TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The process removes 95 wt.% of calcium carbonate from the sludge cellulose source. The sludge cellulose source is homogenized prior to affecting the conditions permitting dissolution of a non-cellulose material and suspension of the cellulose. The conditions permitting dissolution of a non-cellulose material and suspension of the cellulose include treatment of the sludge cellulose source with a dilute acid or with hydrochloric acid at a temperature of 40-80 degrees C. The acidification is carried out at room temperature, preferably 50-60 degrees C. The process comprises: (a) homogenizing a sludge cellulose source, (b) treating the homogenized source under acidic conditions, allowing dissolution of the non-cellulose materials, where the treatment does not alter the cellulose morphology, (c) repeating step (b) at least twice, and allowing the liquid phase containing the soluble non-cellulose material to separate from a solid phase containing cellulose and optionally washing the separated solid material with water to obtain pure cellulose; or treating a sludge cellulose source to separate pure cellulose, causing preferential degradation of cellulose amorphous domains while maintaining the cellulose crystalline domains intact, isolating the crystalline domains, and dispersing the obtained product to obtain nano crystalline cellulose. In the process, where subsequent to acidification the liquid phase is removed and a fresh volume of acid is introduced to wash the solid phase containing cellulose. The step of washing is repeated 2 or more times. The pure cellulose is separated from the acidic liquid phase and subsequently dried or separated as aqueous suspension. The process further comprises treating the pure cellulose for preparing nano crystalline cellulose. The step of causing preferential degradation of cellulose amorphous domains while maintaining intact the cellulose crystalline domains is achievable by acidification and/or enzyme treatment. The step of acidification is achievable by an acid comprising sulfuric acid, hydrochloric acid, hydrogen bromide and nitric acid. In the process, where subsequent to the degradation of the cellulose amorphous domains, and the nano crystalline cellulose are dispersed. The step (a) is carried out under acidic conditions. The step (b) is carried out under acidic or enzymatic conditions. The steps (a) and (b) are each carried under acidic conditions, where the acidic conditions employed in step (a) are different from the conditions employed in step (b). Preferred Components: The sludge cellulose source contains 5-60 (preferably 40-60)% of cellulose. The sludge cellulose source is paper mill sludge, municipal sludge or paper sludge cellulose source. The dry sludge contains 40-60 (preferably 50) wt.% of calcium carbonate and 40-60 (preferably 50) wt.% of cellulose. The dilute acid has a concentration of 0.1-1 (preferably 0.1-0.3)M acid. The acid comprises organic and inorganic acids, where the acid does not form water-insoluble salts with calcium carbonate. The acid comprises hydrochloric acid, hydrogen bromide, phosphoric acid and nitric acid. The acid is a natural acid comprising citric acid, maleic acid, and tartaric acid. The hydrochloric acid is present at a concentration of 0.4-0.6 (preferably 0.1-0.3)M. The enzyme is cellulase.