Upgrading of Florence wastewater treatment plant: co-digestion and nitrogen autotrophic removal.
In recent years a completely autotrophic nitrogen removal process based on Anammox biomass has been tested in a few European countries in order to treat anaerobic supernatant and to increase the COD/N ratio in municipal wastewater. This work reports experimental results on a possible technical solution to upgrade the S. Colombano treatment plant which treats wastewater from the Florentine urban area. The idea is to use 50% of the volume of the anaerobic digester in order to treat external sewage sludge (as septic tank sludge) together with waste activated sludge and to treat the resulting effluent on a SHARON-ANAMMOX process in order to remove nitrogen from the anaerobic supernatant. Anaerobic co-digestion, tested in a 200 L pilot plant, enables low cost treatment of septic tank sludge and increases biogas production; however, it also increases the nitrogen load re-circulated to the WWTP, where nitrogen removal efficiency is already low (<50%), due to the low COD/N ratio, which limits predenitrification efficiency. Experimental results from a SHARON process tested in a lab-scale pilot plant show that nitrite oxidising bacteria are washed-out and steady nitrite production can be achieved at retention times in the range 1 - 1.5 days, at 35 degrees C. In a lab-scale SBR reactor, coupled with a nitration bioreactor, maximum specific nitrogen removal rate under nitrite-limiting conditions (with doubling time equal to about 26 days at 35 degrees C) was equal to 0.22 kgN/kgSSV/d, about 44 times the rate measured in inoculum Anammox sludge. Finally, a cost analysis of the proposed upgrade is reported.
Caffaz
S
S
Department of Civil Engineering--University of Florence, Italy. scaffaz@dicea.unifi.it
Canziani
R
R
Lubello
C
C
Santianni
D
D
D001421:Bacteria, Anaerobic / Q000378:metabolism; D003365:Costs and Cost Analysis; D007558:Italy; D009566:Nitrates / Q000032:analysis / Q000302:isolation & purification; D009573:Nitrites / Q000032:analysis / Q000302:isolation & purification; D009584:Nitrogen / Q000302:isolation & purification* / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000032:analysis / Q000302:isolation & purification; D012722:Sewage / Q000737:chemistry; D018508:Water Purification / Q000191:economics / Q000295:instrumentation* / Q000379:methods*
D009566:Nitrates; D009573:Nitrites; D000644:Quaternary Ammonium Compounds; D012722:Sewage; D009584:Nitrogen