Effects of substrate type on variation of sludge organic compounds, bioelectric production and microbial community structure in bioelectrochemically-assisted sludge treatment wetland

A bioelectrochemical assisted sludge treatment wetland (BE-STW) is a promising technology used in the elimination of organic compounds and recovery of bio-energy. In this study, four BE-STW systems were constructed to investigate the effects of some substrates (i.e. graphite particles, zeolite, ceramsite, and gravel) on organic compounds biodegradation and transformation, electricity production, and anodic bacterial community. The maximum output voltages were 0.939, 0.870, 0.741 and 0.835 V, and the maximum power densities were 0.467, 0.143, 0.110, and 0.131 W/m(3) for the graphite particles (BS-GP), zeolite (BS-Z), ceramsite (BS-C), and gravel (BS-G) systems, respectively. Also, the dissolved organic carbon (DOC) removal rates were 61.84%, 28.54%, 25.56%, and 18.34% in BS-GP, BS-G, BS-Z, and BS-C, respectively. The degradation of aromatic compounds in sludge extracellular biological organic matter (EBOM) was mainly due to the decrease of hydrophilic fraction (HPI) and transphilic acid fraction (TPI-A) contents. Moreover, aromatic proteins were preferentially removed in BS-Z. For BS-C, the tyrosine-like proteins and humic acid-like substances in TPI-A were totally removed. An excitation-emission matrix (EEM) analysis showed that the fluorescent intensity of the humic acid-like substances was the lowest in BS-GP, and no fluorescence peaks of fulvic acid-like substances were observed. Finally, at the genus level, Longilinea, Terrimonas, Ottowia, and Saccharibacteria_genera_incertae_sedis were the dominant bacteria in BE-STW, and Methylophilus was also only detected in BS-GP. These results confirmed that substrate materials have a significant impact on the preferentially degraded organic matter in BE-STWs, which can provide a theoretical basis for the practical application of STW in the future.

Automated summary

A study constructed four different bioelectrochemical assisted sludge treatment wetland (BE-STW) systems using different substrates to investigate their effects on organic compounds degradation, electricity production, and bacterial community. The results showed that the substrate materials significantly affected the output voltage, power density, and organic carbon removal rate of the systems. The degradation of aromatic compounds was mainly achieved by reducing the hydrophilic fraction and transphilic acid fraction. The substrates also influenced the removal of specific proteins and the fluorescent characteristics of humic acid-like substances. At the genus level, certain bacterial genera dominated the BE-STW systems, and different substrates introduced different bacterial genera.