NOVELTY - Producing transportation or heating fuel, comprises: e.g. pretreating cellulosic feedstock in processing step that release extractives of at least acetic acid and/or acetate from feedstock; conducting solids-liquid separation to produce aqueous stream of soluble extractives and solids stream of insoluble components; feeding aqueous stream to anaerobic digester to produce crude biogas; removing carbon dioxide to produce purified biogas; introducing inorganic salt-containing liquid stream to anaerobic digester; and providing solids to thermal process to produce energy product.    USE - The process is useful for producing transportation or heating fuel from cellulosic feedstock.    ADVANTAGE - The process: improves thermal processing of cellulose feedstock by releasing various extractives present in cellulosic feedstock and preventing production of slag, pollutants and other undesirable components by the extractives, during thermal processing, thus provides solids stream, which improves the economics of producing energy products from the cellulosic feedstock; provides product, from which energy can be captured more economically; utilizes solid-liquid separation in advance of anaerobic digestion enables microorganism recycle in an anaerobic digester, which can improve the productivity of anaerobic digestion due to higher microbe concentration in the digester, removing solids before anaerobic digestion simplifies the process and can be carried out with greater ease and at lower cost; utilizes extractives fed to the anaerobic digester, improves renewable fuel yield from cellulosic feedstock, which is especially beneficial in that it can enable generation of a greater number of fuel credits and provides product with significantly reduced life cycle green house gas (GHG) emissions.    DETAILED DESCRIPTION - Producing a transportation or heating fuel, comprises: (a) pretreating a cellulosic feedstock in at least one processing step that release extractives comprising at least acetic acid, and/or acetate from the feedstock; (b) conducting a solids-liquid separation on a process stream comprising the extractives and solids, thus producing an aqueous stream comprising soluble extractives and a solids stream comprising insoluble components; (c) feeding at least a portion of an aqueous stream comprising the soluble extractives to an anaerobic digester to produce crude biogas; (d) removing at least 80 wt.% of carbon dioxide present in the crude biogas to produce purified biogas; (e) providing an inorganic salt-containing liquid stream originating from the anaerobic digester and introducing at least a portion of the liquid stream to the anaerobic digester, a stage upstream of the anaerobic digester and/or downstream of step (a); (f) purging a stream comprising inorganic salt from the inorganic salt-containing liquid stream; (g) providing solids from at least one stream comprising solids stream comprising the insoluble components and a second solids stream comprising insoluble components to a thermal process to produce an energy product; (h) introducing the purified biogas produced in step (d) to a pipeline an apparatus for transporting methane and causing withdrawal of an amount of methane from at least one of the pipeline and a connected pipeline apparatus; (i) providing at least one product obtained or derived from step (g) and/or (h) for use as a transportation or heating fuel; and (j) generating or causing the generation of a renewable fuel credit.