Abstract
Environmental regulations for dairy farms and milk-plants tend to be tightened in Asian countries, particularly in Japan, because the milk-including wastewater discharged from them causes serious regional environmental problems. For small and medium-sized dairy farms and milk plants, we propose a novel process of using ozone which has very strong oxidative power. This proposed process is different from conventional treatment processes with ozonation, and rapidly reduces BOD, TOC, total nitrogen (T-N) and chromaticity of the wastewater containing milk. This new ozonation process imposed partial polymerization of the unsaturated fatty acids including carbon-double bonds as well as simple decomposition of the above acids into low molecules. Whitish solid-like products formed from the polymerized fatty acids (i.e. ozonide) and the insoluble proteins were adsorbed to the ozone bubbles. The solidification and purification efficiency of this process depended on the initial condition of the milk-containing wastewater. Thus, we propose a two-stage process against this wastewater treatment method. Under an acid initial condition, the ozonation increases yield on the solid-like products which are compounded from the polymerized fatty acids and the insoluble proteins. When these solid-like products were removed from the wastewater, the pollutants (i.e. BOD, TOC, T-N and chromaticity) in the wastewater were decreased almost simultaneously. Accordingly the water quality was improved in a short time. The ozonation under an alkaline initial condition with a low temperature also improved the water quality, despite the fact that the yield of the solid-like products was small. In this condition, the solubility of the ozone was higher than that under the high temperature condition, hence the OH-radicals generated from the ozone were enhanced in the alkaline condition and decomposed the pollutants powerfully. These two reaction pathways depending on the pH and temperature were strongly related to the decomposition of the pollutants by ozone. Thus, the ozonation under an acid condition is more useful for small and medium-sized dairy farms and milk plants, because they do not need the control of the wastewater temperature under an acid condition.
