Suspended Growth Bioreactor Research Articles

New perspectives for bio-technical treatment of oxalate-containing waste streams from bauxite processing

Alumina is typically produced from bauxite ore using the Bayer process, in which the ore is mixed with alkaline liquor under elevated temperatures. Australian bauxite ore contains a wide range of organics, which detrimentally affect the Bayer process. Therefore, the removal of organic compounds from the alkaline Bayer process liquor is critical in maintaining process efficiency and alumina quality. Oxalate (C2O42−) is a key organic impurity in the Bayer process liquors that requires removal as it increases in concentration in the processing circuit as the Bayer liquor is continually recycled. Compared to conventional physiochemical or physical methods (e.g., chemical precipitation, wet-oxidation, liquor burning), microbial bioreactor treatment processes have the potential to be more economical and environmentally sustainable for oxalate removal. Some Australian alumina refineries have implemented full-scale bioreactors such as moving bed biofilm reactors (MBBRs) and aerobic suspended growth bioreactors (ASGB). While these bioreactors are robust and effective in removing oxalate, they have some limitations, such as the need for pre-acidification of influent and the loss of ammonia (nutrient) through volatilization. Therefore, this study aimed to provide an overview of the fundamentals and recent advances in biotechnical processes for the treatment of alkaline oxalate-containing liquor. Laboratory-scale studies on promising new biotreatment concepts, such as the use of bioelectrochemical systems to facilitate concurrent oxalate degradation and caustics recovery, as well as the utilization of nitrogen-fixing microorganisms to obviate the requirement for external nutrient dosage, are discussed. Perspectives for further research on oxalate-containing waste streams are also proposed.

Recent Advances in 1,4-Dioxane Removal Technologies for Water and Wastewater Treatment

1,4-Dioxane is a contaminant of emerging concern and a probable human carcinogen that has been widely detected in aqueous environments. However, the removal of 1,4-dioxane by conventional water and wastewater treatment plants had proven to be ineffective due to its unique physicochemical properties. The development of innovative technologies for both in-situ and ex-situ treatment of 1,4-dioxane to meet increasingly strict standards is in urgent need. This review summarizes the current available physicochemical and biological treatment technologies for the removal of 1,4-dioxane from both water and wastewater and the strategies that may potentially fulfill the stringent 1,4-dioxane standard were discussed. Advanced oxidation processes (AOPs), such as ultraviolet radiation coupled with H2O2 (8–10 mg L−1), had shown efficient 1,4-dioxane destruction and had already been applied for both water and wastewater treatment processes. On the other hand, more than 30 pure microbial strains and microbial communities that can metabolically or metabolically degrade 1,4-dioxane were reported. Biodegradation has been proven to be a feasible and cost-effective approach for 1,4-dioxane remediation. Suspended growth bioreactor, immobilized cell bioreactor, and biofiltration systems were the most commonly used biological approaches to remove 1,4-dioxane from contaminated water. Though 1,4-dioxane easily desorbs after the adsorption by materials such as granular activated carbon (GAC) and zeolite, temporary 1,4-dioxane removal by adsorption followed by 1,4-dioxane biodegradation in the bioaugmented adsorption media may be a feasible strategy treating 1,4-dioxane contaminated water. Overall, the treatment chain that combines physical-chemical processes and biodegradation has a great potential for synergistic removal of 1,4-dioxane at lower operating costs.

Investigating the conversion from nitrifying to denitrifying water-treatment efficiencies of the biofloc biofilter in a recirculating aquaculture system

In the current study, two nitrifying suspended growth bioreactor processes (denoted as R1 and R2) was investigated based on biofloc technology (BFT) in recirculating aquaculture systems (RAS). The conversion of nitrifying R1 to denitrifying biofilter via adding carbohydrates was studied. It was observed that the dominant functional microbes of nitrifying BFT biofilters were ammonia-oxidizing bacteria (AOB), denitrifying bacteria (DNB), phosphorus/glycogen accumulating organisms (PAOs/GAOs), and nitrite-oxidizing bacteria (NOB). The removal efficiencies of the total ammonium nitrogen and nitrite were prominent, while the treatment efficiencies respected to nitrate and soluble reactive phosphate (SRP) were insignificant. More than 16 h after the addition of carbohydrates to R1, the regular dynamics of dissolved oxygen (DO), dissolved organic carbon, and C/N ratio became conducive to the notable removal of nitrate and SRP. Furthermore, the relative abundances of AOB and NOB decreased, and that of PAOs, GAOs, and DNB increased. Redundancy analysis indicated that, among the environmental factors and functional microbes involved in converting to a denitrifying biofilter, DO was the most important. Also, Spearman correlation heatmap elucidated Flavobacterium sp. and Norank_Nitrosomonadaceae were the dominants bacteria affected by environmental factors. This study found a high abundance of functionally active microbes participated in nitrogen and phosphorus removal in the BFT biofilters. Thus, the water-treatment efficiency of the BFT biofilter could be flexibly and controlled by adding carbohydrates.

Comparison of hybrid membrane aerated biofilm reactor (MABR)/suspended growth and conventional biological nutrient removal processes.

Mathematical modelling was used to investigate the possibility to use membrane aerated biofilm reactors (MABRs) in a largely anoxic suspended growth bioreactor to produce the nitrate-nitrogen required for heterotrophic denitrification and the growth of denitrifying phosphorus accumulating organisms (DPAOs). The results indicate that such a process can be used to achieve a variety of process objectives. The capture of influent biodegradable organic matter while also achieving significant total inorganic nitrogen (TIN) removal can be achieved with or without use of primary treatment by operation at a relatively short suspended growth solids residence time (SRT). Low effluent TIN concentrations can also be achieved, irrespective of the influent wastewater chemical oxygen demand (COD)/total nitrogen (TN) ratio, with somewhat larger suspended growth SRT. Biological phosphorus and nitrogen removal can also be effectively achieved. Further experimental work is needed to confirm these modelling results.

Comparison and application of biofilter and suspended bioreactor in removing gaseous o-xylene

Two bioreactors, suspended-growth bioreactors (SPB) and biofilter (BF), were compared for the performances in removing gaseous o-xylene. Their efficiencies were investigated by varying the o-xylene loadings, gas flow rates, and gas-water ratios. High-throughput techniques were applied for the microbial populations assay. The conversion rate of carbon in o-xylene was calculated, and the relationship between biomass and removal efficiencies was also analyzed. Results indicated that both the SPB and BF could effectively treat gases containing o-xylene. The average removal efficiencies were 91.8% and 93.5%, respectively. The elimination capacity of the BF was much higher than that of the SPB when the intake load was below 150 g m−3 h−1. When the o-xylene loadings were over 150 g m−3 h−1, both the SPB and BF achieved similar o-xylene removal rates. The maximum elimination capacities were 28.36 g m−3 h−1 for the SPB and 30.67 g m−3 h−1 for BF. The SPB was more sensitive to the changes in the gas flow rate. Results of microbial assay indicated that bacteria e.g. Mycobacterium sp. and Rhodanobacter sp. might play important roles in removing o-xylene in the SPB, while the bacteria Pseudomonas sp., Sphingomonas sp., and Defluviicoccus sp., and the fungi Aspergillus sp. and Scedosporium sp., were the o-xylene degraders in the BF. The successful application of the integrated bioreactor in treating gases containing o-xylene exhausted from the electroplating plant indicated that the integration of SPB and BF could be an effective method for removing VOCs with Henry coefficient in the range of 0.01–1.

Biological attenuation of arsenic and nitrate in a suspended growth denitrifying-sulphidogenic bioreactor and stability check of arsenic-laden biosolids

ABSTRACT Co-occurrence of arsenic and nitrate in groundwater sources at a wide range of concentrations is reported. In this work, performance of suspended growth semi-batch reactor was assessed for co-removal of arsenic and nitrate from simulated groundwater to meet the drinking water standards in the absence of iron. The bioreactor was inoculated with mixed bacterial culture and operated in the absence of oxygen for more than 450 days under varying influent arsenate (200–800 µg/L), nitrate concentrations (50–250 mg/L), and hydraulic retention time of 3–6 days. Complete nitrate removal was observed at all tested concentrations. Arsenic removal was found to meet drinking water standards from initial concentrations and up to 600 µg/L. The extended toxicity characteristic leaching procedure leaching experiments indicated that arsenic-laden biosolids would not constitute a hazardous waste. The arsenic leaching was found to increase with an increase in dissolved oxygen and the final leachate concentrations of arsenic were below 150 µg/L. The leaching experiments suggested maintaining non-alkaline conditions for minimum arsenic release from arsenic biosolids formed under sulphidogenic conditions. This study is the first to report that nitrate and arsenic can be simultaneously removed to meet drinking standards in a suspended growth bioreactor.

Removal of formaldehyde from the air with a suspended growth bioreactor

In the present study, the root zone of Canna flaccida Salisb. was selected as the biological component. We found that the adsorption rate of formaldehyde (FA) by C. flaccida was initially low, before increasing substantially. 13CNMR analysis indicated that C. flaccida can metabolize H13CHO and the major metabolic products were organic acid and amino acids. On this basis, we had designed a suspended growth bioreactor (SGB) to remove FA. An SGB was tested under a series of different conditions and the results showed that FA removal efficiency was strongly influenced by water volume, root zone weight, and gas flow rate. More than 52% of the FA was removed in 1 h and the maximum elimination capacity reached 35.112 mg m−3 h−1. After 24 h, no FA remained in the SGB. Running for 15 days, the concentration of FA in the lab space decreased from 1.12 to 0.82 mg m−3, and the concentration of FA in the SGB reached a low level. These results confirmed that SGB is an effective way to remove FA.

Effect of Carbon to Nitrogen Ratio on Water Quality and Community Structure Evolution in Suspended Growth Bioreactors through Biofloc Technology

Application of biofloc technology could effectively treat wastewater. However, the effect of influent carbon to nitrogen ratio (C/N ratio) on water quality and microbial community structure evolution in suspended growth bioreactors (SGBRs) through biofloc technology is still unclear. Here, we show that the total ammonia nitrogen (TAN) and nitrite nitrogen in the effluent of the C/N 10 treatment was significantly higher than that in the C/N 15, C/N 20 and C/N 25 treatments (p < 0.05). Higher TAN removal efficiency was obtained in treatments of C/N 15, C/N 20 and C/N 25, and there was no accumulation of nitrite nitrogen and nitrate nitrogen. Increasing the C/N ratio strengthened the elimination ability of total phosphorus and chemical oxygen demand (COD). The concentrations of TAN and COD first dropped to the lowest level and then increased slightly within one cycle in all treatments. The accumulation of biomass in the reactors increased with the increasing C/N ratio, indicating that a higher C/N ratio was conducive to microbial proliferation. The 16S rRNA sequencing revealed that the microbial community diversity in SGBRs was significantly higher than that in the natural wastewater (P0). The predominant phylum were Proteobacteria, Bacteroidetes and Verrucomicrobia, but Saccharibacteria occupied a dominant position in the late period of the experiment. Pathogens, such as Aeromonas, Acidovorax, Flavobacterium, and Malikia were significantly decreased after high C/N ratio simulative wastewater treating natural wastewater in the reactors. In summary, the water quality and biomass concentrations in SGBRs can be improved under the conditions of influent C/N ratio, equal to or greater than 15.

Pilot study on water quality regulation in a recirculating aquaculture system with suspended growth bioreactors

In situ suspended growth aquaculture systems for oligotrophic species suffer from excess total suspended solids, low dissolved oxygen, and other associated problems. To address these disadvantages, this study designed and tested a closed recirculating aquaculture system containing 3 pilot-scale suspended growth bioreactors (SGBRs) for the water treatment of pollutants. These SGBRs were designed to control extra carbon addition at carbon/nitrogen ratios of 12, 8, and 4, respectively. It was determined that the culture tanks removed total ammonia nitrogen (TAN) and nitrite (NO2−-N) by nitrification, and the SGBRs removed nitrate (NO3−-N) by denitrification and also soluble reactive phosphate (SRP). Concentrations of NO3−-N and SRP in the effluent decreased, as the controlled carbon/nitrogen ratio of the SGBR increased. When carbon was controlled at a carbon/nitrogen ratio of 12, the influent concentrations of NO3−-N (35.41 ± 1.22 mg·L−1) and SRP (4.60 ± 0.67 mg·L−1) were reduced to 7.70 ± 3.58 mg·L−1 and 0.30 ± 0.16 mg·L−1, respectively. Thus, this proposed system had the ability to control simultaneously TAN, NO2−-N, NO3−-N and SRP. The survival rate of Anguilla marmorata was 98.00 ± 1.41%, with a final stocking density of 56.46 ± 0.51 kg·m−3. We suggest that various adjustments in the carbon/nitrogen ratios of SGBRs can be practically controlled according to the concentrations of pollutants in the culture tanks.

Performance and Kinetics Evaluation of Integrated Suspended Growth Bioreactor Treating Beverage Industry Wastewater

In this research, feasibility of using a continuous flow integrated suspended growth bioreactor (i-SGBR) pilot plant was explored to treat beverage industry wastewater. The bioreactor treatment units comprise of three sequentially arranged suspended growth bioreactors with anoxic (ANX-C), aerobic (AER-C), and aerobic digester chambers (AD-C). Clarifier (CLR) was installed as last chamber to settle sludge. Parameters such as total chemical oxygen demand (TCOD) were monitored and validated with biochemical oxygen demand (BOD5). Other parameters measured include soluble COD (sCOD), mixed liquor suspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS), total suspended solids (TSS), and pH. Transformational behavior of aerobic metabolic performance for extended aeration process was investigated by operating regimes of variable aerobic hydraulic retention time (HRT) and organic loading rate (OLR) between 20 and 30 h and 0.49–0.79 kg COD/m3 day, respectively. Solids retention time (SRT) between 20 and 40 days was operated. The aim was to generate data for bacterial growth and substrate utilization kinetics from modified Monod’s model. Removal of TCOD, BOD5, and TSS were achieved in the range of 95.2–97.9% (Influent 995 ± 21–1028 ± 25 mg/L and Effluent 21 ± 2–4.9 ± 3 mg/L), 98–98.7% (Influent 489 ± 19–507 ± 7 mg/L and Effluent 27 ± 2–41 ± 1.8 mg/L), and 91.2–94.6% (Influent 500 ± 23–653 ± 11 mg/L and Effluent 6.3 ± 7–41 ± 1.8 mg/L), respectively. The maximum substrate utilization rate (k), half velocity constant (Ks), growth yield co-efficient (Y), and decay coefficients (kd) were determined as 2.81 days−1, 979 mg sCOD/L, 0.72 mg VSS/mg sCOD, and − 0.0172 day−1, respectively. Maximum specific growth rate (μmax) was found as 2.03 days−1. Treatment efficiencies declined with reduction of HRT and with increased OLR applied to the bioreactor. The aerobic digester (AD) achieved between 9.8% (Influent 15,021 mg/L) and 18.6% (10,893 mg/L) MLVSS reduction, where performance decreased with additional solids concentration from influent aerobic digester (IAD). i-SGBR has accomplished effective removal of pollutants and simultaneous sludge degradation of beverage industry wastewater. Kinetic parameters obtained could be useful for design and modeling of aerobic treatment unit to improve effluent quality.

Kinetics of heavy metal removal in a suspended and immobilized bioreactors

The capacity of microorganisms to remove heavy metal from wastewater has been a subject of diverse interest. Whereas some heavy metals are essential for effective microbial activity, some heavy metals could be toxic to the microorganisms at concentrations higher than their minimal inhibitory limit. The kinetics of Zn2+ removal from aqueous solution was evaluated in terms of substrate removal rate for two identical suspended and immobilized bioreactors. The suspended growth bioreactor was used as a control system (CS) and contains only biomass. The immobilized bioreactor (IB) contains both biomass and microwave incinerated rice husk ash (MIRHA). The bioreactors were operated at a fixed HRT of 29.1 hours, whereas Zn2+ influent concentration was varied in the range of 0.5, 1, 2, 5, 10 and 15 mg/L. At steady state conditions, the results show that Zn2+ removal was in the range of 72, 75, 72.5, 68.2, 70.3 and 58.7% for CS, whereas it was in the range of 88, 90, 83, 88.6, 86.2 and 83.7% for IB. The substrate removal rate was found as 1.1856 g/L.d for CS and 4.2693 g/L.d for IB. The results clearly show that Zn2+ removal was more favorable in IB, indicating that the performance of the bioreactor was enhanced by the addition of MIRHA.

Efficiency of producing bioflocs with aquaculture waste by using poly-β-hydroxybutyric acid as a carbon source in suspended growth bioreactors

With additional organic carbon, fish waste can be used as a substrate to produce bioflocs, a protein source for aquaculture animals. In choosing a carbon source, one should consider convenience, cost and biodegradability. This study investigates the efficiency of poly-β-hydroxybutyric acid (PHB), a biologically degradable polymer, as a carbon source to produce bioflocs in suspended growth bioreactors (SGRs), PHB-SGRs, compared with glucose (GLU-SGRs). The C:N ratio in PHB-SGRs could be maintained around 15:1. The volatile suspended solids (VSS) yield was 2.94±0.72 gVSS/g fish waste for PHB-SGRS and 4.90±0.23 gVSS/g fish waste for GLU-SGRs. The recycling rate of nitrogen in aquaculture solid waste was 56±2% and 87±7% for the PHB-SGRs and Glu-SGRs. No significant differences were found in the bioflocs produced and in the crude protein content of the produced bioflocs between PHB-SGRs and GLU-SGRs. PHB-SGRs and GLU-SGRs could remove dissolved inorganic nitrogen from aquaculture wastewater, with average values of 11.82±8.95 and 16.27±3.95mg/g TSS/d. Because the calculation of the added amount of carbon and the multiple additions of carbon was avoided, PHB is considered to be a good choice as an organic carbon source for this process, even though not all parameters used for assessment were better than those of GLU-SGRs.

Bio-physical removal of heavy metal from aqueous solution

The aim of this study was to compare the performance of a suspended growth bioreactor and a combined bio-physical bioreactor for Zn2+ removal from aqueous solution. Two identical bioreactors (8.5 L each) were operated at a fixed HRT of 29.1 h. The suspended growth bioreactor was used as the control reactor and contained only sludge. The bio-physical bioreactor contains sludge and a low-cost adsorbent derived from groundwater treatment plant sludge. The influent Zn2+ concentration was varied from 0.5 to 15 mg/L in 8 experimental phases. Influent and effluent Zn2+ concentration was monitored daily. Phase 1 (day 1–15) and phase 2 (day 16–29) were used as acclimation period for both bioreactors, respectively. Results show that Zn2+ removal increased with increasing influent Zn2+ concentration from 0.5 to 1.0 mg/L (phases 3–4) but fluctuated thereafter for the suspended growth bioreactor. Zn2+ removal in the bio-physical bioreactor increased with increasing influent Zn2+ concentration from 0.5 to 10 mg/L (phases 3–7) and decreased with further increase in influent Zn2+ concentration to 15 mg/L (phase 8). The effluent Zn2+ concentration in phase 8 for the suspended growth and the bio-physical bioreactors were 58.7 and 90%, respectively. The higher removal of Zn2+ in the bio-physical bioreactor was due to heavy metal tolerance and the resistance in heavy metal toxicity on the microbial community of the combined system.

Geochemical and Temporal Influences on the Enrichment of Acidophilic Iron-Oxidizing Bacterial Communities.

Two acid mine drainage (AMD) sites in the Appalachian bituminous coal basin were selected to enrich for Fe(II)-oxidizing microbes and measure rates of low-pH Fe(II) oxidation in chemostatic bioreactors. Microbial communities were enriched for 74 to 128 days in fed-batch mode, then switched to flowthrough mode (additional 52 to 138 d) to measure rates of Fe(II) oxidation as a function of pH (2.1 to 4.2) and influent Fe(II) concentration (80 to 2,400 mg/liter). Biofilm samples were collected throughout these operations, and the microbial community structure was analyzed to evaluate impacts of geochemistry and incubation time. Alpha diversity decreased as the pH decreased and as the Fe(II) concentration increased, coincident with conditions that attained the highest rates of Fe(II) oxidation. The distribution of the seven most abundant bacterial genera could be explained by a combination of pH and Fe(II) concentration. Acidithiobacillus, Ferrovum, Gallionella, Leptospirillum, Ferrimicrobium, Acidiphilium, and Acidocella were all found to be restricted within specific bounds of pH and Fe(II) concentration. Temporal distance, defined as the cumulative number of pore volumes from the start of flowthrough mode, appeared to be as important as geochemical conditions in controlling microbial community structure. Both alpha and beta diversities of microbial communities were significantly correlated to temporal distance in the flowthrough experiments. Even after long-term operation under nearly identical geochemical conditions, microbial communities enriched from the different sites remained distinct. While these microbial communities were enriched from sites that displayed markedly different field rates of Fe(II) oxidation, rates of Fe(II) oxidation measured in laboratory bioreactors were essentially the same. These results suggest that the performance of suspended-growth bioreactors for AMD treatment may not be strongly dependent on the inoculum used for reactor startup. This study showed that different microbial communities enriched from two sites maintained distinct microbial community traits inherited from their respective seed materials. Long-term operation (up to 128 days of fed-batch enrichment followed by up to 138 days of flowthrough experiments) of these two systems did not lead to the same, or even more similar, microbial communities. However, these bioreactors did oxidize Fe(II) and remove total iron [Fe(T)] at very similar rates. These results suggest that the performance of suspended-growth bioreactors for AMD treatment may not be strongly dependent on the inoculum used for reactor startup. This would be advantageous, because system performance should be well constrained and predictable for many different sites.

Anaerobic digestion of waste biomass from the production of L-cystine in suspended-growth bioreactors

Waste biomass from the industrial production of the amino acid L-cystine contains above-average concentrations of organic pollutants and significant concentrations of nitrogen and sulfur. The specific biogas production (SBP) of waste biomass was monitored in parallel suspended-growth laboratory anaerobic bioreactors. After severe inhibition was observed, three different procedures were applied to inhibited reactor sludge to counter-attack the inhibitory effects of sulfides, respectively hydrogen sulfide: micro-aeration, dilution with water and precipitation by ferrous iron cations. The performance of bioreactors was weekly monitored. Organic loading rates (as chemical oxygen demand, COD) ranged from 1.07 to 1.97 g L(-1) d(-1). At the end of the experimentation, SBP averaged 217, 300 and 320 l kg(-1) COD with a methane content of 21%, 52% and 54%; specific sludge production averaged 133, 111 and 400 g total solids kg(-1) COD, and inhibition was 49%, 27% and 25%; for the applied procedures of micro-aeration, dilution and precipitation respectively.

Use of aerated magnetic biofilm reactor to treat wastewater

A novel aerated magnetic biofilm reactor is introduced in this study. The biofilm has a high biomass concentration and can be formed instantaneously. A 1 L laboratory-scale bioreactor packed with 160 flat ring magnets as biofilm carriers was used. Each piece of magnet has 1.6 cm outer diameter, 0.7 cm inner diameter, and 0.3 cm thickness. Magnetic field intensity at the surface of the magnet was 700 gauss. The bioreactor was seeded with flocculated activated sludge supplemented with Fe3O4 powder. Calculated organic loading rate per unit volume of the reactor and unit area of the packing material was 1.5g COD/L d and 17.44g COD/m2 d, respectively. The effluent TSS was relatively very low and can be easily separated from water by a small gravity clarifier. The efficiency of nitrogen removal was much better for the thick magnetic biofilm reactor than of a control suspended growth bioreactor. Simultaneous nitrification and denitrification during aerobic phase was observed. These features make this technology an attractive and promising one to be used for intensive nitrogen removal along with organic load removal.

Physiological activities associated with biofilm growth in attached and suspended growth bioreactors under aerobic and anaerobic conditions

This research work evaluated the biofilm succession on stone media and compared the biochemical changes of sludge in attached and suspended biological reactors operated under aerobic and anaerobic conditions. Stones incubated (30 ± 2°C) with activated sludge showed a constant increase in biofilm weight up to the fifth and seventh week time under anaerobic and aerobic conditions, respectively, where after reduction (>80%) the most probable number index of pathogen indicators on ninth week was recorded. Reduction in parameters such as biological oxygen demand (BOD) (47.7%), chemical oxygen demand (COD, 41%), nitrites (60.2%), nitrates (105.5%) and phosphates (58.9%) and increase in dissolved oxygen (176.5%) of sludge were higher in aerobic attached growth reactors as compared with other settings. While, considerable reductions in these values were also observed (BOD, 53.8%; COD, 2.8%; nitrites, 28.6%; nitrates, 31.7%; phosphates, 41.4%) in the suspended growth system under anaerobic conditions. However, higher sulphate removal was observed in suspended (40.9% and 54.9%) as compared with biofilm reactors (28.2% and 29.3%). Six weeks biofilm on the stone media showed maximum physiological activities; thus, the operational conditions should be controlled to keep the biofilm structure similar to six-week-old biofilm, and can be used in fixed biofilm reactors for wastewater treatment.

Waste gas treatment in bioreactors: environmental engineering aspects

This paper gives an overview of the most important bioreactor configurations used in waste gas treatment, i.e., conventional and trickling biofilters, the bioscrubber, suspended-growth bioreactors, as well as two-liquid phase systems (stirred tank bioreactor and biotrickling filter). The historical evolution, main characteristics, and recent developments are described in each case.

Steady- and transient-state performance of a thermophilic suspended-growth bioreactor for α-pinene removal from polluted air

The removal of α-pinene from polluted air was examined under thermophilic conditions (50°C) in one- and two-liquid phase continuous stirred tank bioreactors (CSTBs). Steady-state experiments were performed at different gas residence times, and α-pinene concentrations, corresponding to inlet loading rates between 0.5 and 38gm−3h−1 in the one-liquid phase CSTB, and between 2.9 and 176gm−3h−1 in the two-liquid phase CSTB. The presence of a second liquid-phase (5% v/v silicone oil) increased the maximum elimination capacity (85.7gm−3h−1) by ∼6-fold compared to the one-liquid phase CSTB. During transient-state experiments, the CSTB with silicone oil could withstand a higher α-pinene shock load (110gm−3h−1) than the CSTB operated without silicone oil (70gm−3h−1). Besides, the thermophilic specific substrate utilization rates were estimated from batch assays, reaching 89 and 340μgα-pinenemgbiomass-1d-1, in the absence of or presence of silicone oil, respectively.

Relative performance of biofilm configuration over suspended growth operation on azo dye based wastewater treatment in periodic discontinuous batch mode operation

Functional role of biofilm and suspended growth bioreactor configurations in response to the treatment of azo-dye (C.I. Acid Black 10B) bearing wastewater was evaluated in periodic discontinuous batch mode operation at varying dye concentrations. The biofilm system depicted higher dye removal efficiency (93.14%) compared to suspended mode (84.29%) at 350 mg dye/l operation. Both the reactor configurations did not show much process inhibition at higher dye loads studied. Azo reductase and dehydrogenase enzyme activities showed significant variation indicating the different metabolic capabilities of the native-microflora, stable proton shuttling between metabolic intermediates and differences in the delivery of reducing powers from the substrate metabolism towards dye removal. Voltammograms visualized marked variations in electron discharge properties with the function of reactor configuration, time intervals and dye load. Higher redox catalytic currents, lower Tafel slopes and polarization resistance showed good correlation with enzyme activities and dye removal.