The two methods of water elimination, centrifugation and air-drying, from sediments (river, lake, marine) were compared for analytical variation to establish sample preparation methods. Fourteen analytes elements (4 determinations × 10 points) were tested for this purpose.
Mean analytical values of lead, moisture content, cadmium, mercury and COD_sed for some of sediment samples differed by more than 10% between two methods.
The t test results indicated that copper, COD_sed, pH and moisture content had significant differences between two methods at the 5% level.
Coefficients of variation of lead, cadmium and COD_sed in centrifuged method became often greater than 10%. This is because mixing of centrifuged sediment after water elimination is difficult. On the other hand, low coefficients of variation in air-dried sediments were obtained because of easy mixing.
Therefore, air-dried sample is superior to centrifuged sample with regard to homogeneity and handling.
Air-drying for a day was sufficient practicaly.

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An estimation method of decay coefficients of anaerobic bacteria involved with methanogenesis is experimentally discussed from the aspect that decay phenomena have an important role in biofilm development and its composition.
Attached biomass in a methanogenic fluidized bed was collected and incubated for more than 100 days without any substrate addition. During the incubation, batch tests of substrate consumption were conducted to estimate each concentration of “active” biomass which decomposes acetate, propionate or butyrate. The growth increment in bacteria during the batch tests was taken into consideration, when the “active” biomass concentrations were estimated. In addition, the biomass concentrations were corrected by subtracting biomass increment due to the production of fatty acids from decomposition of biomass decayed during incubation. Neglecting the increments of the biomass during the batch tests and incubation caused a significant error in the estimation of decay coefficients.
The decay cefficients of acetate, propionate and butyrate decomposing bacteria were estimated at 0.014, 0.015 and 0.024 [day^-1] , respectively, based on the decrease in “active” biomass concentrations with incubation time. The coefficients are available to investigate the accumulation of inactive biomass in the anaerobic biofilm.

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Raw sludge from a wastewater treatment plant was anaerobically digested by utilizing ultrafiltration (UF) membrane separation in laboratory-scale experiments. Biomass, undigested solids and high molecular weight organic matters were accumulated in the reactor until they were digested to low molecular weight substances. COD of permeate from the UF membrane had been less than 300mg·l^-1 during more than 100 days of operation. MLSS concentration in the reactor varied from 10,000 mg·l^-1 depending on VSS loading rate and temperature.
Organic substances in the sludge were almost all converted into biogas. Inorganic solids in the sludge were dissolved into liquid phase through a biological reaction and then passed through the membrane preventing the accumulation of solids in the reactor.

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Acid-effluent containing salt was treated by diffusion dialysis (DD) and acid retardation (AR), and the effect of co-existing salt was discussed.
Acid permeate through membrane preferentially, and nitric acid removal rate was greater than those of other acids in DD.
Salt was eluted faster than acid in the case of nitric acid and sulfuric acid solution system in AR. But good separation was not obtained in the case of hydrochloric acid solution system.
Salt enhanced the elution peak height of nitric acid in AR and the removal rate of acid in DD. This effect was explained by the fact that the amount of acid adsorbed by anion exchange resin in the presence of salt was more than that adsorbed in the absence of salt.
Sulfuric acid enhanced the concentration of salt in the elution front. This suggested that anion exchange resin adsorbed cupric sulfate and ferric sulfate in neutral and slightly acidic condition.

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