Enhanced Microbial Removal of H2S Using Chlorobium in an Optical-Fiber Bioreactor

The removal rate of H₂S in a scratched optical fiber bioreactor using Chlorobium thiosulfatophilum was 0.87 µmol H₂S oxidized·l/min·mg protein, which was 6.7 times that in an external illuminating reactor. Available light intensity with scratched fibers in the bioreactor was 41 µmol/m²·s about 5 times as much as that with unscratched ones.     

Anaerobic treatment of synthetic medium-strength wastewater using a multistage biofilm reactor

A laboratory-scale multistage anaerobic biofilm reactor of three compartments with a working volume of 54-L was used for treating a synthetic medium-strength wastewater containing molasses as a carbon source at different influent conditions. The start-up period, stability and performance of this reactor were assessed at mesophilic temperature (35 °C). During the start-up period, pH fluctuations were observed because there was no microbial selection or zoning, but as the experiment progressed, results showed that phase separation had occurred inside the reactor. COD removal percentages of 91.6, 91.6, 90.0 and 88.3 were achieved at organic loading rates of 3.0, 4.5, 6.75 and 9.0 kg COD/m³ day, respectively. A decrease in HRT from 24 to 16 h had no effect on COD removal efficiency. When HRT decreased to 8 h, COD removal efficiency was still 84.9%. Recirculation ratios of 0.5 and 1.0 had no effect on COD removal but other factors such as the volatile fatty acid (VFA) content were affected. The effect of toxic shock was also investigated and results showed that the main advantage of using this bioreactor lies in its compartmentalized structure.     

Start-up and operation of a propionate-degrading fluidized-bed reactor

Summary A laboratory-scale fluidized-bed reactor was inoculated with a syntrophically propionate-degrading co-culture. After 24 days of batch operation with propionate and acetate in the medium, the reactor was operated for 8 months with propionate as the sole substrate. The loading rate was 8.5 kg chemical oxygen demand/m³ ·day, yielding a maximal gas production of 4.5 l/l·day at a removal efficiency of 94–99%. The degradation was not inhibited by up to 85mm propionate in pulse experiments, but short-time changes in redox potential above — 300 mV led to a drop in the propionate degradation rate. While Methanocorpusculum sp. and Methanospirillum sp. adhered to the sand in the early phase of the start-up, the consortium in the mature biofilm consisted of Desulfobulbus sp., Methanothrix soehngenii and species of at least three different genera of hydrogenotrophic methanogens. A syntrophic relationship between the sulphate-reducing Desulfobulbus sp. and hydrogenotrophic and acetotrophic methanogens is discussed.Offprint requests to: G. Zellner     

Biofilm Growth and Bed Fluidization in a Fluidized Bed Reactor Packed with Support Materials of Low Density

Support materials of low‐density for fluidized bed reactors provide several operational advantages, including lower energy requirements and proper biofilm growth balance. The aim of this investigation was to study the extent of biofilm growth and bed fluidization in an experimental reactor, using polyester resin (ρ_pr = 1220 kg/m³) and vitrified expanded perlite (ρ_vep = 1710 kg/m³) as alternative support materials to conventional silica sand. A noteworthy amount of biofilm was observed to be attached to both support materials from the very beginning of the bioreactor operation. Nevertheless, there were significant variations in biofilm growth and activity over the course of the experimental trials. For both perlite and polyester beds, the highest biofilm mass and the highest total number of mesophilic bacteria were observed between the 7^th and the 10^th day, showing a steady state trend at the end of the experimental runs. The chemical oxygen demand (COD) removal levels were concomitant with biofilm mass and total mesophilic bacteria changes, although the polyester bed efficiency was slightly higher than that for the perlite bed. As expected, the polyester bed was fluidized at a lower re‐circulation flow compared to the perlite bed. Reactor back‐washing was not required for these support materials since biomass excess was adequately separated by means of a special internal device. The efficiencies of removal of organic matter achieved were acceptable (up to 78 %) despite the low volume of the support material (25 %) and the low hydraulic retention time (30 min).     

Biotreatment of phenol-contaminated wastewater in a spiral packed-bed bioreactor

A spiral packed-bed bioreactor inoculated with microorganisms obtained from activated sludge was used to conduct a feasibility study for phenol removal. The reactor was operated continuously at various phenol loadings ranging from 53 to 201.4 g m⁻³ h⁻¹, and at different hydraulic retention times (HRT) in the range of 20–180 min to estimate the performance of the device. The results indicated that phenol removal efficiency ranging from 82.9 to 100% can be reached when the reactor is operated at an HRT of 1 h and a phenol loading of less than 111.9 g m⁻³ h⁻¹. At an influent phenol concentration of 201.4 g m⁻³, the removal efficiency increased from 18.6 to 76.9% with an increase in the HRT (20–120 min). For treatment of phenol in the reactor, the maximum biodegradation rate (V _m) was 1.82 mg l⁻¹ min⁻¹; the half-saturation constant (K _s), 34.95 mg l⁻¹.     

A new bioreactor with a semi-fixed packing: investigation of degradation of phenol

A new bioreactor using a semi-fixed packing of frames with “sacks” made of a fabric of “Raschell” type stretched on them is proposed. The construction provides not only a large surface area of the biofilm carrier per unit volume of the apparatus, but also the possibility for an easy removal of the biomass after reaching a certain thickness of the biofilm increasing the gas velocity. Aerobic degradation of phenol in the new bioreactor, using microorganisms of the strain Pseudomonas putida, was studied. The experiments are carried out using water containing 0.7?g/l of phenol at a temperature of 27–30?°C. Different specific surface area of the packing (within 176 and 387?m²/m³) are studied. Degradation rates from 60 to 140?mg/(1?h) are attained. A retardation of the process at the end is observed, probably due to inhibition effect. This rate is 5–6 times higher than the rate observed when using free cells. At air velocity of 0.03–0.035?m/s (related to the total cross section of the bioreactor) the vibrations of the packing material lead to destruction and removal of the old biomass.     

Degradation of reactive dyes in a photocatalytic circulating-bed biofilm reactor

Decolorization and mineralization of reactive dyes by intimately coupled TiO₂‐photocatalysis and biodegradation (ICPB) on a novel TiO₂‐coated biofilm carrier were investigated in a photocatalytic circulating‐bed biofilm reactor (PCBBR). Two typical reactive dyes—Reactive Black 5 (RB5) and Reactive Yellow 86 (RY86)—showed similar first‐order kinetics when being photocatalytically decolorized at low pH (～4–5) in batch experiments. Photocatalytic decolorization was inhibited at neutral pH in the presence of phosphate or carbonate buffer, presumably due to electrostatic repulsion from negatively charged surface sites on TiO₂, radical scavenging by phosphate or carbonate, or both. Therefore, continuous PCBBR experiments were carried out at a low pH (～4.5) to maintain high photocatalytic efficiency. In the PCBBR, photocatalysis alone with TiO₂‐coated carriers could remove target compound RB5 and COD by 97% and 47%, respectively. Addition of biofilm inside macroporous carriers maintained a similar RB5 removal efficiency, but COD removal increased to 65%, which is evidence of ICPB despite the low pH. ICPB was further proven by finding microorganisms inside carriers at the end of the PCBBR experiments. A proposed ICPB pathway for RB5 suggests that a major intermediate, a naphthol derivative, was responsible for most of the residual COD, while most of the nitrogen in the azo‐bonds (? N?N? ) was oxidized to N₂. Biotechnol. Bioeng. 2012; 109:884–893. © 2011 Wiley Periodicals, Inc.     

Heterotrophic cultivation of Paracoccus denitrificans in a horizontal rotating tubular bioreactor

In this work, the heterotrophic cultivation of bacterium Paracoccus denitrificans has been studied in a horizontal rotating tubular bioreactor (HRTB). After development of a microbial biofilm on the inner surface of the HRTB, conditions for one-step removal of acetate and ammonium ion were created. The effect of bioreactor process parameters [medium inflow rate (F) and bioreactor rotation speed (n)] on the bioprocess dynamics in the HRTB was studied. Nitrite and nitrogen oxides (NO and N₂O) were detected as intermediates of ammonium ion degradation. The biofilm thickness and the nitrite concentration were gradually reduced with increase of bioreactor rotation speed when the medium inflow rate was in the range of 0.5–1.5 l h⁻¹. Further increase of inflow rate (2.0–2.5 l h⁻¹) did not have a significant effect on the biofilm thickness and nitrite concentration along the HRTB. Complete acetate consumption was observed when the inflow rate was in the range of 0.5–1.5 l h⁻¹ at all bioreactor rotation speeds. Significant pH gradient (cca 1 pH unit) along the HRTB was only observed at the highest inflow rate (2.5 l h⁻¹). The results have clearly shown that acetate and ammonium ion removal by P. denitificans can be successfully conducted in a HRTB as a one-step process.     

Biotreatment of ammonia- and butanal-containing waste gases

The biological removal of ammonia and butanal in contaminated air was investigated by using, respectively, a laboratory-scale filter and a scrubber-filter combination. It was shown that ammonia can be removed with an elimination efficiency of 83% at a volumetric load of 100 m³·m^–2·h^–1 with 4–16 ppm of ammonia. During the experiment percolates were analysed for nitrate, nitrite, ammonium and pH. It was found that the nitrification in the biofilter could deteriorate due to an inhibition of Nitrobacter species, when the free ammonia concentration was rising in the percolate. It should be easy to control such inhibition through periodic analysis of the liquid phase by using a filter-scrubber combination. Such a combination was studied for butanol removal. Butanal was removed with an elimination efficiency of 80% by a scrubber-filter combination at a volumetric load of 100 m³·m^–2·h^–1 and a high butanal input concentration. Mixing the filter material with CaCO₃ and pH control of the liquid in the scrubber resulted in an increase of the elimination efficiency. These results, combined with previous results on the biofiltration of butanal and butyric acid, allow us to discuss the influence of odour compounds on the removal efficiency of such systems and methods for control. The results were used to construct a full-size system, which is described.     

Enrichment and granulation of Anammox biomass started up with methanogenic granular sludge

A sequencing batch reactor (SBR) seeded with methanogenic granular sludge was started up to enrich Anammox (Anaerobic Ammonium Oxidation) bacteria and to investigate the feasibility of granulation of Anammox biomass. Research results showed that hydraulic retention time (HRT) was an important factor to enrich Anammox bacteria. When the HRT was controlled at 30 days during the initial cultivation, the SBR reactor presented Anammox activity at t = 58 days. Simultaneously, the methanogenic granular sludge changed gradually from dust black to brown colour and its diameter became smaller. At t = 90 days, the Anammox activity was further improved. NH₄⁺-N and NO₂⁻N were removed simultaneously with higher speed and the maximum removal rates reached 14.6 g NH₄⁺-N /(m³ _reactor·day) and 6.67 g NO₂⁻-N /(m³ _reactor·day), respectively. Between t = 110 days and t = 161 days, the nitrogen load was increased to a HRT of 5 days (70 mg/l NH₄⁺ and 70 mg/l NO₂), the removal rates of ammonium and nitrite were 60.6% and 62.5% respectively. The sludge changed to red and formed Anammox granulation with high nitrogen removal activity.     

Effect of pH on phase separated anaerobic digestion

A pilot scale experiment was performed for a year to develop a two-phase anaerobic process for piggery wastewater treatment (COD: 6,000 mg/L, BOD: 4,000 mg/L, SS: 500 gm/L, pH 8.4, alkalinity 6,000 mg/L). The acidogenic reactor had a total volume of 3 m³, and the methanogenic reactor, an, anaerobic up-flow sludge filter, combining a filter and a sludge bed, was also of total volume 3 m³ (1.5 m³ of upper packing material). Temperatures of the acidogenic and methanogenic reactors kept at 20°C and 35°C., respectively. When the pH of the acidogenic reactor was controlled at 6.0–7.0 with HCl, the COD removal efficiency increased from 50 to 80% over a period of six months, and as a result, the COD of the final effluent fell in the range of 1,000–1,500 mg/L. BOD removal efficiency over the same period was above 90%, and 300 to 400 mg/L was maintained in the final effluent. The average SS in the final effluent was 270 mg/L. The methane production was 0.32 m³ CH₄/kg COD_removed and methane content of the methanogenic reactor was high value at 80–90%., When the pH of the acidogenic reactor was not controlled over the final two months, the pH reached 8.2 and acid conversion decreased compared with that of pH controlled, while COD removal was similar to the pH controlled operation. Without pH control, the methane content in the gas from methanogenic reactor improved to 90%, compared to 80% with pH control.     

Biological decomposition of dichloromethane from a chemical process effluent

The application of specialized microorganisms to treat dichloromethane (DM) containing process effluents was studied. An aerobic fluidized bed reactor with a working volume of 801 filled with sand particles as carriers for the bacteria was used. Oxygen was introduced into the recycle stream by an injector device. DM was monitored semi-continuously. A processor controlled the feed volume according to the DM effluent concentration. Mineralization rates of 12 kg DM/m_bioreactor ³ · d were reached within about three weeks using synthetic wastewater containing 2000 mg/l DM as single carbon compound. DM from process water of a pharmaceutical plant was reduced from about 2000 mg/l in the feed to below 1 mg/l in the effluent at volumetric loading rates of 3 to 4 kg DM/m_bioreactor ³ · d. Degradation of wastewater components like acetone and isopropanol were favoured, thus making the process less attractive for waste streams containing high amounts of DOC other than of DM. DM concentrations of up to 1000 mg/l were tolerated by the immobilized microorganisms and did not influence their DM degradation capacity. The ability to mineralize DM was lost when no DM was fed to the reactor for 10 days.     

Nitrogen removal performance in a novel combined biofilm reactor

Experiments have been performed to investigate the nitrogen removal performance in a novel combined biofilm reactor using synthetic wastewater. In the reactor, one cubic box was separated by two baffles into three zones: aerobic zone, buffering zone and anoxic zone. Nitrification and denitrification were supposed to be mainly accomplished in the aerobic and anoxic zones, respectively. When the influent total nitrogen (TN) and organic carbon loadings were averaged at 0.093 and 0.40 kg/m³/d, 84% TN removal efficiency was achieved by adjusting the aeration rate and the configuration of the reactor. Continuous experimental results demonstrated that NH₃-N removal efficiency increased by adjusting the clapboards of the reactor at a certain aeration rate. Energy produced by aeration was used for liquid recycle, so TN could be more efficiently removed at lower cost in this reactor.     

Anammox start-up in sequencing batch biofilm reactors using different inoculating sludge

In this study, anammox bacteria were rapidly enriched in sequencing batch biofilm reactors (SBBRs) with different inoculations. The activated sludge taken from a sequencing batch reactor was used and inoculated to SBBR1, while SBBR2 was seeded with stored anaerobic sludge from an upflow anaerobic fixed bed (2-year stored at 5–15 °C). Nitrogen removal performance, anammox activity, biofilm characteristics and variation of the microbial community were evaluated. The maximum total nitrogen loading rate (NLR) of SBBR1 gradually reached to 1.62 kg?N/(m³/day) with a removal efficiency higher than 88 % and the NLR of SBBR2 reached to 1.43 kg?N/(m³/day) with a removal efficiency of 86 %. SBBR2 was more stable compared to SBBR1. These results, combined with molecular techniques such as scanning electron microscope, fluorescence in situ hybridization, and terminal restriction fragment length polymorphism, indicated that different genera of anammox bacteria became dominant. This research also demonstrates that SBBR is a promising bioreactor for starting up and enriching anammox bacteria.     

Organic Matter Degradation Kinetics in an Anaerobic Thermophilic Fluidised Bed Bioreactor

This paper describes the thermophilic anaerobic biodegradation of wine distillery wastewater (vinasses) in a laboratory fluidised bed reactor (AFB) with a porous support medium. The experimental protocol was defined to examine the effect of increasing organic loading rate on the efficiency of AFB and to report on its steady-state performance. Moreover, in order to evaluate treatment efficiency and to investigate fermentation kinetics in an AFB reactor, experimental data were used to estimate the ‘active biomass’ concentration using an autocatalytic kinetic model proposed in this paper, since viable biomass in AFB reactors is very difficult to measure experimentally. The AFB reactor was subjected to a program of steady-state operation over a range of hydraulic retention time (HRTs) of 2.5–0.37 days and organic loading rate (OLRs) up to 5.88 kgCOD/m³/day in order to evaluate its treatment capacity. The AFB reactor was initially operated with organic loading rate of 5.88 kgCOD/m³/day and HRT of 2.5 days. The chemical oxygen demand (COD) removal efficiency was found to be 96.5% in the reactor while the methane content of biogas produced in the digester reached 1.08 m³/m³digester/day. Over 94 days operating period, an OLR of 32 kgCOD/m³/day at a food-to-micro-organisms (F:M) ratio of 0.55 kgCOD/kgVS_att/day was achieved with 81.5% COD removal efficiency in the experimental AFB reactor. At this moment, the methane content of biogas produced in the digester reached 9.0 m³/m³digester/day. The proposed kinetic model is able to estimate kinetic constants of the biodegradation process: non-biodegradable substrate (S_nb) and active adhered biomass concentration (X_a). The parameters of the model were obtained by the curve-fitting method to the proposed kinetic model using the COD as substrate of the anaerobic process and assuming a maximum specific μ_max: 0.72 per day. The comparison of the measured concentration of volatile attached solids (VS_att) with the estimated ‘active’ biomass concentration indicated that extremely high ‘active biomass’ concentrations can be maintained in the system because biofilm thickness is limited by the liquid flow rate applied. This is due to the fact that the anaerobic fluidised bed system retains the growth support medium in suspension by drag forces exerted by upflowing wastewater, and the distribution of biomass holdup (in the form of a biofilm) is thus relatively uniform.     

Capacities and limits of three different technologies for the biological treatment of leachate from solid waste landfill sites

Leachate from a municipal waste landfill site was treated using an activated sludge bioreactor, a fluidized bed biofilm reactor and a packed-bed column reactor (trickling filter). The leachate contained high organic matter (2.0–2.6 g/l of COD), high ammonium (300–700 mg/l) and sulphide (200–800 mg/l) concentrations, as well as low metal concentrations. The continuously operating reactors were employed to study the effects of TOC loading on the removal of TOC as well as on the nitrification and denitrification processes. Among the three biological treatment technologies investigated, the fluidized bed biofilm reactor was best with respect to removing ammonia and TOC. More than 90% of TOC and 99% of ammonia were removed when TOC loading was less than 0.5 kg/m³ × d. At a TOC loading of 4 kg/m³ × d, the removal of TOC and ammonia was 80% and 99%, respectively. In contrast, the treatment of leachate with the packed-bed reactor was successful in TOC removing only at TOC loading less than 0.3 kg/m³ × d (TOC elimination decreased from 86% at 0.06 kg/m³ × d to 60% at 0.3 kg/m³ × d). However, the reactor was active in nitrification even at a higher TOC loading (more than a 98% ammonia elimination at a TOC loading of 0.5 kg/m³ × d). Leachate was processed in the activated sludge reactor when TOC loading was less than 0.5 kg/m³ × d (with a removal of TOC and ammonia up to 83% and 99%, respectively). The activated sludge reactor was also effective in TOC removal at a higher TOC loading (e.g. a 74% TOC removal at a TOC loading of 1 kg/m³ × d), but for ammonia elimination, the activity continuously decreased (less than 60% ammonia removal at a TOC loading of 1 kg/m³ × d). Overloading in the activated sludge system was indicated by a high concentration of ammonia and nitrite in the effluent. In the packed bed reactor, overloading was characterized by a progressively incomplete TOC removal. No significant overloading was found in the fluidized bed reactor up to a TOC loading of 4 kg/m³ × d.     

Startup of anaerobic biofilm fluidized bed reactors on molasses and phenol under various conditions

Fluidized sand bed anaerobic biofilm reactors were operated in parallel to study the effects of inoculum, loading, residence time and carrier type on the startup dynamics for the degradation of molasses and phenol. Degradation rates generally depended most directly on concentrations rather than on other operating variables. Residence times did not appear to directly influence startup. Short residence times and high loadings gave the highest specific activities for both substrates. The type of inoculum was found to be most important for the molasses system, and inoculation on fresh carrier was found to be better than reinoculation. The two times higher specific biomass retention on Siran porous glass gave essentially the same degradation rates on a volume basis.List of Symbols L kg/h loading of reactor - M kg/kg biomass per carrier mass - Red. % reduction of feed concentration due to degradation - R kg/(m³ · h) reaction rate - S kg/m³ substrate concentration in reactor and effluent - S ₀ kg/m³ substrate concentration in feed - t h time     

Verification studies of a simplified model for the removal of dichloromethane from waste gases using a biological trickling filter

The removal of dichloromethane from waste gases in a biological trickling filter was studied experimentally as well as theoretically within the concentration range of 0–10,000 ppm. A stable dichloromethane elimination performance was achieved during two years of operation, while the start-up of the system only amounted to several weeks at constant inlet concentrations. The trickling filter system was operated co-currently as well as counter-currently.However, experimental and theoretical results revealed that the relative flow direction of the mobile phases did not significantly affect the elimination performance. Moreover, it was found that the gas-liquid mass-transfer resistance in the trickling filter bed applied was negligible, which leaves the biological process inside the biofilm to be the rate limiting step.A simplified model was developed, the Uniform-Concentration-Model, which showed to predict the filter performance close to the numerical solutions of the model equations. This model gives an analytical expression for the degree of conversion and can thus be easily applied in practice.The dichloromethane eliminating performance of the trickling filter described in this paper, is reflected by a maximum dichloromethane elimination capacity EC _max=157 g/(m³ · h) and a critical liquid concentration C _lcr=45 g/m³ at a superficial liquid velocity of 3.6 m/h, inpendent of the gas velocity and temperature.List of Symbols a _s m²/m³ specific area - a _w m²/m³ specific wetted area - A m² cross-sectional area - C _g g/m³ gas phase concentration - C _go g/m³ inlet gas phase concentration - C _gocr g/m³ critical gas phase concentration - C _g ^* C_g/C_go dimensionless gas concentration - C _l g/m³ liquid concentration - C _lcr g/m³ critical liquid concentration - C _lcr ^* mC_lcr/C_go dimensionless critical concentration - c _li g/m³ substrate concentration at liquid-biofilm interface - C _l ^* mC_l/C_go dimensionless liquid concentration - C _o g/m³ oxygen concentration inside the biofilm - C _oi g/m³ oxygen concentration at liquid-biofilm interface - C_s g/m³ substrate concentration inside the biofilm - C _si g/m³ substrate concentration at liquid-biofilm interface - D _eff m²/h effective diffusion coefficient in the biofilm - D _o m²/h effective diffusion coefficient for oxygen in the biolayer - E mu_g/u_l extraction factor - E _act kJ/mol activation energy for the biological reaction - EC g/(m³· h) K _o a _w : elimination capacity, or the amount of substrate degraded per unit of reactor volume and time - EC _max g/(m³ · h) K _o a_w: maximum elimination capacity - f degree of conversion - h m coordinate in height - H m height of the packed bed - K ₀ g/(m³ · h) _maxX_b/Y zeroth order reaction defined per unit of biofilm volume - k _og m/h overall gas phase mass transfer coefficient - K ^* dimensionless constant given by Eq. (A.5) - K _l ^* dimensionless constant given by Eq. (A.6) - K ₂ ^* dimensionless constant given by Eq. (A.6) - m C _g /C_l gas liquid distribution coefficient - N g/(m² · h) liquid-biofilm interfacial flux of substrate - N _og k_oga_wH/u_g number of gas phase transfer units - N _r k_o a_w H/u_g C_go number of reaction units - OL g/(m³· h) u _g C _go /H organic load - r _s g/(m³ ·h) zeroth order substrate degradation rate given by Eq. (1) - R _s g/(g TSS ·h) specific activity - T K absolute temperature - u _g m/h superficial gas velocity - u _t m/h superficial liquid velocity - X _b g TSS/m₃ biomass concentration inside biofilm - X _s g TSS/m₃ liquid suspended biomass concentration - x m coordinate inside the biofilm - Y g TSS/(g_DCM) yield coefficient Greek Symbols dimensionless parameter given by Eq. (2) - m averaged biofilm thickness - biofilm effectiveness factor given by Eqs. (7a)–(7c) - m penetration depth of substrate into the biofilm - _max d^–1 microbiological maximum growth rate - v _o stoichiometric utilization coefficient for oxygen - v _s stoichiometric utilization coefficient for substrate - dimensionless height in the filter bed - h H/u _g superficial gas phase contact time - _o (K ₀ /DC _ii )^1/2 - _o C _o /C _oi dimensionless oxygen concentration inside the biofilm - _s C _s /C _si dimensionless substrate concentration inside the biofilm Experimental results, verifying the model presented will be discussed Part II (to be published in Vol. 6, No. 4)     

Degradation of synthetic reactive azo dyes and treatment of textile wastewater by a fungi consortium reactor

In this paper, two microbial cultures with high decolorization efficiencies of reactive dyes were obtained and were proved to be dominant with fungi consortium in which 21 fungal strains were isolated and 8 of them showed significant decolorization effect to reactive red M-3BE. A 4.5 l continuous biofilm reactor was established using the mixed cultures to investigate the decolorization performance and the system stability under the conditions of simulated and real textile wastewater as influents. The optimal nutrient feed to this bioreactor was 0.5 g l⁻¹ glucose and 0.1 g l⁻¹ (NH₄)₂SO₄ when 30 mg l⁻¹ reactive black 5 was used as initial dye concentrations. Dye mineralization rates of 50–75% and color removal efficiencies of 70–80% were obtained at 12 h hydraulic retention time (HRT) in this case. Higher glucose concentrations in the influents could significantly improve color removal, but was not helpful for dye mineralization. Besides reactive black 5, the bioreactor could effectively decolorize reactive red M-3BE, acid red 249 and real textile wastewater with efficiency of 65%, 94% and 89%, respectively. In addition, the microbial community on the biofilm was monitored in the whole running process. The results indicated fungi as a dominant population in the decolorization system with the ratio of fungi to bacteria 6.8:1 to 51.8:1 under all the tested influent conditions. Analysis of molecular biological detection indicated that yeasts of genus Candida occupied 70% in the fungal clone library based on 26S rRNA gene sequences.     

Effect of shear on morphology,viability and metabolic activity of succinic acid-producing Actinobacillus succinogenes biofilms

Two custom-designed bioreactors were used to evaluate the effect of shear on biofilms of a succinic acid producer, Actinobacillus succinogenes. The first bioreactor allowed for in situ removal of small biofilm samples used for microscopic imaging. The second bioreactor allowed for complete removal of all biofilm and was used to analyse biofilm composition and productivity. The smooth, low porosity biofilms obtained under high shear conditions had an average cell viability of 79% compared to 57% at the lowest shear used. The maximum cell-based succinic acid productivity for high shear biofilm was 2.4 g g⁻¹DCW h⁻¹ compared to the 0.8 g g⁻¹DCW h⁻¹ of the low shear biofilm. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays confirmed higher cell metabolic activities for high shear developed biofilm compared to biofilm developed at low shear conditions. Results clearly indicated that high shear biofilm cultivation has beneficial morphological, viability, and cell-based productivity characteristics.