[Liquid hospital waste]

Hospital sewage is distinct both from that of industrial origin and that from human housing, and is unique from the qualitative and quantitative standpoints. In fact the hospital is clearly different from a residential setting for the addition of technological activities, which are realised inside it, and it is not comparable to a traditional productive complex, because of the extreme variability--from one hospital to the other--of the presence of activities themselves, and this means important quali--quantitative differences of sewage produced from case to case. After all, the hospital cannot be compared to a centre of tertiary activities, which has, as regards sewage, the characteristics and the constancy of great inhabited places. Actually, its daily amount per patient is up to 1,000 L (3-5 times more than a standard citizen), because hospitals include, besides patients, physicians, nurses, technical and clerical staff and, for "teaching hospitals", also professors and students; in addition, the sewage from hospitals is composed of standard human sewage, plus: discharges from laboratories and technical equipments; drugs and their metabolites; disinfectants; and microorganisms, which are often characterized by the presence of antibiotic resistance of "infectious" nature (i.e. transmitted by resistance plasmids). Such contaminants are not evenly generated, but focal points in the hospital and given hours during the day can help to identify where and when most of each contaminant is produced. A special problem arises from the interference of contaminants in hospital sewage on activated sludge plants; another is connected with the presence of toxic substances originated from biochemical laboratories, but the concentration of such substances appears to be lower than that tolerated according to the italian regulations.