Biomedical Engineering Reference
In-Depth Information
Chapter 12
S
HORT
-
TERM
E
FFECTS OF
G
LUCOSE
A
DDITION
ON
N
ITRIFICATION AND
A
CTIVATED
S
LUDGE
S
ETTLEMENT IN
S
EQUENCING
B
ATCH
R
EACTORS
Guangxue Wu
1
and Yuntao Guan
2
1
Department of Civil Engineering, National University of Ireland, Galway, Ireland
2
Research Center of Environmental Engineering and Management, Graduate School of
Shenzhen, Tsinghua University, Shenzhen 518055, China
Abstract
The short-term effects of glucose addition on nitrification and activated sludge settlement
were investigated in two laboratory-scale sequencing batch reactors (SBRs): one with the
addition of glucose (G-Reactor) and the other without the addition of glucose (N-Reactor).
The characteristics of nitrification activity, nitrite accumulation, and activated sludge
settlement were examined. A high specific nitrification rate was obtained in the N-Reactor,
while a high volumetric nitrification rate was obtained in the G-Reactor. Nitrite accumulation
occurred in both reactors, and the nitrite/total oxidized nitrogen ratio in both reactors was over
67%. Nitrite accumulation in both reactors was due to low pH caused by the processing of
nitrification. In the G-Reactor, the biomass concentration did not change much; in the N-
Reactor, the biomass concentration decreased with time. The reason for decreasing biomass
concentration in the N-Reactor was as follows: (1) high extracellular polymeric substances
(EPS) produced in the N-Reactor due to shortage of organic carbon substrate, resulting in poor
settlement of activated sludge flocs; (2) poor settlement of activated sludge flocs causing
activated sludge wash out of the system, and, consequently, a low sludge retention time
occurred; and, finally, (3) the low sludge retention time further encouraged the poor
settlement of activated sludge flocs.
1. Introduction
Nitrification plays an important role in the nitrogen cycle. Nitrification includes two
steps: (i) ammonia (NH
4
-N) is oxidized to nitrite (NO
2
-N) in the nitritation step, and then (ii)
NO
2
-N is oxidized to nitrate (NO
3
-N) in the nitratation step. These two steps are carried out
