Mechanisms Of Rhamnolipid Enhanced Hydrogen Production From Anaerobic Fermentation Of Waste Activated Sludge

As a by-product of biological treatment of wastewater,waste activated sludge(WAS)has a huge output and high treatment cost,which brings a huge economic burden to the operation of wastewater treatment plants(WWTPs).As a common sludge treatment technology,anaerobic fermentation can reuse a large amount of organics in WAS,reduce the amount of sludge while recovering energy,and compensate part of the operating cost of WWTPs.Rhamnolipid(RL),as a kind of environmentally compatible biosurfactant,has been extended the field of sludge treatment to enhance anaerobic fermentation of WAS by some researchers.However,most of the studies on RL focused on promoting the production of short-chain fatty acids(SCFAs).Although there had been literature reported the performance of RL enhancing hydrogen accumulation from anaerobic fermentation,the underlying mechanism was still unclear,which greatly limited the application of RL.Therefore,this work targets to investigate the mechanism of RL-based anaerobic fermentation system on hydrogen production of WAS.Firstly,the effect of different RL concentrations on hydrogen accumulation in anaerobic fermentation was explored by batch tests.It was found that the maximum production of hydrogen increased from1.76 ± 0.26 to 11.01 ± 0.30 mL/g VSS(volatile suspended solid),when RL concentration increased from 0 to 0.10 g/g TSS(total suspended solid).Further enhancement of RL level to 0.12 g/g TSS slightly reduced the production to 10.80 ±0.28 mL/g VSS.Meanwhile,experimental findings revealed that although RL could be degraded to generate hydrogen,it did not play a major role in enhancing hydrogen accumulation.Secondly,the mechanism of RL enhancing hydrogen production from anaerobic fermentation of WAS was deeply explored through simulating different stages of fermentation experiments and microbial community analysis.Mechanism analysis suggested that RL decreased the surface tension between sludge liquid and hydrophobic compounds,thus accelerating the solubilization of WAS,improving the proportion of biodegradable substances which could be used for subsequent hydrogen production.Regardless of the fact that adding RL suppressed all the fermentation processes,the inhibition effect of processes associated with hydrogen consumption was much more serious than that of hydrogen production.Further investigations of microbial community revealed that RL enriched the relative abundance of hydrogen producers but reduced that of hydrogen consumers.Finally,the feasibility of anaerobic hydrogen production by RL in WWTPs was discussed,which could lay a theoretical foundation for the practical application of RL.In this work,the details of how RL enhanced hydrogen production were revealed,which could benefit the large-scale application of RL and advance the understanding of RL-based system in anaerobic fermentation.