NOVELTY - Treating a hot syngas stream (11) for conversion to chemical products by removing various components from the stream comprises: passing hot syngas stream to scrubber (14); adding aldehyde to scrubber water; capturing ammonia and hydrogen cyanide (HCN) and condensing water from the hot stream into the scrubber water; withdrawing a scrubber waste water effluent from the scrubber; withdrawing treated syngas stream effluent from the scrubber; and passing at least a portion of the waste water effluent stream to a biological treatment zone (18) to produce biologically treated waste water effluent.    USE - The method is useful for treating a hot syngas stream for conversion to chemical products by removing various components from the hot syngas stream.    ADVANTAGE - The method enables greater removal of ammonia and HCN from syngas in a cost effective, and environmentally benign and sustainable fashion.    DETAILED DESCRIPTION - Treating a hot syngas stream (11) for conversion to chemical products by removing various components from the hot syngas stream comprises: passing the hot syngas stream to a scrubber (14); adding an aldehyde to a circulating scrubber water; capturing ammonia and hydrogen cyanide (HCN) in the circulating scrubber water and condensing water from the hot syngas stream into the circulating scrubber water; withdrawing a scrubber waste water effluent from the scrubber, where the waste water effluent comprises absorbed ammonia, ammonium, absorbed HCN, and glycol nitriles formed from the reaction of the aldehyde with HCN; withdrawing a treated syngas stream effluent having a reduced concentration of ammonia and HCN from the scrubber; and passing at least a portion of the scrubber waste water effluent stream to a biological treatment zone (18) for removing ammonia, absorbed HCN and glycol nitriles to produce a biologically treated waste water effluent.    DESCRIPTION OF DRAWING(S) - The figure shows a block diagram of the steps of a method as carried out by a syngas conversion system.    Hot syngas (11)    Water based scrubber (14)    Biological treatment system (18)    Anoxic reactor (24)    Aerobic reactor (26)