NOVELTY - Comprehensive utilization of sludge, by adding water to dehydrated sludge, adjusting pH, heating mixture, dissolving produced ammonia gas in water to obtain ammonia solution, filtering reacted material to obtain filter cake (F1), adding magnesium chloride solution to ammonia solution, adjusting pH, adding disodium hydrogen phosphate solution, drying filter cake to obtain guano fertilizer, mixing filter cake (F1) with activator and recarburizer, performing calcination, filtering and washing crude activated carbon and drying washed filter cake to obtain activated carbon.    USE - The method is useful for comprehensive utilization of sludge for preparation of guano fertilizer and activated carbon product (claimed).    ADVANTAGE - The method enables extraction of nitrogen, carbon and metal elements from the sludge, which in turn used for preparation of guano fertilizer and activated carbon product, and recovery of metals respectively. The method enables comprehensive utilization of sludge, and hence environmental pollution is also reduced.    DETAILED DESCRIPTION - Method for comprehensive utilization of sludge, involves (a) recovering ammonia from sludge by adding water to dehydrated sludge, adjusting pH of sludge mixture using sodium hydroxide solution, heating reaction mixture, dissolving ammonia gas produced during the reaction in water to obtain ammonia solution, and filtering reacted material to obtain filter cake, (b) adding magnesium chloride solution to the ammonia solution, adjusting pH of obtained solution using sodium hydroxide solution, adding disodium hydrogen phosphate solution to the solution until no precipitate is produced, filtering mixture, and drying filter cake to obtain guano fertilizer, and (c) mixing the filter cake obtained in the step (a) with activator and recarburizer, subjecting obtained mixture to soaking, heating and drying processes, putting dried material into calciner to obtain activated carbon as crude product, washing crude activated carbon with hydrochloric acid, filtering washed product, washing filter cake with water until filter cake becomes neutral, and drying washed filter cake to obtain activated carbon product.