Technical and economic impact of photocatalysis as a pretreatment process step in olive mill wastewater treatment by membranes

In this work, the technical and economic benefit of using photocatalysis as a pretreatment step for a subsequent olive mill wastewater (OMW) treatment process by membranes will be discussed. Membrane processes appear to be suitable to purify aqueous wastewater streams polluted by organic matter such as OMW, but suffer severe fouling. In order to avoid fouling, the use of operating conditions below the boundary flux are suggested. The problem is that in many cases, boundary flux values are extremely low, making the process economically not feasible. In order to overcome this limitation, pretreatment steps are necessary to increase boundary flux values accordingly. Photocatalysis appears to be capable to achieve these requirements: on one hand, the process is capable to reduce the organic load of the feedstock and on the other hand, particle size distributions of the suspended organic matter are changed. Both principles are known in literature to lead to boundary flux value changes. In this paper, the authors report the obtained results of the experimental work concerning membrane performances with and without photocatalysis as a pretreatment step, by treating 2-phase and 3-phase olive mill wastewater streams from Spain and Italy, respectively; furthermore, the economic impact of the different design choices and the evaluation of the general process scheme will be reported in all cases.