Co-treatment of benzene and toluene vapours in a biofilter: A factorial design approach

[Abstract] Biofiltration has now become an indispensable treatment technique for the removal of low concentrations of Volatile Organic Compounds (VOCs) from process vent streams. This study involves performance evaluation of a laboratory scale compost based biofilter for the treatment of mixtures of benzene and toluene (BT) vapours. Experiments were conducted as per a statistical design of experiment, the 2k full factorial design, with the initial concentrations of benzene and toluene and the gas flow rate as the independent variables and the elimination capacity (EC) and removal efficiency (RE) as response variables. The maximum EC attained was 31.7 g/m3.h for benzene and 85.9 g/m3.h for toluene, while the total maximum EC at an inlet loading rate (ILR) of 150.2 g/m3.h was 91.2 g/m3.h. It was also observed that while there was mutual inhibition, benzene removal was severely inhibited by the presence of toluene than toluene removal by the presence of benzene. Statistical analysis in the form of analysis of variance (ANOVA) was carried out to determine the main and interaction effects of variables on the RE and EC values. This study establishes the potential application of biofilters to handle mixtures of VOCs effectively through a statistically authentic approach

Editorial: Integrated water management for enhanced water quality and reuse to create a sustainable future

Safe drinking water and sanitation are very important for the survival of human life. With the rapid proliferation of industries, growth in population and different forms of pollution, i.e. in water, air, soil and sediments, the living environment and the ecosystem is constantly polluted. In this context, integrating different water resources for enhanced water quality and reuse is important to solve the persisting problems and challenges in developing and the developed nations. Integrated water management offers environmental, economic and social benefits because it aims at maximizing the existing resources and prevents further depletion of the ecosystem

Bioprocesses for air pollution control

Bioprocesses have been developed as relatively recent alternatives to conventional, non-biological technologies, for waste gas treatment and air pollution control in general. This paper reviews major biodegradation processes relevant in this field as well as both accepted and major innovative bioreactor configurations studied or used nowadays for the treatment of polluted air, i.e. biofilters, one- and two-liquid phase biotrickling filters, bioscrubbers, membrane bioreactors, rotating biodiscs and biodrums, one- and two-liquid phase suspended growth bioreactors, as well as hybrid reactor configurations. Some of these bioreactors are being used at full-scale for solving air pollution problems, while others are still at the research and development stage at laboratory- or pilot-scale

Biodegradation of gas-phase styrene using the fungus Sporothrix variecibatus: Impact of pollutant load and transient operation

Biofiltration of gas-phase styrene was studied using a newly isolated fungus Sporothrix variecibatus, in a perlite biofilter, at inlet concentrations and gas-flow rates ranging from 0.13 to 14 g m−3 and 0.075 to 0.34 m3 h−1, respectively, corresponding to empty bed residence times (EBRT) ranging between 91 and 20 s. Styrene loading rates were varied between 50 and 845 g m−3 h−1and a maximum elimination capacity of 336 g m−3 h−1 was attained with nearly 65% styrene removal. On the other hand, the critical inlet loads to achieve more than 90% removal were 301, 240 and 92 g m−3 h−1 for EBRT of 91, 40, and 20 s, respectively. In order to test the stability and shock bearing capacity of the fungal biofilter, short-term tests were conducted by suddenly increasing the gas-phase styrene concentration, while maintaining the gas-flow rate constant. The response, a restoration in the removal performance to previous high values, after subjecting the biofilter to shock loads proves the resilient nature of the attached Sporothrix sp. and its suitability for biofiltration under non-steady state conditions

Performance of a biofilter for the removal of high concentrations of styrene under steady and non-steady state conditions

The performance of a laboratory scale perlite biofilter inoculated with a mixed culture was evaluated for gas phase styrene removal under various operating conditions. Experiments were carried out by subjecting the biofilter to different flow rates (0.15–0.9 m3 h−1) and concentrations (0.03–17.3 g m−3), corresponding to inlet loading rates varying from as low as 3 g m−3 h−1 to as high as 1390 g m−3 h−1. A maximum elimination capacity (EC) of 382 g m−3 h−1 was achieved at an inlet loading rate of 464 g m−3 h−1 with a removal efficiency of 82%. The high elimination capacity reached with this system could have been due to the dominant presence of filamentous fungi among others. The impact of relative humidity (RH) (30%, 60% and >92%) on the biofilter performance was evaluated at two constant loading rates, viz., 80 and 260 g m−3 h−1, showing that inhibitory effects were only significant when combining the highest loads with the lowest relative humidities. Biomass distribution, moisture content and concentration profiles along the bed height were significantly dependent on the relative humidity of the inlet air and on the loading rate. The dynamic behaviour of the biofilter through vigorous short and long-term shock loads was tested at different process conditions. The biofilter was found to respond apace to rapid changes in loading conditions. The stability of the biomass within the reactor was apparent from the fast response of the biofilter to recuperate and handle intermittent shutdown and restart operations, either with or without nutrient addition

Treatmet of gas phase styrene in a biofilter under steady-state conditions

[Abstract] Preliminary studies on the performance of a laboratory scale perlite biofilter inoculated with a mixed culture taken from petrochemical refinery sludge was evaluated for gas phase styrene removal under various operating conditions. Initially, the biofilter was acclimatized for 53 days at constant loading rates (40-60 g/m3.h), wherein the performance gradually improved with fluctuations in the removal profiles. Experiments were carried out by subjecting the biofilter to different flow rates (150, 300 l/h) and concentrations (0.5 – 5 g/m3), that corresponds to inlet loading rates between 60 – 200 g/m3.h. The results from this study show100% styrene removal with a maximum elimination capacity of 190 g/m3.h

Combined biological and physicochemical waste-gas cleaning techniques

This review presents a general overview of physical, chemical and biological waste-gas treatment techniques such as adsorption, absorption, oxidation and biodegradation, focusing more extensively on combined processes. It is widely recognized that biological waste-gas treatment devices such as biofilters and biotrickling filters can show high performance, often reaching removal efficiencies above 90 % for pollutant concentrations below 5 g/m3. However, for concentrations exceeding this limit and under transient shock-load conditions that are frequently encountered in industrial situations, a physicochemical gas cleaning process can sometimes be advantageously combined with a biological one. Besides improving the overall treatment efficiency, the non-biological, first-stage process could also serve as a load equalization system by reducing the pollutant load during periodic shock-loads, to levels that can easily be handled in the second-stage bioreactor. This article reviews the operational advantages of integrating different non-biological and biological processes, i.e., adsorption pre-treatment+bioreactor, bioreactor+adsorption post-treatment, absorption pre-treatment+bioreactor, UV pre-treatment+bioreactor, and bioreactor/bioreactor combinations, for waste-gas treatment, where different gas-phase pollutants have been tested

Experimental and neural model analysis of styrene removal from polluted air in a biofilter

BACKGROUND: Biofilters are efficient systems for treating malodorous emissions. The mechanism involved during pollutant transfer and subsequent biotransformation within a biofilm is a complex process. The use of artificial neural networks to model the performance of biofilters using easily measurable state variables appears to be an effective alternative to conventional phenomenological modelling. RESULTS: An artificial neural network model was used to predict the extent of styrene removal in a perlite-biofilter inoculated with a mixed microbial culture. After a 43 day biofilter acclimation period, styrene removal experiments were carried out by subjecting the bioreactor to different flow rates (0.15–0.9 m3 h−1) and concentrations (0.5–17.2 g m−3), that correspond to inlet loading rates up to 1390 g m−3 h−1. During the different phases of continuous biofilter operation, greater than 92% styrene removal was achievable for loading rates up to 250 g m−3 h−1. A back propagation neural network algorithm was applied to model and predict the removal efficiency (%) of this process using inlet concentration (g m−3) and unit flow (h−1) as input variables. The data points were divided into training (115 × 3) and testing set (42 × 3). The most reliable condition for the network was selected by a trial and error approach and by estimating the determination coefficient (R2) value (0.98) achieved during prediction of the testing set. CONCLUSION: The results showed that a simple neural network based model with a topology of 2–4–1 was able to efficiently predict the styrene removal performance in the biofilter. Through sensitivity analysis, the most influential input parameter affecting styrene removal was ascertained to be the flow rate

Artificial neural network based model for evaluating performance of immobilized cell biofilter

[Abstract] Artificial neural networks (ANNs) are powerful data driven modelling tools which has the potential to approximate and interpret complex input/output relationships based on the given sets of data matrix. In this paper, a predictive computerised approach has been proposed to predict the performance of an immobilized cell biofilter treating NH3 vapours in terms of its removal efficiency (RE) and elimination capacity (EC). The input parameters to the ANN model were inlet concentration, loading rate, flow rate and pressure drop, while the output parameters were RE and EC respectively. The data set was divided into two parts, training matrix consisting of 51 data points, while the test matrix had 16 data points representing each parameter considered in this study. Earlier, experiments from continuous operation in the biofilter showed removal efficiencies from 60 to 100% at inlet loading rates varying between 0.5 to 5.5 g NH3/m3.h. The internal network parameters of the ANN model during simulation was selected using the 2k factorial design and the best network topology for the model was thus estimated. The predictions were evaluated based on their determination coefficient values (R2). The results showed that a multilayer network (4-4-2) with a back propagation algorithm was able to predict biofilter performance effectively with R2 values of 0.9825 and 0.9982. The proposed ANN model for biofilter operation could be used as a potential alternative for knowledge based models through proper training and testing of the state variables

Styrene removal from polluted air in one and two-liquid phase biotrickling filter: Steady and transient-state performance and pressure drop control

A Sporothrix variecibatus-inoculated biotrickling filter (BTF) was examined for styrene removal, without and with the addition of silicone oil, at different empty bed residence times. The highest elimination capacities (ECs) were 172.8 (without silicone oil) and 670 g m−3 h−1 (with silicone oil), respectively, corresponding to a 4-fold improvement in presence of oil. The addition of silicone oil formed a well-coalesced emulsion of fungi and silicone oil, resulting in filter-bed clogging. Clogging prevention strategies adopted were; (i) lowering the volume ratio of silicone oil from 10% to 2% (v/v), and (ii) periodic increase in trickling rate of the medium from 50 to 190 mL min−1. During shock-load experiments, the BTF with silicone oil (2% v/v) could withstand high styrene loads, of up to 1900 g m−3 h−1, when compared to the BTF without silicone oil (400 g m−3 h−1)