Nitrate addition improves hydrogen production from acidic fermentation of waste activated sludge.

In this work, a low-cost alternative method (i.e., adding nitrate into WAS) to significantly enhance hydrogen production was reported. Experimental results showed that with an increase of nitrate addition from 0 to 362 mg/L, the maximal hydrogen production from acidic (pH 5.5) fermentation of WAS obviously increased from 12.6 ± 0.5 to 19.3 ± 0.9 mL per gram volatile suspended solids (VSS). The mechanism investigations illustrated more substrates were provided for subsequent hydrogen production. Although the nitrate added inhibited all the biological processes, its inhibition to the hydrogen consumption processes was much severer than that to the hydrogen production processes. The enzyme analyses on the long-term semi-continuous fermenters showed that the nitrate addition slightly inhibited the relative activities of protease, butyrate kinase, acetate kinase, CoA-transferase, and [FeFe] hydrogenase but largely suppressed the relative activities of coenzyme F 420 , carbon monoxide dehydrogenase, and adenylyl sulfate reductase. Image 1 •The presence of nitrate enhanced hydrogen production from waste activated sludge. •Nitrate accelerated the disruption of extracellular polymeric substances. •Nitrate inhibited all the biological processes in anaerobic fermentation. •Inhibition to hydrogen consumption was severer than that to hydrogen production. •A new "closed-loop" concept for the energy cycle of WWTPs was proposed. [ABSTRACT FROM AUTHOR]