The changes in biofilm physical properties and microbial activities with respectto acid production, acetate production, methane productions from H₂ and from acetate, wereinvestigated during initial biofilm formation in anaerobic fluidized bed reactor, at fourdifferent upflow velocities, i. e., 4, 7, 14 and 25 m·hr^-1. An initial biofilm formationdue to the direct adhesion of inoculum sludge onto the carrier surface occerred significantlywithin 1 to 2 days in runs at 14 and 25 m·hr^-1 and the biofilm thickness developed up to 200pm. Succeedingly to the initial adhesion, the biofilm thickness decreased eventually to100 μm with time, while the biofilm density increased gradually to 120 and 60 mg·cm^-3, forrespective runs. For a run at 4 m·hr^-1, the whole bed was occupied by granulated sludge, having a size ranging 1 to 5 mm and containing several carriers. The microbial activitiesfor all four items increased rapidly to 5 to 30 times those of inoculum sludge in all runs.When the larger upflow velocity was imposed, the more quickly those activities attained atthe respective saturation values. The biofilm activities, excluding in the item of acidproduction, rose up to 5 to 7 times as large as those sludge grown in a suspended system.

View full abstract

The objectives of this study are to evaluate the distribution of specific activity within attached biofilm in afluidized bed and to investigate the detachment of each “active” biomass from the biofilm. A fluidized bed was operated in asteady state as a methanogenic reactor with supply of a synthetic wastewater, a mixture of acetate, propionate, and butyrate.Batch experiments were conducted to measure the specific activities of biomass in effluent, stepwise sloughed biomass, andattached biomass in bed. The results indicated that the biomass in the surface layer of biofilm had much higher activity thanthat inside the layer. The highest activity was obtained for biomass in effluent. The distributions of the activities illustrated thatmore “active” biomass existed in the biofilm surface where more frequent detachment of biomass occurred.The trend of the activity distribution was explained by a newly developed model considering accumulation of inert biomassand biomass detachment from biofilm surface. A first order rate constant of detachment for each “active” biomass was roughlyestimated at 0.013, 0.022, and 0.055 [day^-1] for acetate, propionate, and butyrate decomposing biomasses, respectively. Theestimated values were much larger than literature values based on whole biomass. The model predicts that bacteria with highergrowth rates are able to exist predominantly in the surface layer against high biomass detachment and that the decay biomassmainly accumulates inside the biofilm.

View full abstract

Anaerobic digestion is an important process in the sewage sludge treatment systemby reason of sludge solid reduction, stabilization, and producing methane gas which is used asenergy source. This paper shows the result of basic study on CO₂ concentration control in thedigester gas for increasing methane gas production in the anaerobic digestion process ofsewage sludge.
The methane gas production increased at a rate of approximately 30-% in comparison withthat of the conventional process by controlling CO₂ concentration in the digester gas to 50 to60 v/v-%. It was supposed that the increasing of methane gas production was might be relatedto the acceleration of the biological decomposition of hardly decomposable carbohydrates inthe feeding sewage sludge, and to the existence of the biological oxidation-reduction reactionof sulfides in the sewage sludge digestion.

View full abstract

Effect of temperature and hydraulic retention time (HRT) on the characteristics of acidogenesis in anaerobic digestion were investigated using anaerobic chemostat-type reactor, which soluble starch was fed as a substrate.
The HRTs were 0.25d, 0.5d, 1.0d and 2.0d. The experimental temperature was changed in the rangefrom 10°C to 30°C. The degradation efficiency of the substrate and the composition of volatile fatty acids (VFA) produced in anaerobic acidogenesis were significantly affected by the temperature and HRT. The necessary HRT for obtaining the high degradation efficiency of 95% at the temperature ranges of 20°Cto 30°C and 10°C to 20°C were 1.0d and 2.0d, respectively. At the condition that the temperature ranged from 20°C to 25°C and the HRT rangedfrom 1.0d to 2.0d, the COD yields of various products to the influent substrate in the reactors ranged in the following percentage; VSS: 20 to 22%, VFA: 41 to 54%, Others: 9 to 30%, H₂: 6 to 12% and CH₄: 0.4 to 0.8%. The effects of temperature and HRT on the distribution of acidogenc bacteria, homoacetogenic bacteria, acetate-consuming methanogenic bacteria and H₂-consuming methanogenic bacteria were studied by enumerating the bacterial population levels. From this investigation, it was elucidated that the complete phase separation of acidogenesis and methanogenesis was possible by conducting the acidogenesis below the temperature of 25°C.

View full abstract

Polyphosphate rich anaerobic aerobic activated sludges were fed with acetate and/or propionate under anaerobic condition to produce polyhydroxyalkanoate (PHA), a biodegradable plastic. All the carbon sources anaerobically uptaken by the sludges were converted into PHA, and the maximum PHA accumulation in the sludges was 12% of the mixed liquor suspended solid. The amount and the composition of the accumulated PHA were affected by the composition of the carbon sources for the PHA production and that for the sludge acclimatization. All the sludges used in the present research produced 3-hydroxybutyrate rich PHA from acetate. Sludges acclimatized with substrates containing acetate and propionate produced PHA composed mainly of the same amounts of 3-hydroxyvalerate and 3-hydroxy-2-methylvalerate from propionate. But a sludge acclimatized with a substrate without propionate held little ability to produce 3-hydroxy-2-methylvalerate, and took up less propionate than the other sludges. All the sludges metabolized intracellular carbohydrates simultaneously with the anaerobic uptake of acetate and/or propionate, and converted not only the carbon sources but also the intracellular carbohydrates into PHA, except for a sludge acclimatized with a substrate containing lactate. The sludge had accumulated less carbohydrates, and converted less carbohydrates into PHA than the other sludges did.

View full abstract

Excessive growth of Phormidium tenue and musty odor due to it have been observedrecent years in lake Kusaki located in Gunma, Japan. Variations of the algal growth and water qualities in the lake were observed for two years, and investigated a possibility of forecasting the excessive growth from a simple ecological model with known parameters which were generally reported in former studies. The field surveys showed that distributions of temperature and nutrient concentrationswere significant in the vertical direction but not in horizontal, therefore, a vertical one-dimmensional mathematical model consisted of the heat and mass balance equations was used. The model fairly evaluated the seasonal changes in water qualities of TN, TP, TOC, and Chl. a as well as the thermal stratification and turnovers. Although some modifications of the model should be necessary to evaluatethe P.tenue population exactly. the growth pattern which had two peaks in earlyand late summer in 1990 were estimated reasonably well by assuming a maximum specific growth rate of 2.5 d^-1.

View full abstract

Effects of aeration on Coefficient of oxygen utilization rate of floated muddy sediments in the estuarine environment with aeration, and quiescent settling analysis of the muddy sediments were examined experimentally.In quiescent settling analysis of aerated SS of muddy sediments, over-all SS removal ratio and turbidityremoval ratio could obtain 96%, 88% each during 1 hour of settling time. Also, overflow rate was 60m³/m²·day. under this situation, scour velocity in SS of muddysediment was about 7cm/s in the case of D=0.0065m.

View full abstract

The coagulation characteristics of four kinds of suspension, such as Chlorella sp., Dictyosphaerium sp., Microcystis viridis and Kaoline, was discussed by the results of Jar test and photograph of Scanning Electron Microscope (SEM) and Energy Dispersive System (EDS). Although the turbidity of Dictyosphaerium sp. is the highest of the four kinds of suspension at the optimum Alum dosage, its zeta potential is -35mV and the smallest of the four kinds of suspension. From the photograph of SEM and the analysis of EDS, although Aluminium hydroxide insuffciently absorped on the surface of Chlorellasp., it stronglly absorped on that of Dictyosphaerium sp., Although the floc of Microcystis viridis and Kaoline was easy to be formed by sweep flocculation, the floc of Chlorella sp. and Dictyosphaerium sp. was easy to be formed by adsorption of Aluminium hydroxide on the algae surface. Therefore, the coagulant dosage of Dictyosphaerium sp. and Chlorella sp. becomes larger than that of Kaoline.

View full abstract

Three-dimensional numerical model that can predict the wind field and pollutant concentration in meso-scale was applied over the Osaka Plain. The surface temperature and specific humidity is determined by solving the surface heat budget equation including the effect of a vegetation layer.The vertical coefficients of momentum, heat and specific humidity in the surface layer are given by Businger's universal function and above it are obtained by level 2 model of the turbulence closure proposed by Mellor and Yamada. Pollutant concentration is simulated with the effect of dry deposition and photochemical reaction. This photochemical reaction model includes 11 species and 18 chemical reactions. The model simulation was carried out for two days, which assumed that it is fine on summer. The calculation results were compared with the observation data.In the daytime when the sea breeze significantly develops, the calculation values of the wind speed, the wind direction and S02, NO2 and NO concentration agreed relatively well with the observation ones.In the nighttime, except for NO concentration there wasn't a great difference between calculations and observations.

View full abstract

Pseudospectral Method is one of the methods to solve the partial differential equations numerically. Pseudospectral methods involve the expansion of the solution to a differential equation in high-order orthogonal expansion, the coefficients of which are determined by a weighted-residual projection technique. The main attraction of pseudospectral method is accuracy; however complex flow problems are typically difficult to solve. Several problems in practical solution of pseudospectral method for atmospheric diffusion equation are considered. The accuracy of Fourier expansion and Chebyshev expansion methods, FFT (Fast Fourier Transform) algorithm, the treatment of boundary condition and Gibbs phenomenon etc. are discussed, and the results of pseudospectral solution are compared with the results of analytical solution at steady state.

View full abstract

Influence of sulfate reduction on filamentous bulking in the activated sludge process was examined in two types of laboratory units. One is the conventional system and the other is the anaerobic-oxic system. When the units were operated with acetate, sulfate reduction occur in the oxic tank and filamentous bulking due to Type 021N occurred. However, in the high mineral conditions, Type 021N could not grow predominantly. When the units were cultivated with acetate and peptone, sulfate reduction occurs in the anaerobic tank and/or settling tank. Sulfate reducing bacteria did not utilize acetate. They utilized organic acids or amino acids similar to lactate produced from peptone and decomposed biomass. Sulfate reduction could be a cause for filamentous bulking due to Type 021N which could utilize sulfide as energy source.

View full abstract

De composition of organic substances, nitrification and denitrification occur consecutively in a completely mixing type reactor of activated sludge process.
These phenomena were demonstrated by modelling the reaction of microorganisms from the point of view of the chemical thermodynamics. The standard oxidation reduction potentials (ORP) for decompositions of the organic substances are minus at pH 7.0. The ORP for nitrification was 430 mV and that for denitrification was 747 mV at pH 7.0. Then, the organic substances may be sufficiently decomposed under the foregoing ORP level for nitrification. And if the potential of the system is maintained between these two values, both nitrification and denitrification may be occured simultaneously. Thus, the ORP is an important index for the simultaneously proceeding of nitrification and denitrification in a completely mixing type reactor.

View full abstract

Operational conditions, in solid-liquid separation, of a cross-flow type ultra membrane filtration system were experimentally examined to make a proper formulation of permeation flux.
Pure water with and without selected constituent substance such as polyethylene glycol and activated sludge as used as water sample.
Pure water was used to obtain the basic information of filtration. Permeation flux as well as membrane resistance (Rm) was affected predominantly by applied pressure to the filter (P). Rm was increased consistently according to the increase of P and formulated as a function of P. The other samples showed various behavior of the flux and filtration resistance. The resistance caused by cake-layer and/or gel-layer (Rcg) was obtained by reducing Rm from the filtration resistance and formulated by substance weight attached on unit filter surface area, compression factor (n) of the attached substance and P. The permeation flux was satisfactorily expressed by introducing Rm and Rcg, and the behavior of it to P was explained by the magnitude of the compression factor (n).

View full abstract

The foulings of membranes are very serious problem. in activated sludge processes.
In this paper, the extracting and seperation methods of the fouling substances have been examined and discussed when the ultrafilter membrane was applied to the activated sludge process for artificial night soil.
The fouling of membrane occ ured both on the surface and in the pores. The fouling substances were extracted into phosphate buffer solutions or interfacial active agents. Biochemical substances were detected with liquid chromatography at 215 nm of UV. The biochemical substances on the surface of membrane are probably peptides with thousands of molecular weights and the glycoproteins with millions of molecular weights. And the biochemical substances in the pores of membrane may be similar to the peptides on the surface.

View full abstract

An automatic measuring system to monitor the filtration and backwashing process of cross flow type ultrafiltration was developed using a personal computor. Using this system and Kaoline suspension, we discussed the backwashing effects by initial concentration, filtration cycle number, filtration time, backwashig time and backwashing pressure. Separating the cake layer from the membrane was occured in a 0.6sec at least and the change of the backwashing effect is not large with the increase of the backwashing time. Although backwashing effect decreased with the increase of filtration time and initial concentration of Kaoline suspension, and with the decrease of backwashing pressure and backwashing time, the effect of separating cake layer from the membrane is not large.

View full abstract

Laboratory experiments using sequencing batch reactors have been carried out on the cases of both constant substrate feeds consisting of approx. 800mg and 400mg respectively of TOC supplied in a cycle, and varied substrate feeds consisting of either approx. 800mg and 400mg of TOC supplied continuous three times each in a day. The stoichiometry on the nitrified liquor re cycling process was studied from the behavior on carbon and nitrogen compounds variations during the biological treatment operation.
The stoichiometric equations for anoxic stage were proposed on the denitrification reaction with cell synthesis using the parameters of carbon atom (C) and hydrogen molecular (H₂) as well as endogenousrespiration reaction using nitrate-ion (oxygen atom). It was found that these two reactionswere occurred simultaneously. The occurrence ratios of denitrification reaction to endogenousrespiration reaction were approx. 5.5 to 1 at the cases of higher and lower constant substratefeed tests and lower varied substrate feed series, while the reaction was approx. 2.9 to 1 atthe case of higher varied substrate feed series because of non-competitive inhibition in thedenitrification reaction. A stoichiometric equation for oxic stage was proposed on the nitrificationreaction with cell synthesis. It was found that this reaction was occurred with theendogenous respiration reaction simultaneously. The occurrence ratio of nitrification reaction toendogenous respiration reaction was approx. 12.5 to 1 at the cases of higher and lower constantsubstrate feed tests, while the ratio was approx. 15 to 1 at the case of lower varied substratefeed series.

View full abstract

A sequencing batch reactor operating by nitrified liquor recycling process has been added 10% of poly-urethane form sponge cubes (size 12×12×15mm) as a biomass support medium to the reactor. The laboratory experiments using artificial sewage have been carried out to collect the data of effects on biomass support to the sponge cubes vs. mixing intensity magnitude in the reactor. And, the nitrification and denitrification coefficients have been measured comparing to a suspended growth reactor as controlled.
The mixing intensity magnitude of biomass attached sponge cubes in suspension was almost same as the magnitude of 3g per litre of mixed liquor suspended solids in suspension in the controlled reactor. The dry weight of attached biomass in the cubes was fluctuated depending on the magnitude of mixing intensity. Approx. 22g of biomass in a litre of cubes was yielded from 112 sec^-1 of the G-value, while approx. 10g in a litre was from 560sec^-1 in the reactor. It was found that the magnitude of mixing intensity had influence upon the biomass attached depth in the cube. A space of extremely little biomass attached in the cube was yield near core when 560sec^-1 was given as the G-value, while abundant biomass was found not only in subsurface layer but also at core when 112sec^-1 was given in the reactor. At the range of 14 to 26°C of water temperature, the denitrification and nitrification coefficients were 0.9 to 3.6 mgN·g^-1VSS·h^-1 and 1.2 to 3.4 mgN·g^-1VSS·h^-1 respectively at the reactor and they were exceeded 64% and 52% respectively than those of controlled reactor.

View full abstract

Factors affecting nitrogen removal by filtration - contact aeration process wereinvestigated using a pilot plant which treated 4.1 m3/d of municipal wastewater. Hydraulicretention time was 12 hours and 100% volume of treated wastewater was recircurated to the inletof contact aerator. Whereas effluent BOD and suspended solid (SS) were less than 20mg/L, nitrogenremoval rate was about 30%. Temperature, dissolved oxygen (DO), oxidation-reduction potential (ORP), and BOD were shown to have effects on nitrification and the following operationalguidlines of nitrifying vessels were proposed to meet an effluent nitrogen criteria of 10 mg/L;(1) temperature > 10 °C, (2) DO > 3 mg/L, (3) ORP > 80 mV, (4) BOD < 10 mg/L.

View full abstract

The single basin & high-load biological denitrification system with alternative aeration is an excellent system which consists of simple components & performs flexible operation. Usually indirect parameters such as DO, ORP & p H etc.have been used to control denitrification reactors. The authors tried to monitor NH4-Nin a reactor by using newly developed automated analyzer combined with UF sampler, & then tried to control the operation of a denitrification reactor by using fuzzy inference. The fuzzy control system infers a suitable condition from multi-variables (NH4-N, DO, ORP & p H) obtained in an actual process. The fuzzy control system performed quick response & high nitrogen removal with stability & easy maintenance.

View full abstract