NOVELTY - Sewage is flown through a sewage drain. Material with larger specific gravity is precipitated and floating material is filtered. Suspended material and biological oxygen demand are eliminated. Organic material is oxidized and dispersed to produce floc. Sludge lump is mixed with loess, and discharging purified water and sludge are separated. Sludge is mixed with loess, supernatant and sludge are separated, and sludge is concentrated. Organic material of sludge is dispersed, and byproduct and methane gas are produced. Sludge is solidified and dewatered.    USE - Disposal of sewage of sewage disposal plant of e.g. industrial wastewater, foodstuffs wastewater, and domestic wastewater.    ADVANTAGE - The method shortens settling time, as the precipitation speed is increased. The volume of sludge is reduced and processing efficiency is increased. The method is economical. The discharged water does not cause water pollution.    DETAILED DESCRIPTION - Sewage in sediment place of a sewage disposal plant is flown through a sewage drain. Material with larger specific gravity is precipitated and material which floats on water is filtered through a screen. The precipitate and sewage without solid are pumped to precipitating place (I). Suspended material and biological oxygen demand are eliminated by precipitating suspended material in precipitating place (I) of flown-in sewage. The organic material included in sewage is oxidized and dispersed to produce sludge floc by metabolism of microorganism in an aeration tank of sewage transported from precipitating process. Sludge lump is mixed with loess to shorten precipitating time by increasing precipitating speed of sludge floc, and discharging purified water and sludge are separated by precipitating sludge lump. Purified water cleaned in the final precipitating process is discharged to public water area. Sludge is mixed with loess to increase sludge precipitated in precipitating process (I) and precipitating speed of sludge in the final precipitating process. Supernatant and sludge are separated, and sludge is concentrated in a concentrating tank by gravity. Organic material of sludge is dispersed, and byproduct and methane gas are produced by heating and agitating sludge in a confined digesting tank. Sludge is solidified, transported from the digesting process, dewatered to a water content of less than 60%, and reclaimed or dumped in ocean. The usage amount of loess is 1.5-4 wt.% in both processes. In the mixing process, sludge, loess and coagulant (0.02-0.1 wt.% in first process, and 0.1 wt.% in second process) are mixed. Loess is mixed as a liquid containing water (70 wt.%) and loess (30 wt.%).