Analysis of the pre-treatment efficiency of digestate liquid fraction from a municipal waste biogas plant

Due to the progressing water shortage in agriculture, digestate mass is increasingly being treated not only as an alternative fertilizer but also as a potential source of water. However, it requires the use of advanced technological processes. Due to the fact that the digestate liquid fraction contains large amounts of contaminants, it should be pre-treated before using advanced purification technologies. The conducted experiments determined the effectiveness of coagulation/chemical precipitation process with the use of CaO, FeCl₃ and PIX 112 during the initial purification of the digestate liquid fraction from municipal waste biogas plants. The impact of reaction time and the reagent dose on the effectiveness of reducing the organic compounds and ammonium nitrogen content was analysed. The results show that tested reagents can be applied for the digestate liquid fraction pretreatment. The increasing of the doses of each reagent enabled an increase in the effectiveness of the process. The increase in the reaction time (slow mixing) extension did not improve the efficiency; an adverse effect due to desorption of pollutants was found. The NH₄ ⁺-N concentration did not depend on the dose of the reagent, but only on the reaction time (very high reduction observed after 24 hours).