1,721,010 research outputs found
2,4-Dichlorophenol removal in a solid-liquid two phase partitioning bioreactor (TPPB): Kinetics of absorption, desorption and biodegradation
No full textThe applicability of a sequencing batch two phase partitioning bioreactor (TPPB) to the biodegradation of a highly toxic compound, 2,4-dichlorophenol (DCP) (EC50 = 2.3-40 mg L-1) was investigated. A kinetic study of the individual process steps (DCP absorption into the polymer, desorption and biodegradation) was performed and, based on favourable absorption/desorption characteristics (DCP diffusivity of 6.6 x 10(-8) cm(2) s(-1)), the commercial polymer Tone P787 (Dow Chemical), was utilized as the sequestering phase for TPPB operation. Batch kinetic biodegradation tests were performed in both single-and two-phase modes, and the Haldane equation kinetic parameters were estimated (k = 1.3 x 10(-2) mgDCP mgVSS(-1) h(-1), K-I = 35 mgDCP L-1 and K-s = 18 mgDCP L-1), confirming the highly toxic nature of DCP. Consistent with these findings, operation of the single-phase system showed that for an initial DCP concentration of 130 mg L-1 the biomass was completely inhibited and DCP was not degraded, while the two-phase system achieved near-complete DCP removal. In sequencing batch mode the TPPB had a removal efficiency of 91% within 500 min for a feed of 320 mg L-1, which exceeds the highest concentration previously degraded. These results have confirmed the effectiveness of the use of small amounts (5%, v/v) of inexpensive commercial polymers as the partitioning phase in TPPB reactors for the treatment of a highly toxic substrate at influent loads that are prohibitive for conventional single-phase operation, and suggest that similar detoxification of wastewater influents is achievable for other target cytotoxic substrates
Solid-liquid two-phase partitioning bioreactors (TPPBs) operated with waste polymers. Case study: 2,4-dichlorophenol biodegradation with used automobile tires as the partitioning phase
No full textUsed automobile tire pieces were tested for their suitability as the sequestering phase in a two-phase partitioning bioreactor to treat 2,4-dichlorophenol (DCP). Abiotic sorption tests and equilibrium partitioning tests confirmed that tire "crumble" possesses very favourable properties for this application with DCP diffusivity (4. 8 × 10-8 cm2/s) and partition coefficient (31) values comparable to those of commercially available polymers. Biodegradation tests further validated the effectiveness of using waste tires to detoxify a DCP solution, and allow for enhanced biodegradation compared to conventional single-phase operation. These results establish the potential of using a low-cost waste material to assist in the bioremediation of a toxic aqueous contaminant. © 2012 Springer Science+Business Media B.V
Ex situ remediation of polluted soils by absorptive polymers, and a comparison of slurry and two-phase partitioning bioreactors for ultimate contaminant degradation
No full textThe present study has provided a comparison between a conventional ex situ method for the treatment of contaminated soil, a soil slurry bioreactor, with a novel technology in which a contaminant is rapidly and effectively removed from the soil by means of absorptive polymer beads, which are then added to a two-phase partitioning bioreactor (TPPB) for biodegradation of the target molecule. 4-nitrophenol (4NP) was selected as a model contaminant, being representative of a large class of xenobiotics, and the DuPont thermoplastic Hytrel (TM) 8206 was utilized for its extraction from soil over ranges of soil contamination level, soil moisture content, and polymer:soil ratios. Since the polymers were able to rapidly (up to 77% and 85% in 4 and 24 h respectively) and selectively remove the contaminant, the soil retained its nutrient and microflora content, which is in contrast to soil washing which can remove these valuable soil resources. After 4h of reaction time, the TPPB system demonstrated removal efficiency four times higher (77% vs 20%) than the slurry system, with expected concomitant savings in time and energy. A volumetric removal rate of 75 mg4NP h(-1) L-1 was obtained in the TPPB, significantly greater than the value of 1.7 obtained in the slurry bioreactor. The polymers were readily regenerated for subsequent reuse, demonstrating the versatility of the polymer-based soil treatment technology. (C) 2013 Elsevier B.V. All rights reserved
Biodegradation of 4-Nitrophenol in a Two-Phase System Operating with Polymers as the Partitioning Phase
No full textThe present study has demonstrated the enhanced performance of a two-phase bioreactor, operating with polymers as a partitioning phase, as an alternative to both single phase biotreatment and to the use of an immiscible organic solvent partitioning phase, to deliver a toxic substrate (4-nitrophenol, or 4NP) to a microbial consortium in batch and repeated batch mode. Three commercial polymers were tested, Hytrel, Tone, and Elvax, and were shown to have superior properties related to the use of a consortium, including complete biocompatibility with the biomass and nonbiodegradability. Repeated kinetic tests performed with short reaction times demonstrated the accumulation of 4NP within the polymers in the range of 6-8 mg/g polymer, which reduced polymer performance in subsequent batch operations. Hytrel gave the best performance with residuals of up to 4 mg/g polymer showing no reduction in subsequent use, while for the other polymers a 4NP value lower than 2 mg/g polymer was required to have acceptable performance during repeated polymer use. Polymer reuse without affecting the process efficiency was confirmed with regeneration tests. A conventional methanol extraction method, as well as biological regeneration of the polymers by prolonged contact with the biomass, were assessed for their ability to remove the residual 4NP. Parallel kinetic tests performed with new and regenerated polymers showed a complete overlap of the 4NP concentration profiles indicating that a simple biological regeneration method provides a means of completely restoring polymer performance for repeated batch operation
Two-Phase Partitioning Bioreactors Operating with Polymers Applied to the Removal of Substituted Phenols
No full textSignificant improvement in biodegradation performance has been demonstrated arising from the reduction of cytotoxicity provided by the sequestering of 4-nitrophenol (4NP) within Hytrel polymer beads added to a two-phase partitioning bioreactor (TPPB) operating in sequencing batch reactor (SBR) mode. This reduced toxicity is particularly apparent as the feed substrate concentration is increased; in fact it was shown that at a feed of 1000 mg/L 4NP, the inhibitory effect of the substrate completely prevents degradation from occurring in a single-phase system, whereas at only a 5% polymer loading, rapid and compete biodegradation is achieved. Different polymer/aqueous phase ratios were used to detoxify varying feed concentrations, and degradation rates were enhanced through the use of increased polymer loadings. As demonstrated in oxygen uptake experiments, the addition of polymers also reduces the maximum demand for oxygen, relative to single-phase operation, and smoothes the demand for oxygen throughout the degradation process. Polymer regeneration has also been further characterized by quantifying the number of methanol washes required to achieve satisfactory 4NP residuals, and the addition of a small amount of cosolvent has been shown to dramatically increase the rate of bioregeneration to produce beads ready for reuse
Analysis of the performance and criteria for rational design of a sequencing batch reactor for xenobiotic removal
No full textSubstrate toxicity can impose operability challenges in the biological treatment of xenobiotic compounds. These can arise from transients in the feed to conventional continuous processes, as well as in more challenging systems, sequencing batch reactors (SBRs), whose operation is always inherently dynamic. Via the use of the classic Haldane model for microbial toxicity, and unsteady-state material balance equations for SBR operation, we have analysed the behaviour of an SBR reactor operating over multiple cycles and have shown that both high performance and low performance can be obtained depending on the feed substrate concentration and the selected SBR exchange ratio. That is, both the intrinsic microbial kinetics as well as the selection of process operating conditions can lead either to high performance (high removal efficiency) or low performance (low removal efficiency) operation. Using this approach, we have also discussed the performance for the SBR treatment of 2 "real" substrates possessing widely different kinetic parameters, showing the impact of these parameters, as well as process operating conditions, on the operability of SBR biotreatment systems handling xenobiotic compounds. This could be of significant value to practitioners wishing to select high performance operating regimes for the treatment of a specific xenobiotic compound. To our knowledge, this is the first systematic study of the impact of substrate toxicity on SBR operability, and is also a first step in modeling the impact of substrate detoxification, via the use of discontinuous Two-Phase Partitioning Bioreactors, on the dynamic performance of xenobiotic biotreatment processes. (C) 2013 Elsevier B.V. All rights reserved
Removal of Xenobiotics from Wastewater in Sequencing Batch Reactors: Conventional and Two-Phase Configurations
No full textTreatment of substituted phenol mixtures in single phase and two-phase solid-liquid partitioning bioreactors
No full textThe biological treatment of phenolics is constrained by the inherent cytotoxicity of these compounds. One method to alleviate such toxicity is to add a sequestering phase to absorb, and subsequently release, the substrate(s) to the micro-organisms; such a system is termed a Two Phase Partitioning Bioreactor. Here we have compared the performance of a TPPB, relative to single phase operation, in which a small volume (5%, v/v) of beads of the polymer Hytrel 8206 was used to treat aqueous mixtures of 2,4-dimethylphenol and 4-nitrophenol. Hytrel 8206 was selected from a range of polymers that were tested for their partition coefficients (PCs) for the target molecules, with the more hydrophobic compound (2,4-dimethylphenol) having a higher PC value (201) than 4-nitrophenol (143). Significantly increased removal rates for both substrates were demonstrated in TPPB mode relative to single phase operation. Additionally, the differential release of the compounds to the aqueous phase and their distinct PC values changed the kinetic pattern of the biotreatment system, smoothing out the cellular oxygen demand. Release of the substrates by the polymer over 60 operating cycles was virtually complete (>97%) demonstrating the reusability and robustness of the use of polymers in overcoming cytotoxicity of phenolic substrates. © 2011 Elsevier B.V
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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