Microbial communities of anaerobic digesters fed with palm oil mill effluent with the supplements of surfactant and iron

This study investigated the effects of various surfactants on soluble COD fraction and biogas production from palm oil mill effluent (POME). Cationic surfactant (CTAB) and nonionic surfactant (Tween 80; TW80) were found to adsorb onto POME's particulate matter, markedly reducing the soluble COD, unlike the anionic surfactant (SDS). The mechanism behind this phenomenon might be the adsolubilization of oil on particulate matter induced by the adsorbed surfactants. In terms of biogas production, SDS and CTAB at 0.1%w/v dramatically reduced the biogas yield, while applying TW80 .1%w/v did not show this negative effect. A synergistic effect was observed when combining TW80 (0.1%w/v) with iron(II) sulphate (400 mg/L), resulting in a 17% higher biogas yield compared to treatments using TW80 or FeSO4 alone. Moreover, the combination of TW80 and iron(II) sulphate increased the biogas production rate. Surprisingly, the water-soluble iron fraction remained consistent across all treatments, suggesting that the adsorption of TW80 on particulate matter may limit micelle formation. Importantly, the methane proportion in the generated biogas remained stable in all treatments. Microbial community analysis revealed that the introduction of TW80 and iron(II) sulphate had no discernible impact on the system's microbial community. The pretreatment with TW80 and iron supplement significantly enhanced biogas production and reduced the retention time of the anaerobic digestion system, all while maintaining biogas quality and microbial community stability.