For the denitrification of low C/N ratio wastewater, it is necessary to feed external carbon source as na electron donor. The commonly used carbon source nowadays is methanol. But it is not the most effective carbon source because of its relatively high cost, and low denitrification rate ability.
To find more economical and effective carbon source, two carbon sources were selected for this stuly: hydrolyzed molasses and effluent from acidogenic phase of swine watewater and food waste leachate‘s mixture.
Molasses was hydrolyzed at pH 3.6 and resulted in 0.52㎏ reduced sugar/㎏ molasses. For using the effluent as carbon source, a 1:1 mixture of swine wastewater and food waste leachate was 3 times diluted for acidification at 8 to 30 days hydraulic retention time (HRT). The total volatile acid (TVA) in the effluent from acidogenic phase was up to 4,933 ㎎/L.
The increase of C/N ratio raised the denitrification rate of hydrolyzed molasses and effluent from acidogenic phase. The denitrification rate of the two carbon sources was 1.3-3.9 and 1.1-4.0 ㎎ $NO_3$-n/g VSS·hr and the substrate consumption rate did not change with the change of C/N ratio. The readily biodegradable substrate percent of hydrolyzed molasses and effluent from acidogenic phase were 37.8% and 49.6% respectively.
To consider the effects of hydrolyzed molasses and effluent from acidogenic phase as carbon source, sequence-batch-reactor (SBR) was chosen to treat the artificial municipal wastewater. For one cycle of SBR the required time for denitrification by methanol, hydrolyzed molasses, and effluent from acidogenic phase as carbon source were 4 hr, 3 hr, and 1 hr respectively. The carbon source of effluent from acidogenic phase showed the highest denitrification rate close to the result of batch tests. Comparing the effluents from reactors, hydrolyzed molasses showed the highest nitrogen removal rate 85-90%, higher than that of methanol 75-85%.
Ammonia in effluent from acidogenic phase lowers the total nitrogen removal,in spite of the highest denitrification rate.
By increasing the recycle rate of reactor, which was supplied by effluent from acidogenic phase as carbon source, the nitrogen removal rate increased from 78-82% to 81-87%. During the operation the sludge settling was effective, and the sludge volume index(SVI) of effluent acidogenic phase as carbon source was a little bit higher than those by using methanol and hydrolyzed molasses as carbon source.