Biofiltration for removal of BOM and residual ammonia following control of bromate formation.
Nitrification was developed within a biological filter to simultaneously remove biodegradable organic matter (BOM) and residual ammonia added to control bromate formation during the ozonation of drinking water. Testing was performed at pilot-scale using three filters containing sand and anthracite filter media. BOM formed during ozonation (e.g., assimilable organic carbon (396-572 microg/L), formaldehyde (11-20 microg/L), and oxalate (83-145 microg/L)) was up to 70% removed through biofiltration. Dechlorinated backwash water was required to develop the nitrifying bacteria needed to convert the residual ammonia (0.1-0.5 mg/L NH(3)-N) to nitrite and then to nitrate. Chlorinated backwash water resulted in biofiltration without nitrification. Deep-bed filtration (empty-bed contact time (EBCT) = 8.3 min) did not enhance the development of nitrification when compared with shallow-bed filtration (EBCT = 3.2 min). Variable filtration rates between 4.8 and 14.6 m/h (2 and 6 gpm/sf) had minimal impact on BOM removal. However, conversion of ammonia to nitrite was reduced by 60% when increasing the filtration rate from 4.8 to 14.6 m/h. The results provide drinking water utilities practicing ozonation with a cost-effective alternative to remove the residual ammonia added for bromate control.
Wert
Eric C
EC
Southern Nevada Water Authority (SNWA), 243 Lakeshore Road, Boulder City, NV 89005, USA. eric.wert@snwa.com
Neemann
Jeffrey J
JJ
Rexing
David J
DJ
Zegers
Ronald E
RE
D000447:Aldehydes / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism*; D001419:Bacteria / Q000302:isolation & purification / Q000378:metabolism; D001959:Bromates; D002264:Carboxylic Acids / Q000378:metabolism; D002712:Chlorides; D002713:Chlorine / Q000737:chemistry; D015169:Colony Count, Microbial; D005290:Ferric Compounds / Q000737:chemistry; D005374:Filtration / Q000379:methods; D005427:Flocculation; D009566:Nitrates / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D016877:Oxidants / Q000737:chemistry*; D010126:Ozone / Q000737:chemistry*; D012822:Silicon Dioxide; D014873:Water Pollutants / Q000378:metabolism*; D018508:Water Purification / Q000379:methods*
D000447:Aldehydes; D001959:Bromates; D002264:Carboxylic Acids; D002712:Chlorides; D005290:Ferric Compounds; D009566:Nitrates; D009573:Nitrites; D016877:Oxidants; D014873:Water Pollutants; D002713:Chlorine; D010126:Ozone; D012822:Silicon Dioxide; D000641:Ammonia; C024555:ferric chloride