Abstract: A method and apparatus of anaerobic treatment which makes it possible to prevent disintegration of granular sludge and perform high-load high-velocity anaerobic treatment stably even in the case where treatment is performed under conditions where the granular sludge is easily disintegrated. In a reaction tank 20 which retains the granular sludge, nitric acid or nitrous acid is adjusted so that they have a certain concentration range. For example, nitric acid is added to the liquid to be treated by connecting the nitric acid addition path 12 to a midway point of the path of the liquid to be treated 31 which introduces the liquid to be treated to the reaction tank 20, and nitric acid is mixed with the liquid to be treated. By introducing nitric acids within the reaction tank 20, denitrifying bacteria etc. can multiply, and disintegration of the granules is prevented.

Abstract: A method and apparatus of anaerobic treatment which makes it possible to prevent disintegration of granular sludge and perform high-load high-velocity anaerobic treatment stably even in the case where treatment is performed under conditions where the granular sludge is easily disintegrated. In a reaction tank 20 which retains the granular sludge, nitric acid or nitrous acid is adjusted so that they have a certain concentration range. For example, nitric acid is added to the liquid to be treated by connecting the nitric acid addition path 12 to a midway point of the path of the liquid to be treated 31 which introduces the liquid to be treated to the reaction tank 20, and nitric acid is mixed with the liquid to be treated. By introducing nitric acids within the reaction tank 20, denitrifying bacteria etc. can multiply, and disintegration of the granules is prevented.

Abstract: A multistage activated sludge process involving a predation effect caused by microorganisms realizes further improvement in treatment efficiency and further decrease in the amount of excess sludge generated while a stable quality of the treated water is maintained. This process includes a first biological treatment process for treating BOD in organic wastewater at a high load to convert the BOD to dispersed bacteria, and a second biological treatment process for forming the converted dispersed bacteria into a floc and allowing microorganisms to coexist. The second biological treatment process is performed under a condition of pH 5 to 6.

Abstract: A multistage activated sludge process involving a predation effect caused by microorganisms realizes further improvement in treatment efficiency and further decrease in the amount of excess sludge generated while a stable quality of the treated water is maintained. This process includes a first biological treatment process for treating BOD in organic wastewater at a high load to convert the BOD to dispersed bacteria, and a second biological treatment process for forming the converted dispersed bacteria into a floc and allowing microorganisms to coexist. The second biological treatment process is performed under a condition of pH 5 to 6.

Abstract: Disclosed is an anaerobic fluidized bed which comprises a fluidized bed type reaction tank, a bed of fluidized carries in the reaction tank, and means for recycling a part of treated water from the upper portion of the reaction tank to the lower portion of the same. The reaction tank has raw wastewater introduction means at the lower portion, treated water removing means and produced gas exhaust means at the upper portion. The bed is formed by filling in the reaction tank with granular carriers not larger than 300 .mu.m in diameter and not smaller than 1.1 in specific gravity, and is established so that the ratio h/H of the initial bed height h to the reaction tank effective height H is within a range of from 0.05 to 0.3.