A process for the economical and environmentally acceptable disposal of spent adsorbent recovered from an adsorption column used to remove HPNA compounds and HPNA precursors from hydrocracking unit bottoms and/or recycle streams includes removing the liquid hydrocarbon oil from the spent adsorbent material by a combination of solvent flushing, and/or heating and vacuum treatment, grinding the dried adsorbent material containing the HPNA compounds and HPNA precursors to produce free-flowing particles of a predetermined maximum size, and introducing the particulate adsorbent material into a membrane wall partial oxidation gasification reactor to produce hydrogen and carbon monoxide synthesis gas, or syngas, which can be further processed by the water-gas shift reaction to increase the overall hydrogen recovered from the initial feed to the gasifier.