New Composite Biocarriers Engineered To Contain Adsorptive and Ion-Exchange Properties Improve Immobilized-Cell Bioreactor Process Dependability

Novel biocarriers that combine the adsorptive properties of activated carbon with the ion-exchange properties of zeolite-based type Z inorganic oxide biocarriers (D. R. Durham, L. C. Marshall, J. G. Miller, and A. B. Chmurny, Appl. Environ, Microbiol. 60:3329-3335, 1994.) were developed. These biocarriers, designated Type CZ, possess fundamental properties that heretofore have not been described for available microbial immobilization matrices. Type CZ biocarriers provide an environment that promotes dense microbial colonization and maintains bioreactor productivity by buffering immobilized microorganisms from unfavorable operating conditions. Data demonstrating protection of immobilized bacteria from organic shock loads and extended pH shocks are presented. In addition, bioreactors containing the composite Type CZ biocarriers continue to remove waste stream contaminants during periods of oxygen deprivation and nutrient limitation.     

An Integrated System for the Bioremediation of Wastewater Containing Xenobiotics and Toxcic Metals

An integrated system for the biotreatment of acidic wastewaters containing both toxic metals and organics is presented. It consists of two bioprocess stages (i) an anaerobic, SRB stage (containing alkaline‐tolerant s ulfate‐ r educing b acteria) that at pH 8 (chosen to acclimatize the bacteria in the biomedium) produces high concentrations of total sulfide ions (more than 400 mg/L) which are added to the wastewater to precipitate the heavy metals out at pH 2 as metal sulfides, and (ii) an aerobic, acidophilic stage containing heterotrophic bacteria (WJB3) that degrade organic xenobiotics. The anaerobic system was comprised of a 4‐L fluidized bed bioreactor with immobilized SRB, a mixing tank, and a precipitation tank. The effluent from the bioreactor with a high concentration of sulfide ions was fed into a mixing tank where model wastewaters containing toxic metals and phenol at pH 2 were also fed at increasing loading rates until free metal ions could be detected in the precipitation tank outlet. Then the effluent from the precipitation tank outlet was fed into a 2.5‐L aerobic bioreactor in which phenol was degraded. In this research, 100 % removal efficiencies were obtained with wastewaters containing more than 400 mg/L metal ions and 900 mg/L phenol at a 6‐h HRT of the mixing tank.     

Removal of phenolic compounds from a petrochemical effluent with a methanogenic consortium.

A methanogenic consortium was used to degrade phenol and ortho- (o-) cresol from a specific effluent of a petrochemical refinery. This effluent did not meet the local environmental regulations for phenolic compounds (178 mg/L), oils and greases (61 mg/L), ammoniacal nitrogen (75 mg/L) or sulfides (3.2 mg/L). The consortium, which degrades phenol via its carboxylation to benzoic acid, was progressively adapted to the effluent. Despite the very high effluent toxicity (EC50 of 2% with Microtox), the adapted consortium degraded 97% of 156 mg/L phenol in the supplemented effluent after 13 days in batch cultures (serum bottle). The addition of proteose peptone to the effluent is essential for phenol degradation. o-cresol was also transformed but not meta- or para-cresols. A continuous flow fixed-film anaerobic bioreactor was developed with the consortium. Treating the effluent with the bioreactor reduced phenol and phenolic compounds concentrations by 97 and 83%, respectively, for a hydraulic residence time of 6 h. This treatment also reduced by about half the effluent toxicity. Oils and greases and ammoniacal nitrogen were not affected. Similar microbiological forms were observed in serum bottles and in the bioreactors with or without the petrochemical effluent. These results indicate that this methanogenic consortium can treat efficiently the phenolic compounds in this specific petrochemical effluent.     

A Novel Porous Nylon Biocarrier for Immobilized Bacteria

A highly porous nylon biocarrier was developed to support immobilized bacteria in bioreactors used to treat liquid wastes. Porosity analyses and scanning electron microscopy showed microbial colonization of accessible pores typically in the range of 100 to 1,200 (mu)m, with some as large as 3.9 mm. A bench-scale packed-bed reactor achieved a p-nitrophenol (PNP) removal rate of 5.95 kg of PNP m(sup-3) day(sup-1) for wastes containing 1,200 mg of PNP liter(sup-1). Complete mixing of the biocarrier bed to remove excess surface biomass was routinely achieved with simple air injection. These porous polymer biocarriers are promising as microbial supports in liquid-waste treatment and bioremediation applications.     

Fast kinetics of fe oxidation in packed-bed reactors

Thiobacillus ferrooxidans was used in fixed-film bioreactors to oxidize ferrous sulfate to ferric sulfate. Glass beads, ion-exchange resin, and activated-carbon particles were tested as support matrix materials. Activated carbon was tested in both a packed-bed bioreactor and a fluidized-bed bioreactor; the other matrix materials were used in packed-bed reactors. Activated carbon displayed the most suitable characteristics for use as a support matrix of T. ferrooxidans fixed-film formation. The reactors were operated within a pH range of 1.35 to 1.5, which effectively reduced the amount of ferric iron precipitation and eliminated diffusion control of mass transfer due to precipitation. The activated-carbon packed-bed reactor displayed the most favorable biomass holdup and kinetic performance related to ferrous sulfate oxidation. The fastest kinetic performance achieved with the activated-carbon packed-bed bioreactor was 78 g of Fe oxidized per liter per h (1,400 mmol of Fe oxidized per liter per h) at a true dilution rate of 40/h, which represents a hydraulic retention time of 1.5 min.     

Fast Kinetics of Fe2+ Oxidation in Packed-Bed Reactors

Thiobacillus ferrooxidans was used in fixed-film bioreactors to oxidize ferrous sulfate to ferric sulfate. Glass beads, ion-exchange resin, and activated-carbon particles were tested as support matrix materials. Activated carbon was tested in both a packed-bed bioreactor and a fluidized-bed bioreactor; the other matrix materials were used in packed-bed reactors. Activated carbon displayed the most suitable characteristics for use as a support matrix of T. ferrooxidans fixed-film formation. The reactors were operated within a pH range of 1.35 to 1.5, which effectively reduced the amount of ferric iron precipitation and eliminated diffusion control of mass transfer due to precipitation. The activated-carbon packed-bed reactor displayed the most favorable biomass holdup and kinetic performance related to ferrous sulfate oxidation. The fastest kinetic performance achieved with the activated-carbon packed-bed bioreactor was 78 g of Fe²⁺ oxidized per liter per h (1,400 mmol of Fe²⁺ oxidized per liter per h) at a true dilution rate of 40/h, which represents a hydraulic retention time of 1.5 min.     

Two-liquid-phase bioreactors for enhanced degradation of hydrophobic/toxic compounds

Two-liquid-phase culture systems involve the addition of a water-immiscible, biocompatible and non-biodegradable solvent to enhance a biocatalytic process. Two-liquid-phase bioreactors have been used since the mid-seventies for the microbial and enzymatic bioconversion of hydrophobic/toxic substrates into products of commercial interest. The increasing popularity of bioremediation technologies suggests a new area of application for this type of bioreactor. The toxicity and the limited bioavailability of many pollutants are important obstacles that must first be overcome in order to improve biodegradation processes. Two-liquid-phase bioreactors have the potential to resolve both limitations of biotreatment technologies by the enhancement of the mass-transfer rate of compounds with low bioavailability, and by the controlled delivery of apolar toxic compounds. This technology can also be useful in accelerating the enrichment of microorganisms degrading problematic pollutants. In this paper, we discuss the application of two-liquid-phase bioreactors to enhance the biodegradation of toxic/poorly bioavailable contaminants. Important microbial mechanisms involved in this type of system are described. Uptake of the substrates can be achieved by microorganisms freely dispersed in the aqueous phase and/or bound at the interface between the aqueous and the immiscible phases. Production of surface-active compounds and adhesion abilities are microbial features involved in the process. General guidelines for the design of two-liquid-phase bioreactors for biodegradation purposes are presented. Solvent selection should be established on specific criteria, which depend on the characteristics of target compound(s) and the microorganism(s) implicated in the biodegradation process. The central importance of maximizing the interfacial surface area is highlighted. The potential of this approach as an alternative to current biotreatment technologies is also discussed.     

Application of DNA amplification fingerprinting (DAF) to mixed culture bioreactors

Summary The use of DNA amplification fingerprinting (DAF) as a tool for monitoring mixed microbial populations in bioreactors was evaluated. Short (8-mer or 10-mer) oligonucleotides were used to prime DNA extracts from various biological reactors during polymerase chain reaction (PCR) amplification. The reactors examined in this study included two sets of anaerobic stirred tank continuous flow bioreactors. One set of anaerobic reactors was operated under methanogenic conditions and one set was operated under sulfate-reducing conditions. The anaerobic reactor communities in the methanol-fed reactors showed extensive DAF homology. DAF was also applied to a fixed-film azo dye degrading reactor to examine the degree of uniformity of colonization of the substratum in representative regions of the reactor. This method is a quick and relatively inexpensive means of monitoring microbial community structure during biological processes. Since no cultivation of the sample is involved, the genetic profile of the community is not biased by outgrowth conditions. DAF profiles may be useful for comparisons of population changes over time or of bench-scale vs pilot-scale reactors but not adequate for assessing community diversity.     

Biodegradation and Decolorization of Pulp and Paper Mill Effluent by Anaerobic and Aerobic Microorganisms in a Sequential Bioreactor

Summary Paecilomyces sp. and Pseudomonas syringae pv myricae (CSA105) were isolated from sediment core of drainage of the pulp and paper mill industry. Fungi and bacteria were applied for treatment of pulp and paper mill effluent in a two-step and three-step fixed film sequential bioreactor containing sand and gravel at the bottom of the reactor for immobilization of microbial cells. Degradation of chlorinated phenols and formation of their metabolites were determined by high performance liquid chromatography. The microbes exhibited significant reduction in colour (88.5%), lignin (79.5%), chemical oxygen demand (87.2%) and phenol (87.7%) in two-step aerobic sequential bioreactor, and colour (87.7%), lignin (76.5%), chemical oxygen demand (83.9%) and phenol (87.2%) in three-step anaerobic-aerobic sequential bioreactor.     

Comparison of different pilot scale bioreactors for the treatment of a real wastewater from the textile industry

Wastewater from textile industry usually undergoes activated sludge biotreatment ahead of refining treatments, final discharge or reuse. To identify the most effective bioreactor typology for the secondary treatment of a wastewater resulting from a textile industry of the Biella district (Italy), four pilot units characterized by a different configuration and fluid dynamics (i.e., Bioflotation^®, Fixed Bed Biofilm Reactor (FBBR), flow-jet aeration and standard aerobic sludge reactors) were operated in parallel, inoculated with the same microbial consortium and fed with identical streams of wastewater discharged from wet textile processes of the industy. COD, TC and non-ionic surfactants were monitored in effluents of the compared bioreactors working under continuous mode and the cultivable heterotrophic microorganisms prevailing in each of them were isolated and characterized as the end of the study. The results demonstrated that the air supply system greatly influenced the treatment efficiency which reached the highest value in the case of Bioflotation^® and FBBR technology. A highly specialized bacterial biomass mostly composed by strains of the Pseudomonas, Stenotrophomonas and Ochrobactrum genera was isolated in such reactors, thus suggesting that a direct correlation between reactor configuration, decontamination performances and microbial biomass composition exist.     

Anaerobic dechlorination of pentachlorophenol in fixed-film and upflow anaerobic sludge blanket reactors using different inocula

Longterm performance and stability of two upflow anaerobic sludge blanket (UASB) reactors inoculated with granular sludge and treating a synthetic waste water containing pentachlorophenol (PCP) and phenol were studied. A similar system consisting of two fixed-film reactors inoculated with anaerobic digested sewage sludge were further studied. One reactor in each series received glucose in addition to the phenols. Dechlorination of PCP proceeded via two different dominating pathways in the respective reactor systems, suggesting that two distinct microbial populations were present, probably originating from the different inocula. Dechlorinating activity was maintained for more than 18 months in the UASB reactors and was generally higher than in the fixed-film reactors. In the fixed-film reactors, dechlorination of PCP suddenly decreased after 15.5 months of operation compared to earlier performance. Since no operational parameters had been changed, this indicated that the enriched culture was unstable on a longterm basis. Addition of yeast extract to the medium restored activity. General process stability in both reactor systems was clearly enhanced by the addition of glucose and was superior in the UASB/granular sludge system. The better performance and the higher stability in the UASB/granular sludge reactor highlights the importance of thorough screening of inocular prior to start-up of processes treating waste waters containing xenobiotic compounds.Abbreviations PCP pentachlorophenol - TeCP tetrachlorophenol - TCP trichlorophenol - DCP dichlorophenol - UASB upflow anaerobic sludge blanket - HRT hydraulic retention time     

A comparative study of gel entrapped and membrane attached microbial reactors for biodegrading phenol

A comparative study between two reactors, one using microorganisms entrapped in calcium alginate gel, and the other using microorganisms attached on the surface of a membrane (polymeric microporous sheeting, MPS^TM) to biodegrade phenol is performed. Results indicate that the alginate bead bioreactor is efficient at higher phenol concentrations while the membrane bioreactor shows better performance at lower phenol concentrations. This unique response is primarily attributed to the different techniques by which the microorganisms are immobilized in the two reactors.In batch mode, below a starting concentration of 100 ppm phenol, biodegradation rates in the membrane bioreactor are (7.58 to 12.02 mg phenol/h · g dry biomass) atleast 10 times the rates in alginate bead bioreactor (0.74 to 1.32 mg phenol/h · g dry biomass). Biodegradation rates for the two reactors match at a starting concentration of 250 ppm phenol. Above 500 ppm phenol, the rates in the alginate bead bioreactor are (7.3 to 8.1 mg phenol/h · g dry biomass) on an average 5.5 times the corresponding rates in the membrane bioreactor (2.18 to 1.03 mg phenol/h · g dry biomass).In continuous feed mode the steady state degradation rates in the membrane bioreactor are one to two orders of magnitude higher than the alginate bead bioreactor below 150 ppm inlet phenol concentration. At an inlet concentration around 250 ppm phenol the rates are comparable. Above 500 ppm of phenol the rates in the alginate bioreactor are an order of magnitude high than the membrane bioreactor.Due to substrate inhibition, and its inability to sustain a high biomass concentration, the membrane bioreactor shows poor efficiencies at phenol concentrations above 250 ppm. At low phenol concentrations the apparent reaction rates in the alginate bead bioreactor decrease due to the diffusional resistance of the gel matrix, while biodegradation rates in the membrane bioreactor remain high due to essentially no external diffusional resistance.Results indicate that a combined reactor system can be more effective for bioremediation than either separate or attached microbial reactors.     

Efficiency of ammonia and phosphorus removal from a colombian agroindustrial wastewater by the microalgae Chlorella vulgaris and Scenedesmus dimorphus

The ammonia and phosphorus removal efficiencies of the microalgae Chlorella vulgaris and Scenedesmus dimorphus, during biotreatment of secondary effluent from an agroindustrial wastewater of a dairy industry and pig farming, were evaluated. The microalgae were isolated from a wastewater stabilization pond near Santafé de Bogotá, Colombia. Batch cultures were made using both species in 4-1 cylindrical glass bioreactors each containing 2l of culture. Chlorella vulgaris was also cultivated on wastewater in a triangular bioreactor. Three 216-h experimental cycles were run for each microalga and in each bioreactor. In the cylindrical bioreactor, S. dimorphus was more efficient in removing ammonia than C. vulgaris. However, the final efficiency of both microalgae at the end of each cycle was similar. Both microalgae removed phosphorus from the wastewater to the same extent in a cylindrical bioreactor. Using C. vulgaris, the triangular bioreactor was superior for removing ammonia and the cylindrical bioreactor was superior for removing phosphorus. This study shows the potential of using these microalgae to reduce the environmental pollution of heavily contaminated agroindustrial waters currently disposed of untreated into the waterways and streams of tropical Colombia.     

Effect of hydraulic retention time on inorganic nutrient recovery and biodegradable organics removal in a biofilm reactor treating plant biomass leachate

A fixed-film (biofilm) reactor was designed and its performance was determined at various retention times. The goal was to find the optimal retention time for recycling plant nutrients in an advanced life support system, to minimize the size, mass, and volume (hold-up) of a production model. The prototype reactor was tested with aqueous leachate from wheat crop residue at 24, 12, 6, and 3 h hydraulic retention times (HRTs). Biochemical oxygen demand (BOD), nitrates and other plant nutrients, carbohydrates, total phenolics, and microbial counts were monitored to characterize reactor performance. BOD removal decreased significantly from 92% at the 24 h HRT to 73% at 3 h. Removal of phenolics was 62% at the 24 h retention time, but 37% at 3 h. Dissolved oxygen concentrations, nitric acid consumption, and calcium and magnesium removals were also affected by HRT. Carbohydrate removals, carbon dioxide (CO2) productions, denitrification, potassium concentrations, and microbial counts were not affected by different retention times. A 6 h HRT will be used in future studies to determine the suitability of the bioreactor effluent for hydroponic plant production.     

Long-Term Stability of Mercury-Reducing Microbial Biofilm Communities Analyzed by 16S-23S rDNA Interspacer Region Polymorphism

The composition of mercury-reducing communities in two bioreactors retaining Hg(II) from chloralkali electrolysis wastewater for 485 days was analyzed based on effluent community DNA. Packed bed bioreactors with lava chips as carrier of the biofilm were inoculated with nine Hg(II)-resistant isolates that belonged to the alpha and gamma subdivisions of the proteobacteria. A rapid DNA-fingerprinting method was applied, using the intergenic spacer region (ISR) of the 16S-23S rDNA for analysis of the community composition. This allowed discrimination of the inoculum strains down to subspecies level. A merA specific PCR permitted the discrimination of the community's merA genes. During the 485 days of operation, the bioreactors were exposed to various physical stresses (mixing, gas bubbles, temperature increase up to 41°C, increased flow velocity) and repeated high mercury inflow concentrations, resulting in reduced bioreactor performance and decreased culturable cell numbers in the reactor effluent. Nevertheless, the composition of the microbial community remained rather stable throughout the investigated time period. Of the inoculum strains, two could be detected throughout, whereas three were sometimes present with varying periods of nondetection. Two inoculum strains were only detected within the first month. Two strains of gamma-proteobacteria that were able to reduce ionic mercury invaded the bioreactor community. They did not outcompete established strains and had no negative effect on the Hg(II)-retention activity of the bioreactors. The community comprised diverse merA genes. The abundance of merA genes matched the abundance of their respective strains as confirmed by ISR community analysis. The continuously high selection pressure for mercury resistance maintained a stable and highly active mercury-reducing microbial community within the bioreactors.     

Bioremediation of phenol by a novel partitioning bioreactor using cow dung microbial consortia

A bioreactor has been designed and developed for partitioning of aqueous and organic phases with a provision for aeration and stirring, a cooling system and a sampling port. The potential of a cow dung microbial consortium has been assessed for bioremediation of phenol in a single-phase bioreactor and a two-phase partitioning bioreactor. The advantages of the two-phase partitioning bioreactor are discussed. The Pseudomonas putida IFO 14671 has been isolated, cultured and identified from the cow dung microbial consortium as a high-potential phenol degrader. The methods developed in this study present an advance in bioremediation techniques for the biodegradation of organic compounds such as phenol using a bioreactor. We have also demonstrated the potential of microorganisms from cow dung as a source of biomass.     

Selective removal of transition metals from acidic mine waters by novel consortia of acidophilic sulfidogenic bacteria

Two continuous‐flow bench‐scale bioreactor systems populated by mixed communities of acidophilic sulfate‐reducing bacteria were constructed and tested for their abilities to promote the selective precipitation of transition metals (as sulfides) present in synthetic mine waters, using glycerol as electron donor. The objective with the first system (selective precipitation of copper from acidic mine water containing a variety of soluble metals) was achieved by maintaining a bioreactor pH of ～2.2–2.5. The second system was fed with acidic (pH 2.5) synthetic mine water containing 3 mM of both zinc and ferrous iron, and varying concentrations (0.5–30 mM) of aluminium. Selective precipitation of zinc sulfide was possible by operating the bioreactor at pH 4.0 and supplementing the synthetic mine water with 4 mM glycerol. Analysis of the microbial populations in the bioreactors showed that they changed with varying operational parameters, and novel acidophilic bacteria (including one sulfidogen) were isolated from the bioreactors. The acidophilic sulfidogenic bioreactors provided ‘proof of principle’ that segregation of metals present in mine waters is possible using simple online systems within which controlled pH conditions are maintained. The modular units are versatile and robust, and involve minimum engineering complexity.     

Colour removal of anaerobically treated pulp and paper mill effluent by microorganisms in two steps bioreactor

In the present study sequential anaerobic and aerobic treatment in two steps bioreactor was performed for removal of colour in the pulp and paper mill effluent. In anaerobic treatment, colour (70%), lignin (25%), COD (42%), AOX (15%) and phenol (39%) were reduced in 15 days. The anaerobically treated effluent was separately applied in bioreactor in presence of fungal strain, Paecilomyces sp., and bacterial strain, Microbrevis luteum. Data of study indicated reduction in colour (95%), AOX (67%), lignin (86%), COD (88%) and phenol (63%) by Paecilomyces sp. where as M. luteum showed removal in colour (76%), lignin (69%), COD (75%) AOX (82%) and phenol (93%) by day third when 7 days anaerobically treated effluent was further treated by aerobic microorganisms. Change in pH of the effluent, and increase in biomass of microorganisms substantiated results of the study, which was concomitant to the treatment method.     

Nitrile bioconversion by Microbacterium imperiale CBS 498-74 resting cells in batch and ultrafiltration membrane bioreactors

The biohydration of acrylonitrile, propionitrile and benzonitrile catalysed by the NHase activity contained in resting cells of Microbacterium imperiale CBS 498-74 was operated at 5, 10 and 20°C in laboratory-scale batch and membrane bioreactors. The bioreactions were conducted in buffered medium (50 mM Na₂HPO₄/NaH₂PO₄, pH 7.0) in the presence of distilled water or tap-water, to simulate a possible end-pipe biotreatment process. The integral bioreactor performances were studied with a cell loading (dry cell weight; DCW) varying from 0.1 mg_DCW per reactor to 16 mg_DCW per reactor, in order to realize near 100% bioconversion of acrylonitrile, propionitrile and benzonitrile without consistent loss of NHase activity.     

Scanning electron microscopic examination of Thiobacillus ferrooxidans on different support matrix materials in packed bed and fluidized bed bioreactors

Summary Thiobacillus ferrooxidans was used in fixed-film bioreactors to oxidize ferrous iron to ferric iron. The test support matrix materials included activated carbon particles, glass beads, and ion-exchange resin particles. The experimental systems included a fluidized bed approach, which was evaluated with activated carbon only, and a packed bed approach which was tested with each of the support matrix materials. The colonization of the matrix surface was examined with scanning electron microscopy. There were contrasting differences in the bacterial colonization and accumulation of Fe(III) precipitates on the matrix surface among the test materials. The packed bed activated carbon bioreactor displayed the fastest kinetics and the highest amount of cell sorption as well as the roughest and most porous matrix surface.