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Sustainable Use of Digestate from Biogas Plants: Separation of Raw Digestate and Liquid Fraction Processing
This review provides an overview of the various aspects involved in the digestate separation process with a focus on the best solution. The paper discusses the possibility of processing the liquid fraction using membrane separation processes and evaporation. Despite the identical goal of digestate separation, the solutions presented have many differences. These differences affect each process’s capital, operating costs, efficiency, and complexity. Among the selected solutions, the most popular technology for separating digestate is a screw press. Its advantage is the simplicity of its design compared to the centrifuges or filter presses used. In addition to the economic aspect, a definite advantage of mechanical separation is the possibility of using the liquid fraction to reduce the dry matter of the feedstock for biogas plants. Regardless of the chosen technology, striving for the closed-cycle operation of biogas plants and optimizing production processes is now becoming necessary. Proper management of the digestate is a crucial element of the operational efficiency of any biogas plant in case of the sustainable energy. The prepared article will fill some gaps in knowledge and indicate further directions of action. It is necessary to further develop research on methods of digestate separation.
Economic and Energy Efficiency Analysis of the Biogas Plant Digestate Management Methods
The aim of this study was to conduct a comprehensive economic and energy efficiency analysis of selected digestate management methods, considering their implications on operational costs and resource management. To achieve this aim, the study focuses on a comparative assessment of different digestate management methods, including land application, mechanical separation, the composting process and pellet production. The economic analysis involves the evaluation of the initial investment, operational expenses, and potential revenue streams associated with each method. The most economical and popular solution of digestate management is direct use as fertilizer, with total costs of 1.98 EUR·Mg−1. All of the other methods involve higher digestate management costs, respectively; for separation it is 2.42 EUR·Mg−1, for composting it is 2.81 EUR·Mg−1. The process that is the most energy-intensive, but profitable, is the production of pellets from digestate, resulting in profits of 334,926 EUR·year−1. It should be noted that the other analyzed methods of digestate management also bring many environmental benefits, affecting sustainability and reducing emissions. The results of this research will contribute unique data on the feasibility of managing the digestate and its fractions. The calculations of economic and energy values for different strategies will allow for the optimization of the overall performance of the biogas plant, thus promoting a circular economy.