Combination of physicochemical operations and algal culture as a new bioprocess for olive mill wastewater treatment

Abstract

This work presents a new bioprocess design which allows a substantial reduction of organic and inhibitory compounds and a better quality of the final treated water. The process involves a physicochemical (primary) and a biological (microalgae) treatment, which were tested separately with lab equipment, for olive oil mill wastewater (OMW). Primary treatment of OMW involved flocculation-sedimentation by Flocudex CS-51 and microfiltration using a 0.2 μm membrane. Secondary treatment consisted of Scenedesmus obliquus culture in different OMW dilutions in ultrapure water as culture media: 5, 10, 25, 50, 75 and 100%. Experiments were performed on a laboratory scale in stirred batch tank reactors. The common operating conditions were: pH = 7, temperature = 25 °C, agitation rate = 3.33 Hz, aeration rate = 0.5 min−1 and illumination intensity = 359 μE m−2 s−1. High global removal levels were achieved after primary treatment for chemical oxygen demand (92.6%), total phenolic compounds (98.9%), total organic carbon (75.9%), total nitrogen (63.5%) and inorganic carbon (55.3%). Similar results were obtained for the main OMW constituents after secondary treatment with final harvested biomass rich in energetic compounds, where the highest values of carbohydrates (72.5%) in culture with 5% OMW and lipids (44.9%) in 100% OMW culture were determined.