To solve the problem that a large amount of an ether-based solvent is uneconomically consumed because at least 160 wt% based on a volume reduction-treated waste polystyrene foam is contained in recovered polystyrene gel in the volume reduction treatment process of the waste polystyrene foam which comprises reducing the apparent volume of the waste polystyrene foam into about one fiftieth by causing the waste polystyrene foam to chemically react with the ether-based solvent to convert it into the polystyrene gel which has the properties of deaerating, shrinking and floating, and recovering the polystyrene gel floating on the ether-based solvent.
In the volume reduction treatment process of the waste polystyrene foam, the consumption amount of the ether-based solvent is reduced by about 40% by installing an apparatus for squeezing the polystyrene gel before recovering the polystyrene gel floating on the ether-based solvent.
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