Treatment by acid chemical precipitation of olive mill wastewater

The management of effluents from olive oil production has been conducted by applying various physiochemical and biological treatments, as well as the use in the soil. However, the most commonly used mechanism remains lagoon storage and natural evaporation during the hottest periods of the year. Thus, this work aimed at studying the characterization and treatment of wastewater from olive oil production. In this context, raw wastewater samples were collected from an olive mill with two-phase continuous system, located in the Baixo Alentejo region. These effluents presented acidic properties, with pH between 4 and 5, dark color, intense and unpleasant odor, chemical oxygen demand (COD) between 7000 and 8000 mg L-1, average nutrient contents in calcium of 211 mg L-1, magnesium of 74 mg L-1 and phosphorus of 1050 mg L-1. In addition, these wastewaters had an average electrical conductivity of 2.7 dS m(-1) and a total phenols content of 540 mg of gallic acid equivalents L-1. The treatability tests consisted of the application to raw effluent of acidic chemical precipitation processes under different conditions. This process allowed the clarification of the effluent with maximum removal of turbidity and phosphorus of about 97 and 37%, respectively. Similar results were obtained in the reduction of absorbances at 254 nm (23%), 410 nm (57%) and 600 nm (96%). The final effluent had a content of magnesium between 1070 and 2130 mg L-1, with an increase in the electrical conductivity as a function of pH decrease.