Nitrification-denitrification of waste-waters - using activated sludge, with anaerobic denitrification of a portion then returning to aerobic zone

摘要

The known activated sludge method of purifying waste water in which (i) waste water contg. N-cpds. is mixed in an oxic zone in the presence of C cpds. with an O2-contg. gas and activated sludge contg. C-consuming and N-oxidizing bacteria so that N-cpds. are nitrified; (ii) a nitrified, oxygenated mixed liq. is discharged from the oxic zone and passed to a solids concn. zone to concentrate the solids from the liq.; (iii) a major portion of the concd. solids is returned to the oxic zone as the activated sludge; and (iv) where the total mean residence time of solids (SRT) is not 2 days is improved as follows: (a) nitrified oxygenated liq.-solid is withdrawn and passed to an anoxic zone with a vol. flow rate 1/2 the vol. flow rate of nitrified oxygenated mixed liq. entering the solids concn. zone; (b) the nitrified oxygenated liq.-solid in the anoxic zone is kept under anoxic conditions for 0.4-36 hr. so that the liq.-solid is denitrified and N2 gas is formed; (c) the N2-contg. gas is released and the denitrified liq.-solid is returned to the oxic zone. Integrated biological process not only effectively removes N-cpds. (and can be adjusted to remove phosphate as well), but also requires reduced tankage and power consumption.