Process optimization of continuous dark fermentative hydrogen production from food waste: effects of organic loading rate and feed disturbance strategies.

Dark fermentative hydrogen production from organic waste simultaneously valorizes waste and generates clean energy, yet its practical application demands stable continuous operation under variable feeding conditions. This study systematically investigated the effects of organic loading rates (OLR) and feed disturbance strategies on continuous hydrogen production from food waste. The process was evaluated across three regimes: (i) stepwise OLR reduction from 40 to 5 gVS/L·d, (ii) constant high OLR (40 gVS/L·d), and (iii) disturbed feeding consisting of substrate addition (at OLRs of 60 and 40 gVS/L·d) alternating with intermittent inoculum-only shocks. Results showed that low OLR conditions resulted in poor hydrolysis and were unsuitable for long-term operation. High initial OLR (40 gVS/L·d) achieved a peak hydrogen production rate of 1.26  L/L·d within the first 48  h. However, constant high OLR led to gradual performance decline due to sustained low pH (average 4.71) and accumulation of hydrogen-consuming acids (propionate, valerate). In contrast, deliberately introduced feed disturbances successfully broke the steady inhibition state, reactivated hydrogen production, and achieved a high hydrogen yield (64.1 mL/g VSadded) along with stable hydrogen concentration (40-60%). These findings demonstrate that inoculum-mediated feast-famine perturbations, which consist of alternating substrate addition with pure inoculum shocks, not only overcome the limitations of constant high-rate fermentation but also achieve high hydrogen yield, providing a practical operational strategy for scaling up continuous dark fermentation systems.