Pic. 1: VACUDEST Clearcat system for the processing of oil containing process waters Treatment of oil containing wastewater in the metal processing industry: Comparison of different process technologies Variety of process technologies In the metal processing industry big amounts of waste water like die casting emulsions, vibratory grinding and rinsing water as well as cutting and drilling emulsions (coolants) accumulate on a day to day basis. This water usually contains contaminants preventing disposal into public sewer systems or watercourses without prior treatment. To meet disposal limits reduce amount of waste water or even realize zero discharge production a wide range of different process technologies are available on the market. Chemical physical acid cleavage Acid cleavage is a treatment separating the waster water into an oily and a watery phase. The following process steps are required: Separation of floating oils Filtration of solids Acid cleavage of the emulsion Separation of the oily and watery phase Widely used are chemical physical acid cleavage systems as well as membrane systems or treatment with vacuum distillation systems. Due to corrosivness of used chemicals during acid cleavage often special materials are required when constructing the plant. Prior to disposal into public sewers or watercourses The acid cleavage is obtained by adding of a variety of chemicals. It is of particular im portance to dose the chemicals with care and in the right amount to achieve optimum re sults.

the treated water needs to be neutralised, thus in addition to the acid cleavage chemicals leach is required. The treated water is high in dissolved mineral salts, thus recycling respectively zero discharge is hardly possible. Currently new de emulsifier agents are available on the market; however they must be added with care and exactly in the right amount, thus the process is difficult to handle if process water composition fluctuates. Chemical physical acid cleavage systems become more feasible if the amounts of water to be treated are bigger than 3 m³/h. Then investment is lower compared...

heat pumps or direct vapour compression to recover energy. Heat pump evaporators Heat pump evaporators work at a under pressure of about 40 80 mbars. Under this condition water is evaporating at 30 45 °C. Energy recovery between condensing distillate and incoming process water is ensured by a separate refrigeration circuit. Process water is heated by the condenser of the refrigeration circuit. The steam developing in the system is condensed by means of the refrigeration circuit in the upper part of the system. Distillate is collected and pumped to external distillate receivers. The main disadvantage...

hotter than 100 °C, will condensate in the heat exchanger. The condensation energy is used to evaporate the waste water being fed into the system. Thus no external heating system is required. The condensation energy of the steam is sufficient to heat and evaporate the waste water. The only energy consumer in the evaporator is the vacuum pump, using about 45 – 60 Wh/l. This energy consumption is by 5 times lower compared to heat pump systems. The disadvantage of conventional vapour recompression evaporators is the necessity of post treatment of the distillate with coalescence absorbers or active...