The effluent from olive mill plants (OME) presents a seasonal problem, as although small in volume it has very high organic content, and in consequence it is particularly difficult to meet Italian law discharge limits. This problem has been carefully studied in Apulia where, during the olive milling season, organic pollution exceeds that from domestic use by a factor of three. Preliminary research allowed the estimation of organic load per ton of milled olives, and the comparison of the effectiveness of feasible treatment processes. The results have been utilized in the Water Reclamation Plan of the Apulia Region (WRP). This Plan permits the discharge of OME into public sewers only when its contribution is less than 20% of urban wastewater's (UW) organic load, or provides the transport of a controlled amount to treatment facilities, over a period ranging from 100 to 300 days. Results of full-scale and pilot biological treatment plants for combined UW and OME effluents are reported, together with the main project parameters. Anaerobic processes are more economical but their successful operation needs to be confirmed on full-scale plants.