Recovery of Fatty Waste from Wastewater Treatment Plants through Anaerobic Codigestion: Improvement of the Agronomic Potential of Digestates

Abstract

In the context of increasing effluent production, anaerobic digestion has been identified as a promising solution for waste treatment in a sustainable development approach. This study developed a process for treating fats from wastewater treatment plants, which are mainly composed of triglycerides and free fatty acids. Anaerobic co-digestion of these fats with suitable sludge dilutes the toxic substances and optimizes the carbon/nitrogen ratio, thereby increasing biogas production. The best yields are obtained with an addition of 30% fat for fresh sludge and 45% for biological sludge. From an agronomic point of view, the digestates obtained are rich in ammonium and  phosphorus, but low in potassium, suggesting a potential use for crops, but requiring further study. The digestates have interesting average concentrations of ammonium (NH4⁺) ranging from 322.5 mg/L to 530 mg/L, and total phosphorus (TP) from 159.99 mg/L to 677 mg/L, but low levels of potassium (K⁺) from 0 mg/L to 1.03 mg/L. Effluent management presents several complex challenges. Anaerobic
digestion is a sustainable solution that captures and converts methane into biogas, a renewable energy source that reduces the impact on the climate. This biogas can be used to produce electricity or heat. What's more, this process is part of a circular economy, recovering organic waste to produce energy and compost to improve the soil.