Effect of anionic and nonionic surfactants on the kinetics of the aerobic heterotrophic biodegradation of organic matter in industrial wastewater

While using the contemporary mathematical models for activated sludge systems, it is necessary to describe quantitatively the kinetics of microbiological processes and to characterise substrate (wastewater components in the influent) as well as biomass (activated sludge). In this paper, the kinetic parameters of the aerobic biodegradation of organic matter in wastewater containing synthetic surfactants in an activated sludge system were determined and discussed. Also, the composition of the tested wastewater was estimated and expressed as COD fractions. Five synthetic surfactants, three anionic and two nonionic, of different chemical structure were investigated. Each of them was tested separately and dissolved in wastewater to obtain a concentration of 50 mgl(-1), which can be found in some industrial wastewater. The presence of the elevated amount of synthetic surfactants in wastewater decreased the affinity of biomass to substrate. Nevertheless, maximum specific growth rates (micromax) of heterotrophic biomass exposed to wastewater containing surfactants were high but usually lower than micromax estimated for wastewater without surfactant. Surfactants, which contain a benzene ring, were the most likely to deteriorate wastewater treatment processes in the activated sludge systems.     

BTEX biodegradation by bacteria from effluents of petroleum refinery

Groundwater contamination with benzene, toluene, ethylbenzene and xylene (BTEX) has been increasing, thus requiring an urgent development of methodologies that are able to remove or minimize the damages these compounds can cause to the environment. The biodegradation process using microorganisms has been regarded as an efficient technology to treat places contaminated with hydrocarbons, since they are able to biotransform and/or biodegrade target pollutants. To prove the efficiency of this process, besides chemical analysis, the use of biological assessments has been indicated. This work identified and selected BTEX-biodegrading microorganisms present in effluents from petroleum refinery, and evaluated the efficiency of microorganism biodegradation process for reducing genotoxic and mutagenic BTEX damage through two test-systems: Allium cepa and hepatoma tissue culture (HTC) cells. Five different non-biodegraded BTEX concentrations were evaluated in relation to biodegraded concentrations. The biodegradation process was performed in a BOD Trak Apparatus (HACH) for 20 days, using microorganisms pre-selected through enrichment. Although the biodegradation usually occurs by a consortium of different microorganisms, the consortium in this study was composed exclusively of five bacteria species and the bacteria Pseudomonas putida was held responsible for the BTEX biodegradation. The chemical analyses showed that BTEX was reduced in the biodegraded concentrations. The results obtained with genotoxicity assays, carried out with both A. cepa and HTC cells, showed that the biodegradation process was able to decrease the genotoxic damages of BTEX. By mutagenic tests, we observed a decrease in damage only to the A. cepa organism. Although no decrease in mutagenicity was observed for HTC cells, no increase of this effect after the biodegradation process was observed either. The application of pre-selected bacteria in biodegradation processes can represent a reliable and effective tool in the treatment of water contaminated with BTEX mixture. Therefore, the raw petroleum refinery effluent might be a source of hydrocarbon-biodegrading microorganisms.     

Influence of feed concentration on the kinetics of biodegradation of phenol in a continuous stirred reactor

The rate of phenol degradation by activated sludge was studied in a completely mixed continuous-flow reactor with sludge recycle, operated at steady-state conditions at 20°C. Monod kinetics was followed when the influent concentration (C_s°) was kept constant. When using different C_s° levels, the phenol removal rate was found to have an inverse dependence on C_s°. It is suggested that this kinetic anomaly is due to inhibition of the biooxidation by some secondary reaction product(s). A kinetic model based on this concept is able to interpret experimental facts.     

Effects of influent substrate concentration on the kinetics of natural microbial populations in continuous culture

In order to determine whether the influent substrate concentration exerts an effect upon the kinetics of soluble substrate removal by natural microbial populations growing in continuous culture experiments were run using a multicomponent substrate. A two-level factorial experimental design was employed with reactor dilution rate and influent substrate concentration as the independent variables. Analysis of the results indicated that both variables exerted a significant effect (1% level) upon the effluent soluble COD. It was possible to model the system using the linear approximation of the Monod equation resulting in an equation of the general form: S=K′S₀D + K″S₀The findings of the study indicate that engineers responsible for the design and operation of wastewater treatment facilities should consider the influent substrate concentration when choosing a mean cell residence time for the system.     

Kinetic characterization of saponified domestic lipid residues aerobic biodegradation

As the sanitary landfill dumping of the lipidic residues are now prohibited by French legislation, new treatment ways such as biodegradation or incineration have to be developed. This work carried out on domestic grease demonstrates the effect of their saponification on their aerobic biodegradation. The composition of the lipidic residues mixture used in this work and collected from a wastewater plant was characterized (70% dry matter, 90% HEM, 80% of free and esterified fatty acids, 20% of other lipidic materials, DCO/lipids=2.4). Both the solubilization of grease (apparent CMC=0.7 g HEM/l) and their micellization by saponification highly enhanced the rate of grease degradation by an activated sludge. This pointed out that the elimination reaction was controlled by the grease transfer from lipidic phase to cell. During batch culture (X₀=1.8 g MLSS/l, S₀=3.5 g HEM/l), the degradation rate was more than 0.2 g HEM/l/h and the removal yield was 60% for HEM, namely 70% for fatty acids and 40% for unsaponifiable compounds. This low removal yield could be linked to the high foaming onset which did not allow the biological degradation reaction to continue.     

Temperature effect on aerobic biodegradation of feces using sawdust as a matrix

Temperature is one of the most important factors affecting microbial growth and biological reactions. In this study, the effect of temperature on aerobic biodegradation of feces is described through the comparison and analysis of experimental oxygen utilization rates (OUR) profiles obtained from batch tests conducted at several temperatures covering mainly mesophilic and thermophilic ranges. Additionally, the temperature effect was incorporated into the bio-kinetic model introduced by Lopez Zavala et al. (Water Res 38(5) (2004) 1327) and simulation of experimental OUR profiles was conducted. Results show that mesophilic and thermophilic microorganisms behaved differently to temperature; additionally, results suggest that the optimum temperature from the viewpoint of feces biodegradability is within the thermophilic range, nearly 60 degrees C. The enzymatic activity of microorganisms at 70 degrees C was remarkably diminished. For better predictions in the mesophilic range, two fractions of slowly biodegradable organic matter were identified, easily hydrolyzable organic matter (X(Se)) and slowly hydrolyzable organic matter (X(Ss)).     

Modeling of aerobic biodegradation of feces using sawdust as a matrix

Composting in the bio-toilet system is a continuous thermophilic-aerobic biodegradation process. Unlike to the traditional composting systems, biodegradation rates of organic matter are very important because feces are daily added into the composting reactor of the bio-toilet and an accelerated decomposition is aimed. The models developed for conventional composting processes include simple formulations of biodegradation kinetics and deal mainly with energy and water balances. Therefore, formulation of kinetics that can reasonably describe the biodegradation process in the bio-toilet system is required for better modeling predictions. In this work, a bio-kinetic model was introduced to describe the aerobic biodegradation of feces in the bio-toilet system. This model includes three processes for carbonaceous material degradation and is prepared by using the activated sludge modeling techniques and formulations. Stoichiometric parameters were adopted from literature on activated sludge processes. Kinetic parameters were estimated by conducting batch tests for several organic loadings and by using respirometry, curve-fitting techniques, and sensitivity analysis. Feasibility and applicability of these parameters were assessed by conducting feces intermittent-feeding tests and by simulating the experimental respiration rates. Model, stoichiometric and kinetic parameters proved to be affordable for describing the biodegradation of feces in the bio-toilet system.     

Continuous culture biodegradation of simazine's chemical oxidation products

Experimental studies were conducted to assess the continuous culture biodegradation of s-triazines which originate from the chemical oxidation of simazine. Simazine is a herbicide found widely in surface and groundwaters. The four s-triazines selected for study, didealkyl atrazine (CAAT), ammeline (OAAT), ammelide (OOAT), and cyanuric acid (OOOT), originate from the ozone/UV oxidation of simazine. Decreases in continuous culture net growth rate, decreases in C:s-triazine-N feed ratio, and increases in inorganic nitrogen either through addition to the feed or by nitrogen fixation resulted in poorer s-triazine removal. For each process variable studied, the reduction in removal efficiency was s-triazine specific. In general, the greatest reductions in removal efficiency was observed for CAAT followed by OAAT, OOAT, and OOOT indicating that the s-triazine ring substituent group is an important factor in determining its effectiveness as a nitrogen source for microbial metabolism. The relationship between ring substituent and s-triazine metabolism demonstrates the beneficial role that chemical oxidation can play in subsequent s-triazine biodegradation. The application of chemical oxidation may enable the use of existing biological process infrastructure, primarily municipal POTWs where nitrogen limitations do not typically exist, for the treatment of s-triazines.     

Biokinetics of biodegradation of surfactants under aerobic, anoxic and anaerobic conditions

The present investigation aims at estimating the biodegradation coefficients of surfactants. The biodegradabilities of Triton X-100 and Rhamnolipid were tested under aerobic, nitrate reducing, sulphate reducing and anaerobic conditions using a respirometer. The results indicated that in terms of biodegradability, Rhamnolipid is superior to Triton X-100, since it is biodegradable under all conditions, whereas Triton X-100 is partially biodegradable under aerobic conditions and non-biodegradable under anaerobic, nitrate reducing and sulphate reducing conditions.     

Effect of operating parameters on molinate biodegradation

The effect of operating conditions during molinate degradation by the defined mixed bacterial culture DC, previously described as able to mineralize molinate, was evaluated in a batch reactor. Parameters such as the rate of molinate degradation, the dissolved organic carbon (DOC) consumption and the accumulation of molinate degradation products were monitored along the culture growth. The effect of conditions such as temperature, pH, aeration rate, salinity, and presence of additional carbon and/or nitrogen sources, was tested independently. Degradation of molinate in river water was also evaluated. Culture DC was able to grow and to mineralize molinate at all the conditions assayed. Temperature was the factor with the strongest influence on bacterial growth and molinate mineralization. The lowest and the highest rate values of growth (0.010 and 0.110 h(-1)) and of molinate degradation (0.027 and 0.180 g molinate g(-1)celldrywth(-1)) were obtained at 15 and 35 degrees C, respectively. In cultures with approximately 187 mgl(-1) of molinate, 2-oxo-molinate was the major molinate degradation product accumulated in the medium, in concentrations below 0.133 mgl(-1). Degradation of molinate was also evaluated in a continuous stirred tank reactor (CSTR). Operating the CSTR at a hydraulic retention time (HRT) of 83 h, fed with medium containing molinate concentrations ranging from 1 to 3mM, culture DC degraded the herbicide with specific degradation rates similar to those obtained in the batch systems.     

Inhibition of p-cresol on aerobic biodegradation of carbazole,and sodium salicylate by Pseudomonas putida

A PAH- and phenol-degrading microorganism, Pseudomonas putida (ATCC 17484), was used to study the substrate interactions during cell growth on carbazole-containing mixtures with p-cresol and sodium salicylate. Both p-cresol and sodium salicylate could be utilised by the bacteria as the sole carbon and energy sources. When cells grew on the mixture of carbazole, p-cresol and sodium salicylate, strong substrate interactions were observed. Carbazole degradation started only after p-cresol was significantly or completely removed, and the removal of carbazole was incomplete when the initial p-cresol concentration was higher than 20 mg/l. No carbazole was removed at all when the initial p-cresol concentration in the system was higher than 120 mg/l. When cells grew on the ternary substrates, the specific growth rate was found to increase with p-cresol concentration up to 50 mg/l (from 0.33 to 0.45 h(-1)) but decreased monotonically with higher concentrations. At 120 mg/l p-cresol, specific growth rate fell to 0.33 h(-1). The inhibitory effect of p-cresol was demonstrated where carbazole degradation was immediately halted when 50 mg/l p-cresol was spiked to a system containing carbazole and sodium salicylate. Besides, the addition of p-cresol was also found to inhibit the degradation of sodium salicylate. With p-cresol, an increase in lag time was observed and the utilisation of sodium salicylate as carbon source was severely retarded.     

Batch and continuous culture experiments on nutrient limitations and temperature effects in the marine alga Tetraselmis suecica

Batch growth and chemostat culture experiments were carried out with the marine alga Tetraselmis suecica (Kylin), a unicellular alga which is potentially useful for wastewater treatment by controlled eutrophication. In natural (Mediterranean coastal) seawater enriched with nutrients, at 22°C, under illumination at $\text{12}\text{h}\text{12}\text{h}$ light/dark, with an intensity of 500 ft-candles, the maximal specific growth rate was μ_max = 0.61 day^?1 (base e), measured both in batch and in chemostat experiments. Cell population densities were determined as a function of temperature at fixed dilution rates. The optimal growth temperature was between 25 and 27°C. With an abundant supply of nutrients, it was possible to sustain substantial population densities in the temperature range of 15–32°C.     

Dynamic modeling of biodegradation and volatilization of hazardous aromatic substances in aerobic bioreactor

The aerobic biological process is one of the best technologies available for removing hazardous organic substances from industrial wastewaters. But in the case of volatile organic compounds (benzene, toluene, ethylbenzene, p-xylene, naphthalene), volatilization can contribute significantly to their removal from the liquid phase. One major issue is to predict the competition between volatilization and biodegradation in biological process depending on the target molecule. The aim of this study was to develop an integrated dynamic model to evaluate the influence of operating conditions, kinetic parameters and physical properties of the molecule on the main pathways (biodegradation and volatilization) for the removal of Volatile Organic Compounds (VOC). After a comparison with experimental data, sensitivity studies were carried out in order to optimize the aerated biological process. Acclimatized biomass growth is limited by volatilization, which reduces the bioavailability of the substrate. Moreover, the amount of biodegraded substrate is directly proportional to the amount of active biomass stabilized in the process. Model outputs predict that biodegradation is enhanced at high SRT for molecules with low H and with a high growth rate population. Air flow rate should be optimized to meet the oxygen demand and to minimize VOC stripping. Finally, the feeding strategy was found to be the most influential operating parameter that should be adjusted in order to enhance VOC biodegradation and to limit their volatilization in sequencing batch reactors (SBR).     

Influence of the hydrophilic moiety of anionic and nonionic surfactants on their aerobic biodegradation in seawater

The extent and kinetics of the primary biodegradation have been characterized for the most commonly-used surfactants, employing four homologues with the same alkyl chain: dodecyl ethoxy sulfate (C₁₂AES), sodium dodecyl sulfate (SDS), dodecyl alcohol ethoxylate (C₁₂AEO) and dodecyl benzenesulfonate (C₁₂LAS). A brief acclimatization period has been required to enable an effective degradation of C₁₂LAS and C₁₂AES to take place, but this lag phase has not been detected for SDS and C₁₂AEO. Primary biodegradation percentages at the end of these experiments were higher than 99%, showing a fast degradation rate in all cases (average half-life lower than 2 days). The secondary biodegradation of C₁₂LAS was also monitored. C₁₂LAS external isomers, which are predominant, are preferentially degraded by successive β-oxidations, generating significant amounts of external even isomers of sulfophenylcarboxylic acid (SPC) (mainly 2,3ΦC_4,6SPCs). In ontrast, internal isomers are converted into internal odd isomers of SPC (mostly 4,5ΦC_5,7SPCs) by ω-oxidation followed by α-oxidation and/or β-oxidations.     

Inhibition of aerobic metabolic cis-1,2-di-chloroethene biodegradation by other chloroethenes

The presence of other chloroethenes influences aerobic metabolic biodegradation of cis-1,2-dichloroethene (cDCE). A new metabolically cDCE degrading enrichment culture was identified as also being capable of degrading vinyl chloride (VC), but not 1,1-dichloroethene (1,1DCE), trans-1,2-dichloroethene (tDCE), trichloroethene (TCE), or tetrachloroethene (PCE). The fastest degradation of cDCE was observed in the absence of any other chloroethene. In the presence of a second chloroethene (40-90 μM), the rate of cDCE (60 μM) degradation decreased in the following order: cDCE (+PCE) > cDCE (+tDCE) > cDCE (+VC)> cDCE (+1,1DCE) ≈ cDCE (+TCE). With increasing concentrations of VC, ranging from 10 to 110 μM, the rate of cDCE (60 μM) degradation decreased. This study demonstrates that the inhibiting effects of chloroethene mixtures have to be considered during laboratory studies and bioremediation approaches based on metabolic cDCE degradation.     

Effect of solar radiation on poliovirus: Preliminary experiments

Solar radiation was found to have some inactivating effect on poliovirus type 1 in the absence of any natural or synthetic photosensitizing agent. Nontronite, a three-layer clay, displayed a protective effect against light or thermal inactivation. Photoinactivation of poliovirus in lake water was retarded by the presence of blue-green algae. The light inactivation was less important at a depth of 6 in.     

模拟工厂化培养蒙古裸腹溞的试验研究 Ⅱ .培养技术和产量指标的研究

及时投喂酵母,加大培养用水的日交换率,增大引种种群个体的数量、幼体百分率(80%以上)和成体怀幼数,并在适宜的密度(5000个/L左右)和采获率(30%)下采获,对提高蒙古裸腹MoinamongolicaDaday的日产量有益。在微流水、日投喂200～300万个/mL小球藻并搭配投喂150mg/L干酵母,培养用水日交换率0 5～1 0的条件下,蒙古裸腹的日产量近100g/(m3·d);蒙古裸腹的种群增长可用Logistic曲线方程Nt=11/(1+e1 967-0 318t)描述,并依照种群增长曲线探讨了提高日产量的途径。     

Effect of Temperature on BTEX Permeation Through HDPE and Fluorinated HDPE Geomembranes

The diffusion characteristics of high density polyethylene (HDPE) geomembranes with respect to hydrocarbons are investigated at temperatures of 22±1°C and 6±1°C. Results are reported for an aqueous solution of benzene, toluene, ethylbenzene, and xylene (BTEX). The partitioning coefficient obtained from sorption/immersion test is shown to be effectively the same as that from desorption test. Both conventional untreated (HDPE) and fluorinated (f-HDPE) geomembranes are examined and it is shown that a fluorinated layer on the surface of an HDPE geomembrane increases its resistance to the permeation of BTEX penetrants by about a factor of 2.4 at 22°C and 1.8 at 6°C. An Arrhenius relationship is developed that could be used for estimating hydrocarbon permeation at different temperatures between 6°C and 22°C for both the HDPE and f-HDPE geomembranes examined.     

Transformation and characterisation of dissolved organic matter during the thermophilic aerobic biodegradation of faeces

We conducted a comparison of the characteristics of dissolved organic matter (DOM) taken from the bio-toilet and other sources. A characterisation of DOM was carried out to assess the stability of the compost generated during the thermophilic and aerobic biodegradation of faeces. In addition, levels of soluble microbial products generated in the bio-toilet composting reactor were compared with those taken from other sources. The results showed that (i) the main component of DOM from the bio-toilet are solutes with molecular weight (MW)>30,000 Da (40%), whereas micromolecules (MW< 1000 Da) constituted more than 60% of the DOM from other solid samples, while liquid samples reached even more than 90%; (ii) the DOM stabilisation level in the composting reactor of the bio-toilet system was greater than that shown by DOM from other sources; (iii) stabilisation of DOM in the bio-toilet system was characterised by an increasing amount of macromolecules (MW>30,000 Da) after a decreasing trend was observed in the early stages of the biodegradation process; and (iv) net production of lipopolysaccharide (LPS) in wastewater treatment plants is greater than in the bio-toilet.