Struvite precipitation and COD reduction in a two‐step treatment of olive mill wastewater

BACKGROUND In the present work, a combination of several physicochemical methods has been applied aiming at recovering phosphorus from olive mill wastewater (OMW) in the form of struvite (NH4MgPO4·6H2O, MAP) and at the same time achieving reduction of the chemical oxygen demand (COD) of the wastes. Phosphorus is a valuable raw material used for the production of fertilizers and numerous other products. RESULTS The experiments were conducted in a two-stage process, over a pH range between 5 and 10. The first step consisted of a batch process, in which MgCl2 or MgSO4 were used as coagulants of suspended particles of the OMW. During the second step, a nitrogen source (NH4OH(aq)) was added to the supernatant and solid precipitation took place without delay. The measured COD values of the fluid phase of the OMW was reduced by up to 73% of the initial value, while the final crystalline product consisted of a mixture of struvite and dittmarite (NH4MgPO4·H2O). CONCLUSION Over 90% dissolved phosphorus recovery from OMW samples in the form of struvite was achieved through the application of a two-step process together with a significant reduction of the COD of initial raw wastewaters. © 2017 Society of Chemical Industry