Olive oil mill wastewater, called alpechin, has so far been discharged into lakes, rivers, and on land throughout the Mediterranean region for a long period of time. The danger to the environment lies in that alpechin consists of a large amount of toxic organic and inorganic constituents, such as phenol derivatives. As governmental laws become stricter by forbidding the uncontrolled release of wastewater into the environment, now the majority of alpechin is stored in man-made pools and allowed to naturally degrade and evaporate. Nevertheless, this method still constitutes a significant environmental problem. As 95% of olive oil is produced in the Mediterranean region, the subsequent waste reaches levels of about 10 million cubic metres per year. Another olive oil mill waste product, alpeorujo, compounds this problem. Although a variety of experimental waste treatment processes have been attempted, they have not been implemented successfully. On the other hand, the COOP (Cleaner, controlled and cost efficient olive oil production) project partners from Germany, Spain, Italy and Greece successfully designed an innovative technology that is not only economically feasible, but is also effective in the cleaning of liquid wastes from olive oil mills. Specifically, COOP based the method's design on the study of physical, chemical and biological analyses of effluents, while laboratory studies created a procedure that brought together chemical and physical pre-treatment steps along with a biological process. At a lab-scale miniplant installation, a 97% removal of total organic carbon was attained. Furthermore, the entire method generates a minimum quantity of solid waste that can be disposed of in a way that is environmentally safe. Also, biogas production occurs within the process which benefits energy savings and results in the decrease of the cost of the entire treatment method. It is important to note that the cleaned water is recyclable and could be utilised within olive milling production to wash the olives so as to use much less fresh water. Subsequently, two modular bio-reactor plants were developed and manufactured for installation at two COOP partner mills in Spain and Greece. Treatment process steps were comprised of the separation of solids, adsorption, anaerobic degradation, aerobic degradation, and clarification through filtration. Finally, the treatment process degraded alpechin at a 99.4% efficiency rate, while alpeorujo was degraded with a 93% efficiency rate. In addition, it was found that this biological treatment method is feasible in terms of cost compared to other olive mill waste treatment processes, while the total cost to run a test installation was about 7.67 Euro per cubic metre of processed alpechin. This cost, along with the appropriately priced COOP bio-reactor plants could make this technology widely marketable, especially as a market research study showed that the olive oil mill industry demands improved treatment methods that are environmentally friendly.