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

0.02, respectively. This can be considered that the slowly degradable components in
the yeast effluent are higher than that in the bacterial effluent.
11. The contribution of molecular weight compounds > 50 kDa in the raw leachate was
greater than 80% in terms of BOD and COD concentrations. This found that some
portion of the > 50 kDa compounds was broken down into < 5 kDa after ammonia
stripping. The reduction of molecular weight compounds > 50 kDa significantly
presented after MBR treatment. This showed that the complex higher molecular
weight compounds could be degraded effectively using membrane bioreactor
systems. Considering the BOD content in the effluent, it was found that in both yeast
and bacterial effluents, the molecular weight compounds < 5 kDa contributed to the
maximum BOD when compared with the other fractions. The COD content also
showed a similar trend.
12. For the sludge properties, the bound and soluble EPS of the yeast and bacteria
systems are measured. In comparison between yeast and bacteria systems, 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. Also, the protein to
carbohydrate ratio in the soluble EPS was higher. This indicated that soluble EPS
could be the factor which affected the membrane fouling.
13. The bacterial sludge showed a better dewatering quality than that of the yeast sludge.
The viscosity of the bacterial system was higher than the yeast system.
14. Ammonia stripping pretreatment with MBR was effective in treating leachate with
high ammonium nitrogen concentration but the effluent still contained a large
quantity of refractory organic compounds. This might be due to the contribution of
the slowly biodegradable organics and non-biodegradable organics containing in the
leachate. Therefore, it should be further treated in a post treatment, elevating the
water quality of the final effluent or even increasing the biodegradable organics
5.2 Recommendations for Future Work
Based on the extensive experimental results of this study, the following
recommendations are proposed.
1. For MBR system, membrane fouling is a common problem but it is made more
difficult to predict and control in the MBR. This might be due to the effects of active
microorganisms generating EPS. The EPS is of key significance with respect to
fouling that is dependent on the EPS concentrations and chemical components of
EPS. Fouling is also affected by the floc size and particle size distribution correlated
with membrane permeability. It is recommended that future work should be focused
on the contributions of the various particle fractions (suspended particles, colloidal,
soluble solids), presenting in the sludge on the mechanisms of membrane fouling.
More laboratory and pilot scale experiments are needed to estimate membrane
fouling and the influences of operating parameters.
2. In MBR system, the various soluble organic substances could be retained within the
bioreactor. The components of soluble organic compounds are complex and may
include humic substances, fluvic acids, polysaccharides, proteins, etc. Therefore, the
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