2012 International Summer Water Resources Research School Dept. of Water Resources Engineering, Lund University Nitrification of saline sewage water in biofilter packed with oyster shells By Kajsa Nilsson 2012-07-10 Instructor: Professor Xiaojing Xiong Assistants: Jie Xu and Xi Chen
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2012
International Summer Water Resources Research School
Dept. of Water Resources Engineering, Lund University
Nitrification of saline sewage water in biofilter packed with oyster shells
By Kajsa Nilsson 2012-07-10
Instructor: Professor Xiaojing Xiong Assistants: Jie Xu and Xi Chen
2
Abstract
Fresh water shortages in the world create new challenges to save water and one of them
could be to use seawater as toilet-flushing. This in its turn causes a new, saline, condition
when treating sewage water. In this project the performance of nitrifying bacteria in
addition of oyster shells as packing biofilter has been investigated at different influent
seawater ratios using the sequencing batch reactor (SBR) method. The results showed that
with an influent ammonia concentration of 50mg/L the removal efficiency of ammonia in
seawater ratios from 0 to 100% all were above 99% during 24 hours. It was also found that
for sea water ratios from 40 to 70% the ammonia removal efficiency was above 95% after
only 5 hours residence time. This indicates that nitrifying bacteria could adapt to and
Nitrification of saline sewage water in biofilter packed with oyster shells
11
In figure 6 the ammonium degradation during 24 hours is visible. The vessels with 40, 50 and 60% of
sea water appears to be a little bit faster than the one with 70% of sea water but after about 5 hours
they all have removed more than 95% of the ammonium.
Figure 6 The degradation of ammonium in the vessels during 24 hours.
In figure 7 the time course of the nitrite during 24 hours is visible. It increases slowly and reaches a
maximum at about 5 hours for all the vessels. Then it decreases as the nitrite conversion increases.
The trend of the vessels is almost the same.
Figure 7 The accumulation and degradation of nitrite in the vessels during 24 hours.
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10 12 14 16 18 20 22 24
amm
on
ium
- nit
roge
n c
on
c. (
mg/
L)
time (h)
Time course NH4+-N concentration at a single SBR period
40% SW ratio
50% SW ratio
60% SW ratio
70% SW ratio
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10 12 14 16 18 20 22 24
nit
rite
nit
roge
n c
on
c./m
g/L
time/h
Time course of NO2-N concentration at a single SBR period
40% SW ratio
50% SW ratio
60% SW ratio
70% SW ratio
Nitrification of saline sewage water in biofilter packed with oyster shells
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In figure 8 the nitrate accumulation during 24 hours is visible. The nitrate concentration increases in
all the vessels and is taking a higher speed after 5 hours but slowing down after 12 hours and almost
stops.
Figure 8 The accumulation of nitrate in the vessels during 24 hours.
Discussion and analysis From the results it can be seen that it is possible to adjust the nitrifying bacteria to a saline
environment since they keep up the nitrification process. The salinity tolerance increases with time
and after 1-2 months the bacteria perform very well.14
In table 5 it can be seen that at all seawater ratios the nitrifying bacteria have converted above 99%
of the ammonia after 24hours. This is also confirmed when looking at the data in Appendix. With this
high removal efficiency it can be concluded that the nitrifying bacteria can adapt to a saline
environment, even when using 100% of seawater. There is still a question to answer though; how
fast do they convert it, does it really need a retention time of 24 hours?
In figure 6 it can be seen that about 95% of the ammonium is removed after only 5 hours which is a
fact that could shorten the retention time in a treatment plant radically. Figure 7 shows what is
connected with the ammonium conversion; the nitrite accumulation. This naturally increases when
the ammonium conversion is fast and slows down when the ammonium conversion decreases. Figure
8 visualizes the increasing amount of nitrate and follows the changes in the ammonium conversion
very good. It has to be noticed that this test, when sampling water samples more frequently during
24 hours, has only been made once and doing this several times might gives some more exact results.
In further test projects, the ammonia influent concentration will be changed at ranges of 20 to 80
mg/L. This for testing the stability of nitrification at high salinity conditions of varying ammonia
concentrations in influent.
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Discussion with Professor Xiaojing Xiong
0
5
10
15
20
25
30
35
40
45
0 2 4 6 8 10 12 14 16 18 20 22 24
nit
rate
nit
roge
n c
on
c. (
mg/
L)
time (h)
Time course of NO3-N concentration at a single SBR period
40% SW ratio
50% SW ratio
60% SW ratio
70% SW ratio
Nitrification of saline sewage water in biofilter packed with oyster shells
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Conclusions In this project a complete nitrification of simulated saline sewage water has been accomplished with
the use of a sequencing batch reactor method with biofilter packed with oyster shells at influent
seawater ratio ranging from 40% to 100%. This suggests that nitrifying bacteria shows high tolerance
to relatively high salinity.
Although the results of the project has been satisfying, the fact that other results could come out of
it, if more tests were done and if more variants of conditions were tested, cannot be excluded.
Acknowledgments I would like to thank Professor Xiaojing Xiong for letting me be on his project and for his helpful
thoughts. Thanks to Jie Xu and Chen Xi for all their help with the experimental work and translations.
A special thanks to Jie Xu for putting a lot of time on helping me with material for this report. I would
also like to thank the sponsors Tyréns and Xylem for the financial support making this experience a
possibility.
Nitrification of saline sewage water in biofilter packed with oyster shells
14
References
Avgifta Avloppet, Så funkar ett reningverk, link received 2012-06-28 http://www.avgiftaavloppet.nu/faktaomreningsverk.4.2918eb29123a281ddcf8000154.html
Biocon Labs, Inc., Nitrifying Bacteria Facts, link received 2012-07-02 http://www.bioconlabs.com/nitribactfacts.html
Chemguide, UV Visible Absorption Spectra, link received 2012-07-02 http://www.chemguide.co.uk/analysis/uvvisible/theory.html
Chen Xiaorong, China Daily, 2009-09-10, page 39, link received 2012-06-30 http://www.chinadaily.com.cn/china/2009summerdavos/2009-09/10/content_8675129.html
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Professor Xiaojing Xiong
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XIONG Xiaojing,YE Zhilong, Comparison of Nitrification Behavior Between Shell and Plastics
Ball Carrier in Aerated Biofilter, Journal of Xiamen University(Natural Science),2005-04