NOVELTY - A detrimental species-containing cellulosic biomass solid, base solution having pH of more than 9, aqueous solution having pH of 8 or less and removal stream comprising gas stream or organic solvent solution are introduced to treatment container to produce pretreated cellulosic biomass solid. The pretreated cellulosic biomass solid is discharged from outlet and transferred to digestion and/or reaction zone. Portion(s) of aqueous effluent is recycled to produce base solution and another portion(s) of the aqueous effluent is recycled as aqueous solution.    USE - Selective removal of chlorine and phosphorus from cellulosic biomass solid used for producing chemical and transportation fuel for propulsion engine and internal combustion engine of transportation vehicle.    ADVANTAGE - Chlorine and phosphorus are removed from cellulosic biomass solid by effective method with high selectivity and reduced usage of water.    DETAILED DESCRIPTION - A detrimental species-containing cellulosic biomass solid is provided and introduced from an inlet into a treatment container. Base solution having pH of more than 9 is introduced from inlet to cellulosic biomass solid-containing container at 0-60 degrees C in amount to fill 5-40% bed volume of the true interstitial volume. Aqueous solution having pH of 8 or less is introduced from an inlet to basic cellulosic biomass solid-containing container to produce washed cellulosic biomass solid having reduced detrimental species content compared to the detrimental species-containing cellulosic biomass solid and basic water effluent. A removal stream comprising a gas stream or organic solvent solution is introduced from an inlet to the container containing the washed cellulosic biomass solids to produce pretreated cellulosic biomass solid with reduced water content compared to water washed cellulosic biomass solids and aqueous effluent. The pretreated cellulosic biomass solid is discharged from outlet and portion(s) of the discharged pretreated biomass solid is transferred to digestion and/or reaction zone. Portion(s) of aqueous effluent is recycled to produce base solution and another portion(s) of the aqueous effluent is recycled as aqueous solution. The cellulosic biomass solid has a true interstitial volume in the container. The content of basic water effluent is 3-0.5 pts. wt. relative to about 1 pt. wt. detrimental species-containing cellulosic biomass solid (dry basis).