Companies handling their wastewater disposal through a disposal contractor collect their wash waters, emulsions, coolant/lubricant emulsions, tank cleaning residues, oil-polluted wastewaters, oil-water mixtures etc. in storage tanks on their premises and keep them there until they are picked up. These various wastewaters often end up being mixed in the process. Processing of the wastewater is done by the disposal contractor. They often employ vacuum evaporators to concentrate the wastewaters. The resultant concentrates can then be disposed of cheaply by the disposal contractor. The many valuable substances often found in wastewaters are often recovered by the disposal contractors, providing them a source of additional income. The costs savings for the customer provided by the low personnel costs are more than offset by the costs of even small amounts of wastewater. The disposal costs quickly reach a critical point at which this process becomes too expensive.