Date

2022-11-28

Author

Şanlı, Mert

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Anaerobic digestion (AD) is a common method used for treatment of complex wastes with additional benefit of biogas production. Yet, the process has several limitations such as slow kinetics, long start-up periods and low methane (CH4) production yield. With the integration of microbial electrolysis cells (MECs) into AD, it is anticipated that these limitations of AD will be reduced. The reasons of such improvements in the AD-MEC integrated systems may stem from the enhanced electron transfer in microbial consortium involved in AD and promotion of an additional methane production pathway. In this study, important process conditions of the AD-MEC integrated system were tested on two different experimental sets. Firstly, the impact of external voltage on methane production performance of two different complex wastes, namely cattle manure (C) and wastewater biosolids (WBS) were studied in batch AD-MEC reactors. The wastes were provided in four different mixtures (based on COD) as 100C:0WBS, 70C:30WBS, 30C:70WBS and 0C:100WBS and three different voltages of 0.3 V, 0.7 V and 0.9 V were tested in AD-MECs. Results showed that, there was not a significant impact of applied voltage on methane production in the WBS reactors, yet, in C added reactors applied voltage showed a significant enhancement. Among C dominant reactors the highest improvement was recorded at 0.9 V application. Net methane yield of 100C:0WBS reactors at an applied voltage of 0.9 V were 128.3 mL CH4/g volatile solids (VS) added which corresponds to a 70% increase in comparison to the conventional AD reactors (75.5 mL CH4/g VSadded) operated as control. The highest improvement at around 40% were attained with 0.3 V application in WBS added reactors. Yet, this increase may not be linked to a bioelectrochemical process based on significantly low current production in these reactors. Further, the impact of using biofilm attached electrodes, i.e. bioelectrodes were assessed in a sequential experimental part. The results showed that using bioelectrodes from the first part, increased the maximum methane potential and methane production rate based on Gompertz fitting to the cumulative methane production data. In the second experimental set of this thesis, the impact of autoclave pretreatment and application of lower voltages in the range of 0.3 – 0.7 V were tested on the anaerobic treatability of WBS in AD-MEC systems. AD-MEC integrated systems showed similar performance enhancement compared to corresponding AD controls, regardless of the feed pretreatment. Additionally, the impact of using bioelectrodes were investigated and experiments were designed to compare methane production performance of bioelectrode and bare electrode AD MECs, yet no significant difference was recorded in the case of WBS feed.

Subject Keywords

Microbial electrolysis cell, AD-MEC, Methane, Cattle manure, Wastewater biosolids

URI

https://hdl.handle.net/11511/101940

Collections

Graduate School of Natural and Applied Sciences, Thesis