Composting as an Alternative for Final Disposal of Digested Sludge from UASB Reactors: A Case Study in the Small Municipalities of the State of Bahia, Brazil

Abstract

This work evaluated the composting process as an alternative for the valorization of anaerobic digested sludge from an upflow anaerobic sludge blanket (UASB) reactor. The process stability and performance were investigated by monitoring physicochemical and microbiological parameters during two distinct and sequential phases. In the first phase, the composting process was evaluated by assembling two composting piles (490 l each) with anaerobic digested sludge and wood chips as structural material (volumetric ratio 1:1). In the second one, the piles were put together and putrescible food waste was added to form a pile with approximately 523 l. In addition, a net present value (NPV) calculation was made seeking to investigate the financial viability of the initiative. The results of the first phase showed that the piles did not reach thermophilic temperatures, indicating low microbiological activity. On the other hand, in the second phase, after addition of the food waste as an amendment agent, temperatures above 55 °C were registered and maintained during five consecutive days. The result of the NPV showed that it is necessary to adopt adequate criteria for the sampling frequency and the number of analyzed parameters, in order to enable the implementation of composting as an alternative to anaerobic sludge valorization in small municipalities of the State of Bahia, Brazil.