Toxic VOCs Research Articles

Ceramic membrane reactor integrated with UV/O3/Catalyst Beads for treating real textile wastewater: Enhanced effluent quality, fouling control and molecular transformations of DOM

A ceramic membrane reactor (CMR) was employed to treat real textile wastewater with the simultaneous use of UV, O3, and photocatalytic beads for dissolved organic matter (DOM) transformation and membrane fouling control. The O3 treatment exhibited high performance in color removal. Simultaneous use of UV and ozonation (UV/O3) resulted in 91% and 64% color and chemical oxygen demand (COD) removal, respectively, and delayed (3-fold) fouling time compared to UV alone. A combination of TiO2-loaded polymeric beads with UV/O3 (UV/O3/Beads) further enhanced the color (96%) and COD (86%) removal as well as improved fouling control by 9-folds compared to the control (Air alone) experiment. Three-dimensional excitation-emission matrix (3-D EEM) fluorescence spectra revealed minimum DOM and synergistic effects of UV, O3, and photocatalytic beads (UV/O3/Beads) in the degradation of fluorescent DOM. The •OH radicals were leading in degrading organic pollutants during the treatment. Transformations of heteroatomic DOMs were confirmed by the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). S-containing compounds in the treated samples appeared in a reduced state (lower H/C and O/C ratios), indicating the transformation of R–SO3 to R–S–R. Whereas N-containing DOM was mostly oxidized. UV/O3 rapidly transformed dye molecules to colorless, creating suitable conditions for photocatalytic beads for accelerated degradation of pollutants. Also, the PTR-TOF-MS analysis revealed the successful removal of toxic VOCs (Methanethiol, Allylamine, Cyclohexenes, Butanes, Propanes, and Hydrazines) from wastewater by the UV/O3/Beads treatment. Based on these findings, DOM transformations could be better understood, and the simultaneous application of heterogeneous photocatalysis and UV/O3 could be safely recommended as a promising technology for treating industrial wastewater.

Synchronously enhanced biofilm formation and m-dichlorobenzene removal in biotrickling filters by rhamnolipid chelating rare earth elements

ABSTRACT The effects of rhamnolipid chelating La (III) or Nd (III) on m-dichlorobenzene removal and biofilm growth were investigated. The rhamnolipid chelating La (III) or Nd (III) significantly increased the average m-dichlorobenzene elimination capacity by 24% and 29%, respectively, on day 70–130, and the average wet weights of biomass ranged from 11 kg/m3 to 15 kg/m3 in BTFs on day 100–180 at an inlet load of at 47–98 gm3/h and an EBRT of 60s-90s. Microbial community functional genes about biofilm growth and m-dichlorobenzene removal were also increased. In addition, the rhamnolipid chelating La (III) or Nd (III) can improve the membrane permeability, extracellular polymeric substance (EPS) production, catechol 2,3 dioxygenase (C23O) enzyme, and chlorobenzene dioxygenase activity. These results demonstrate that rhamnolipid chelating La (III) or Nd (III) have the potential to improve the performance of BTFs treating hydrophobic and highly toxic VOCs.

Volatile-Mediated Induced and Passively Acquired Resistance in Sagebrush (Artemisia tridentata)

Plants produce a diversity of secondary metabolites including volatile organic compounds. Some species show discrete variation in these volatile compounds such that individuals within a population can be grouped into distinct chemotypes. A few studies reported that volatile-mediated induced resistance is more effective between plants belonging to the same chemotype and that chemotypes are heritable. The authors concluded that the ability of plants to differentially respond to cues from related individuals that share the same chemotype is a form of kin recognition. These studies assumed plants were actively responding but did not test the mechanism of resistance. A similar result was possible through the passive adsorption and reemission of repellent or toxic VOCs by plants exposed to damage-induced plant volatiles (DIPVs). Here we conducted exposure experiments with five chemotypes of sagebrush in growth chambers; undamaged receiver plants were exposed to either filtered air or DIPVs from mechanically wounded branches. Receiver plants exposed to DIPVs experienced less herbivore damage, which was correlated with increased expression of genes involved in plant defense as well as increased emission of repellent VOCs. Plants belonging to two of the five chemotypes exhibited stronger resistance when exposed to DIPVs from plants of the same chemotypes compared to when DIPVs were from plants of a different chemotype. Moreover, some plants passively absorbed DIPVs and reemitted them, potentially conferring associational resistance. These findings support previous work demonstrating that sagebrush plants actively responded to alarm cues and that the strength of their response was dependent on the chemotypes of the plants involved. This study provides further support for kin recognition in plants but also identified volatile-mediated associational resistance as a passively acquired additional defense mechanism in sagebrush.

Air pollution scenario analyses of fleet replacement strategies to accomplish reductions in criteria air pollutants and 74 VOCs over India

Traffic emissions are a major source of air pollution and associated damage to human health in India. Many of the Indian metro cities urgently require cleaner transportation technologies to ensure cleaner air. Here, using newly compiled spatially disaggregated, gridded, high-resolution (0.1° × 0.1°) road transport emission inventory for India for 2030 (RTEII) of 74 speciated VOCs, CO, SO 2 , NOx, NH 3 , CH 4 , CO 2, BC, OC and PM 2.5 from varied fuels and vehicle technologies that are currently in use in India, we investigated changes in emission in response to substitution of the existing vehicular fleet by cleaner alternatives. Three “what-if” intervention scenarios were considered to assess the extent in improvement of air quality due to the reduction in the primary emission of air pollutants. The results show that significant reductions in direct emission of pollutants (Non-Methane VOCs, −91%; CO, −80%; PM 2.5 , 44%) including toxic VOCs (e.g., isocyanic acid, −76%; BTEX, −93%; as well as individual VOC classes (e.g., sum of OVOCs, −61% and sum of alkenes, −80%) can likely be achieved in 2030 by shifting from highly polluting Internal Combustion Engine (ICE) based 2 and 3-wheeled vehicles to Electric Vehicles (EVs) under scenario 1. The amount of secondary pollutants such as SOA and O 3 that can potentially be formed from traffic also showed significant reduction of 94% and 84%, respectively, under scenario 1. Conversion of diesel fuelled vehicles to CNG under scenario 2 can lead to a larger reduction in black carbon emissions (−50%). Scenario 3, in which the benefits of scenarios 1 and 2 are combined, represents the best long-term strategy moving forward, which can result in massive emission reductions of pollutants through existing technologies of greener transport fleets over India. Large scale conversion of the vehicle fleets as explored here can lead to a substantial reduction of air pollution and fewer lives lost. • Study examines 2030 road-transport emission reductions for India. • Three “what-if” intervention scenarios with electric vehicles and greener fuels. • 2&3-wheeler vehicles replacement by EVs reduced NMVOC emissions by 91%. • Conversion of diesel fuelled vehicles to CNG reduced primary BC by 50%. • Combining EVs and diesel to CNG for HDVs can improve air quality over India greatly.

A Wide Range of Toxic Vocs Measured by Dual-Sorbent Passive Sampling With Validation by Field Online Measurements

A Wide Range of Toxic Vocs Measured by Dual-Sorbent Passive Sampling With Validation by Field Online Measurements

Camellia meal-based formaldehyde-free adhesive with self-crosslinking, and anti-mildew performance

The development of eco-friendly adhesives from renewable biomass materials has attracted considerable attention in recent years. Many researchers continue to study and use expensive chemical crosslinking agents that release toxic VOCs and use environmentally unfriendly mildew-proofing agents that improve the bonding strength of plywood. In this study, a high-strength formaldehyde-free adhesive was prepared by using low-cost modified camellia meal, soybean meal, and a low epoxy crosslinker content. Plywood bonded using the optimum modified camellia meal with soybean meal showed a wet shear strength of 1.822 MPa, which was 93.3% higher than that of the unmodified adhesive. We found that the oxidized camellia meal could completely replace the epoxy crosslinker, and the adhesive strength reached 0.83 MPa while maintaining its adhesive properties. This study provides a new biomass self-crosslinking network design strategy for the wood-based panel industry to prepare high-performance environmentally friendly adhesives. Its excellent anti-mildew properties and low VOC content give it great potential in wood composites and allow it to be used as a substitute for formaldehyde resin adhesives.

Flavin mononucleotide-stimulated microbial fuel cell for efficient gaseous toluene abatement

Chemical park is regarded as a major contributor of VOCs emissions in China. Currently, a green and safe technology, microbial fuel cells (MFCs), is being developed for the VOCs abatement. Noting that effective electron transfer is critical to the MFC performance. In this work, flavin mononucleotide (FMN) was dosed as an electron shuttle to improve the removal of the typical toxic VOCs, toluene. The experimental results revealed that the performance of toluene removal and power generation were accelerated with the dosage of 0.2–2 μM FMN. With the addition of 1 μM FMN, the removal efficiency, the maximum output voltage and the coulombic efficiency of MFC were increased by 18.4%, 64.4% and 56.3%, respectively. However, a further increase in FMN concentration to 2 μM caused a reduction in the removal efficiency and coulombic efficiency. The images of scanning electron microscopy and confocal laser scanning microscopy showed that the presence of FMN greatly promoted the microbial growth and its activity. Furthermore, microbial community analysis also implied that the moderate dosage of FMN (0.2–1 μM) was beneficial for the growth of the typical exoelectrogens, Geobacter sp., and thus the coulombic efficiency was increased. In addition, an electron transfer pathway involving in cytochrome b, OMCs, cytochrome c, and MtrA was proposed based on the cyclic voltammetry analysis. This work will provide a fundamental theoretical support for its application of toxic VOCs abatement from the chemical park.

Genomic Analyses of Penicillium Species Have Revealed Patulin and Citrinin Gene Clusters and Novel Loci Involved in Oxylipin Production.

Blue mold of apple is caused by several different Penicillium species, among which P. expansum and P. solitum are the most frequently isolated. P. expansum is the most aggressive species, and P. solitum is very weak when infecting apple fruit during storage. In this study, we report complete genomic analyses of three different Penicillium species: P. expansum R21 and P. crustosum NJ1, isolated from stored apple fruit; and P. maximae 113, isolated in 2013 from a flooded home in New Jersey, USA, in the aftermath of Hurricane Sandy. Patulin and citrinin gene cluster analyses explained the lack of patulin production in NJ1 compared to R21 and lack of citrinin production in all three strains. A Drosophila bioassay demonstrated that volatiles emitted by P. solitum SA and P. polonicum RS1 were more toxic than those from P. expansum and P. crustosum strains (R27, R11, R21, G10, and R19). The toxicity was hypothesized to be related to production of eight-carbon oxylipins. Putative lipoxygenase genes were identified in P. expansum and P. maximae strains, but not in P. crustosum. Our data will provide a better understanding of Penicillium spp. complex secondary metabolic capabilities, especially concerning the genetic bases of mycotoxins and toxic VOCs.

Simulation of VOC Emission During Loading Operations in a Crude Oil Tanker

“Volatile Organic Compounds” (VOCs) are known to contribute significantly to environmental pollution. Crude oil loading operations in a marine oil tanker produces a significant quantity of hydrocarbon (HC) vapours in the surrounding atmosphere. A large percentage of these HC vapour emission consists of ‘Volatile Organic Compounds’ (VOCs). This VOC emission has not been previously analysed in detail to understand health and environmental impact. The scope of the study reported in this paper demonstrates the use of chemical processing simulation software (Aspen HYSYS ®) to model and identify significant VOCs in this HC vapour emission during crude oil loading operations. The objective is to determine the detailed variation in the volume and the composition of the HC vapour emission and hence, VOCs, as the level in a ship's tank rises while being filled and the influence of crude oil temperature and pressure in the filled tank has on the extent of VOC emission. Total VOC emission per tonne of crude oil is calculated and compared with other similar field measurements. The analysis identifies the concentration of toxic VOCs in the hydrocarbon emission, as well as the liquid fraction lost in the loading operation. The simulation data is analysed for crude oil temperature between 10°C to 45°C and tank level from empty to 90% full. The resulting information is useful to assess the environmental and health impact and efficiency of the current crude oil loading operations. Potential to recover the monetary loss by increasing tank pressure and installation of the 'VOC Recovery Unit' is analysed.

Removal of toluene as a toxic VOC from methane gas using a non-thermal plasma dielectric barrier discharge reactor

Methane is the main component of biogas, which could be used as a renewable energy source for electricity, source of heat, and biofuel production after upgrading from biogas. It also contains toxic compounds which cause environmental and human health problems. Therefore, in this work, the removal of a toxic compound (toluene) from methane gas was studied using a dielectric barrier discharge (DBD) reactor. It was observed that the removal of the toxic compound could be achieved from methane carrier gas using a dielectric barrier discharge reactor, and it depends on plasma input power. The maximum removal of the toxic compound was 85.9% at 40 W and 2.86 s. The major gaseous products were H2 and lower hydrocarbons (LHC) and the yield of these products also increases with input power. In the current study, the yield of gaseous products depends on the decomposition of toxic compounds and methane, because the decomposition of methane also produces H2 and lower hydrocarbons. The percentage yield of H2 increases from 0.43–4.74%. Similarly, the yield of LHC increases from 0.56–7.54% under the same reaction conditions. Hence, input power promoted the decomposition of the toxic compound and enhanced the yield of gaseous products.

Toxic volatile organic compounds in 20 homes in Shanghai: Concentrations, inhalation health risks, and the impacts of household air cleaning

Exposure to VOCs causes a variety of adverse health effects, with much of the exposure occurring at home during sleep. The use of an air cleaner maybe an effective and convenient way to reduce associated exposures and health risks. Studies about the impacts of air cleaner on VOCs are limited. The main objective of this paper was to assess the inhalation health risks that toxic VOCs present during nighttime sleep and to estimate the removal effectiveness of an indoor air cleaner on these VOCs. Asthmatic children, who are especially vulnerable to the detrimental effects of air pollutants, were recruited and the VOC concentrations in their bedrooms were measured during two periods - once with a true air cleaner and once with a sham air cleaner. Among the toxic VOCs quantified, formaldehyde, acetaldehyde and toluene had the highest concentrations (median: 18.0, 14.0 and 12.1 μg/m³, respectively) in the bedrooms. Health risk assessments were conducted to identify compounds of greatest concern. During nighttime sleep, 7 VOCs presented inhalation cancer risk above the acceptable risk (1 × 10−6), 4 VOCs exceeded the non-cancer risk threshold (1) in most of the homes tested. The results indicate that the use of an air cleaner in residences may lead to significant reductions in VOC concentrations indoors, but even with this reduction, the associated health risks are still of concern. This study highlights the need for reductions in toxic VOCs at home, points to the imminent need for improvements in control of VOC sources.

VOC emissions from the combustion of low-grade lignocellulosic waste

ABSTRACTEuropean Commission is promoting the usage of renewable energy and the replacement of fossil fuels with biomass. Two-thirds of renewable energy will be derived by biomass by 2020 (European Commission. 2012. Roadmap 2050. DOI: 10.2833/10759). However, increasing need for biomass generates sustainability issues by land-use change. Biomass waste as biofuels do not affect land-use, therefore the sustainability potential is improved (Searchinger T, Heimlich R, Houghton RA, Dong F, Elobeid A, Fabiosa J, Tokgoz S, Hayes D, Yu T-H. 2008. Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change. Science. 319:1238–1240). However, biomass waste contaminates could release toxic VOCs, and also particulates and ash may contain non-VOCs such as heavy metals (Pitman RM. 2006. Wood ash use in forestry-a review of environmental impacts. Forestry. 79(5):563–588). This study investigates the VOC combustion emissions of low-grade lignocellulosic waste to determine the suitability wood wastes as bio-fuel.

Quantification of BTEX in Soil by Headspace SPME–GC–MS Using Combined Standard Addition and Internal Standard Calibration

There is a great demand for simple, fast and accurate methods for quantification of volatile organic contaminants in soil samples. Solid-phase microextraction (SPME) has a huge potential for this purpose, but its application is limited by insufficient accuracy caused by a matrix effect. The aim of this research was to develop the method for BTEX quantification in soil using combined standard addition (SA) and internal standard (IS) calibration. Deuterated benzene (benzene-d6) was used as the internal standard for all analytes. The optimized method includes spiking replicate samples with different concentrations of BTEX standards and the same concentration of benzene-d6, equilibration of soil samples at 40 °C during 2 h, and SPME–GC–MS analysis. Precision and accuracy of IS and SA methods were compared on different soil matrices. Combined SA + IS method provided more precise calibration plots compared to the conventional SA calibration. The SA + IS calibration provided more precise and accurate results compared with a reference method based on solvent extraction followed by GC–MS when applied to BTEX quantification in real soil samples (spiked with diesel fuel and aged). Recoveries of BTEX from soil samples spiked with known concentrations of analytes using the developed method were in the range of 73–130% with RSD values less than 15% for all BTEX. The proposed simultaneous standard addition and internal standard approach can be advantageous and adopted for improved quantification of other toxic VOCs in soil.

Contribution of post-harvest agricultural paddy residue fires in the N.W. Indo-Gangetic Plain to ambient carcinogenic benzenoids, toxic isocyanic acid and carbon monoxide

In the north west Indo-Gangetic Plain (N.W.IGP), large scale post-harvest paddy residue fires occur every year during the months of October–November. This anthropogenic perturbation causes contamination of the atmospheric environment with adverse impacts on regional air quality posing health risks for the population exposed to high concentrations of carcinogens such as benzene and toxic VOCs such as isocyanic acid. These gases and carbon monoxide are known to be emitted from biomass fires along with acetonitrile. Yet no long-term in-situ measurements quantifying the impact of this activity have been carried out in the N.W. IGP. Using high quality continuous online in-situ measurements of these gases at a strategic downwind site over a three year period from 2012 to 2014, we demonstrate the strong impact of this anthropogenic emission activity on ambient concentrations of these gases. In contrast to the pre-paddy harvest period, excellent correlation of benzenoids, isocyanic acid and CO with acetonitrile (a biomass burning chemical tracer); (r≥0.82) and distinct VOC/acetonitrile emission ratios were observed for the post-paddy harvest period which was also characterized by high ambient concentrations of these species. The average concentrations of acetonitrile (1.62±0.18ppb), benzene (2.51±0.28ppb), toluene (3.72±0.41ppb), C8-aromatics (2.88±0.30ppb), C9-aromatics (1.55±0.19ppb) and CO (552±113ppb) in the post-paddy harvest periods were about 1.5 times higher than the annual average concentrations. For isocyanic acid, a compound with both primary and secondary sources, the concentration in the post-paddy harvest period was 0.97±0.17ppb. The annual average concentrations of benzene, a class A carcinogen, exceeded the annual exposure limit of 1.6ppb at NTP mandated by the National Ambient Air Quality Standard of India (NAAQS). We show that mitigating the post-harvest paddy residue fires can lower the annual average concentration of benzene and ensure compliance with the NAAQS. Calculations of excessive lifetime cancer risk due to benzene amount to 25 and 10 per million inhabitants for children and adults, respectively, exceeding the USEPA threshold of 1 per million inhabitants. Annual exposure to isocyanic acid was close to 1ppb, the concentration considered to be sufficient to enhance risks for cardiovascular diseases and cataracts. This study makes a case for urgent mitigation of post-harvest paddy residue fires as the unknown synergistic effect of multi-pollutant exposure due to emissions from this anthropogenic source may be posing grave health risks to the population of the N.W. IGP.

Oxygen mass transfer and hydrodynamics in a multi-phase airlift bioscrubber system

Abstract The addition of select polymer beads to stirred tank bioscrubber systems has been shown to greatly enhance the removal and treatment of toxic VOCs via the capture and sequestration of poorly soluble compounds such as benzene, and the release of these materials, based on equilibrium partitioning, to microorganisms in the aqueous phase. In this study, oxygen volumetric mass transfer coefficients were determined for an 11 L airlift vessel containing tap water alone, tap water with Nylon 6,6 polymer beads (10% v/v), and tap water with silicone rubber beads (10% v/v), over various inlet gas flow rates, with the aim of initially characterizing a low-energy pneumatically agitated reactor (concentric tube airlift). In addition, oxygen transfer rates into the airlift with and without polymers with high oxygen affinity were determined. To further characterize this reactor system, a residence time distribution analysis was completed to determine hydrodynamic parameters including the Peclet number ( Pe ), circulation time ( t c ) and mixing time ( t m ) over various gas flow rates for the airlift containing tap water with and without silicone rubber. It was found that the addition of silicone rubber beads, which has a high affinity for oxygen, reduced the measured volumetric mass transfer coefficient relative to a system without polymers due to oxygen sorption during the dynamic period of testing, but increased the overall amount of oxygen that was transferred to the system during the dynamic period. The addition of Nylon 6,6, which has very low oxygen uptake, allowed for estimation of the physical effect of solids addition on gas–liquid mass transfer and it was found that there was no effect on the measured volumetric mass transfer coefficient relative to a system without polymers. However, hydrodynamic parameters revealed that the addition of silicone rubber into an airlift vessel improves liquid phase mixing. This investigation has defined key operational features of a low-energy three-phase airlift bioscrubber system for the treatment of toxic VOC substrates.

Spore release by the green alga Ulva: A quantitative assay to evaluate aquatic toxicants

A toxicity test using spore release of the aquatic green alga, Ulva, was developed and evaluated by assessing the toxicity of different organic and inorganic chemicals and elutriates of sewage or waste sludge. The toxic ranking of four metals was: Cu (EC 50 of 0.040 mg L −1) > Cd (0.095 mg L −1) > Pb (0.489 mg L −1) > Zn (0.572 mg L −1). The EC 50 for TBTO ranged from 24 to 63 μg L −1. The most toxic VOC was formalin (EC 50 of 0.788 μl L −1) and the least toxic was acetone. Spore release was significantly inhibited in all elutriates; the greatest and least toxic effects were for industrial sewage (3.29%) and filtration bed (10.08%), respectively. The bioassay is simple, inexpensive and sensitive. The cosmopolitan distribution of Ulva means that the test would have a potential application worldwide.

Nanofibrous Manganese Dioxide for Decomposition of Volatile Organic Compounds

AbstractVolatile organic compounds (“VOCs”) are widely used in industrial process, transportation fuels, and households. It is inevitable that some VOCs will escape into the atmosphere. Emission of VOCs will cause three major problems, including (1) increased exposure level of the population to know carcinogenic compounds such as benzene and carbon tetrachloride, (2) increased ozone concentration in the atmosphere at ground level, and (3) stratospheric depletion of the ozone layer, which alters global climate and increases exposure to UV radiation. Reducing the concentrations of VOCs will greatly improve air quality. A common method for VOC removal is catalytic decomposition. Most works have only focus on reducing VOC concentrations down to a few parts per million (ppm). Very little research has been conducted on reducing the VOCs down to parts per billion (ppb) levels, or less. This paper reports the decomposition of VOCs using a unique class of nanofibrous bird's-nest superstructure material. This open-inter-woven nanofibrous superstructure provides superb host for catalytic reactions and permits relatively easy flow of the gas stream through the structure. The nanofibrous MnO2 is highly effective in destroy more than 50 VOCs on USEPA's top priority list toxic VOCs to ppb level or less at a 200 − 350°C temperature.

Applicability of gasoline containing ethanol as Thailand's alternative fuel to curb toxic VOC pollutants from automobile emission

Emission rates of benzene, toluene, m-xylene, formaldehyde and acetaldehyde were measured in a fleet of 16 in-use vehicles. The test was performed on a chassis dynamometer incorporated with Bangkok Driving Cycle test mode. Three different test fuels: unleaded gasoline, gasoline blended with 10% ethanol (E10) and gasoline blended with 15% ethanol (E15) were used to determine the different compositions of exhaust emissions from various vehicles. The effects of ethanol content fuels on emissions were tested by three types of vehicles: cars with no catalytic converter installation, cars with three-way catalytic converter and cars with dual-bed catalytic converter. The test result showed wide variations in the average emission rates with different mileages, fuel types and catalytic converters (benzene: 3.33–56.48 mg/km, toluene: 8.62–124.66 mg/km, m-xylene: 2.97–51.65 mg/km, formaldehyde: 20.82–477.57 mg/km and acetaldehyde: 9.46–219.86 mg/km). There was a modest reduction in emission rate of benzene, toluene and m-xylene in cars using E10 and E15 fuels. Use of ethanol fuels, however, leads to increased formaldehyde and acetaldehyde emission rates. Our analysis revealed that alternative fuels and technologies give significant reduction in toxic VOC pollutants from automobile emission—particularly car with dual-bed catalytic converter using E10 fuel.

Prediction of optimal biofilm thickness for membrane-attached biofilms growing in an extractive membrane bioreactor

This article presents a mathematical model of membrane-attached biofilm (MAB) behavior in a single-tube extractive membrane bioreactor (STEMB). MABs can be used for treatment of wastewaters containing VOCs, treatment of saline wastewaters, and nitrification processes. Extractive membrane bioreactors (EMBs) are employed to prevent the direct contact between a toxic volatile pollutant and the aerated gas by allowing counterdiffusion of substrates; i.e., pollutant diffuses from the tube side into the biofilm, whereas oxygen diffuses from the shell side into the biofilm. This reduces the air stripping problems usually found in conventional bioreactors. In this study, the biodegradation of a toxic VOC (1,2-dichloroethane, DCE) present in a synthetic wastewater has been investigated. An unstructured model is used to describe cell growth and cell decay in the MAB. The model has been verified by comparing model predicted trends with experimental data collected over 5 to 20-day periods, and has subsequently been used to model steady states in biofilm behavior over longer time scales. The model is capable of predicting the correct trends in system variables such as biofilm thickness, DCE flux across the membrane, carbon dioxide evolution, and suspended biomass. Steady states (constant biofilm thickness and DCE flux) are predicted, and factors that affect these steady states, i.e., cell endogeneous decay rate, and biofilm attrition, are investigated. Biofilm attrition does not have a great influence on biofilm behavior at low values of detachment coefficient close to those typically reported in the literature. Steady-state biofilm thickness is found to be an important variable; a thin biofilm results in a high DCE flux across the membrane, but with the penalty of a high loss of DCE via air stripping. The optimal biofilm thickness at steady state can be determined by trading off the decrease in air stripping (desirable) and the decrease in DCE flux (undesirable) which occur simultaneously as the thickness increases. (c) 1996 John Wiley & Sons, Inc.

Prediction of optimal biofilm thickness for membrane‐attached biofilms growing in an extractive membrane bioreactor

This article presents a mathematical model of membrane-attached biofilm (MAB) behavior in a single-tube extractive membrane bioreactor (STEMB). MABs can be used for treatment of wastewaters containing VOCs, treatment of saline wastewaters, and nitrification processes. Extractive membrane bioreactors (EMBs) are employed to prevent the direct contact between a toxic volatile pollutant and the aerated gas by allowing counterdiffusion of substrates; i.e., pollutant diffuses from the tube side into the biofilm, whereas oxygen diffuses from the shell side into the biofilm. This reduces the air stripping problems usually found in conventional bioreactors. In this study, the biodegradation of a toxic VOC (1,2-dichloroethane, DCE) present in a synthetic wastewater has been investigated. An unstructured model is used to describe cell growth and cell decay in the MAB. The model has been verified by comparing model predicted trends with experimental data collected over 5 to 20-day periods, and has subsequently been used to model steady states in biofilm behavior over longer time scales. The model is capable of predicting the correct trends in system variables such as biofilm thickness, DCE flux across the membrane, carbon dioxide evolution, and suspended biomass. Steady states (constant biofilm thickness and DCE flux) are predicted, and factors that affect these steady states, i.e., cell endogeneous decay rate, and biofilm attrition, are investigated. Biofilm attrition does not have a great influence on biofilm behavior at low values of detachment coefficient close to those typically reported in the literature. Steady-state biofilm thickness is found to be an important variable; a thin biofilm results in a high DCE flux across the membrane, but with the penalty of a high loss of DCE via air stripping. The optimal biofilm thickness at steady state can be determined by trading off the decrease in air stripping (desirable) and the decrease in DCE flux (undesirable) which occur simultaneously as the thickness increases. © 1996 John Wiley & Sons, Inc.