Measures taken against water pollution in dairies and milk processing industries.

Dairy waste, more than any other trade waste has long since attracted the attention of specialists in the field of waste water purification. Many experiments have been made with artificial waste water, made from milk or milk products. Dairy wastes provide an excellent nutrient medium for many types of bacteria and fungi and, contrary to opinions held at one time, are very amenable to aerobic biological treatment. The rapid oxygen consumption of dairy waste is, on the other hand, a disadvantage. Discharge into public water will lead to lack of oxygen, much quicker than in the case of domestic sewage. Anaerobic conditions can be observed in small streams at a short distance from the point of discharge. Dairies discharging effluent into local sewers must generally comply with requirements as to volume and strength of the waste in order to safeguard the purification plant. The need for purification of domestic sewage and trade wastes is obvious in almost every country in the world. The efforts made to reach or safeguard a healthy milieu are, generally speaking, very expensive. Sometimes they hardly seem economical. It is therefore of the utmost importance for industry to reduce the pollution load to the bare minimum, thus lowering the purification costs. Many countries now have their laws which enable the government or local authorities to require purification up to certain standards. This may be done in plants built and run by the individual factory, in those cases where discharge into a public sewage works is impossible e.g. through distance between factory and works and the absence of a sewerage system. In an increasing number of cases however, private purification will be more economical. The tax tariffs rise due to higher purification standards required and to growing investments and labour costs. The industry can derive profit from low energy prices for their plants, by using existing laboratory and technical workshop facilities and from certain tax facilities in the capital costs. These and the fact that dairy waste is nonpathogenic and non-toxic can explain that all over the world dairy waste treatment plants can be found ranging from simple sedimentation plants up to advanced waste treatment systems, eventually with re-use of effluent. The methods generally used for aerobic biological treatment are filtration and activated sludge.Filtration only gives a reliable performance in the modification of alternating double filtration, popular especially in the United Kingdom. Filtration by means of plastic media can be used as a roughening treatment prior to full biological treatment. The conventional activated sludge system may produce an acceptable effluent but needs considerable care in maintaining a good quality sludge. The extended aeration process,