AbstractBACKGROUNDThe inhibitory effect of a moisture‐absorbent sodium polyacrylate (SPA), that is commonly used in disposable diapers, on the bio‐hydrogen (H2) generation from waste diaper‐like material (WDM) was assessed in dark fermentation studies. Three types of treatments were evaluated in batch bioreactors at 37 °C: mixture of bond paper and filter paper (WDM, no SPA), SPA alone (only SPA or control), and WDM spiked with SPA [paper plus sodium polyacrylate hydrogel (WDM‐SPA)]. The WDM simulated the cellulosic fraction of diaper composition.RESULTSThe units with only SPA did not produce H2. The WDM‐SPA units exhibited H2production 25% lower than those of bioreactors loaded with only WDM but no SPA. Cumulative H2 production was 0.03, 4.22 and 5.50 mmolH2 gTS–1 for the SPA, WDM‐SPA and WDM reactors, respectively (0.04, 5.90 and 8.77 mmolH2 gVS–1; 0.89, 132.19 and 196.45 NmLH2 gVS–1). BioH2 generation was related to predominance of the fermentation route that produces 1 mol L–1 of butyric acid (HBu) plus 2 mol L–1 H2 in the WDM and WDM‐SPA units, as suggested by the ratio A:B (acetic: butyric acids; A:B < 0.79 mg HAc‐COD mg HBu‐COD–1 in both cases).CONCLUSIONIt seems that this is the first documented result on the inhibitory effect of SPA on the bioH2 fermentation of cellulosic wastes. However, further research should be carried out at different levels of SPA to determine, for instance, the half‐inhibition value of SPA, that is, the concentration of SPA that would cause a 50% drop in H2 generation of the non‐SPA treatment. © 2019 Society of Chemical Industry