Investigations into the application of a combination of bioventing and biotrickling filter technologies for soil decontamination processes--a transition regime between bioventing and soil vapour extraction.

Bioventing has emerged as one of the most cost-effective in situ technologies available to address petroleum light-hydrocarbon spills, one of the most common sources of soil pollution. However, the major drawback associated with this technology is the extended treatment time often required. The present study aimed to illustrate how an intended air-injection bioventing technology can be transformed into a soil vapour extraction effort when the air flow rates are pushed to a stripping mode, thus leading to the treatment of the off-gas resulting from volatilisation. As such, a combination of an air-injection bioventing system and a biotrickling filter was applied for the treatment of contaminated soil, the latter aiming at the treatment of the emissions resulting from the bioventing process. With a moisture content of 10%, soil contaminated with toluene at two different concentrations, namely 2 and 14 mg g soil(-1), were treated successfully using an air-injection bioventing system at a constant air flow rate of ca. 0.13 dm(3) min(-1), which led to the removal of ca. 99% toluene, after a period of ca. 5 days of treatment. A biotrickling filter was simultaneously used to treat the outlet gas emissions, which presented average removal efficiencies of ca. 86%. The proposed combination of biotechnologies proved to be an efficient solution for the decontamination process, when an excessive air flow rate was applied, reducing both the soil contamination and the outlet gas emissions, whilst being able to reduce the treatment time required by bioventing only.

Biological treatment of a contaminated gaseous emission from a leather industry in a suspended-growth bioreactor.

A suspended-growth bioreactor (SGB) was operated for the treatment of a gaseous stream mimicking emissions generated at a leather industrial company. The main volatile organic compounds (VOCs) present in the gaseous stream consisted of 1-methoxy-2-propanol, 2,6-dimethyl-4-heptanone, 2-butoxyethanol, toluene and butylacetate. A microbial consortium able to degrade these VOCs was successfully enriched. A laboratory-scale SGB was established and operated for 210-d with an 8h cycle period and with shutdowns at weekends. Along this period, the SGB was exposed to organic loads (OL) between 6.5 and 2.3 x 10(2) g h(-1) m(-3). Most of the compounds were not detected at the outlet of the SGB. The highest total VOC removal efficiency (RE) (ca 99%) was observed when an OL of 1.6 x 10(2) g h(-1) m(-3) was fed to the SGB. The maximum total VOC elimination capacity (1.8 x 10(2) g h(-1) m(-3)) was achieved when the OL applied to the SGB was 2.3 x 10(2) g h(-1) m(-3). For all the operating conditions, the SGB showed high levels of degradation of toluene and butylacetate (RE approximately equal to 100%). This study also revealed that recirculation of the gaseous effluent improved the performance of the SGB. Overall, the SGB was shown to be robust, showing high performance after night and weekend shutdown periods.

Biological treatment of a contaminated gaseous emission containing monochlorobenzene.

This study presents the operation of a biotrickling filter when treating a monochlorobenzene (MCB) contaminated gaseous emission. Treatment dynamics were characterised by exposing the reactor to various MCB Organic Loads (OL). The use of different growth support materials, namely limestone, sand, ceramic and PVC pall-rings, was investigated. Limestone led to dogging of the reactor due to the accumulation of surface precipitates, but PVC pall-rings allowed for a uniform biofilm growth. The biotrickling filter presented maximum removal efficiency (RE, 95%) under OL regimes of 10 g m(-3)-reactor h(-1). Treatment inhibition was observed when the reactor was exposed to OL of 45 g m(-3)-reactor h(-1), with RE reaching a minimum value (8%) and elimination capacity of 8 g m(-3)-reactor h(-1). The first half of the reactor height was the predominant section for MCB biodegradation and increasing the mineral medium recirculation rate was beneficial for the overall treatment.

Microbial dynamics in an extractive membrane bioreactor exposed to an alternating sequence of organic compounds.

Wastewaters containing organic compounds have been treated using extractive membrane bioreactors (EMBs). During treatment, a biofilm normally develops on the surface of the membrane, on the biological side. This study investigates the dynamics of biofilm growth in an EMB exposed to an alternating sequence of organic compounds. Microbial dynamics of both suspended and attached cultures were investigated experimentally in a single-tube extractive membrane bioreactor (STEMB), which comprised a continuous stirred-tank bioreactor (CSTB) coupled to eight single-tube extractive membrane modules (STEMMs) via a recirculating biomedium. A model microbial culture consisting of a Burkholderia sp. strain JS150 (ATCC No. 51283), able to degrade monochlorobenzene, and a Xanthobacter autotrophicus sp. strain GJ10 (ATCC No. 43050), able to degrade 1, 2-dichloroethane, was used. Both microbial strains exhibited exclusive degradative capabilities. The CSTB was monitored by quantification of individual strains and by product and organic compound evolution. To investigate the biofilm growth dynamics, eight STEMMs were run in parallel with the same operating conditions. Every week, STEMMs were stopped for biofilm analysis and the organic compound in the wastewater was changed. Biofilm growth was investigated by quantification of individual strains, by evaluation of the overall biofilm growth, and by microscopic analysis. A biofilm composed of both strains was developed and maintained during the whole experiment in the STEMMs. The biofilm that developed on the membrane improved the response of the system to changes in the wastewater.

Microbial dynamics in a continuous stirred tank bioreactor exposed to an alternating sequence of organic compounds.

Microbial dynamics during aerobic biodegradation of an alternating mixture of organic compounds was investigated experimentally in a continuous stirred tank bioreactor (CSTB). A mathematical model describing this system was developed and tested using the experimental results. A model microbial culture consisting of Pseudomonas sp. JS150, a monochlorobenzene (MCB) degrader, and Xanthobacter autotrophicus GJ10, a 1,2-dichloroethane (DCE) degrader, each with exclusive degradation capabilities, was used. The CSTB was inoculated with both microbial strains and exposed to an alternating sequence of the two compounds at noninhibitory concentrations. Concentrations of each microbial strain, of each organic compound, and of degradation product evolved, as well as specific microbial activities via oxygen uptake tests, were monitored. Reduction of the residual DCE discharged from the bioreactor after an MCB to DCE transition was successfully achieved by continuously feeding a low flow of a concentrated solution of both compounds.