Thesis - faculty.ait.ac.th - Asian Institute of Technology
Thesis - faculty.ait.ac.th - Asian Institute of Technology
Thesis - faculty.ait.ac.th - Asian Institute of Technology
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Chapter 5<br />
Conclusions and Recommendations<br />
This study investigated biological processes by using mixed yeast cultures and mixed<br />
b<strong>ac</strong>teria cultures for treating landfill le<strong>ac</strong>hate containing high organic and ammonium<br />
nitrogen concentrations. Basic studies on biokinetic coefficient <strong>of</strong> yeast and b<strong>ac</strong>teria sludge<br />
were carried out. The effects <strong>of</strong> high ammonium nitrogen on <strong>th</strong>e yeast and b<strong>ac</strong>teria sludge<br />
were evaluated using a respirometric me<strong>th</strong>od.<br />
The main part <strong>of</strong> <strong>th</strong>is study was focused on <strong>th</strong>e membrane biore<strong>ac</strong>tor. The potential<br />
for developing a membrane biore<strong>ac</strong>tor using mixed yeast sludge (YMBR) and mixed<br />
b<strong>ac</strong>teria sludge (BMBR) for treating raw le<strong>ac</strong>hate and stripped le<strong>ac</strong>hate was examined. The<br />
last section <strong>of</strong> <strong>th</strong>is study was focused on <strong>th</strong>e sludge properties, and membrane performance<br />
was investigated. The summary and conclusions drawn from <strong>th</strong>e experimental results are<br />
presented below.<br />
5.1 Conclusions<br />
1. In a membrane biore<strong>ac</strong>tor which was used to treat raw le<strong>ac</strong>hate, it was found <strong>th</strong>at <strong>th</strong>e<br />
average COD removal efficiency <strong>of</strong> <strong>th</strong>e YMBR was slightly higher <strong>th</strong>an <strong>th</strong>at <strong>of</strong> <strong>th</strong>e<br />
BMBR for varied HRT. The average COD removal efficiency in YMBR system was<br />
65±2% when HRT was in <strong>th</strong>e range <strong>of</strong> 16 to 24 h, whereas in BMBR system, <strong>th</strong>e<br />
average COD removal efficiency was 62±2% at <strong>th</strong>e same range <strong>of</strong> HRT. At HRT <strong>of</strong><br />
12 h, <strong>th</strong>e average COD removal efficiency in YMBR and BMBR were 60% and 51%,<br />
respectively. The decrease in removal efficiency in <strong>th</strong>e b<strong>ac</strong>terial system at a lower<br />
HRT was obviously seen. This can be due to <strong>th</strong>e presence <strong>of</strong> ammonia in <strong>th</strong>e le<strong>ac</strong>hate<br />
which posed toxicity to <strong>th</strong>e b<strong>ac</strong>terial culture. In addition to a better COD removal<br />
efficiency, YMBR was more stable <strong>th</strong>an BMBR. This could be considered as a<br />
specific advantage wi<strong>th</strong> <strong>th</strong>e yeast sludge over <strong>th</strong>e b<strong>ac</strong>teria sludge.<br />
2. The average TKN removal efficiency for bo<strong>th</strong> YMBR and BMBR systems, treating<br />
raw le<strong>ac</strong>hate at different HRT, was from 19-29% and 14-25%, respectively. The<br />
concentration <strong>of</strong> nitrite and nitrate (NO2 - and NO3 - ) in YMBR and BMBR effluents<br />
were in <strong>th</strong>e range <strong>of</strong> 0.8 to 6.4 mg/L and less <strong>th</strong>an 1.0 mg/L, respectively. This can be<br />
due to high organic and ammonium nitrogen concentrations and pH ranges.<br />
3. For <strong>th</strong>e ammonia striping process, <strong>th</strong>e average ammonia removal efficiency <strong>of</strong> 86%<br />
could be <strong>ac</strong>hieved <strong>th</strong>rough a stripping process carried out wi<strong>th</strong> a high speed velocity<br />
gradient (G) <strong>of</strong> 2,850 s -1 at pH from 11 to 12 for 5 h.<br />
4. In MBR which was used to treat stripped le<strong>ac</strong>hate, it was found <strong>th</strong>at <strong>th</strong>e fluctuations<br />
in terms <strong>of</strong> COD removal wi<strong>th</strong> ammonia stripping were lower <strong>th</strong>an <strong>th</strong>at wi<strong>th</strong>out<br />
ammonia stripping. The COD removal in bo<strong>th</strong> YMBR and BMBR wi<strong>th</strong> <strong>th</strong>e ammonia<br />
stripping was <strong>th</strong>e same. Bo<strong>th</strong> <strong>th</strong>e membrane re<strong>ac</strong>tors showed a COD removal <strong>of</strong> 72%<br />
at 16 h HRT and 76% at 24 h HRT. It was clear <strong>th</strong>at <strong>th</strong>e ammonia stripping improved<br />
<strong>th</strong>e performance <strong>of</strong> COD removal <strong>of</strong> <strong>th</strong>e BMBR much more <strong>th</strong>an <strong>th</strong>at <strong>of</strong> <strong>th</strong>e YMBR<br />
system as anticipated from <strong>th</strong>e toxicity studies. The BOD removal in bo<strong>th</strong> YMBR<br />
and BMBR systems was above 94%. This means <strong>th</strong>at <strong>th</strong>e membrane biore<strong>ac</strong>tors were<br />
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