AERATED REMOVAL OF NITROGEN POLLUTANTS FROM BIOLOGICALLY DEGRADABLE WASTEWATERS

摘要

A cyclic activated sludge method and apparatus uses multi-reactor facilities (typically 2, 3, 4, or multiples of 2, e.g., 6, 8, 12, 16, etc.), without separate secondary clarifiers, to accommodate a continuous hydraulic profile. Each reactor is configured with an admixture volume as an initial unaerated mixing zone followed by repetitive mixing gradients to nucleate and promote large activated sluge floc sizes followed by a second intermittently aerated hydraulically connected reaction zone using partial baffle walls. The second reaction zone in each reactor is collectively, but out of phase, operated with successive air-on and air-off sequences. The air-off sequence enables solids-liquid separation and a depletion of biomass oxidation reduction potential to take place after an air-on sequence, with subsequent withdrawal of a fraction of the reactor upper level liquid contents using a variable rate moving box weir decanter. Sludge containing heterotrophic and autotrophic micro-organisms is directed from the second zone to the initial volume for admixture with biodegradable wastewaters containing more than 3:1 parts of BOD:TKN. The period of each air-on sequence depends upon the relative oxygen demanding mass load input. There is provision for influent flow during an extended air-off sequence after removal of the supernatant fraction. The air-on sequence typically operates with filling of influent into the reactor. Air-on sequencing in the second reactor volume is used to mix and elevate the oxidation reduction potential of the settled separated microbial culture from negative to mixed positive values. Air-off sequencing in the second reactor volume provides separated liquid-solids phases with a dynamic depletion to negative oxidation reduction potential (about -150 mV reference hydrogen electrode).