Xenobiotic substrate reduces yield of activated sludge in a continuous flow system

Stoichiometric ratios for biotics and xenobiotics capture effective metabolic coupling to re(de)fine biodegradation

Preserving human and environmental health requires anthropogenic pollutants to be biologically degradable. Depending on concentration, both nutrients and pollutants induce and activate metabolic capacity in the endemic bacterial consortium, which in turn aids their degradation. Knowledge on such 'acclimation' is rarely implemented in risk assessment cost-effectively. As a result, an accurate description of the mechanisms and kinetics of biodegradation remains problematic. In this study, we defined a yield 'effectivity', comprising the effectiveness at which a pollutant (substrate) enhances its own degradation by inducing (biomass) cofactors involved therein. Our architecture for calculation represents the interplay between concentration and metabolism via both stoichiometric and thermodynamic concepts. The calculus for yield 'effectivity' is biochemically intuitive, implicitly embeds co-metabolism and distinguishes 'endogenic' from 'exogenic' substances' reflecting various phenomena in biodegradation and bio-transformation studies. We combined data on half-lives of pollutants/nutrients in wastewater and surface water with transition-state rate theory to obtain also experimental values for effective yields. These quantify the state of acclimation: the portion of biodegradation kinetics attributable to (contributed by) 'natural metabolism', in view of similarity to natural substances. Calculated and experimental values showed statistically significant correspondence. Particularly, carbohydrate metabolism and nucleic acid metabolism appeared relevant for acclimation (R² = 0.11-0.42), affecting rates up to 10^4.9(±0.7) times: under steady-state acclimation, a compound stoichiometrically identical to carbohydrates or nucleic acids, is 10^3.2 to 10^4.9 times faster aerobically degraded than a compound marginally similar. Our new method, simulating (contribution by) the state of acclimation, supplements existing structure-biodegradation and kinetic models for predicting biodegradation in wastewater and surface water. The accuracy of prediction may increase when characterizing nutrients/co-metabolites in terms of, e.g., elemental analysis. We discuss strengths and limitations of our approach by comparison to empirical and mechanism-based methods.

Enhanced azo dye biodegradation performance and halotolerance of Candida tropicalis SYF-1 by static magnetic field (SMF)

Enhancing Acid Red B (ARB) decolorization by growing cells of a halotolerant yeast Candida tropicalis SYF-1 with static magnetic field (SMF) was investigated. Activity of key enzymes and membrane phospholipid fatty acids (PLFAs) were analyzed for estimating the change of metabolic activity and membrane salt-stress response, respectively. Possible enhancement mechanisms were revealed through comparative transcriptome analysis. The results showed that 95.0 mT SMF enhanced ARB decolorization by growing cells of a yeast SYF-1, as well as cell growth and halotolerance capability. Activity of intracellular lignin peroxidase (LiP) and laccase (Lac) was 1.51- and 1.47-fold higher with 95.0 mT SMF than that without SMF, respectively. Unsaturation degree and chain length of dominant PLFAs was increased by 95.0 mT SMF treatment. Several functional protein encoding unigenes related to organics biodegradation, cell growth and halotolerance were 1.17- to 4.19-fold up-regulated in response to 95.0 mT SMF.

Technologies for reducing sludge production in wastewater treatment plants: State of the art

This review presents the state-of-the-art sludge reduction technologies applied in both wastewater and sludge treatment lines. They include chemical, mechanical, thermal, electrical treatment, addition of chemical un-coupler, and predation of protozoa/metazoa in wastewater treatment line, and physical, chemical and biological pretreatment in sludge treatment line. Emphasis was put on their effect on sludge reduction performance, with 10% sludge reduction to zero sludge production in wastewater treatment line and enhanced TS (total solids) or volatile solids removal of 5-40% in sludge treatment line. Free nitrous acid (FNA) technology seems good in wastewater treatment line but it is only under the lab-scale trial. In sludge treatment line, thermal, ultrasonic (<4400kJ/kg TS), FNA pretreatment and temperature-phased anaerobic digestion (TPAD) are promising if pathogen inactivation is not a concern. However, thermal pretreatment and TPAD are superior to other pretreatment technologies when pathogen inactivation is required. The new wastewater treatment processes including SANI®, high-rate activated sludge coupled autotrophic nitrogen removal and anaerobic membrane bioreactor coupled autotrophic nitrogen removal also have a great potential to reduce sludge production. In the future, an effort should be put on the effect of sludge reduction technologies on the removal of organic micropollutants and heavy metals.

Application of ethylene diamine tetra acetic acid degrading bacterium Burkholderia cepacia on biotreatment process

Ethylene diamine tetra acetic acid (EDTA), the effluent of secondary biotreatment units, can be properly biodegraded by Burkholderia cepacia. Through batch degradation of EDTA, the raw wastewater of EDTA was controlled at 50 mg/L, and then nutrients was added in diluted wastewater to cultivate activated sludge, which the ratio of composition is depicted as "COD:N:P:Fe = 100:5:1:0.5". After 27 days, the removal efficiency of Fe-EDTA and COD was 100% and 92.0%, correspondingly. At the continuous process, the raw wastewater of EDTA was dictated at 166 mg/L before adding nutrients to cultivate activated sludge, in which the ratio of composition did also follow with batch process. After 22 days, the removal efficiency of Fe-EDTA and COD for experimental group was 71.46% and 62.58%, correspondingly. The results showed that the batch process was more suited for EDTA biodegradation.

Model development with defined biological mechanisms for xenobiotic treatment activated sludge at steady state

Activated sludge treatment of a xenobiotic organic compound, much different from treatment of biogenic organics, must be modeled with interactions involving a two-part biomass of degrader and nondegrader, which selectively or competitively grow on a two-part substrate of input xenobiotic and its biogenic metabolites. A xenobiotic treatment model was developed which incorporates kinetics of the growth of degrader and nondegrader, the line dividing metabolites into xenobiotic and biogenic, yields of degrader and nondegrader from utilization of their parts of substrates, and kinetics of degrader reversion to nondegrader due to instability of the degradative element degraders carry. Experimental activated sludge operated for treatment of a xenobiotic generated data for calibration of the model. With the input of influent xenobiotic concentration, mean cell and hydraulic residence times, and calibrated parameters, the model readily outputs concentrations of degrader, nondegrader, and effluent biogenic residue that closely match the results obtained from experiments.

Production of xenobiotic degrader for potential application in bioaugmentation

Continuous-flow chemostats were operated at different mean-cell-residence-times (θc) and influent concentrations of a xenobiotic (2,4-D) and biogenic substrates. Steady state chemostat biomasses' performances in 2,4-D degradation were analyzed with a mathematical model to determine the quantities of degrader the biomasses contained. The qualification for microbial cells to become degraders is a high grade of degradation kinetics. This qualification uniformly applies to all biomasses. The quantities of degraders vary inversely with the chemostats'θc. Biogenic substrates increase degrader yield such that a high biogenic and a high xenobiotic influent optimize degrader mass output. Economics evaluation performed around the optima finds the influent containing 5-25% 2,4-D carbon (TOC) in approximately 900 mg/l biogenic TOC, and the θc of 2-5d, are suitable operating conditions for a degrader producing bioreactor that may serve as a selector of biomass for bioaugmentation purposes.