Abstract
The effect of hydrogen pulse addition on digestion performance of sewage sludge was evaluated as a means for studying the increase in efficiency of methane production. Microbial communities were also evaluated to get an insight of the changes caused by the operational modifications of the digester. An energy evaluation of this alternative was performed considering the theoretical process of coupling bioelectrochemical systems (BES) for the treatment of wastewater along with hydrogen production and the subsequent anaerobic digestion. The addition of hydrogen to sewage sludge digestion resulted in an increase of 12% in biogas production over the control (1353 mL CH4 d−1 at an injection flow rate of 1938 mL H2 d−1). The liquid phase of the sludge reactor and the H2 supplemented one did not show significant differences, thus indicating that the application of hydrogen as the co-substrate was not detrimental. High-throughput sequencing analysis showed slight changes in archaeal relative abundance after hydrogen addition, whereas eubacterial community structure and composition revealed noteworthy shifts. The mass and energy balance indicated that the amount of hydrogen obtained from a hypothetical BES can be assimilated in the sludge digester, improving biogas production, but this configuration was not capable of covering all energy needs under the proposed scenario.
Highlights
The most widely used technology for the treatment of municipal wastewaters is based on an activated-sludge process in spite of its high energy cost [1]
The benefit of hydrogen addition to the digestion of sludge was associated with the increase in biogas production owing to the conversion of hydrogen into acetate and subsequent transformation into methane
This process did not lead to a high enrichment in the composition of biogas produced, but on the contrary, significantly increased the productivity of the digester in terms of the volumetric gas production rate
Summary
The most widely used technology for the treatment of municipal wastewaters is based on an activated-sludge process in spite of its high energy cost (up to ~75% of the total energy costs of a plant) [1]. The number of wastewater plants has increased due to rapid urbanisation and it has brought along a significant increase of the volume of sludge needing adequate management [2]. This sewage sludge is characterised by high organic content needing to be properly disposed of. Sludge is treated by extended aeration when the size of a wastewater treatment plant (WWTP) is too small, making it unfeasible to install an anaerobic digester. Some disadvantages are associated with the digestion of waste activated sludge (WAS) such as low methane
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