title: Experimental investigation of the external nitrification biological nutrient removal activated sludge (ENBNRAS) system.
abstract: A systematic lab-scale experimental investigation is reported for the external nitrification (EN) biological nutrient removal (BNR) activated sludge (ENBNRAS) system, which is a combined fixed and suspended medium system. The ENBNRAS system was proposed to intensify the treatment capacity of BNR-activated sludge (BNRAS) systems by addressing two difficulties often encountered in practice: (a) the long sludge age for nitrification requirement; and (b) sludge bulking. In the ENBNRAS system, nitrification is transferred from the aerobic reactor in the suspended medium activated sludge system to a fixed medium nitrification system. Thus, the sludge age of the suspended medium activated sludge system can be reduced from 20 to 25 days to 8 to 10 days, resulting in a decrease in reactor volume per ML wastewater treated of about 30%. Furthermore, the aerobic mass fraction can also be reduced from 50% to 60% to <30% and concommitantly the anoxic mass fraction can be increased from 25% to 35% to >55% (if the anaerobic mass fraction is 15%), and thus complete denitrification in the anoxic reactors becomes possible. Research indicates that both the short sludge age and complete denitrification could ameliorate anoxic aerobic (AA) or low food/microorganism (F/M) ratio filamentous bulking, and hence reduce the surface area of secondary settling tanks or increase the treatment capacity of existing systems. The lab-scale experimental investigations indicate that the ENBNRAS system can obtain: (i) very good chemical oxygen demand (COD) removal, even with an aerobic mass fraction as low as 20%; (ii) high nitrogen removal, even for a wastewater with a high total kjeldahl nitrogen (TKN)/COD ratio, up to 0.14; (iii) adequate settling sludge (diluted sludge volume index [DSVI] <100 mL/g); and (iv) a significant reduction in oxygen demand.
authors.affiliation: Water Research Group, Department of Civil Engineering, University of Cape Town, Rondebosch Cape, South Africa.
authors.forename: Zhi-Rong
authors.initials: ZR
authors.lastname: Hu
authors.forename: S
authors.initials: S
authors.lastname: Sötemann
authors.forename: R
authors.initials: R
authors.lastname: Moodley
authors.forename: M C
authors.initials: MC
authors.lastname: Wentzel
authors.forename: G A
authors.initials: GA
authors.lastname: Ekama
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D001673:Biodegradation, Environmental; D019149:Bioreactors / Q000382:microbiology*; D002244:Carbon / Q000378:metabolism*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D017672:Nitrogen Compounds / Q000378:metabolism*; D017553:Phosphorus Compounds / Q000378:metabolism*; D010865:Pilot Projects; D012722:Sewage / Q000382:microbiology*; D014874:Water Pollutants, Chemical / Q000378:metabolism; D018508:Water Purification / Q000295:instrumentation* / Q000379:methods
chemical_list: D017672:Nitrogen Compounds; D017553:Phosphorus Compounds; D012722:Sewage; D014874:Water Pollutants, Chemical; D002244:Carbon