Two-phase Partitioning Bioreactor Research Articles

The Ultimate Fate of Reactive Dyes Absorbed onto Polymer Beads: Feasibility and Optimization of Sorbent Bio-Regeneration under Alternated Anaerobic–Aerobic Phases

Dyes employed in many production cycles are characterized by high toxicity and persistence in the environment, and conventional wastewater treatments often fail to reach high removal efficiencies. Consequently, there is an increasing research demand aimed at the development of more efficient and sustainable technologies. A two-step strategy consisting of dye sorption followed by sorbent bio-regeneration is proposed here, with a special focus on the regeneration step. The objective of this study was to establish the best operating conditions to achieve regeneration of dye-loaded polymers and concurrently the ultimate removal of the dyes. To this aim, the bio-regeneration of the Hytrel 8206 polymer, used as a sorbent material to remove Remazol Red dye from textile wastewater, was investigated in a two-phase partitioning bioreactor (TPPB) under alternated anaerobic–aerobic conditions. Comprehensive analysis of operational parameters, including sorbent load and initial contamination levels, was conducted to optimize bio-regeneration efficiency. Experimental data demonstrated high regeneration efficiencies (91–98%) with biodegradation efficiencies up to 89%. This study also examines the biodegradation process to investigate the fate of biodegradation intermediates; results confirmed the successful degradation of the dye without significant by-product accumulation. This research underscores the potential of TPPB-based bio-regeneration of polymeric sorbent material for sustainable wastewater treatment, offering a promising solution to the global challenge of dye pollution in water resources.

Isolation and Identification of Naphthalene-Degrading Bacteria and its Application in a Two-phase Partitioning Bioreactor.

Naphthalene is a persistent environmental pollutant for its potential teratogenic, carcinogenic and mutagenic effects. In this study, 10 strains of bacteria capable of degrading naphthalene were isolated from crude-oil contaminated soil. Among them, Pseudomonas plecoglossicida 2P exhibited prominent growth with 1000 mg/L naphthalene as the sole carbon source and degraded 94.15% of naphthalene in 36 h. Whole genome sequencing analysis showed that P. plecoglossicida 2P had a total of 22 genes related to naphthalene degradation, of which 8 genes were related to the salicylic acid pathway only, 5 genes were related to the phthalic acid pathway only, 8 genes were common in both the salicylic acid and phthalic acid pathways, and 1 gene was related to the gentisic acid pathway. P. plecoglossicida 2P was applied in a two-phase partition bioreactor (TPPB) to degrade naphthalene in wastewater. The optimal operating conditions of the reactor were obtained through response surface optimization: initial naphthalene concentration (C0) =1600 mg/L, bacterial liquid concentration (OD600) = 1.3, and polymer-to-wastewater mass ratio (PWR) = 2%. Under these conditions, the naphthalene degradation rate was 98.36% at 24 h. The degradation kinetics were fitted using the Haldane equation with a high coefficient of determination (R2=0.94). The present study laid foundations for naphthalene degradation mechanism of genus Pseudomonas and its potential application in TPPB.

Techno-environmental and economic assessment of color removal strategies from textile wastewater

The textile industry is one of the most chemical-intensive processes, resulting in the unquestionable pollution of more than a quarter of the planet's water bodies. The high recalcitrant properties of some these pollutants resulted on the development of treatment technologies looking at the larger removal efficiencies, due to conventional systems are not able to completely remove them in their effluents. However, safeguarding the environment also implies taking into account indirect pollution from the use of chemicals and energy during treatment. On the other hand, the emerged technologies need to be economically attractive for investors and treatment managers. Therefore, the costs should be kept under control. For this reason, the present study focuses on a comparative Life Cycle Assessment and Life Cycle Costing of four scale-up scenarios aiming at mono and di-azo reactive dyes removal from textile wastewater. Two reactors (sequencing batch reactor and two-phase partitioning) were compared for different reaction environments (i.e., single anaerobic and sequential anaerobic-aerobic) and conditions (different pH, organic loading rates and use of polymer). In accordance with the results of each scenario, it was found that the three technical parameters leading to a change in the environmental profiles were the removal efficiency of the dyes, the type of dye eliminated, and the pollutant influent concentration. The limitation of increasing organic loading rates related to the biomass inhibition could be overcame through the use of a novel two-phased partitioning bioreactor. The use of a polymer at this type of system may help restore the technical performance (84.5 %), reducing the toxic effects of effluents and consequently decreasing the environmental impact. In terms of environmental impact, this is resulting into a reduction of the toxic effects of textile effluents in surface and marine waters compared to the homologous anaerobic-aerobic treatment in a sequencing batch reactor. However, the benefits achieved for the nature comes with an economic burden related to the consumption of the polymer. It is expected that the cost of investment of the treatment with the two-phase partitioning bioreactor rises 0.6–8.3 %, depending on market prices, compared to the other analyzed sequential anaerobic-aerobic technologies. On the other side, energy and chemical consumption did not prove to be limiting factors for economic feasibility.

Roles of n-hexadecane in the degradation of dibenzofuran by a biosurfactant-producing bacterium Rhodococcus sp.

The hydrophobic nature of dioxins is a major obstacle to their bioremediation. The present study attempted to improve the bioaccessibility of dioxins in two-phase partitioning bioreactors and activated sludge reactors. Dibenzofuran and n-hexadecane were used as model compounds for dioxins and non-aqueous phase liquids (NAPLs), respectively. First, biosurfactants produced by dioxin-degrading Rhodococcus sp. strain p52 were analyzed. Then, the role of n-hexadecane during the biodegradation of dibenzofuran was evaluated. The results showed that high NAPL ratios (n-hexadecane ≥40 g/L) in the two liquid-phase systems favored dibenzofuran removal, while the cell surface of strain p52 became extremely hydrophobic (>97%), which promoted its adhesion to NAPLs and subsequent transport of dibenzofuran from NAPL to the cells. In addition, a bioaugmented activated sludge reactor with n-hexadecane as the supplemented carbon source could not only facilitate the aerobic granular sludge formation but also improve dibenzofuran removal and the activated sludge settling properties. Simultaneously, conjugative transfer of catabolic plasmids was promoted. This study demonstrated the potential application of strain p52 with NAPLs for the bioremediation of dioxins.

Novel magnetic non-aqueous phase liquid with superior recyclability for efficient and sustainable removal of gaseous n-hexane using two-phase partitioning bioreactor

Two-phase partitioning biotechnology has been recognized as effective alternative in enhancing the purification of hydrophobic waste-gas. However, current available non-aqueous phases (NAPs) are either difficult to be recovered or exhibit low affinity for hydrophobic pollutants, causing secondary pollution, high operating costs, or limited removal efficiency. Herein, nano silicon oil-based ferrofluid (SOF), featured with high pollutants affinity and magnetism, was synthesized and employed as an innovative NAP liquid in airlift reactors for gaseous n-hexane removal. The removal efficiency of n-hexane (540 mg m−3) reached about 90.0% during 90-day operation, and the used SOF could be quickly recovered via magnetism with a high ratio of 95.6%. Mechanism analysis found, the microbial cell surface hydrophobicity was sustainably improved under the induction of SOF, allowing abundant bacteria adhered on SOF-water interface, thereby enhancing the n-hexane mass transfer directly from SOF to microorganisms. Furthermore, the microbial activity was accelerated, and potential n-hexane-degrading functional microorganisms might be domesticated.

Removal of volatile methyl siloxanes in an anoxic two-phase partitioning bioreactor operated with hydrophobic biomass

Volatile methyl siloxanes (VMS) generated during the anaerobic digestion of organic matter laden with polydimethylsiloxane are key biogas pollutants responsible of irreversible damage to energy-production equipment. This study presents a next-generation two-phase partitioning bioreactor operated with hydrophobic biomass under anoxic conditions for the removal of octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) as model VMS commonly found in biogas. When supplied in mixture, D4 and D5 average removal efficiencies (RE) of 26.7 ± 6.4 and 24.1 ± 5.9 % were achieved in the control operating phase using only aqueous mineral salt medium. Addition of 15 % (v/v) of silicone oil boosted the reactor performance, resulting in RE of up to 69.4 ± 9.7 and 85.1 ± 1.6 % for D4 and D5, respectively. D5 removal was enhanced when no D4 was fed, reaching a D5 RE of 91.8 ± 4.0 % and revealing a competitive inhibition between both VMS. The VMS removal in presence of silicone oil was concomitant with nitrate consumption rates of 412 ± 267–1846 ± 1605 mg m−3h−1. Microbial attachment on the water/silicone oil interface was confirmed by observations in the microscope at a 100 × magnification as well as by changes in the silicone oil color and texture. 16S rRNA high-throughput sequencing showed that while Mycobacterium was by far the predominant genera attached to silicone oil with a relative abundance of 92.2 %, Mycobacterium, Romboutsia, Clostridium, Intestinibacter, and Terrisporobacter were the predominant bacterial genera in aqueous phase after 127 days of operation with relative abundances of 25.3, 25.2, 12.3, 7.7, and 5.9 %, respectively.

Two-Phase Partitioning Bioreactor for the Treatment of Crude Oil- Contaminated Aqueous Solution

A new application of a combined solvent extraction and two-phase biodegradation processes using two-liquid phase partitioning bioreactor (TLPPB) technique was proposed and developed to enhance the cleanup of high concentration of crude oil from aqueous phase using acclimated mixed culture in an anaerobic environment. Silicone oil was used as the organic extractive phase for being a water-immiscible, biocompatible and non-biodegradable. Acclimation, cell growth of mixed cultures, and biodegradation of crude oil in aqueous samples were experimentally studied at 30±2ºC. Anaerobic biodegradation of crude oil was examined at four different initial concentrations of crude oil including 500, 1000, 2000, and 5000 mg/L. Complete removal of crude oil was achieved biphasic bioreactor after 3 weeks compared to 73-82% in the monophasic bioreactor for the same time period.

Two liquid phase partitioning bioreactor system for toxicant free water production from phthalates contaminated aqueous medium

Biodegradation of DMP (dimethyl phthalate) and DEP (diethyl phthalate) is a global environmental concern due to their endocrine disrupting nature. In the present study, biodegradation of DEP as the single substrate and a mixture of DMP and DEP as dual substrates were examined in a two-phase partitioning bioreactor (TPPB) using Cellulosimicrobium funkei. The TPPB system was run under batch and fed-batch modes of operation at different initial concentrations of DEP and mixture of DMP and DEP. Under the batch mode of operation, 93% degradation was achieved by C. funkei within 60 h with 38.75 mgL−1h−1 degradation rate. In the fed-batch system, complete degradation was observed up to 3500 mg/L total initial concentration of the phthalates (1500 mg/L DEP and 2000 mg/L DMP) within 24h. Phytotoxicity assessment of the treated water by seed germination and brine shrimp lethality assays revealed a germination index value of 86.17 and 13.33% brine shrimp mortality. Overall, this study revealed a very good potential of the TPPB system for detoxification of endocrine disrupting chemicals in the environment.

Airlift two-phase partitioning bioreactor for dichloromethane removal: Silicone rubber stimulated biodegradation and its auto-circulation.

Solid non-aqueous phases (NAPs), such as silicone rubber, have been used extensively to improve the removal of volatile organic compounds (VOCs). However, the removal of VOCs is difficult to be further improved because the poor understanding of the mass transfer and reaction processes. Further, the conventional reactors were either complicated or uneconomical. In view of this, herein, an airlift bioreactor with silicone rubber was designed and investigated for dichloromethane (DCM) treatment. The removal efficiency of Reactor 1 (with silicone rubber) was significantly higher than that of Reactor 2 (without silicone rubber), with corresponding higher chloride ion and CO2 production. It was found that Reactor 1 achieved a much better DCM shock tolerance capability and biomass stability than Reactor 2. Silicone rubber not only enhanced the mass transfer in terms of both gas/liquid and gas/microbial phases, but also decreased the toxicity of DCM to microorganisms. Noteworthily, despite the identical inoculum used, the relative abundance of potential DCM-degrading bacteria in Reactor 1 (91.2%) was much higher than that in Reactor 2 (24.3%) at 216h. Additionally, the silicone rubber could be automatically circulated in the airlift bioreactor due to the driven effect of the airflow, resulting in a significant reduction of energy consumption.

Preparation and physicochemical characterization of deep eutectic solvents and ionic liquids for the potential absorption and biodegradation of styrene vapors

Styrene emissions can be treated by physicochemical, biological, or physicochemical/biological means. Due to its low solubility in water an alternative to eliminate styrene emissions from air is the use of two-phase partitioning bioreactors (TPPBs) which comprised a hydrophobic non-aqueous phase (NAP) which can improve mass transfer of styrene. This study was devoted to prepare and evaluate the main physicochemical characteristics of novel NAPs such as Ionic liquids (ILs), Deep Eutectic Solvents (DESs) and Natural Deep Eutectic Solvents (NADEs) as well as their toxicity and biodegradability to treat styrene vapors. Absorption experiments of styrene showed that the best NAPs were the DESs formed with Tetrabutylammonium bromide and decanoic acid and the ILs [C6mim][FAP], [C4mim] [NTf2] and [C4mim] [PF6], since they presented a styrene partition coefficient between 0.0015 and 0.0041. Finally, the IL [C6mim][FAP] was used as a NAP in a TPPB batch process given its high styrene affinity, low solubility in water and non-biodegradability; styrene mineralization was three times higher in the TPPB compared with the control. ILs are potential adjuvant phases in biological degradation systems, as well as other solvents like DESs and NADESs.

Removal of a Mixture of Seven Volatile Organic Compounds (VOCs) Using an Industrial Pilot-Scale Process Combining Absorption in Silicone Oil and Biological Regeneration in a Two-Phase Partitioning Bioreactor (TPPB)

The treatment of a synthetic polluted gas containing seven volatile organic compounds (VOCs) was studied using a pilot plant in real industrial conditions. The process combined VOC absorption in silicone oil (PolyDiMethylSiloxane, i.e., PDMS), a biological regeneration of the PDMS in a two-phase partitioning bioreactor (TPPB), and a phase separation including settling and centrifugation. The TPPB was operated at a water/PDMS volume ratio of 75/25. The VOCs treatment performance was efficient during the entire test, corresponding to 10 PDMS regeneration cycles. The analysis of the content of the aqueous phase and PDMS confirmed that VOCs are progressively degraded until mineralization. The nitrogen consumption and the characterization of the microorganisms highlighted possible anoxic functioning of the biomass within the first decanter. Moreover, although the absorption and biodegradation performances were very satisfactory, the separation of all phases, essential for the PDMS recycling, was problematic due to the production of biosurfactants by the microorganisms, leading to the formation of a stable emulsion and foaming episodes. As a consequence, the packed column showed slight fouling. However, no significant increase in the pressure drop of the packed bed, as well as no significant impact on VOC absorption efficiency was observed.

Coping with mass transfer constrains in dark fermentation using a two-phase partitioning bioreactor

In dark fermentation systems, the accumulation of byproducts (i.e., carboxylic acids, hydrogen) in the aqueous phase can cause the inhibition of key metabolic pathways. Two-phase partitioning reactors are an alternative solution for reducing the concentration of hydrogen (H2) and CO2 in the aqueous phase by improving the mass transfer of these gases to the organic phase. From batch reactors, it was found that silicone oil at a proportion of 10% (v/v) led to the highest volumetric H2 production rate (VHPR, 4.1 L H2/L-d). The results in continuous reactors showed that using silicon oil the VHPR and carboxylic acids production increased up to 13% and 24%, respectively (i.e., VHPR = 27.6 L H2/L-d and 29.8 g/L of carboxylic acids at a substrate loading of 138 g total carbohydrates/L-d). These results could be explained by the enhancement of the following mass-transfer mechanisms: i) H2 and CO2 transfer from microorganisms to the extractive organic phase, ii) Diffusion of dissolved H2 and CO2 into the extractive organic phase, and iii) Transfer by convection of dissolved H2 and CO2 to the gas phase. Furthermore, the thermodynamic analysis revealed that the addition of silicone oil also improved the feasibility of the fermentation process by increasing the Gibbs free energy up to 27% compared to the control without silicone oil (i.e., –172.6 kJ/mol vs –219.23 kJ/mol, at a substrate loading of 60 g total carbohydrates/L-d). Overall, the use of an organic extractive phase is a novel and effective strategy to increase the performance of dark fermentation systems for biofuel production.

Enhanced biodegradation of n-hexane in a two-phase partitioning bioreactor inoculated with Pseudomonas mendocina NX-1 under chitosan stimulation

Two-phase partitioning bioreactors (TPPBs) have been extensively used for volatile organic compounds (VOCs) removal. To date, most studies have focused on improving the mass transfer of gas phases/non-aqueous phases (NAPs)/aqueous phases, whereas the NAP/biological phases and gas/biological phases transfer has been neglected. Herein, chitosan was introduced into a TPPB to increase cell surface hydrophobicity (CSH) and improve the n-hexane mass transfer. The performance and stability of the TPPB with chitosan for n-hexane biodegradation were investigated, and it was found out that the TPPB with chitosan achieved maximum removal efficiency and elimination capacity of 80.6% and 26.5 g m−3 h−1, thereby reaching much higher values than those obtained without chitosan (61.3% and 15.2 g m−3 h−1). Chitosan not only obvio usly increased cell surface hydrophobicity and cell dry biomass on the surface of silicone oil, but might also allow hydrophobic cells in aqueous phases to directly capture and biodegrade n-hexane, resulting in an obvious improvement of mass transfer from the gas phase to biomass. Stability enhancement was another attractive advantage from chitosan addition. This study might provide a new strategy for the development of TPPB in the hydrophobic VOCs treatment.

A mathematical model for VOCs removal in a treatment process coupling absorption and biodegradation

Biological treatments are used in gas treatment when containing Volatile Organic Compounds (VOC). Key factor to enhance treatment efficiency is to maximize mass transfer from gas to liquid. VOCs can be removed from the gas flow by absorption in a separate gas–liquid contactor before entering a Two-Phase Partitioning Bioreactor (TPPB) (Two-stage unit). The Non-Aqueous Phase Liquid (NAPL), a silicone oil in this study, is able to solubilize large amounts of hydrophobic VOCs while avoiding toxicity effects on the microorganisms.The aim of this study is to provide a designing tool for the degradation process occurring in the TPPB. Simulations considering mass transfer coupled with biodegradation kinetics were considered when investigating the TPPB mechanisms. A single VOC (toluene) was first taken as a reference to assess the accuracy of the model in comparison with experimental results. A mixture of seven VOCs (toluene, m-xylene, 1,3,5 trimethylbenzene, n-heptane, ethyl acetate, methyisobutylketone and isopropyl alcohol) presenting a wide range of hydrophobicity was then implemented in the model considering no interaction regarding their biodegradation. Degradation kinetics of the mixture (representing an actual exhaust gas from an industrial plant) were compared with experimental results. The developed model tends to highlight that modeling results are closed to experimental results. The results delivered by the model shows that mass transfer, through the “kLa” value, is a key parameter to enhance efficiency of NAPL renewal by biological regeneration.

Pilot-Scale VOC Treatment Process Combining Absorption in Silicone Oil and Biological Regeneration in a Two-Phase Partitioning Bioreactor (TPPB) by Activated Sludge

Pilot-Scale VOC Treatment Process Combining Absorption in Silicone Oil and Biological Regeneration in a Two-Phase Partitioning Bioreactor (TPPB) by Activated Sludge

Batch degradation of trichloroethylene using oleaginous Rhodococcus opacus in a two-phase partitioning bioreactor and kinetic study

In the present study, we present the biodegradation of trichloroethylene (TCE) for the first time using pure bacterial strain of Rhodococcus opacus PD630. TCE utilized as the sole carbon substrate by R. opacus in single phase system and was reached to highest specific growth rate of 0.015 h−1 at the concentration of 75 mg L−1. To further enhance the degradation performance even at high concentration (1000 mg L−1), two-phase partitioning bioreactor (TPPB) was developed. Silicone oil (20%, v/v) was selected as non-aqueous phase solvent to achieve high metabolic activity of bacteria. Furthermore, the experimental results of TCE degradation and specific TCE utilization rate were fitted to various kinetic models. Our experimental results clearly revealed that TPPB system having R. opacus as biological source and silicone oil as solvent was highly efficient and successful for removing high concentrated TCE compared with single phase system.

Self-regenerating tubing bioreactor for removal of toxic substrates: Operational strategies in response to severe dynamic loading conditions

A tubing TPPB (Two-Phase Partitioning Bioreactor) was operated with the objective of verifying the effective treatment of a phenolic synthetic wastewater with simultaneous polymeric tubing bioregeneration by introducing tubing effluent recycle and modifications to the Hydraulic Retention Time (HRT). 2,4-dichlorophenol (DCP) was employed as the target substrate and the bioreactor was operated for a 3 month period under severe loading conditions (from 77 to 384 mg/L d) with HRT in the tubing in the range of 2–4 h. Tubing effluent recycle (recycle flow rate/influent flow rate ratio = 0.3) was applied when a loss of performance was detected arising from the increased load. For HRT values of 3 and 4 h, almost complete DCP removal was achieved after a few days (1–5) of operation while for the 2 h HRT (i.e. in the most severe loading condition) the DCP removal was ≥97%. A beneficial effect on the process performance arising from recycle application was evident for all the operating conditions investigated, and was confirmed by statistical analysis. Essentially complete polymer bioregeneration was achieved when the bioreactor was operated at the lowest HRT (i.e. 2 h), combined with the application of tubing effluent recycle. The results of this study highlighted several advantages of the tubing TPPB configuration in a comparative analysis of different regeneration options, including the possibility of operating continuously with simultaneous bioregeneration and without the need for additional units or operational steps and extra-energy consumption.

Performance evaluation and neural network modeling of trichloroethylene removal using a continuously operated two-phase partitioning bioreactor

Abstract Biological reactors have widely used in waste gas treatment. The inclusion of non-biodegradable organic solvents (silicone oil) to these reactors is a way to improve/enhance the removal capacity of the biological systems. This study aimed to evaluate the performance of a two-phase continuous stirred tank bioreactor (CSTB) for the removal of trichloroethylene (TCE) by Rhodococcus opacus. The effect of inlet TCE concentration in the range 0.3–3.44 g m−3 on TCE removal studied for 77 days continuously in the CSTB system. During the operation, complete TCE removal has obtained for a high TCE concentration of 1.12–2.62 g m−3 due to the addition of silicone oil as the non-aqueous phase. The maximum elimination capacity was found 372.55 g m−3 h−1 at the inlet TCE loading rate of 423.36 g m−3 h−1. The carbon dioxide (CO2) concentration profile and biomass growth profile from the CSTB revealed that the robustness of the oleaginous bacteria R. opacus in TCE removal. The artificial neural network (ANN) based model was able to successfully predict the performance of the bioreactor using the Levenberg–Marquardt (LM) back propagation algorithm. The prediction accuracy of the model was high as the experimental data and is in good agreement (R 2 = 0 .9923) with the ANN predicted data. This is the first report that used ANN to model a two-phase CSTB treating high TCE polluted stream. Overall, the results indicated that the addition of silicone oil could efficiently improve TCE removal in a two-phase continuous bioreactor.

Biological Treatment Processes for the Removal of Organic Micropollutants from Wastewater: a Review

Micropollutants or contaminants of emerging concern (CECs) are released into the environment from a wide variety of sources. Due to the adverse effect on human health, micropollutant-containing wastewater needs to be treated before its discharge. A number of conventional physicochemical methods have been extensively studied for micropollutant degradation. However, owing to their one or more disadvantages, biological treatment using suitable microorganisms is of recent interest. Numerous bacteria and fungi are capable of degrading these micropollutants even at high concentrations. However, in order for the biological treatment to be commercially viable and industrially scalable, bioprocess development with efficient bioreactor systems is highly essential. This paper reviews state-of-the-art techniques for the removal of micropollutants by conventional biological systems such as activated sludge process, biofilm-based reactor, and trickling bed bioreactor. However, compared with conventional systems, advanced biological systems, namely two-phase partitioning bioreactor, membrane-based reactor, and cell-immobilized bioreactor systems, have not been examined and, hence, need detailed exploration. Such advanced treatment systems are capable of tolerating high pollutant load and are also able to treat highly water insoluble pollutants. Furthermore, hybrid systems comprising of a combination of different physicochemical and biological processes are discussed in this paper, which are not only capable of improving the treatment efficiency but also eliminate any accumulation of the toxic by-product produced during the treatment. Among the different hybrid systems, a combination of different biological systems is found to be highly efficient in treating micropollutant-containing wastewater. Finally, scope for future research prospects in the field are derived and addressed in details.

Enhancing biodegradation of toxic industrial wastewaters in a continuous two-phase partitioning bioreactor operated with effluent recycle

In this study, we propose the application of a Continuous Two-Phase Partitioning Bioreactor (C-TPPB) operated with the tubing effluent recycle to enhance the biodegradation of toxic substrates in industrial wastewaters under severe loading conditions. Stepwise increasing influent concentrations (from 200 to 900 mg L−1) of 2,4-dichlorophenol (2,4-DCP) were fed to a C-TPPB operated with Hytrel G3548 tubing to simulate phenolic wastewater. Practically complete 2,4-DCP removal has been achieved during the entire experimental period, but the increased load reduced biodegradation efficiency. At influent concentration of 700 mg L−1, the first effluent recycle (recycle /influent flow rate ratio = 0.3) was applied: biodegradation efficiency doubled from 40 to 80% and was maintained until influent concentrations of 800 mg L−1. Higher influent concentrations caused a decrease in 2,4-DCP biodegradation, so the effluent recycle ratio was increased to 0.5 at 900 mg L−1 and, also in this case, the bioreactor showed a fast recovery (∼ 24 h) of the biodegradation efficiency at 80%. Mass transfer data analysis showed that the effluent recycle resulted in an increase of the mass transfer coefficient. This positive effect, joined with the reduction of the influent concentrations, demonstrated the feasibility of recycle application in enhancing the C-TPPB performance.