Bioconversion processes

Compared to conventional chemical technologies and other similar industrial processes, bioprocesses represent a more sustainable and environmentally-friendly alternative for the production of fuels and platform chemicals. In biorefineries, different kinds of feedstocks, such as biomass or lignocellulosic materials in general, can be used and fermented by microorganisms (e.g., bacteria, fungi, algae), after some pretreatment steps, to produce high added-value metabolites. More recently, wastes, wastewaters and also waste gases have been shown to be suitable for resource recovery or for their bioconversion to (bio)fuels (e.g., ethanol, butanol, hexanol, biodiesel, biohydrogen, biogas) or other commercial products (e.g., biopolymers). In this sense, much effort has also been made to bioconvert greenhouse gases, such as CO2, into useful products.The goal of this Special Issue is to publish both recent innovative research data, as well as review papers on the fermentation of different types of substrates to commercial (bio)fuels and (bio)products, mainly focusing on the bioconversion of pollutants in solid, liquid, or gas phases (wastes, wastewaters, waste gases)

Inert filter media for the biofiltration of waste gases – characteristics and biomass control

Soil biofilters and related systems based onthe use of natural filter beds have been usedfor several years for solving specific airpollution problems. Over the past decade,significant improvements have been brought tothese original bioprocesses, among which thedevelopment and use of new inert packingmaterials. The present paper overviews the mostcommon inert packings used in biofiltration ofwaste gases and their major characteristics. Apotential problem recently encountered whenusing inert filter beds is the heterogenousdistribution of biomass on the packingmaterial, and the excessive growth andaccumulation of biomass when treating highorganic loads, eventually leading to cloggingof the biofilter and reduced efficiency.Several strategies that have been proposed forsolving such problems are described in thispaper. Technologies for controlling excessbiomass accumulation can be grouped into fourcategories based on the use of mechanicalforces, the use of specific chemicals, thereduction of microbial growth, and predation

Fungal biocatalysts in the biofiltration of VOC-polluted air

Gas-phase biofilters used for the treatment of waste gases were originally packed with compost or other natural filter beds containing indigenous microorganisms. Over the past decade much effort has been made to develop new carrier materials, more performant biocatalysts and new types of bioreactors. Elimination capacities reached nowadays are 5 to 10 times higher than those originally reported with conventional compost biofilters. With the recently developed inert filter beds, inoculation is a prerequisite for successful start-up and operation. Either non-defined mixed cultures or pure bacterial cultures have originally been used. The search for efficient fungal biocatalysts started only a few years ago, mainly for the biofiltration of waste gases containing hydrophobic compounds, such as styrene, α-pinene, benzene, or alkylbenzenes. In this review, recently isolated new fungal strains able to degrade alkylbenzenes and other related volatile organic pollutants are described, as well as their major characteristics and their use as biocatalysts in gas-phase biofilters for air pollution control. In biofiltration, the most extensively studied organism belongs to the genus Exophiala, although strains of Scedosporium, Paecilomyces, Cladosporium, Cladophialophora, and white-rot fungi are all potential candidates for use in biofilters. Encouraging results were obtained in most of the cases in which some of those organisms were present in gas-phase biofilters. They allow reaching high elimination capacities and are resistant to low pH values and to reduce moisture conten

Parameters affecting performance and modeling of biofilters treating alkylbenzene-polluted air

Both short-term and long-term biofiltration experiments were undertaken with a biofilter inoculated with a defined microbial consortium and treating an alkylbenzene mixture. The results obtained with such a biofilter in short-term experiments were very similar to those obtained with a biofilter inoculated with a non-defined mixed culture, in terms of maximum elimination capacities (70–72 g m–3 h–1) and the corresponding removal efficiencies (>95%). However, in long-term experiments, a better performance was reached, with a maximum elimination capacity of 120 g m–3 h–1, corresponding to a removal efficiency >99% after 2 years of operation. Inoculation proved to be useful for shortening the start-up period. In the long term, it appeared that biomass distribution was not homogenous along the biofilter, which in some cases resulted in a bad fit between simple model equations and experimental data

Formaldehyde biodegradation and its inhibitory effect on nitrification

The simultaneous removal of formaldehyde and ammonium in aerobic cultures and the inhibitory effect of formaldehyde on ammonium oxidation were investigated. The influence of a co-substrate, methanol, on formaldehyde biodegradation and on the nitrification process was also evaluated. Formaldehyde was completely removed at all concentrations tested (30–3890 mg dm−3) in assays with that compound as the single carbon source and in the presence of methanol as co-substrate. An initial formaldehyde biodegradation rate of 4.6 g CH2O g−1 VSS d−1 was obtained for 2000 mg CH2O dm−3 as single carbon source compared with a rate of 7.3 g CH2O g−1 VSS d−1 when methanol was added. Formaldehyde was inhibitory to the nitrification process at initial concentrations higher than 350 mg dm−3. Increasing the initial formaldehyde concentration or adding a co-substrate such as methanol resulted in a longer lag phase before ammonium oxidation and caused a decrease in the degree of nitrification. Nitrification was completely inhibited at initial formaldehyde concentrations higher than 1500 mg dm−3

Removal of methanol from air in a low-pH trickling monolith bioreactor

A novel ceramic monolith bioreactor colonized by a methanol-degrading culture was investigated in order to assess its suitability for waste gas treatment. The acidotolerant yeast Candida boidinii was identified as dominant organism in the biofilm. The culture was able to efficiently biodegrade methanol at a pH as low as 2, both in batch and in continuous bioreactor studies. Operational parameters that were considered include start-up of the bioreactor, methanol loading, mineralization of methanol, pressure drop and biofilm accumulation during steady-state operation. A high maximal elimination capacity of 234 g m−3 h−1 was reached, with more than 80% removal efficiency and complete conversion of methanol into biomass and end products. Removal efficiencies exceeding 90% were obtained up to loads of about 200 g m−3 h−1. Problems of excess biomass accumulation and pressure drop after long-term operation can easily be solved by temporarily increasing the liquid trickling rate. This is the first report on the treatment of methanol-polluted air in such a low-pH monolith bioreactor

Biofiltration of waste gases with the fungi Exophiala oligosperma and Paecilomyces variotii

Two biofilters fed toluene-polluted air were inoculated with new fungal isolates of either Exophiala oligosperma or Paecilomyces variotii, while a third bioreactor was inoculated with a defined consortium composed of both fungi and a co-culture of a Pseudomonas strain and a Bacillus strain. Elimination capacities of 77 g m−3 h−1 and 55 g m−3 h−1 were reached in the fungal biofilters (with removal efficiencies exceeding 99%) in the case of, respectively, E. oligosperma and Paecilomyces variotii when feeding air with a relative humidity (RH) of 85%. The inoculated fungal strains remained the single dominant populations throughout the experiment. Conversely, in the biofilter inoculated with the bacterial–fungal consortium, the bacteria were gradually overgrown by the fungi, reaching a maximum elimination capacity around 77 g m−3 h−1. Determination of carbon dioxide concentrations both in batch assays and in biofiltration studies suggested the near complete mineralization of toluene. The non-linear toluene removal along the height of the biofilters resulted in local elimination capacities of up to 170 g m−3 h−1 and 94 g m−3 h−1 in the reactors inoculated, respectively, with E. oligosperma and P. variotii. Further studies with the most efficient strain, E. oligosperma, showed that the performance was highly dependent on the RH of the air and the pH of the nutrient solution. At a constant 85% RH, the maximum elimination capacity either dropped to 48.7 g m−3 h−1 or increased to 95.6 g m−3 h−1, respectively, when modifying the pH of the nutrient solution from 5.9 to either 4.5 or 7.5. The optimal conditions were 100% RH and pH 7.5, which allowed a maximum elimination capacity of 164.4 g m−3 h−1 under steady-state conditions, with near-complete toluene degradation. Applied Microbiology and Biotechnology Applied Microbiology and Biotechnology Look Inside Article Metrics 28 Citations Other actions Export citation Register for Journal Updates About This Journal Reprints and Permissions Add to Papers Share Share this content on Facebook Share this content on Twitter Share this content on LinkedI

Simultaneous nitrification and formaldehyde biodegradation in an activated sludge unit

The simultaneous removal of formaldehyde and ammonium in a lab-scale activated sludge unit was investigated. The unit was operated at a hydraulic retention time of 2.4 days with an ammonium concentration in the influent of 350 mg 〖NH〗_4^+-N/L, maintaining the ammonium loading rate at 0.15 g 〖NH〗_4^+-N/L d during the operation time. However, the applied organic loading rate was increased stepwise by increasing the formaldehyde concentration from 26 up to 3168 mg/L, corresponding to 0.01–1.40 g COD/L d. High formaldehyde removal efficiencies, around 99.5% (±0.38), were maintained at all the formaldehyde concentrations. Ammonium removal was also very high during the operation period, around 99.9% (±0.01). The ammonium concentration in the effluent was lower than 0.1 mg 〖NH〗_4^+-N/L at all applied organic loading rates, indicating that there was no inhibition of nitrification by formaldehyde

Behaviour and optimization of a novel monolith bioreactor for wasre gas treatment

[Abstract] Treatment of waste gases in bioreactors is cost-effective and environmental-friendly compared to the conventional techniques used for treating large flow rates of gas streams with low concentrations of pollutants. Nowadays, significant research is dedicated at the development of new bioreactor configurations, improved biocatalysts or new packing materials, among others. In the present study, a novel bioreactor packed with ceramic monolith was developed for treating VOCs (toluene or methanol) polluted air. Operational parameters that were considered included start-up of the bioreactor, inlet loading, changes in gas flow rate, liquid feed mode, and monolith blockage and biomass growth. Preliminary data on performance and stability have been obtained showing that this system can efficiently be used for waste gas treatment

Kinetics of inhibition in the biodegradation of monoaromatic hydrocarbons in presence of heavy metals

The toxicity and inhibitory effects of heavy metals such as cadmium, nickel and zinc on alkylbenzene removal were evaluated with a Bacillus strain. The kinetics of alkylbenzene biodegradation with the different heavy metals at various concentrations were modeled using the Andrews equation which yielded a good fit between model and experimental data. Additional experiments undertaken with a Pseudomonas sp. in presence of nickel confirmed a good fit between experimental data and the Andrews model for this strain as well. The heavy metals inhibition constants (Ki) were calculated for different combinations of volatile organic compounds (VOC) and heavy metals. The present approach provides a method for evaluating and quantifying the inhibition effect of heavy metals on the biodegradtion of pollutants by specific microbial strain