Effects of daily variation of flow and accumulation of suspended solids on the performance of submerged anaerobic/aerobic biofilm systems were investigated by laboratory study using synthetic wastewater and by field study using grey water.
The concentration of dissolved organic carbon (DOC) in effluent from anaerobic filter did not change corresponding to the change in flow both in laboratory and in field study when daily average hydraulic retention time in anaerobic filter (HRTa) was 20 h. In field study, however, percent removal of DOC by anaerobic filter was considerably smaller (20-30%) than that of laboratory study (90-95%) at HRTa of 20 h. The low percent removal of DOC by anaerobic filter was caused firstly by organic release from suspended solids accumulated in the anaerobic filter and secondly by channering flow with the accumulation of the suspended solids. Nitrogen release from suspended solids was also observed in anaerobic filter

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Changes in pollutant loadings during the flowing-down of a river joined by five tributaries were estimated. The estimation involved flowing-down rates and inclusive self-purification coefficients observed weekly during one year period. The flowing-down rate of pollutant loading was obtained for three cases : (1) high water days ; (2) low water days ; and (3) both. Generally, the flowing-down rates for almost all water quality indicators in high water days were greater as compared with those in low water days. However, the flowing-down rates for NH₄-N Org-N, and PO₄-P, which are mainly drained out from point sources, showed the opposite tendency. The pollutant loadings of NH₄-N, org-N, and PO₄-P are known to account for a greater portion of the annual total loading during dry weather runoff than do during stormy weather runoff.
The flowing-down rate became nearly 1.0 when the river discharge became more than about 5.5 m3·s^-1. The self-purification coefficient, k, was estimated for water quality indicators related with organic matter by using the first-order equation of Streeter-Phelps. In most cases, the k values were greater in low water days than those in high water days ; however, the k values for TOC, DOC, T-N, and DTN exhibited the opposite tendency.

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A model of the mechanism of phosphate release from lake sediments was proposed and its validity was examined experimentally.
The complex process of phosphate release from sediments was assumed to be composed of three elementary processes : oxygenation of Fe(II) to Fe(III), formation of ferric hydroxides and adsorption of phosphate to ferric hydroxides. The model was examined experimentally by studying the transient behaviors of ferrous iron, ferric iron and phosphate concentrations and that of redox potential. The experimental results agreed with the calculated results assuming the oxygenation kinetics of Fe(II), the solubility product of ferric hydroxides and the adsorption ratio of phosphate to ferric hydroxides.
It suggests that the mechanism of phosphate release from sediments can be quantitatively described by our model. The difference of phosphate release rate under aerobic and anaerobic conditions can be also explained by our model considering the dependence of oxygenation rate of Fe(II) on DO.

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Nitrification of total Kjeldahl nitrogen (TKN) by an activated sludge process with cross-flow filtration was examined by using an artificial organic wastewater. To determine the maximum nitrification rate of the reactor, the TKN loading was increased by adding ammonium sulfate to the influent. The step increase rate of the TKN loading was smaller than that had been in a similar experiment with the same influent BOD concentration in the previous work. The nitrification rate reached 0.59gTKN·l^-1·d^-1, which was twice higher than the maximum value obtained in the previous work. The result indicates that a smaller rate of the step increase of the TKN loading is required to make the nitrification rate of the reactor higher, especially when the nitrification rate of the reactor is higher.

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