The specific growth rates of the culture at different concentrations of phenol were fitted to different models such as Haldane, Han-Levenspiel, Edward, Luong and Yano-Koga. Statistical analyzes of the specific growth rate of the culture in the mixed substrate system were performed in the form of analysis of variance (ANOVA) and Student's 't'.
Generalities
In wastewater treatment processes, it is generally practiced as a tertiary treatment mainly to remove color. Biological treatment with pure and mixed microbial strains is an attractive alternative for the treatment of contaminated soil, surface and wastewater containing recalcitrant substances such as phenols (Monteiro et al., 2000; Banerjee et al., 2001; Hao et al., 2002 ; Abhuhamed et al., 2004; Kumar et al., 2005; Rodriguez et al., 2006).
Biological Processes Involving Microbes
What should be the optimum loading rate or flow rate through the reactor to achieve complete degradation of the toxic compounds. By studying the degradation kinetics of various toxic compounds and growth kinetics of microorganisms, knowledge can be gathered about the kinetic properties of different biological systems and this information can be useful to understand more complex systems step-by-step.
Heterogeneous Photocatalysis
Details of the materials and methods used in the current study are described in Chapter 3. Concentrations of the substrates in the biomass-free sample were quantified using HPLC (High Performance Liquid Chromatography). The culture biomass concentration profile (as OD600) at different initial phenol concentrations is shown in Fig.
Culture growth also followed a similar pattern to m-cresol degradation. 4.10, where the biomass growth (OD600) of the culture is shown against time for different initial concentrations of m-cresol in the culture media. Figure 4.7: Experimental and predicted rate of culture phenol degradation due to different models.
Bioreactor for Wastewater Treatment
Objective and Scope
This finding confirms the fact that substrate inhibition in culture growth occurs only in high concentration intervals of substrates.
Organization of Thesis
L ITERATURE R EVIEW 18
Sources and Major Components of Phenolic Wastewater
Plastics, resins and plasticizers: Phenol is mainly used in this type of industry in the production of plastics and phenol-formaldehyde resins. Plant hormones and detergents: Phenol is used directly in the production of these types of compounds.
Major Treatment Techniques for Phenolic Wastewater
- Adsorption
- Air Stripping
- Electrochemical Oxidation
- Advanced Oxidation Processes
The photocatalytic degradation of phenolic compounds using Degussa P-25® in the presence of sunlight has been successfully studied by many researchers (Minero et al., 1994; Curcó et al. studied the degradation of phenol and benzoic acid in the presence of sunlight to the sun with a commercial TiO2 Wackherr's Photocatalyst.
Pros and Cons of the above Wastewater Treatment Techniques
Matthews (1990) reported that more than 90% of the nitrobenzene (NB) mineralization was achieved with TiO2 and sunlight. 1994) studied the photocatalytic degradation of NB on TiO2 and ZnO and reported complete mineralization with TiO2. To achieve maximum removal efficiency, additional oxidants such as O3 and H2O2 are required, resulting in higher costs.
Biological Treatment Processes Involving Microbes
- Biodegradation by Yeast and Fungi
- Biodegradation of Phenolics by Bacteria
They observed a strong interaction effect between the two during culture growth on the degradation of the substrates. They also evaluated the biokinetic parameters of the growth of the cells in batch experiments. 2005) investigated the degradation of o-cresol using waste activated sludge in a gas-.
Design of Experiments
- Factorial Design of Experiments
- Analysis of Variance
- Students ‘t’ Test
A test of the null hypothesis is that the means of two normally distributed populations are equal. Paired so that each member of one sample has a unique relationship with a particular member of the other sample (eg, the same individuals measured before and after an intervention).
Microbial Growth Kinetics and Substrate Inhibition Models for
In the mentioned model, the specific rate of degradation is expressed by the following equation: where q is specific substrate degradation/utilization rate, qmax is the maximum specific substrate degradation/utilization rate, S is substrate concentration, Sm is critical inhibitor concentration above which the reaction stops, n and m are empirical constants. In their study, growth inhibition occurred at high concentration of rate-limiting substrate, e.g. the acetic acid fermentation from ethanol, the gluconic acid fermentation from glucose, the tannase fermentation with tannic acid as the only carbon source, a bacterial production from pentane, etc.
Treatment of Phenolics in Airlift Bioreactors
The overall results obtained in the present study showed improved performance of ILALR in batch supply mode operation.
M ATERIALS AND M ETHODS 50
Indigenous Mixed Microbial Culture and Culture Conditions… 50
An indigenous mixed microbial culture, potent in degrading phenolic compounds, was isolated and enriched from a sewage treatment plant in Guwahati, India. Then the culture was initially grown in 250 ml Erlenmeyer flask containing 100 ml Mineral Salt Medium (MSM) with glucose 2 g/L and pH 7.0 under agitation (150 rpm) at 27 oC. Fresh culture grown in glucose and MSM was used as inoculum in 250 ml Erlenmeyer flasks containing autoclaved 100 ml MSM solution initially containing phenol (50 mg/L) or m-cresol (50 mg/L) as the only carbon- and contained energy source.
The degradation of phenol or m-cresol was monitored during the incubation and after complete depletion of the carbon source the culture was now grown in MSM containing a higher concentration of the phenolic compound. The completed enrichment of the indigenous mixed culture took more than a month each time.
Characterization and Identification of the Indigenous Mixed
- Biochemical Characterization
- Scanning Electron Microscopy (SEM)
The procedure was repeated up to a maximum concentration of 800 mg/L in the case of phenol, and in the case of m-cresol the maximum concentration was 1000 mg/L (Nuhoglu and Yalcin, 2005). Staining tests were performed according to the standard procedure detailed in Benson's Microbiological Applications Laboratory Manual (Brown, 2001). Each well in the kit was inoculated with 50 µL of fresh culture suspension by surface inoculation method and the incubation temperature was maintained at 27±2ºC for 18-24 hours.
Freshly cultured cells in MSM containing phenol were centrifuged, dried and covered with gold film in a sputter coater, and finally the cell morphology was recorded in the LEO 1430VP SEM instrument at a magnification of 4350 at 15 KV.
Biodegradation Studies in Batch Shake Flasks
- Single Substrate System
- Mixed Substrate System
Mixed substrate degradation study containing both phenol and m-cresol as the substrates were planned according to 22 factorial design of experiments. Three midpoint replicates were included in the design to control for experimental error; in total, seven combinations (experimental runs) of initial concentrations of m-cresol and phenol were investigated in this mixed substrate degradation system. As before, samples were collected during the experiments and analyzed for the biomass and phenol concentrations.
The results of biomass growth and substrate degradation in the study were statistically analyzed in the form of analysis of variance (ANOVA) and student's 't' test using the statistical software MINITAB (version 12.2 PA, USA).
Phenol Biodegradation in a Batch Stirred Tank Reactor
- Experimental Set up
Feasibility of the Indigenous Mixed Culture to Treat a Refinery
Oxygen Demand (COD), pH, Dissolved Oxygen (DO) and heavy metals (lead, chromium, nickel) were analyzed and are shown in Table 3.3. The samples were collected at regular time intervals and analyzed for the more acceptable wastewater quality parameter - Chemical Oxygen Demand (COD) concentration.
Phenol Degradation in a Solar Photoreactor
- Characterization of the Photocatalysts
- X-Ray Diffraction (XRD) Analysis
- BET Surface Area Analysis
- Particle Size Distribution
From the XRD peaks, the crystallite size of the catalysts was calculated by applying the Scherrers formula. The surface area of the catalysts was examined with a surface area analyzer (Beckman Coulter Model No. SA 3100). Nitrogen gas was used in the analysis to determine the adsorption isotherm, from which the surface area of the catalyst was calculated.
A laser particle size analyzer (Malvern, model no. Mastersizer 2000) with wet distribution mode was used to determine the particle size distribution.
Biodegradation Studies in an Internal Loop Airlift Bioreactor
- Experimental Setup
- Hydrodynamic Studies with the ILALR
- Residential Time Distribution (RTD)
- Volumetric Mass Transfer Coefficient (k L a)
- Bubble Diameter Analysis in the Riser and
- Batch Biodegradation Studies with the ILALR
- Single Substrate System
- Fed-batch Biodegradation Study with the ILALR
- Single Substrate System
- Mixed Substrate System
- Continuous Degradation Studies with the ILALR
- Single Substrate System
- Mixed Substrate System
- Stability Studies on the Performance of the
The mean bubble diameter was calculated and their effects on the RTD and the liquid mixing pattern in the reactor were also analyzed. 10% v/v of the appropriate freshly grown enriched culture was added to the reactor initially treated with phenol or m-cresol as inoculum. Continuous degradation of phenol and m-cresol in ILALR was carried out at two different HRTs of 4.1 h and 8.3 h, respectively, by providing feed flow rates of 5 mL/min and 10 mL/min using a peristaltic pump.
Samples collected from the ILALR outlet were analyzed three times for residual phenol and m-cresol concentrations. Initially the reactor was operated with low substrate concentration (phenol or m-cresol) of 100 mg/L (in single substrate system only) and the substrate concentration was gradually increased to 200 mg/L and suddenly to 600 mg/L. 800 mg/L (in the case of phenol) and 800 mg/L (in the case of m-cresol) in continuous mode to check the stability of the reactor performance.
Analytical Methods
- Determination of Biomass
- HPLC Analysis
- Chemical Oxygen Demand (COD) and Heavy Metal
Biological treatment with mixed microbial strains is an attractive alternative for the treatment of contaminated soils, surfaces and wastewater containing phenols. This research contributes to the study and development of a novel degradation technique that uses an indigenous mixed microbial consortium in an internal loop air-lift bioreactor to treat recalcitrant organics present in industrial wastewater. After Gram staining, the enriched mixed microbial culture, examined under a light microscope, revealed uniformly small Gram-negative bacterial rods of various lengths (Figures 4.1).
The SEM image of the culture also confirmed the above observation which showed the average size of 1.3 to 1.8 µm (Fig. 4.2). Detailed and routine biochemical characterization tests performed with the indigenous mixed culture further confirmed the predominant presence of the Pseudomonas species group in the mixed consortium.
Batch Biodegradation of the Phenolics in Shake Flasks
- Characterization Results of the Photocatalysts
- Effect of Photocatalyst Concentration on Phenol
- Effect of Initial Concentration of Phenol
- Analysis of Intermediates during phenol degradation…. 107
- Hydrodynamics and Mass Transfer Studies
- Residence Time Distribution (RTD)
- Volumetric Oxygen Mass Transfer Coefficient
- Batch Biodegradation of Phenol and m-Cresol in the
- Phenol Biodegradation and the Culture Growth 113
- Biodegradation of Phenol and m-Cresol in
- Fed-batch Biodegradation of Phenolics
- Single Substrate System
- Mixed Substrate System
- Biodegradation of Phenol and m-Cresol in the
- Single Substrate System
- Performance of the ILALR under Shock
- Mixed Substrate System
Furthermore, the final biomass output of the culture was found to be proportional to the phenolic concentration in this area. The observation of the biomass profile of the culture in the mixed substrate system differed significantly with the patterns observed in the single substrate system. It is also observed that relatively high specific degradation rates of the compounds were obtained in the low concentration ranges.
The result of reactor studies on the degradation of phenols by culture is further discussed. The growth pattern of the culture in the presence of phenol and m-cresol in the media was quite different from that of the single substrate study. In the second step, for a concentration of 100 mg/L of each of the substrates, phenol degraded relatively faster, i.e.
show the performance profile of the ILALR operated at 8.3 and 4.1 h HRT, respectively, under these shock loading conditions in the reactor.
Phenol degradation profile followed during the enrichment
Schematic of the simple batch stirred tank reactor
Schematic of the solar photoreactor
Schematic of the ILALR
Photograph of the ILALR used in the study
Schematic of the ILALR in continuous operation
Calibration curve obtained for phenol estimation using the HPLC 74
Photograph of the Gram stained culture taken under light
SEM image of the enriched mixed microbial culture confirming
Time profile of phenol biodegradation by the culture in the batch
Variation of phenol degradation rate with initial phenol
