Thesis - faculty.ait.ac.th - Asian Institute of Technology

Table 4.16 MLSS and MLVSS Concentrations in Yeast and Bacteria Reactors
Sample Reactor MLSS (mg/L) MLVSS (mg/L) MLVSS/MLSS
1
YMBR
BMBR
12,750
12,867
9,866
8,467
0.77
0.66
2
YMBR
BMBR
13,267
14,133
9,834
9,066
0.74
0.64
3
YMBR
BMBR
12,433
12,167
9,667
8,167
0.78
0.67
4
YMBR
BMBR
13,367
13,233
9,833
8,333
0.74
0.63
4.5.4 EPS Formation
The sludge surface is polymeric in nature comprising of protein, polysaccharides,
nucleic acid and lipid (Goodwin and Foster, 1985). These extracellular polymeric
substances excreted by the microorganisms in the microbial floc are a major foulant in the
membrane coupled activated sludge process (Chang, et al., 1996; Nagaoka, et al., 1996).
So, in addition to the sludge properties, EPS of the mixed liquor of the bacterial and yeast
system was measured. Table 4.17 and 4.18 summarizes the variation in bound and soluble
EPS of YMBR and BMBR. The EPS components could be sub-divided into two parts;
namely the bound and soluble EPS. The bound EPS corresponds to the polymeric
substances adhered together with each other and to the microorganisms. The soluble EPS
indicates the microbial products which have been produced by the microorganisms and
suspended in the mixed liquor in a soluble form. Both the bound and soluble EPS were
measured as TOC.
Table 4.17 Bound EPS Concentration in the YMBR and BMBR Systems
Sample Reactor MLSS
(mg/L)
TOC
(mg/g SS)
Protein
(mg/g SS)
Carbohydrate
(mg/g SS)
Protein/Carbohydrate
1 YMBR 12,750 46.7 35.4 24.1 1.47
BMBR 12,867 47.3 35.5 26.2 1.35
2 YMBR 13,267 43.5 34.5 21.0 1.64
BMBR 14,133 42.3 30.6 25.0 1.23
Table 4.18 Soluble EPS Concentration in the YMBR and BMBR Systems
Sample Reactor MLSS
(mg/L)
TOC
(mg/g SS)
Protein
(mg/g SS)
Carbohydrate
(mg/g SS)
Protein/Carbohydrate
1 YMBR 12,750 133.1 53.4 41.2 1.29
BMBR 12,867 138.3 74.8 44.9 1.66
2 YMBR 13,267 123.2 50.3 46.9 1.07
BMBR 14,133 147.9 72.1 46.4 1.55
While measuring the bound and soluble EPS of the bacterial and yeast system, it was
found that in comparison between YMBR and BMBR, bound EPS concentration in terms
of TOC was not different while, soluble EPS of mixed bacterial sludge was higher than
that of mixed yeast sludge. Thus, this indicates soluble EPS could be the factor affecting
the membrane biofouling. In the soluble EPS, the protein content was also less. A yeast
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