| The carbon to nitrogen ratio of below 1:1 in digested sludge liquor, i.e. centrate, need to be elevated to at least 4:1 by the addition of external carbon sources to enhance total nitrogen removal. The applicability as exogenous carbon sources of four industrial wastewaters, i.e. potato processing, canola processing and oil refining, biodiesel production byproduct (mainly glycerol) and deicing liquid from Winnipeg International Airport (mainly glycol), was evaluated because of their high carbon but negligible ammonia content and easy accessibility in Manitoba, Ca. Three bench-scale sequencing batch reactors (SBRs) were operated at 10 d SRT (solids residence time), 2.5 d HRT (hydraulic residence time) and room temperatures (21+/-2°C). One reactor was aerated all the time while alternating aerobic/anoxic condition was maintained in the other two reactors during the investigation. Nitrate uptake rate (NUR) and ammonia uptake rate (AUR) tests were performed to determine specific denitrification rate (SDNR) and specific nitrification rate (SNR) after a steady state was achieved. Both glycerol and potato wastewater showed promising potential with SDNRs of 13 mgNO3-N/gVSS*h and 12 mgNO 3-N/gVSS*h, respectively. The SDNRs were better than 10 mgNO3-N/gVSS*h with methanol but lower than 17 mgNO3-N/gVSS*h with ethanol. The additional benefit was that the bacterial response times needed were only 4 days and 2 days for glycerol and potato wastewater, respectively. The times were lower than 6 d response for ethanol and much lower than 26 days for methanol. Glycol was also a good substrate to replace purchased carbon sources as it required a 3-day response time and could enhance the SDNR to 8 mgNO3 -N/gVSS*h. However, the canola oil wastewater was eliminated because of the lowest SDNR of 5 mgNO3-N/gVSS*h it produced, a long response time of 24 days required, and the inhibitory effect on nitrification it exerted. Compared to the reference SNR of 36 mgNH3-N/gVSS*h, a hindered SNR of 10 mgNH3-N/gVSS*h was detected when canola oil wastewater was used. Potato wastewater, a byproduct of biodiesel production (glycerol) and deicing wastewater from WIA (glycol) were recommended in this study as good substitutes to the purchased chemicals as an external carbon source in denitrification. |
