Model description and kinetic parameter analysis of MTBE biodegradation in a packed bed reactor

A dynamic modeling approach was used to estimate in-situ model parameters, which describe the degradation of methyl tert-butyl ether (MTBE) in a laboratory packed bed reactor. The measured dynamic response of MTBE pulses injected at the reactor's inlet was analyzed by least squares and parameter response surface methodologies. Response surfaces were found to be statistically significant and thus suitable for estimating the global minimum as well as the 95% parameter uncertainty regions. The linear parameter uncertainty estimates for the half-saturation constant (K(S)) and the maximum growth rate (micro(max)) were: 0相似文献   

Experimental investigation of natural smoldering of char granules in a packed bed

The natural smoldering of a packed bed of wood char granules was investigated experimentally. Parameters characterized experimentally included two types of ignition heaters (a rod heater and a plate heater), a range of four particle sizes (<1, 1-2, 2-3, and <3 mm), different fuel bed heights, and different ignition temperatures. The temperature inside the fuel bed and the concentration of flue gases were measured. Observations and results showed that upward smoldering is affected by many factors, and operational conditions must be rigidly controlled to achieve repeatability, while downward smoldering is stable, and smoldering time is dominated by fuel mass. This is in agreement with our earlier theoretical prediction that upward smoldering is controlled both kinetically and by mass transport, while downward smoldering is dominated only by mass transport. Experiments also showed that smoldering in the reactor is a quasi-one-dimensional process when a plate heater was utilized. Calculated results based on this case are in qualitative agreement with experiments.     

Aerated treatment pond technology with biofilm promoting mats for the bioremediation of benzene, MTBE and ammonium contaminated groundwater

A novel aerated treatment pond for enhanced biodegradation of groundwater contaminants was tested under field conditions. Coconut fibre and polypropylene textiles were used to encourage the development of contaminant-degrading biofilms. Groundwater contaminants targeted for removal were benzene, methyl tert-butyl ether (MTBE) and ammonium. Here, we present data from the first 14 months of operation and compare contaminant removal rates, volatilization losses, and biofilm development in one pond equipped with coconut fibre to another pond with polypropylene textiles. Oxygen concentrations were constantly monitored and adjusted by automated aeration modules. A natural transition from anoxic to oxic zones was simulated to minimize the volatilization rate of volatile organic contaminants. Both ponds showed constant reductions in benzene concentrations from 20 mg/L at the inflow to about 1 μg/L at the outflow of the system. A dynamic air chamber (DAC) measurement revealed that only 1% of benzene loss was due to volatilization, and suggests that benzene loss was predominantly due to aerobic mineralization. MTBE concentration was reduced from around 4 mg/L at the inflow to 3.4-2.4 mg/L in the system effluent during the first 8 months of operation, and was further reduced to 1.2 mg/L during the subsequent 6 months of operation. Ammonium concentrations decreased only slightly from around 59 mg/L at the inflow to 56 mg/L in the outflow, indicating no significant nitrification during the first 14 months of continuous operation. Confocal laser scanning microscopy (CLSM) demonstrated that microorganisms rapidly colonized both the coconut fibre and polypropylene textiles. Microbial community structure analysis performed using denaturing gradient gel electrophoresis (DGGE) revealed little similarity between patterns from water and textile samples. Coconut textiles were shown to be more effective than polypropylene fibre textiles for promoting the recruitment and development of MTBE-degrading biofilms. Biofilms of both textiles contained high numbers of benzene metabolizing bacteria suggesting that these materials provide favourable growth conditions for benzene degrading microorganisms.     

Evaluation on the microbial interactions of anaerobic ammonium oxidizers and heterotrophs in Anammox biofilm

Anaerobic ammonium oxidation (Anammox) is a cost-effective new process to treat high-strength nitrogenous wastewater. In this work, the microbial interactions of anaerobic ammonium oxidizers and heterotrophs through the exchange of soluble microbial products (SMP) in Anammox biofilm and the affecting factors were evaluated with both experimental and modeling approaches. Fluorescent in situ hybridization (FISH) analysis illustrated that Anammox bacteria and heterotrophs accounted for 77% and 23% of the total bacteria, respectively, even without addition of an external carbon source. Experimental results showed the heterotrophs could grow both on SMP and decay released substrate from the metabolism of the Anammox bacteria. However, heterotrophic growth in Anammox biofilm (23%) was significantly lower than that of nitrifying biofilm (30-50%). The model predictions matched well with the experimental observations of the bacterial distribution, as well as the nitrogenous transformations in batch and continuous experiments. The modeling results showed that low nitrogen surface loading resulted in a lower availability of SMP leading to low heterotrophic growth in Anammox biofilm, but high nitrogen surface loading would lead to relative stable biomass fractions although the absolute heterotrophic growth increased. Meanwhile, increasing biofilm thickness increased heterotrophic growth but has little influence on the relative biomass fractions.     

Occurrence and fate modeling of MTBE and BTEX compounds in a Swiss Lake used as drinking water supply

Emissions of fuel components from boating use on multiple-use lakes and reservoirs are of high concern with regard to the drinking water supply from such water bodies. We report results of a detailed study on the occurrence, sources and fate of aromatic hydrocarbons and methyl tert-butyl ether (MTBE) in a typical holomictic lake, Lake Zurich, that supplies drinking water for the largest Swiss city. Emphasis of the investigation was on the fuel oxygenate MTBE, which was found in concentrations up to 1.4 microg/L in the epilimnion and up to 0.05microg/L in the hypolimnion of the lake. The concentration difference was due to the stratification of the lake during the boating season with very limited water exchange across the thermocline. MTBE and BTEX nearly completely volatilized before vertical lake mixing occurred in winter. Spatial and temporal variations of MTBE concentrations in the lake were observed and successfully predicted using two complementary box models (MASAS Light and Aquasim). The drinking water supply from holomictic lakes is not at risk for the scenarios studied if water is extracted from well below the thermocline. Since emissions of unburned gasoline into such water bodies are caused predominantly by boating activities, restrictions of highly emitting two-stroke engines could substantially reduce the MTBE and BTEX load of the epilimnion during the boating season.     

Oxidation kinetics and effect of pH on the degradation of MTBE with Fenton reagent

The fundamentals of the Fenton reagent-based degradation of low concentrations of methyl tert-butyl ether (MTBE) in batch reactors under initially anaerobic conditions are discussed in this work. The objective of the study was to quantitatively verify the feasibility of MTBE degradation with Fenton reagent under such conditions. The conclusions may be potentially helpful to further develop an effective in situ treatment of MTBE-contaminated groundwater. Initial MTBE concentrations ([MTBE](0)) of 11.4 and 22.7 microM (approximately 1.0 and 2.0 mg/L, respectively) were treated with Fenton reagent (FR) using a [FR](0):[MTBE](0) molar ratio of 10:1. FR was used in equimolar mixture of Fe(2+)and H(2)O(2) (i.e., [Fe(2+)](0):[H(2)O(2)](0)=1:1). This analysis considers the hydroxyl radicals (OH(*)) produced by FR as the main species responsible for the degradation processes. The effects of [MTBE](0) and pH on the oxidation kinetics were investigated. Under these conditions it was observed that: (i) MTBE was degraded at high extent (90-99%) after 1h of reaction time, (ii) MTBE mineralization was low in all cases and reached only 31.7% at the best conditions, and (iii) In all cases, most of MTBE degradation occurred during the initial 3-5 min of reaction. During this brief initial phase, MTBE transformation followed pseudo-first order kinetics, while the subsequent phase exhibited a sharp drop in degradation rate and had almost negligible contribution to the overall degradation. Experiments performed at acidic pH exhibited the best degradation results, while at neutral pH the degradation rates dropped significantly. Other parameters included in this analysis were: TOC reduction and total concentration of compounds containing the tert-butyl group in their structure (tBC). These compounds were analyzed because of the concerns related to their potential toxicity. Tert-butyl formate (TBF), Tert-butyl alcohol (TBA), acetone and methyl acetate were identified and quantified as major reaction intermediates.     

Fluidized bed reactor for the biological treatment of ion-exchange brine containing perchlorate and nitrate

The removal of perchlorate and nitrate from contaminated drinking water using regenerable ion-exchange processes produces a high salt brine (3-10% NaCl) laden with high concentrations of perchlorate and nitrate. This bench-scale research describes the operation of acetate-fed granular activated carbon (GAC) based fluidized bed reactors (FBR) for perchlorate-only, and combined nitrate and perchlorate removal from synthetic brine (6% NaCl). The GAC was inoculated with a salt-tolerant culture developed by the authors and used previously in batch systems. An FBR was an effective design for perchlorate reduction and exhibited first-order degradation kinetics with respect to perchlorate concentrations. Nitrate was also removed by the organisms in the column and had no negative effects on the removal of perchlorate using the FBR design. However, at higher concentrations of nitrate the FBR was more difficult to operate due to loss of carbon and biomass from the formation of nitrogen bubbles and the high recycle flow rates needed.     

有机物浓度对复合反应器生化降解特性的影响

本试验在连续运行的条件下,考察了C／N对连续运行的复合生物反应系统有机物、氨氮去除效果的影响,结果表明,复合生物反应器在试验运行条件下,对COD,NH3一N的去除率都在90％以上,其中的生物膜对去除效果起主要作用。但C／N在30左右时,系统会发生污泥膨胀,且随着C／N的增加,污泥膨胀发生的更加频繁。     

Nonylphenol polyethoxylate degradation in aqueous waste by the use of batch and continuous biofilm bioreactors

An aerobic bacterial consortium (Consortium A) was recently obtained from textile wastewater and was capable of degrading 4-nonylphenol and nonylphenol polyethoxylates (NPnEOs). In the perspective of developing a biotechnological process for the treatment of effluents from activated sludge plants fed with NPnEO contaminated wastewater, the capability of Consortium A of biodegrading an industrial mixture of NPnEOs in the physiological condition of immobilized cells was investigated. Two identically configured packed bed reactors were developed by immobilizing the consortium on silica beads or granular activated carbon. Both reactors were tested in batch and continuous mode by feeding them with water supplemented with NPnEOs. The two reactors were monitored through chemical, microbiological and molecular integrated methodology. Active biofilms were generated on both immobilization supports. Both reactors displayed comparable NPnEO mineralization under batch and continuous conditions. FISH analyses evidenced that the biofilms evolved with time by changing the reactor operation mode and the organic load. Taken together, the data collected in this study provide a preliminary strong indication on the feasibility of Consortium A-based biofilm technology for the decontamination of NPnEO containing effluents.     

Adsorption behavior of pesticide methomyl on activated carbon in a high gravity rotating packed bed reactor

High gravity rotating packed bed (HGRPB) reactor possesses the property of high mass transfer rate, which is expected to promote the adsorption rate for the process. In this study, HGRPB has been applied on adsorption removal of methomyl from solution, adopting the adsorbent of activated carbon F400. The influence of operating parameters of HGRPB on mass transfer such as the rotating speed (N_R), the flow rate of solution (F_L) and initial concentration of methomyl (C_b0) were examined. The traditionally internal mass transfer models combined with Freundlich isotherm were used to predict the surface and effective diffusion coefficients. In addition, the results have also been compared with those obtained from the traditional basket stirred batch reactor (BBR). The results showed that the larger values of N_R and F_L enhanced the effective intraparticle diffusion and provided more accessible adsorption sites so as to result in lower equilibrium concentration in HGRPB system when compared to SBR system. The results of adsorption kinetics demonstrated that surface and effective diffusions were both significantly greater in HGRPB system instead of BBR system. Furthermore, the values of Bi_S also manifested less internal mass transfer resistance in HGRPB system. The contribution ratio (R_F) of the surface to pore diffusion mass transport showed that the larger contribution resulted from the surface diffusion in HGRPB system. Therefore, the results reasonably led to the conclusion that when the HGRPB system applied on the adsorption of methomyl on F400, the lower equilibrium concentration and faster internal mass transfer can be obtained so as to highly possess great potential to match the gradually stricter environmental standard.     

Effects of inhibitors on nitrification in a packed-bed biological flow reactor

The individual effect of trivalent arsenic, hexavalent chromium and fluoride on nitrification is studied under continuous load in a packed bed biological flow reactor. The results show that Michaelis-Menten rate expression gives the best representation of nitrification data in the absence of inhibitors. However, in the presence of inhibitors, the system follows a non-competitive mode of inhibition with the following rate expression: The values of V_max and K_s are estimated as 1.466 mg l⁻¹ min⁻¹ and 2.349 mg l⁻¹ respectively. The inhibitor constant K_i is evaluated as 273 mg l⁻¹ for trivalent arsenic, 56 mg l⁻¹ for hexavalent chromium and 1185 mg l⁻¹ for fluoride.     

不同填充率下紊动床处理城镇废水的性能研究

研究了填充率为60％和30％两种情况下紊动床处理城镇废水的各种性能和特点,对其实验装置及填料性质进行了介绍,并分析了其实验结果,指出紊动床生物膜反应器对COD,NH4-N有很好的去除效果,为实际工程实现短程反硝化提供了可行性。     

Identification and characterization of bacterial activities involved in wastewater treatment by aerobic fixed-bed reactor

Bacterial colonization of an aerobic fixed bed reactor was studied as a function of reactor height and time during three days. After the colonization, the evolution of the quantity of fixed biomass, their hydrolytical activities and the influence of periodic backwashing were measured, weekly. Approximatively 100 bacteria were identified and classified in different metabolic groups. A decreasing gradient of biomass from top to bottom of the reactor was observed. Backwashing operation permitted the removal of 48% of the fixed biomass. In terms of bacterial strains and their potential hydrolytical abilities (glucidolytical, proteolytical, and lipolytical), no zonation was observed. Most of the species isolated from the granular support belong to the following genera and family: Acinetobacter, Enterobacteriaceae, Aeromonas, Flavobacterium, and Pseudomonas.     

Effect of residual chlorine on the analysis of geosmin, 2-MIB and MTBE in drinking water using the SPME technique

The effect of chlorine on the analysis of three organic compounds (geosmin, 2-methylisoborneol (2-MIB) and methyl tert-butyl ether (MTBE)) in drinking water is elucidated. Three fibers for solid-phase microextraction (SPME) were employed for the extraction of the organic compounds from drinking water samples with and without free residual chlorine present. A gas chromatograph coupled with a mass spectrometer was used to analyze the compounds trapped by the fibers. The presence of chlorine substantially reduces the observed geosmin, 2-MIB, and MTBE concentrations. Depending on the analyte and chlorine concentrations, an experimental error of 10-70% may be observed due to the presence of free residual chlorine. The impact is larger for lower organic compound concentrations, and under higher residual chlorine conditions. To counteract the effect from residual chlorine, sodium thiosulfate was used to dechlorinate the water. After dechlorination the experimental error was less than 10%, suggesting that dechlorination is necessary when applying SPME for the extraction of organic compounds from chlorinated drinking water.     

New model for performance prediction in fixed-bed reactors based on the approach of the unused bed zone

In the present study a practical model useful for designers dealing with pilot scale reactors for pollutant control has been developed. Investigations were undertaken for a single-component lead study on New Zealand clinoptilolite at the temperature of 25+/-1 degrees C. Fifteen runs under different operating conditions such as particle characteristics (expressed as d*(p)/D), column geometry (as l*/D) and flow speed (as R*e) have been performed. The results were interpreted by a response surface method (RSM) from which an equation giving the unused bed zone (UBZ) was obtained. From those dimensionless parameters, a sequence of contour plots was drawn, making it easy for a designer to choose optimum design parameters while controlling the operation performance. The flow rate (R*e) range was established over the laminar flow conditions from 1 to 8, (l/D*) was extended from 7 to 20 and (d(p)/D*) varied from 3% to 10%. Optimization of performance of the reactor as UBZ could vary from 10% to 40% of the material operating capacity.     

对循环流化床锅炉的应用及工艺设计的思考

结合循环流化床运行实践，介绍了其技术特点，从风机的选型、给煤系统的设计等方面，就循环流化床锅炉的工艺设计进行了阐述，提出了运行中存在问题的处理措施。     

Systematic study of the effect of operating variables on reactor performance and microbial diversity in laboratory-scale activated sludge reactors

Biological treatment processes are “complex systems” where many different kinds of microbes grow and interact in a dynamic manner. Understanding the relationship between microbial diversity and bioreactor performance could facilitate the optimisation of bioreactor design and enable the solution of bioreactor-related problems. However, systematic studies of the effects of operating variables on microbial diversity and reactor performance are rare. In this study, we determined the effects of different operating conditions and system configurations on the performance of laboratory-scale activated sludge reactors and microbial diversity, based on experiments designed using the factorial design approach. We found that the overall system performance and the diversity of the microbial communities in the reactors were affected by changes in the operating parameters. However, the relationship between diversity and performance was sometimes counterintuitive, as increases in system performance were not always associated with increased community diversity. Reactor configuration and addition of soil had the biggest effects on reactor performance, while the effects of organic loading rates and feed composition were less marked. Of all these parameters, reactor configuration was the only one that had a consistent effect on reactor community diversity.     

New approach to optimize operational conditions for the biological treatment of a high-strength thiocyanate and ammonium waste: pH as key factor

Biological treatment of coke and steel-processing wastewaters has to satisfy both industrial economic needs and environmental protection regulations. Nevertheless, as some of the pollutants contained in these waters or produced during the treatment are highly toxic, an effective and safe treatment has proved to be difficult to obtain. This paper reports the study of a biological method for the treatment of wastewaters containing free cyanide, thiocyanate and ammonium (NH4). Laboratory-scale activated-sludge reactors were fed with a synthetic solution reproducing a steel-processing industrial wastewater and inoculated with the same industrial bacterial seeding used on-site (Ecosynergie Inc.). The results demonstrated that free cyanide and thiocyanate were efficiently degraded. Nevertheless, thiocyanate degradation and nitrification processes were actually inhibited by the free ammonia form (NH3) in place of the ionized NH4 form (NH4+) currently dosed and often unproperly named "ammonia" [IUPAC, 1997. In: McNaught, A.D., Wilkinson, A. (compilers). Compendium of Chemical Terminology. Royal Society of Chemistry, Cambridge, UK]. Optimum degradation rates were obtained for very narrow ranges of ammonia nitrogen (NH3-N) concentrations. This result can be explained by the role of pH, which mainly controls the NH3/NH4 equilibrium. Pollutants and NH3 concentrations influenced degradation rates of main pollutants. This influence was determined and expressed through elementary equations. Although the Michaelis-Menten equation could have been used to describe thiocyanate degradation, a Haldane-inhibition model was used to satisfactorily describe cyanide degradation. On the other hand, a slightly modified Haldane model was applied to describe both NH4 oxidation using NH3-N as substrate and thiocyanate degradation using NH3-N as inhibitor. These findings emphasize the role of pH on degradation rates and allow one to optimize operational conditions in the biological treatment of coke and steel industrial wastewaters.     

Influence of detachment on substrate removal and microbial ecology in a heterotrophic/autotrophic biofilm

Competition between heterotrophic bacteria oxidizing organic substrate and autotrophic nitrifying bacteria in a biofilm was evaluated. The biofilm was grown in a tubular reactor under different shear and organic substrate loading conditions. The reactor was initially operated without organic substrate in the influent until stable ammonia oxidation rates of 2.1 g N/(m² d) were achieved. A rapid increase of fluid shear in the tubular reactor on day 156 resulted in biofilm sloughing, reducing the biofilm thickness from 330 to 190 μm. This sloughing event did not have a significant effect on ammonia oxidation rates. The addition of acetate to the influent of the reactor resulted in decreased ammonia oxidation rates (1.8 g N/(m² d)) for low influent acetate concentrations (17 mg COD/L) and the breakdown of nitrification at high influent acetate concentrations (55 mg COD/L). Rapidly increasing fluid shear triggered biofilm sloughing in some cases—but maintaining constant shear did not prevent sloughing events from occurring. With the addition of acetate to the influent of the reactor, the biofilm thickness increased up to 1350 μm and individual sloughing events removed up to 50% of the biofilm. Biofilm sloughing had no significant influence on organic substrate removal or ammonia oxidation. During 325 days of reactor operation, ammonia was oxidized only to nitrite; no nitrate production was observed. This lack of nitrite oxidation was confirmed by fluorescent in situ hybridization (FISH) analysis, which detected betaproteobacterial ammonia oxidizers but not nitrite oxidizers. Mathematical modeling correctly predicted breakdown of nitrification at high influent acetate concentrations. Model predictions deviated systematically from experimental results, however, for the case of low influent acetate concentrations.