Using heated volcanic ash soil with ferrous sulfate that adsorbed phosphoric acid ions, phosphorus regeneration is experimentally examined, and the reuse of used phosphorus adsorbent is investigated. The phosphate adsorption quantity of the used phosphorus adsorbent is high, similar to that of phosphate rock. The phosphorus adsorbent pattern is aluminum-type phosphorus > iron-type phosphorus > calcium-type phosphorus. The ideal desorption liquid for used phosphorus adsorbent is sulfuric acid solution. It completely (100%) desorbs phosphate, but needs a sixfold increase in the amount of what to regenerate phosphate. Additionally, the effect of volcanic ash soil on the growth of Brassica campestris cv. komatsuna is investigated using used phosphorus adsorbent, and the reuse of the adsorbent in agriculture is also discussed. The application of used phosphorus adsorbent to the subsoil of andosol facilitates the growth of komatsuna; this effect is higher than that of superphosphate application. Therefore, used phosphorus adsorbent offers promising advantages for reuse in agriculture.

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The mathematical model of biofiltration which was developed for the treatment of precoagulated sewage from a grid chamber is applied to explain the experimental performance of a biofilter used for tertiary treatment of secondary effluent. Its applicability is discussed by comparing the results simulated using the model with the experimental data. This model can favorably estimate the 525-day treatment performance, biomass concentrations and details of water-quality profiles through the filter bed in continuous treatment without changing any parameters of the proposed model, including rate constants, half-saturation concentrations and yield coefficients. Then some design and operational parameters are discussed referring to this model. Under large fluctuation of nitrate concentration in the filter, McCarty's equation can be used to determine the appropriate amount of methanol to be added. The maximum ammonium nitrogen loading rate in the nitrification filter is shown to be 0.55 kgN·m^-3·d^-1 in winter. Also, the maximum nitrate nitrogen loading rate in the denitrification part of the polishing filter is shown to be 5 kgN·m^-3·d^-1 in winter. The developed model is proved to be a promising tool for discussing the design and operational parameters of full plants.

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MRP soil washing is physical-chemical separation based on mining and mineral processing principles for removing a broad range of organic and inorganic contaminants from soil. Generally, contaminants reside and are concentrated in a fine fraction. Grain-size distributions and load curves (contaminant distributions) of feed soil are studied to understand and characterize the soil particle/contaminant relationship. A small amount of contaminated fine particles is separated to the underflow (sand fraction) due to the misplacement of a hydrocyclone. Flotation is very useful for removing contaminated fine particles that remain in the cyclone underflow. In a flotation unit, contaminated particles are selectively made hydrophobic by modifying their surface properties with selective reagents. The hydrophobic particles attach to air bubbles and are carried to a froth layer. The separation of these contaminated particles is achieved by removing the froth layer. The separation of contaminated soil particles is investigated in a large-scale plant to understand the performance and validity of the hydrocyclone and flotation unit. A mathematical model that considers both the contaminant concentration ratio of the froth layer and the amount of froth is introduced and used in evaluating the removal efficiency of flotation.

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