Impact of feedstock dilution on the performance of urine-fed ceramic and membrane-less microbial fuel cell cascades designs

Recent advancements in the microbial fuel cell (MFC) field have led to the deployment of pilot-scale autonomous sanitation systems converting the organic content of urine into electricity to power lights in decentralised areas. Two designs have been deployed successfully, namely ceramic cylinder based MFCs (c-MFC) and membrane-less self-stratifying MFCs (s-MFC), but only one research has tested simultaneously these two designs under similar conditions. To complement this single study, the present work investigated the response of these two designs to the dilution of feedstock. Both designs were assembled as cascades, a configuration close to the conditions of implementation. The tested conditions were 100%, 75%, 50%, 25% urine diluted with tap water. Results have shown that under the 100% condition (neat urine), the s-MFC had a higher energy output (2.29 ± 0.04 kJ d−1) and treatment (4.16 ± 0.15 gCOD.d−1; 1.39 ± 0.15 gNH4.d−1) than the c-MFC. Under the 25% condition, the c-MFC had a higher energy output (0.75 ± 0.04 kJ d−1) but a lower treatment (0.40 ± 0.05 gCOD.d−1; 0.01 ± 0.02 gNH4.d−1) than the s-MFC. Both type of cascade designs could be fed a 75% concentration feedstock for a week without a significant performance decrease. Overall, the c-MFC cascade had higher energy conversion efficiency and the s-MFC had higher power generating performance.