Conductive adsorbents enhance phenol removal from wastewater by direct interspecies electron transfer "DIET"-based anaerobic biodegradation process

This study examined the hybrid adsorption and anaerobic biodegradation processes of phenol by using activated carbon cloth (CC) to stimulate direct interspecies electron transfer (DIET). Phenol biodegradation was tested over three sequential runs using 100 mL lab-scale bioreactors and compared with two different types of CC and granular activated carbons (GAC). The addition of the carbon adsorbents to the bioreactors significantly accelerated the methane production rate. This high rate of methane production was also accompanied by the complete removal of phenol, and a high COD(s) removal rate of about 95%, compared to 43.68% and 48.65% in the control sets in the first and second runs, respectively. The enhancement of the phenol biodegradation is attributed to the synergy of the adsorption and biodegradation processes. An initial adsorption stage has contributed to a significant and rapid reduction of phenol, leading to a lower inhibition effect of phenol, followed by anaerobic biodegradation of the adsorbed phenol stimulated by the DIET process. Specifically, the optimal concentration for Single Weave carbon cloth (CCSW) of 1.6 g L⁻¹ promoted both the DIET and the adsorption processes. Microbial community composition analysis revealed that CCSW facilitated the growth of syntrophic bacterial groups (Rikenellae, Syntrophorhabdaceae, Gracilibacteraceae, and DTU014), and archaea (Methanosaetaceae and Methanoregulaceae), previously reported as key players in the DIET processes to promote phenol degradation. To the best of our knowledge, this is the first work that demonstrates the contribution of CC to stimulate DIET mechanism of anaerobic biodegradation synergistically combined with adsorption process for enhanced phenol removal.