NOVELTY - Hyacinth and dewatered sludge are mixed and fermented by pressing and dewatering hyacinth; crushing; uniformly and completely mixing hyacinth, dewatered sludge, microbial agent, heavy metal purifying agent and rice chaff or peanut shells; compost fermenting and aging the mixed material in a fermentor; uniformly mixing decomposed material, humic acid and urea to the mixer; crushing; drying; cooling; sieving; and packaging qualified finished product to obtain commercial organic fertilizer.    USE - Mixing and fermentation of hyacinth and dewatered sludge for preparation of an organic fertilizer (claimed).    ADVANTAGE - The method solves problem in conventional innocuous treatment by using hyacinth which absorbs nitrogen and phosphorus in water to prevent eutrophication of water mass; avoids secondary environmental pollution caused by improper treatment of hyacinth and sludge; and is more beneficial for the development of organic agriculture in China and saving the environment. The commercial organic fertilizer satisfies the NY525-2002 quality standard. Nitrogen and phosphorus can be recycled and transferred to farms from water mass and urban sewage.    DETAILED DESCRIPTION - Mixing and fermentation of hyacinth and dewatered sludge comprises:    (A) pressing and dewatering hyacinth to reduce 95% water content to 50%, crushing hyacinth to controlled fineness of 3 cm, respectively mixing (wt.%) hyacinth (40), dewatered sludge (40), microbial agent (2), heavy metal purifying agent (8) and rice chaff or peanut shells (10) using a proportioning machine, uniformly and completely mixing the mixed product in a mixer, and transferring mixed material to a fermentor through a belt conveyor;    (B) compost fermenting and aging the mixed material in the fermentor provided with an aeration pipe for a composting period of 12-15 days, increasing compost temperature to 60-70 degrees C, carrying out second fermentation and aging for 15-20 days, reducing compost temperature to 30-40 degrees C, where water content of mixed material is reduced to 15-35%, and automatically discharging aged decomposed material using a spiral discharging machine to a discharging belt conveyor which transfers material to a warehouse for storage; and    (C) respectively feeding (wt.%) decomposed material (80), humic acid (12.5) and urea (7.5) to the mixer, crushing uniformly mixed material, drying, cooling, sieving, and packaging qualified finished product to obtain commercial organic fertilizer.    After crushing, the larger materials are returned to the mixer. The weights of hyacinth and dewatered sludge are in wet basis. The dewatered sludge is obtained from a sewage treatment plant, with water content of 75-80%. The microbial agent is an organic material-decomposing inoculant. A blast blower forcibly ventilates the aeration pipe to supply oxygen. During compost fermentation, oxygen supplied is 0.05-0.2 m3/m3.minute, initial compost water content of mixed material is 50-60%, carbon nitrogen ratio of mixed material during composting is 20-30, carbon phosphorus ratio of mixed material is 75-150, pH value is reduced to 5.5-6.0 at beginning of composting period for functioning of acidic bacteria, and void percentage of mixed material is controlled to not less than 20%; where compost material is acidic and pH value increases caused by the growth and propagation of acid bacteria. After composting process, the pH value of material increases to 8.5-9.0. The heavy metal purifying agent comprises fly ash and phosphorite powder having a weight ratio of 5:4. The aged decomposed material has contents of heavy metals, including cadmium, lead, copper, zinc and chromium, which are less than the national agricultural standards GB 4284-84 and GB 8173-87.