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An integrated model of a two-step process for the ex situ bioremediation of xenobiotic contaminated soil has been formulated. The process is characterized by an initial extraction step of the organic contaminants from the polluted soil by contact with inexpensive and commercially-available polymer beads, followed by release and biodegradation of the xenobiotics, with parallel polymer bioregeneration, in a Two-Phase Partitioning Bioreactor (TPPB). The regenerated polymer is cyclically reused in the extraction step, so reflecting the robust and otherwise-inert properties of such polymers. The model was calibrated and validated for a soil contaminated with 4-nitrophenol (4NP) and treated with the DuPont polymer Hytrel 8206. In the model calibration, the partition coefficient polymer-soil, P ps , and the mass transfer coefficient, K, were evaluated, as 105.3 and 0.24 h -1 respectively. A diffusion coefficient within the polymer of 6.3 10 -8  cm 2  s -1 was determined from the fitting of sorption/desorption data. The model was then tested for two alternative process configurations consisting of either one or two soil extraction units, followed by the biodegradation/bioregeneration step. The latter configuration resulted in more effective polymer utilization and is suitable if each extraction step requires a shorter time than the regeneration step. The model predicted that an extraction time of 12 h was sufficient to reach removal efficiencies ≥90% while the biodegradation/bioregeneration step required 24 h to reach efficiencies ≥93%, with a good agreement with experimental data (R 2  > 0.98 for both cases). The simulation of the process operated with two extraction units showed a better performance with a final concentration ∼0.2 g 4NP kg ds -1 vs. 1.69 g 4NP kg ds -1 obtained with single extraction unit, for a soil contaminated with 10 g 4NP kg ds -1 . Corresponding extraction efficiencies were 96 and 83%, respectively., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The removal of a xenobiotic (4-chlorophenol) from contaminated water was investigated in a simulated continuous two-phase partitioning bioreactor (C-TPPB), fitted with coiled tubing comprised of a specifically-selected extruded polymer, Hytrel 8206. Wastewater flowed inside the tubing, the pollutant diffused through the tubing wall, and was removed in the aqueous bioreactor phase at typical biological removal rates in the C-TTPB simulated by varying aqueous phase throughput to the reactor. Operating over a range of influent substrate concentrations (500-1500mgL(-1)) and hydraulic retention times in the tubing (4-8h), overall mass transfer coefficients were 1.7-3.5×10(-7)ms(-1), with the highest value corresponding to the highest tubing flow rate. Corresponding mass transfer rates are of the same order as biological removal rates, and thus do not limit the removal process. The C-TPPB showed good performance over all organic and hydraulic loading ranges, with removal efficiencies of 4CP in the tubing wastewater stream always ≥96%. Additionally, the presence of the Hytrel tubing was able to buffer increases in organic loading to the hybrid system, enhancing overall process stability. Biological testing of the C-TPPB confirmed the abiotic test results demonstrating even higher 4-chlorophenol removal efficiency (∼99%) in the tubing stream., (Copyright © 2016 Elsevier B.V. All rights reserved.)

This paper proposes a dynamic model simulating the performance of a fed batch system operated as solid–liquid two-phase partitioning bioreactor, with polymer beads as the sequestering phase, applied to the removal of xenobiotic compounds from concentrated aqueous streams, in which substrate inhibition is significant. The model takes into account substrate mass transfer into, and within, the solid particles. Outputs of the models are xenobiotic concentrations in the liquid and solid phases and the concentration profile within the solid polymer beads. Sensitivity analyses have been performed on the influent concentration and on the main operating parameters, which can be modified to control the process performance (i.e. polymer/feed ratio, reaction and loading times). With an inhibitory substrate, the selected duration of the reaction period exhibits a critical value which determines the transition from high to low efficiency of the bioreactor. Application examples are provided for a target compound, 4-nitrophenol, previously investigated in TPPBs with an immiscible organic solvent, while Hytrel 8206 has been considered as the polymer partitioning phase. The proposed model has been shown to be a powerful tool to predict suitable operating conditions for TPPB systems treating inhibitory substrates. [ABSTRACT FROM AUTHOR]

Waste tyres were utilized as the sorption phase in a two-phase partitioning bioreactor (TPPB) for the biodegradation of a binary mixture of 2,4-dichlorophenol (DCP) and 4-nitrophenol (4NP). These compounds are extensively used in the chemical industry and are found in many industrial effluents. Although both compounds are toxic and are on the EPA list of priority pollutants, a higher inhibitory effect on microorganisms is exerted by DCP, and our experimental tests were focused on strategies to reduce its negative impact on microbial activity. Sorption/desorption tests for the DCP–4NP mixture were first performed to verify the related uptake/release rates by the tyres, which showed that the tyres had a higher capacity for DCP uptake and practically no affinity for 4NP. An acclimatized mixed culture was then utilized in a sequencing batch reactor (SBR) operated in conventional and two-phase mode. For the binary DCP-4NP mixture a significant reduction in DCP toxicity, and a concomitant enhancement in substrate removal efficiency (up to 83%for DCP and ∼ 100% for 4NP) were clearly seen for the TPPB operated with 10% and 15% v/v tyres, for influent concentrations up to 180 mg/L, with practically negligible biodegradation in the conventional single phase reactor. The long-term utilization of tyres was confirmed at an influent loading of 180 mg/L with a test performed over 20 work cycles showing an improvement of the removal performance for both compounds. [ABSTRACT FROM PUBLISHER]

Highlights: [•] We investigate absorptive polymers for ex-situ soil bioremediation. [•] We compare the performance of the novel technology with a slurry bioreactor. [•] The polymer is very effective in decontaminating the soil (77% removal in 4h). [•] The polymer is readily regenerated in a two phase partitioning bioreactor. [Copyright &y& Elsevier]

The toxicity of four xenobiotic compounds 3,5-dichlorophenol, formaldehyde, 4-nitrophenol and dichloromethane, representative of industrial wastewater contaminants was evaluated by a simple respirometric procedure set up on the basis of OECD Method 209 and by the Microtox® bioassay. Very good reproducibility was observed for both methods, the variation coefficients being in the range of 2–10% for the respirometric procedure and 6–15% for Microtox®, values that can be considered very good for a biological method. Comparison of EC50 data obtained with the two methods shows that in both cases 3,5-dichlorophenol is more toxic than other compounds investigated and dichloromethane has a very low toxicity value. Intermediate EC50 values were found for the two other chemicals, formaldehyde and 4-nitrophenol. Moreover, the Microtox® EC50 values are generally lower (except for dichloromethane) than the respirometric ones: these differences could be explained by the fact that the Microtox® method uses a pure culture of marine species and, therefore, should not necessarily be expected to behave like a community of activated sludge bacteria.In conclusion, both methods can be usefully applied for toxicity detection in wastewater treatment plants but it is advisable to take into account that Microtox® is more sensitive than respirometry in estimating the acute toxicity effect on the biomass operating in the plant. [Copyright &y& Elsevier]

In this paper, the biodegradation process of 4-nitrophenol (4NP) in a sequencing batch reactor has been investigated. Kinetic tests have been carried out on biomass grown on mixed substrate (4NP plus biogenic substrate) both in the presence of a biogenic substrate fraction in the feed and with 4NP as the sole carbon source. Removal kinetics for all tests is well described by the typical substrate inhibition pattern as predicted by the Haldane equation. In both sets, estimated kinetic parameters are very similar: no beneficial effect of the biogenic fraction is observed on the 4NP removal while increasing trend of 4NP maximum removal rate with the 4NP/CODTOT ratio in the feed has been observed. This finding has been modelled by estimating the fraction of the total biomass involved in 4NP biodegradation as a function of 4NP concentration in the feed.High removal rates, short acclimation times and good settling characteristics of produced sludge (observed during the whole working period) confirm the suitability of periodic systems in enhancing the bacterial potentialities for biodegradation of xenobiotic compounds. [Copyright &y& Elsevier]

Highlights: [•] The influence of substrate inhibition on biodegradation performance of SBRs has been analysed. [•] Two original cases studies of “real” xenobiotic substrate degradation have been reported. [•] Substrate removal efficiency can be either very high or very low, depending on the chosen operating conditions. [Copyright &y& Elsevier]