less than 35 gl −1. The chemical oxygen demand of the effluent increased steadily with increasing sodium chloride concentrations, but biochemical oxygen demand values remained very low (less than 5 mg l −1) which indicated that the increase in chemical oxygen demand was due to the portion that cannot be degrated biologically. The effect of sodium sulfate on the system was even less profound. In addition to the effluent being very clear and low in suspended solids, the chemical oxygen demand removal efficiency remained high.