Biomedical Engineering Reference
In-Depth Information
Chapter 5
U
NCOUPLED
E
NERGY
M
ETABOLISM FOR
S
LUDGE
R
EDUCTION IN THE
A
CTIVATED
S
LUDGE
P
ROCESS
Bo Jiang
1
, Yu Liu
1
, Guanghao Chen
2
and Etienne Paul
3
1
School of Civil and Environmental Engineering, Nanyang Technological University, 50
Nanyang Avenue, Singapore 639798
2
Department of Civil and Environmental Engineering, Hong Kong University of Science
and Technology, Hong Kong
3
Université de Toulouse; INSA, UPS, INP; LISBP, 135 Avenue de Rangueil, F-31077
Toulouse, France; INRA, UMR792 Ingénierie des Systèmes Biologiques et des Procédés,
F-31400 Toulouse, France; CNRS, UMR5504, F-31400 Toulouse, France
Abstract
The activated sludge process is a mature and widely-adopted biotechnology for treating both
municipal and industrial wastewater for more than one century. However, a large quantity of
excess sludge is inevitably generated as a byproduct of biological conversion of organic
matters during the process. Treatment and disposal of this byproduct usually accounts for up
to 60% of the total capital and operation cost; thus it poses a great challenge in the field of
environmental biotechnology. In order to solve this problem, some strategies for minimizing
sludge production have been explored and developed, e.g. lysis-cryptic growth, bacteriovoric
metabolism, maintenance metabolism and uncoupled energy metabolism-associated sludge
reduction, etc. Lysis-cryptic growth technique is using either physical or chemical forces (e.g.
heat treatment, ozonation, chlorination, etc.) to disintegrate and mineralize sludge. However,
this method is difficult to control, expensive to implement and have a low efficiency. Such
drawbacks weaken its capability in practice. Bacteriovoric metabolism method highly depends
on the properties of predators and requires strict control of growth conditions to promote
specific predator to bloom. Uncoupled energy metabolism of activated sludge is an alternative
to reduce excess sludge generation in the activated sludge process. Microbial metabolism is
basically includes interrelated catabolic and anabolic reactions. Under normal conditions,
catabolism of microbes is tightly coupled with anabolism in the light of energy requirements.
However, energy uncoupling can be triggered when some abnormal conditions are present,
such as excess carbon source and nutrients limitation; high temperature; alternative aerobic-
anaerobic cycle; and presence of metabolic inhibitors. Under such conditions, energy
generation from catabolizing substrate is in excess with respect to the anabolism requirement,
