Kinetic behaviour of waste tyre rubber as microorganism support in an anaerobic digester treating cane molasses distillery slops

The kinetics of anaerobic digestion of cane molasses distillery slops was investigated using a continuous-flow bioreactor which contained waste tyre rubber as support, to which the microorganisms became immobilized. Hydraulic retention times (HRT) ranging from 1 to 10 days were investigated at an average influent chemical oxygen demand (COD) concentration of 47.7?g/l. The maximum substrate utilization rate, k, and half saturation coefficient, K _L, were determined to be 1.82?kg COD_removed/kg VSS day and 0.33?kg COD/kg VSS day. The yield coefficient, Y, and sludge decay rate coefficient, K _d, were also determined to be 0.06?kg VSS/kg COD_removed and 0.05?day^-1, respectively. Methane production was maximum (6.75?l/l day) at a 2 day HRT corresponding to a biomass loading rate of 2.578?kg COD/kg VSS day. Biogas yield ranged between 0.51?l/g COD (HRT=2 days) and 0.25?l/g COD (HRT=1?day). In addition, the methane percentage in the biogas varied between 70.5% (HRT=10?days) and 47.5% (HRT=1?day). The close relationship between biomass loading rate and specific substrate utilization rate supported the use of Monod equations. Finally, the experimental values of effluent substrate concentration were reproduced with deviations equal to or less than 10% in every case.     

Mathematical modelling of the aerobic degradation of two-phase olive mill effluents in a batch reactor

A laboratory-scale study was conducted on the aerobic degradation of two-phase olive mill effluents (TPOME) made up of the mixture of the washwaters derived from the initial cleansing of the olives and those obtained in the washing and purification of virgin olive oil. The process was carried out in a 1-l working volume stirred tank reactor operating in batch mode at room temperature (25 °C). The reactor was operated at influent substrate concentrations of 2.80 g COD/l (TPOME 25%), 5.45 g COD/l (TPOME 50%), 8.18 g COD/l (TPOME 75%) and 10.90 g COD/l (TPOME 100%). After five days of operation time, total and soluble COD removal efficiencies of 64.3% and 66.6% were achieved respectively for the most concentrated influent used (TPOME 100%). A simplified kinetic model for studying the hydrolysis of insoluble organic matter, oxidation of soluble substrate and biomass production was proposed on the basis of the experimental results obtained. The following kinetic constants with their standard deviations were obtained for the above stages in the case of the most concentrated influent used (TPOME 100%): k₁ (kinetic constant for hydrolysis of suspended organic matter): 0.11 ± 0.01 l/(g VSS day); k₂ (kinetic constant for total consumption of soluble substrate): 0.30 ± 0.02 l/(g VSS day); k₃ (endogenous metabolism constant): 0.07 ± 0.01 per day). Finally, the biomass yield coefficient was found to be 0.30 g VSS/g COD_removed. The values of non-biodegradable total and soluble CODs obtained from the model were found to be 3 and 2 g/l, respectively. The kinetic constants obtained and the proposed equations were used to simulate the aerobic degradation process of TPOME and to obtain the theoretical values of non-soluble and soluble CODs and biomass concentration. The small deviations obtained (equal or lower than 10%) between the theoretical and experimental values suggest that the parameters obtained represent and predict the activity of the microorganisms involved in the overall aerobic degradation process of this wastewater.     

Treatment of distillery spentwash by hybrid UASB reactor

A laboratory-scale hybrid UASB reactor, which combined an UASB in the lower part and a filter in the upper part, was used for the treatment of distillery spentwash. The reactor was operated under ambient conditions for 380 days. Using anaerobically digested sewage sludge as a seed, the start-up of the reactor and the cultivation of active granular sludge was completed within three months period. Scanning electron microscopic (SEM) observation of the granules showed the presence of Mehtanonthrix-like bacteria as the dominant species. Following the start-up the organic loading rate (OLR) was increased, stepwise, to 36 kg COD/m³ · d at a constant hydraulic retention time (HRT) of 6 h. COD removal efficiency was 80% even at a high OLR of 36 kg COD/m³ · d. Biogas rich in methane content (80%), with a maximum specific biogas yield of 0.40 m³ CH₄/kg · COD was produced. Polypropylene pall rings filter medium in the upper-third of the reactor was very effective as a gas-liquid-solid (GLS) separator, and retained the biomass in addition. The study indicated that hybrid UASB is a very feasible alternative for the treatment of high-strength wastewaters like distillery spentwash.     

The optimum substrate to biomass ratio to reduce net biomass yields and inert compounds in biological leachate treatment under pure-oxygen conditions

To investigate the effect of both initially present soluble inert COD (S_I) and soluble inert COD formed by microbial activities (S_PM) on the effluent soluble residual COD (S_R) and to determine biokinetic constants, the pure-oxygen was employed for the batch assays of biological leachate treatment. The results of this work showed that the effluent residual soluble COD was entirely composed of S_I and S_PM, therefore, could not be reduced below 7-10% of total influent soluble COD (S_T0.inf), corresponding to the organics removal efficiency of 93-90%. The value of S_I of leachate, which is associated with the types of wastewaters, was determined as approximately 7.84% of S_T0.inf, and the soluble inert COD by microbial activities was assessed by means of the coefficient f_PM of 0.0474. These results mean that significant amount of feed leachate COD may pass the biological system without any change. On the basis of the concept that microorganisms must satisfy their maintenance energy requirements prior to synthesizing new biomass, a set of batch assays with various ratios of S_T0.inf /X₀ were carried out to evaluate their effects on the excess biomass production. Decreasing the supply of substrate per unit biomass resulted in gradual decrease in the biomass yields, but, at the same time, it resulted in gradual increase in the bacteria mediated inert COD as a side effect. The optimum ratios of S_T0.inf /X₀ were concluded as 0.2-0.6 according to the careful consideration of both aspects on the reduction of net sludge yields and inert COD from microbial activities.     

Granulation in anaerobic sludge bed reactors treating food industry wastes

Three parallel laboratory reactors, R1, R2 and R3, received food industry wastewater: R1 unadulterated; R2 supplemented with calcium and phosphate; R3 supplemented with ferric chloride and traces of nickel and cobalt. Reactors were packed with active granular sludge from a large scale pilot reactor treating the same wastewater. Addition of calcium and phosphate was found to be detrimental to the granule formation at naturally established reactor pH = 6·9–7·4 in R2 while iron promoted granulation in R3. Conditions of upflow velocities of 1·5–6 m h⁻¹, rapid increase of loads up to 15 kg COD m⁻³ day⁻¹ and ratios of recycle to raw waste feed of 20:1–80:1 were imposed on all reactors. The granules in R1 and R2 disintegrated, from 70–100 g liter⁻¹ VSS to a flocculant sludge at 1·5–3 g liter⁻¹. In spite of such severe washout, reactors R1 and R2 were able to maintain a steady COD removal of over 90% at a load of 10kg m⁻³ day⁻¹. R3 retained a VSS concentration around 100 g liter⁻¹ and maintained COD removal at over 95%. R3 exhibited a more stable performance and was less vulnerable to the shock treatment to which all reactors were subjected.     

Physiological energetics of the protobranch bivalve <Emphasis Type="Italic">Yoldia hyperborea</Emphasis> in a cold ocean environment

Yoldia hyperborea is a deposit-feeding circumpolar protobranch that also inhabits muddy sediments of the cold water boreal system of Conception Bay, Newfoundland, Canada. Little is known about this species, despite its wide distribution and frequent high density in the benthos. The present work deals with oxygen consumption and ammonia excretion under cold ambient conditions. Y. hyperborea showed low basal metabolism [0.051 ml O₂ h^у·(g dry weight)^у, T=у°C] and low ammonia excretion rates [4.212 µg·NH₄-N·h^у·(g dry weight)^у, T=у°C]. Low metabolic activity could prove a useful strategy during periods of low food availability. In addition, Y. hyperborea was able to regulate its O₂ consumption rate at very low pO₂ levels, which may be advantageous for a species that may experience periods of hypoxia.     

The influence of anaerobic pretreatment on the nitrogen removal from biosynthetic pharmaceutical wastewaters

The C:N ratio of the pharmaceutical wastewaters is usually suitable for a combination of the anaerobic pretreatment with the high COD removal and aerobic posttreatment with the efficient biological N removal. This kind of anaerobic-aerobic process was tested in semipilot scale by using a UASB reactor and an activated sludge system with a predenitrification (total volume 100 1). It was found that at a total HRT of 2.3 days an average of 97.5% of COD and 73.5% of total N was removed. The UASB reactor was operated at 30°C with a volumetric loading rate of 8.7 kg.m^-3.d^-1, the efficiency of COD removal was 92.2%. The processes, which take part in the biological removal of nitrogen, especially the nitrification, were running with lower rates than usually observed in aerobic treatment systems.Abbreviations AAO anaerobic anoxic oxic configuration - AOO anaerobic oxic oxic configuration - B _V volumetric organic loading rate (kg COD.m^-3. d^-1) - dB _x specific COD removal rate (mg COD. g^-1 VSS. d^-1) - DNR denitrification rate (mg N–NO₃. g^-1 VSS. h^-1) - E_COD efficiency of COD removal (%) - HRT hydraulic retention time (d) - NR nitrification rate (mg N–NO₃. g^-1 VSS. h^-1) - R recirculation ratio (%) - SBP specific biogas production (m³.kg^-1 removed COD) - SRT solids retention time; sludge age (d) - SS suspended solids (g.1^-1) - UASB upflow anaerobic sludge blanket reactor - VSS volatile suspended solids (g.1^-1)     

Biomethanation of white rotted and brown rotted rice straw

Biomethanation of white rotted and brown rotted rice straw was taken for the present investigation and their efficiency on biomethanation has been tested. Rice straw was treated with white rot fungus Phanerochaete chrysosporium (P_C) and brown rot fungus Polyporus ostreiformis (P_O). Biogas and methane production was increased by about 34.73% and 46.19% in P_C-treated straw and 21.12% and 31.94% in P_O-treated straw respectively. VFA production has also been increased in P_C and P_O treated straw compared to control straw which were 76.73% and 30.69% respectively. Reduction of COD has also been found during biomethanation. The rate of reduction of COD during the initial period of digestion was 59.01%, 55.55% and 26.00% in P_C-treated, P_O-treated and control straw respectively after 21 days of digestion.     

Nitrification performance and nitrifier community composition of a chemostat and a membrane-assisted bioreactor for the nitrification of sludge reject water

Nitrification performance of a chemostat and a membrane-assisted bioreactor (MBR) was assessed at pilot scale for the treatment of sludge reject waters with NH₄⁺-N concentrations up to 600 mg/L and low organic content (COD<200 mg/L). To prevent nitrifier washout the 1-m³ chemostat was operated at 20°C with minimum hydraulic retention time of F=2 days. At the 0.71 m³ MBR, F was successively reduced to 6.2 h. Complete sludge retention was achieved by means of a 2-m² 100,000-Dalton PES ultrafiltration membrane. Operation in crossflow mode with flow velocities from v_F=2.4-3.7 m/s and transmembrane pressures (p=0.5-1.2 bar yielded a long-term permeate flux of 110 L/(m²2h). In the MBR, nitrification rates up to 2,500 g N/(m³2d) were measured with biomass concentrations between 4 and 15 g TSS/L. Despite low TSS values, about 0.2 g/L of the chemostat was able to nitrify 180 g N/(m³2d). The microbial community composition differed considerably between the two reactors as determined by fluorescent in situ hybridisation (FISH) with rRNA-targeted oligonucleotide probes. For both reactors, the relative abundance of ammonia and nitrite oxidisers measured by FISH was consistent with results from dynamic simulation of the nitrification process.     

Thermophilic high-rate anaerobic treatment of wastewater containing long-chain fatty acids: effect of washed out biomass recirculation

Biomass washed out from an expanded granular sludge bed (EGSB) reactor treating oleate (82%, w/w) was inves-tigated. This biomass had a 50% higher activity compared to granules present in the EGSB reactor. Recirculationof washed out biomass into reactor remarkably improved the treatment performance. The highest methane conversion rate from oleate, 300 mg CH₄-COD/g VSS.d, was achieved at a concentration of 4 g oleate-COD/l and a volumetric loading rate of 8 g COD/l.d. This revised version was published online in November 2006 with corrections to the Cover Date.     

Determination of multiple steady states in an enzyme kinetics involving two substrates in a CSTR

The multiple steady states in an isothermal, constant-density CSTR involving two-substrates, enzyme- catalyzed reactions is determined by a zero eigenvalue analysis. The hysteresis and bistability occurs for a certain range of the rate constant of product formation from a ternary complex, k_ES1S2MP+E. A two-parameter (k_ES1S2MP+E, k_0MS1) bifurcation diagram for several different values of flow rate k_S1̂ is also presented. It shows that, to maintain the existence of the steady state multiplicity under a fixed flow rate, the larger the rate constant k_ES1S2MP+E is, the larger the feed concentration of a substrate is required and the wider the range of that exists. To maintain the existence of the steady state multiplicity for a lower flow rate, it is required to reduce the feed concentration of substrates.     

Effects of operating parameters on performances of nitrification and denitrification processes

Nitrification and denitrification of synthetic wastewater was studied by using two reactors in series. An activated sludge unit was used for nitrification followed by a downflow biofilter (packed column) for denitrification. A glucose solution was fed to the denitrification column to supply carbon source. Effects of important process variables such as sludge age, hydraulic residence time and feed ammonium concentration on system's performance were investigated. Effluent ammonium-nitrogen (NH4-N) concentration decreased with increasing sludge age and hydraulic residence time and remained constant for sludge age and hydraulic residence times greater than 12 d and 15 h, respectively. Feed ammonium-nitrogen concentration above 200 mg/l resulted in significant levels of NH4-N in the effluent at Š_c = 15 d and Š_H = 12 h in nitrification. Performance of denitrification stage was not satisfactory for feed NO₃-N concentrations above 150 mg N/l resulting in significant effluent NO₃-N levels at hydraulic residence time of Š_H = 6 h.     

Reactor kinetics for submerged aerobic biofilms

Sclerotium rolfsii ATCC 15205 was cultivated in continuous culture (48 l reactor volume) for scleroglucan production. The maximum volumetric productivity (Q_Pvmax) amounted to 7.2 g/ld and was more than twice as high as in comparable batchwise cultivations. In addition, the relation between (a) volumetric productivity (Q_P [g/ld]) and product yield (Y_{Glucan/Glucose} [1]), (b) volumetric productivity and product quality (M_W [g/mol]), and (c) product quality and impeller tip speed (Nd [m/s]) was studied in continuous culture. It was found, that an increase in volumetric productivity led to a decline in product yield and product quality. Furthermore, an impeller tip speed of >0.7 m/s decreased the attainable product quality considerably. Based on these results, the impact of the operational setpoint of the process in terms of oxygen supply and reactor scale on the economics of scleroglucan production was discussed. In contrast to batchwise cultivation, scleroglucan production in continuous culture proved to be not feasible under non-aseptic conditions.     

Joint aerobic biodegradation of wastewater from table olive manufacturing industries and urban wastewater

Wastewater generated in the elaboration of table olives has been treated using activated sludge from a municipal wastewater plant after adequate acclimation. To avoid bactericide properties of some chemical structures present in this type of effluents, synthetic urban wastewater has been used to dilute the original wastewater. The main parameters affecting efficiency of biological processes have been studied. Thus, initial biomass concentration, temperature up to 303 K (upper working temperature limit = 313 K) and initial substrate concentration exerted a positive influence on COD degradation rate. The optimum pH was found to be around 7, experiencing a slight inhibition on cell activity at pH 4. Under the experimental conditions investigated other parameters like polyphenol content, absorbance at 254 nm and total organic carbon were also reduced to some extent. Only nitrates amount was increased after the biological process took place. A kinetic model based on Monod equation was proposed and applied to experimental results. The maximum specific growth rate was calculated by means of the aforementioned kinetic model. The value of this parameter as a function of temperature was fitted to an Arrhenius expression, w_max = 9.43 2 10¹⁰ exp(72021/RT) h^у (R in J mol^у K^у283 K < T < 303 K, pH , 7-10).     

Flocculants effect in biomass retention in a UASB reactor treating dairy manure

The performance and biomass retention of an upflow anaerobic sludge bed (UASB) reactor treating liquid fraction of dairy manure has been investigated at several organic loading rates. Two identical UASB reactors were employed. The biomass of one UASB reactor (FBR) had previously been treated with a cationic polyacrylamide, the other reactor was operated as a control reactor (CR). At 3 and 2 days of HRT both reactors functioned similarly, but at 1.5 days HRT some differences were observed between both effluents. Mean COD(T) removal percentages were 83.4% and 76.5%; COD(VFA) values in effluents were 977 and 2682 mg l(-1) for the FBR and the CR respectively. The VSS initial value in both reactors was 25.66 g VSS, whereas after the experiment the quantities were 31.83 g VSS in the FBR and 23.18 g VSS in the CR reactors. Polymer addition resulted in a higher degree of biomass retention and better performance in the FBR reactor.     

Degradation of 4-chlorophenol in UASB reactor under methanogenic conditions

Treatment of simulated wastewater containing 40 mg/l of 4-chlorophenol (4-CP) was carried out in an upflow anaerobic sludge blanket (UASB) reactor under methanogenic condition. The performance of this test UASB reactor was evaluated in terms of 4-CP removal. Hydraulic retention time (HRT) and substrate:co-substrate ratio for the 4-CP removal was optimized by varying the influent flow rate (13-34.7 ml/min) and sodium acetate concentration (2-5 g/l), respectively. A control UASB reactor, which was not exposed to 4-CP was also operated under similar conditions. Organic loading rate (OLR) was varied in the range of 2-5.3 kg/m(3)/d and 1.7-4.2 kg/m(3)/d, respectively, for HRT and substrate:co-substrate ratio studies, respectively. The optimum HRT and substrate:co-substrate ratio for the removal of 4-CP was 12h and 1:75, respectively. Removal of 4-CP achieved at optimum HRT and substrate:co-substrate ratio was 88.3+/-0.7%. Removal of 4-CP occurred through dehalogenation and caused increase in chloride ion concentration in the effluent by 0.23-0.27 mg/mg 4-CP removed. The ring cleavage test showed the ortho mode of ring cleavage of 4-CP. Change in the elemental composition of the anaerobic biomass of UASB reactors was observed during the study period. Concentration of Ca(2+) increased in the biomass and this could be attributed to the biosoftening. Specific methanogenic activity of the sludge of control and test UASB reactor was 0.832 g CH(4) COD/g VSS d and 0.694 g CH(4) COD/g VSS d, respectively.     

Viable bacterial biomass and functional diversity in fresh and marine waters in the Canadian Arctic

Bacterial biomass and functional diversity in four marine and four freshwater samples, collected from Resolute Bay, Nunavut, Canada, were studied using fluorescent nucleic-acid staining and sole-carbon-source utilization. Viable microbial counts using the LIVE/DEAD BacLight Viability Kit estimated viable marine bacterial numbers from 0.7 to 1.8᎒⁶ cells/l, which were lower than viable bacterial numbers in freshwater samples (2.1-9.9᎒⁶ cells/l) (RCBD-ANOVA). Calculations of the Shannon-Wiener diversity index and average well colour development were based on substrate utilization in ECO-Biolog plates incubated at 4°C and 20°C for 38 and 24 days, respectively. The Shannon-Wiener diversity of the marine water samples was significantly greater ( x _H'=2.40ǂ.08, P <0.005; RCBD-ANOVA) than that of freshwater samples ( x _H'=1.20ǂ.00, P <0.005; RCBD-ANOVA). Differences in microbial diversity between fresh and marine water samples at 4°C ( x _4°C =2.01) and 20°C (x_20°C =2.31) were also detected by RCBD-ANOVA analysis. Interactions between water type and incubation temperature were not significant ( F =1.926, F _c=5.12). Principal component analysis revealed differences in metabolic substrate utilization patterns and, consequently, the microbial diversity between water types and samples.     

Anaerobic digestion of cheese whey using an upflow anaerobic sludge blanket reactor: III. Sludge and substrate profiles

Anaerobic treatment of cheese whey using a 17·5 litre upflow anaerobic sludge blanket reactor was investigated in the laboratory over a range of influent concentration from 4·5 to 38·1 g COD litre⁻¹ at a constant hydraulic retention time of 5 days. The results indicated that two sludge distribution regions, a sludge bed and a sludge blanket, as well as two distinct reaction phases, acidogenic and methanogenic, were formed. However, as the substrate loading was increased, the acidogenic region extended into the methanogenic region in the upper portion of the reactor until the whole region was acidogenic, leading to the failure of the reactor.     

Performance of upflow anaerobic sludge blanket (UASB) reactor treating wastewaters containing carbon tetrachloride

The anaerobic biodegradation of carbon tetrachloride (CT) was investigated during the granulation process by reducing the hydraulic retention time, increasing the chemical oxygen demand (COD) and CT loadings in a 2l laboratory-scale upflow anaerobic sludge blanket (UASB) reactor. Anaerobic unacclimated sludge and glucose were used as seed and primary substrate, respectively. Granules were developed 4 weeks after start-up, which grew at an accelerated rate for 8 months, and then became fully grown. The effect of operational parameters such as influent CT concentrations, COD, CT loading, food to biomass ratio and specific methanogenic activity (SMA) were also considered during granulation. The granular sludge cultivated had a maximum diameter of 2.1 mm and SMA of 1.6 g COD/g total suspended solid (TSS) day. COD and CT removal efficiencies of 92 and 88% were achieved when the reactor was firstly operating at CT and COD loading rates of 17.5 mg/l day and 12.5 g/l day, respectively. This corresponds to hydraulic retention time of 0.28 day and food to biomass ratio of 0.5 g COD/g TSS day. Kinetic coefficients of maximum specific substrate utilization rate, half velocity coefficient, growth yield coefficient and decay coefficient were determined to be 2.4 × 10^–3 mg CT/TSS day^–1, 1.37 mg CT/l, 0.69 mg TSS/mg CT and 0.046 day^–1, respectively for CT biotransformation during granulation.     

Microbial community composition and function beneath temperate trees exposed to elevated atmospheric carbon dioxide and ozone

We hypothesized that changes in plant growth resulting from atmospheric CO₂ and O₃ enrichment would alter the flow of C through soil food webs and that this effect would vary with tree species. To test this idea, we traced the course of C through the soil microbial community using soils from the free-air CO₂ and O₃ enrichment site in Rhinelander, Wisconsin. We added either ¹³C-labeled cellobiose or ¹³C-labeled N-acetylglucosamine to soils collected beneath ecologically distinct temperate trees exposed for 3 years to factorial CO₂ (ambient and 200 µl l^-1 above ambient) and O₃ (ambient and 20 µl l^-1 above ambient) treatments. For both labeled substrates, recovery of ¹³C in microbial respiration increased beneath plants grown under elevated CO₂ by 29% compared to ambient; elevated O₃ eliminated this effect. Production of ¹³C-CO₂ from soils beneath aspen (Populus tremuloides Michx.) and aspen-birch (Betula papyrifera Marsh.) was greater than that beneath aspen-maple (Acer saccharum Marsh.). Phospholipid fatty acid analyses (¹³C-PLFAs) indicated that the microbial community beneath plants exposed to elevated CO₂ metabolized more ¹³C-cellobiose, compared to the microbial community beneath plants exposed to the ambient condition. Recovery of ¹³C in PLFAs was an order of magnitude greater for N-acetylglucosamine-amended soil compared to cellobiose-amended soil, indicating that substrate type influenced microbial metabolism and soil C cycling. We found that elevated CO₂ increased fungal activity and microbial metabolism of cellobiose, and that microbial processes under early-successional aspen and birch species were more strongly affected by CO₂ and O₃ enrichment than those under late-successional maple.