Treatment of waste gas from the breather vent of a vertical fixed roof p-xylene storage tank by a trickle-bed air biofilter

Odor and volatile organic compounds biotreatment using compact trickle bed bioreactors (CTBB) in a wastewater treatment plant

The main aim of this study was to optimize and maximize the impacts of odor and volatile organic compounds (VOCs) biodegradation in a wastewater treatment plant utilizing a pilot-scale compact trickle bed bioreactor (CTBB). A CTBB was built and tested for its long-term performance during which gases were supplied from the tank containing semi-liquid fats, oils, and fat waste. The concentrations of pollutants ranged from 0 to 140.75 mg/m³ H₂S, 0 to 2500 mg/m³ VOCs, and 0 to 21.5 mg/m³ NH₃. The CTBB was tested at different gas flow rates and at two pH values for the liquid phase: pH = 7.0 and 5.0. In the liquid phase, the pollutant removal efficiency was higher at pH = 7.0 than at pH = 5.0. Overall, the removal efficiency was between 81.5 % and 99.5 % for the VOCs and 87.5 % and 98.9 % for H₂S, while NH₃ removals were >99 %.

Enhancement of Catalytic Performance of H-Clinoptilolite in Toluene Abatement from Polluted Air via Controlled Dealumination Method

In this study, the effect of clinoptilolite dealumination on the total oxidation of toluene was reported for the first time. To avoid excess decrease of catalyst crystallinity, chemical modification of zeolite was carried out using a mild acid like oxalic acid. The catalysts were characterized by XRD, XRF, SEM, BET and TPD analyses. It was found that dealumination resulted in a significant enhancement of toluene conversion when 0.050 M acid oxalic was used for a treatment period of 2 h. Dealumination substantially changed the distribution of the concentration of acid sites of different strength and increased the surface area and porosity, so that the temperature corresponding to the maximum conversion shifts around 50 °C towards lower temperatures (in case of CLP 050). The effect of dealumination on the activity of the zeolite samples and the total oxidation of toluene was discussed in terms of Si/Al ratio, crystallinity, distribution of acid site strength and textural characteristics of the samples.

Modelling the removal of volatile pollutants under transient conditions in a two-stage bioreactor using artificial neural networks

A two-stage biological waste gas treatment system consisting of a first stage biotrickling filter (BTF) and second stage biofilter (BF) was tested for the removal of a gas-phase methanol (M), hydrogen sulphide (HS) and α-pinene (P) mixture. The bioreactors were tested with two types of shock loads, i.e., long-term (66h) low to medium concentration loads, and short-term (12h) low to high concentration loads. M and HS were removed in the BTF, reaching maximum elimination capacities (EC_max) of 684 and 33 gm^-3h^-1, respectively. P was removed better in the second stage BF with an EC_max of 130 gm^-3h^-1. The performance was modelled using two multi-layer perceptrons (MLPs) that employed the error backpropagation with momentum algorithm, in order to predict the removal efficiencies (RE, %) of methanol (RE_M), hydrogen sulphide (RE_HS) and α-pinene (RE_P), respectively. It was observed that, a MLP with the topology 3-4-2 was able to predict RE_M and RE_HS in the BTF, while a topology of 3-3-1 was able to approximate RE_P in the BF. The results show that artificial neural network (ANN) based models can effectively be used to model the transient-state performance of bioprocesses treating gas-phase pollutants.

Start-up, performance and optimization of a compost biofilter treating gas-phase mixture of benzene and toluene

The performance of a compost biofilter inoculated with mixed microbial consortium was optimized for treating a gas-phase mixture of benzene and toluene. The biofilter was acclimated to these VOCs for a period of ∼18d. The effects of concentration and flow rate on the removal efficiency (RE) and elimination capacity (EC) were investigated by varying the inlet concentration of benzene (0.12-0.95g/m(3)), toluene (0.14-1.48g/m(3)) and gas-flow rate (0.024-0.072m(3)/h). At comparable loading rates, benzene removal in the mixture was reduced in the range of 6.6-41% in comparison with the individual benzene degradation. Toluene removal in mixture was even more affected as observed from the reductions in REs, ranging from 18.4% to 76%. The results were statistically interpreted by performing an analysis of variance (ANOVA) to elucidate the main and interaction effects.

Emission characteristics of VOCs from three fixed-roof p-xylene liquid storage tanks

This study evaluates emission characteristics of volatile organic compounds (VOCs) caused by standing loss (L S) and working loss (L W) of three vertical fixed-roof p-xylene (p-X) liquid tanks during 1-year storage and filling operation. The annual net throughput of the tanks reached 70,446 t, resulting in 9,425 kg of p-X vapor emission including 5,046 kg of L S (53.54 %) and 4,379 kg of L W (46.46 %). The estimated L W of AP-42 displayed better agreement with the measured values of a VOC detector than the estimated L S of AP-42. The L S was best correlated with the liquid height of the tanks, while the L W was best correlated with the net throughput of the tanks. As a result, decreasing vapor space volume of the tanks and avoiding high net throughput of the tanks in a high ambient temperature period were considered as effective means to lessen VOC emission from the fixed-roof organic liquid storage tank.

Biofiltration of ethyl acetate by Pseudomonas putida immobilized on walnut shell

A biofilter packed with walnut shells was used to eliminate ethyl acetate from an air stream. The shells treated with NaOH were used as medium for immobilization of Pseudomonas putida PTCC 1694. At an empty bed residence time (EBRT) of 60s, a removal efficiency of 99% was achieved at inlet concentrations lower than 430ppm of ethyl acetate. The removal efficiency decreased below 80% with an increase in inlet concentration of ethyl acetate. When the EBRT was increased to 75 s, the removal efficiency remained above 80% even though the inlet loading rate was increased to 421g/m(3)h. Michaelis-Menten type and zero-order diffusion limited models were employed and the predicted data perfectly matched the experimental data. Thus P. putida immobilized on walnut shell has potential for the removal of ethyl acetate from air streams.

Waste gas biofiltration: advances and limitations of current approaches in microbiology

As confidence in gas biofiltration efficacy grows, ever more complex malodorant and toxic molecules are ameliorated. In parallel, for many countries, emission control legislation becomes increasingly stringent to accommodate both public health and climate change imperatives. Effective gas biofiltration in biofilters and biotrickling filters depends on three key bioreactor variables: the support medium; gas molecule solubilization; and the catabolic population. Organic and inorganic support media, singly or in combination, have been employed and their key criteria are considered by critical appraisal of one, char. Catabolic species have included fungal and bacterial monocultures and, to a lesser extent, microbial communities. In the absence of organic support medium (soil, compost, sewage sludge, etc.) inoculum provision, a targeted enrichment and isolation program must be undertaken followed, possibly, by culture efficacy improvement. Microbial community process enhancement can then be gained by comprehensive characterization of the culturable and total populations. For all species, support medium attachment is critical and this is considered prior to filtration optimization by water content, pH, temperature, loadings, and nutrients manipulation. Finally, to negate discharge of fungal spores, and/or archaeal and/or bacterial cells, capture/destruction technologies are required to enable exploitation of the mineralization product CO(2).