The patent-pending integrated waste-to-energy system comprises both a novel bio-hydrogen reactor with a gravity settler (Biohydrogenator), followed by a second stage conventional anaerobic digester for the production of methane gas. This chemical-free process has been tested with a synthetic wastewater/leachate solution, and was operated at 37 degrees C for 45 d. The biohydrogenator (system (A), stage 1) steadily produced hydrogen with no methane during the experimental period. The maximum hydrogen yield was 400 mL H(2)/g glucose with an average of 345 mL H(2)/g glucose, as compared to 141 and 118 mL H(2)/g glucose for two consecutive runs done in parallel using a conventional continuously stirred tank reactor (CSTR, System (B)). Decoupling of the solids retention time (SRT) from the hydraulic retention time (HRT) using the gravity settler showed a marked improvement in performance, with the maximum and average hydrogen production rates in system (A) of 22 and 19 L H(2)/d, as compared with 2-7 L H(2)/d in the CSTR resulting in a maximum yield of 2.8 mol H(2)/mol glucose much higher than the 1.1-1.3 mol H(2)/mol glucose observed in the CSTR. Furthermore, while the CSTR collapsed in 10-15 d due to biomass washout, the biohydrogenator continued stable operation for the 45 d reported here and beyond. The methane yield for the second stage in system (A) approached a maximum value of 426 mL CH(4)/gCOD removed, while an overall chemical oxygen demand (COD) removal efficiency of 94% was achieved in system (A). (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.