hydraulic characteristics of anaerobic granules under different operation conditions prof. he...
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Hydraulic characteristics of anaerobic granules under different operation conditions
Prof. He Yan-Ling Dr. Liu Yong-Hong
Department of Environmental
Science and Engineering, Jiaotong university
2009 年 西安交通大学承办“ The International Workshop on Strategy for
Anaerobic Biotechnology ” 邀请到来自荷兰、美国等 10 多个国家和我国著名大学厌氧生物技术领域的代表人物, 2007 年“泰勒环境成就奖” 获得者、 UASB 发明人 Lettinga 教授也应邀参会。这是我国首次高水平厌氧国际会议。
思考:我们的英语???思考:我们的英语???
1. Introduction
The successful operation of UASB-like ( UASB / EGSB 、IC ) reactors relies on the formation and maintenance of anaerobic granules under upflow hydraulic condition.
Question 1: • The hydraulic characteristics of the granules
(such as settling and expansion characteristic) are
very important to the formation and maintenance of
the granules of good quality;• The hydrodynamics of UASB-like reactors
have notable influence on the structure stability of
the granules and the removal capacity of the reactors .
But the internal relation between both side above is seldom discussed before .
学问中的问
Question 2:
For most anaerobic granules, settling velocities ( 18~100 m/h) are much more than the maximum upflow velocities (<15m/h) applied in practical operation .
However, considerable sludge washout often occurs but there is no reasonable explanation.
settling velocities ( 18~100 m/h)
Granule
Upflow velocities (<15m/h)
Why-sludge washout ???
2. Study on the settling characteristics of anaerobic granules
Almost all previous research suggest that the settling velocity of the granules could be calculated by Stokes’ law.However, Ret have scarcely been discussed before, and this is important for further convincing of the earlier results .
生物反应器 ???
独立思考、敢于怀疑!
Types of wastewater
Measured Ret
Ref.
Sample 4 5.22 Liu et al. 2006
Beet sugar factory 2
11.91 Hulshoff 1989
Sample 1 18.05 Liu et al. 2006
Sample 2 19.95 Liu et al. 2006
Sample 3 23.53 Liu et al. 2006
Distillery wastewater
22.04 Hulshoff 1989
Potato processing 47.81 Hulshoff 1989
Beet sugar factory 1
43.73 Hulshoff 1989
Wastepaper plant 60.44 Hulshoff 1989Hulshoff pol LW.1989. The phenomenon of granular of anaerobic sludge. Ph.D. Thesis.Liu Yong-hong, He Yan-ling et al. 2006.The settling characteristics and mean settling velocity of granular sludge in UASB-like reactors. Biotechnol Lett. , 28(20):1673-1678.
Ret >1?
Table 2. Measured Settling velocities and Ret of nine samples
According to Table 2, both the literature data and our experimental results on Ret values are in the range of 5 to 61. It is obviously that the settling process of these samples is not in laminar flow regime.
论证的逻辑性
0.0 0.5 1.0 1.5 2.0 2.5 3.00
102030405060708090
100110120130140150
Re t
ut (
m/h
)
dp(mm)
0.0 0.5 1.0 1.5 2.0 2.5 3.00
102030405060708090
100110120130
dp(mm)
Fig. 2 Calculated u t and Ret of sludge granules with different density
For most sludge granules ( 0.3-2.5mm), Ret are from 1 to 110.
So we suppose that the settling process is in transition flow regime (1< Ret < 500) .
数学的论证方法 : 点 - 线 -面(区域)
0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.40
10
20
30
40
50
60
70
80
90
100
110
u t Re t
dp/mm
Measured u t
Calculated ut
Measured Ret
Calculated Ret
Fig.3 The comparison between calculated and measured values of u t and Ret (the average relative errors are 4.04% and 1.68%, respectively. )
Now we can finally draw a conclusion that the settling process is in transition flow regime.
实验验证!
As we know, anaerobic flocs is smaller and sparse compared with the granules, so it is reasonable to take the settling process of the flocs as laminar flow one, and it may be the reason why most researchers take the process of the granules as laminar flow one.
So we surmised that the changes of flow regime from laminar to transition flow one may be the hydraulic boundary between anaerobic flocs and granules.
凝练总结!
3. Study on the expansion characteristics of the granules
定性- 定量的讨论:思维模式的差异
There are several papers dealing with sludge bed expansion. It is suggested that those reactors can be still studied as classic two-phase (solid –liquid) system, since they found that the effect of biogas flow rate on the bed expansion can be ignored without introducing important error. On the other hand, it was also found that the biogas has little effect on expansion behavior in our experiments. In current studies, we focus on the bed expansion presented in EGSB reactors, as a function of upflow liquid velocity. 假设的合理性!
The bed expansion here can be well represented by Richardson and Zaki correlation for bio-fluidization:
the expansion index n is a function of Ret only .
ntu u
4.1 Model development
Then expansion model was developed as follows:
0.1
0.1
ln
4.4Re100%
ln
4.4Re
0.4
1
t
t
uut
uut
e
e
0
0.1
0.1
ln
4.4Re100%
ln
4.4Re
0.41
1
t
t
uut
uut
H H e
e
4.2 Model discussion 4.2.1 bed with smaller granules (diameter in 1-2mm)
Fig. 4 The simulation analysis between bed expansion and upflow liquid velocity
Ret of smaller granules (30-40)
When Vup is lower than 2 m/h, the bed behaves as a static bed;
The bed expansion will exceed
20% when Vup is above 4 m/h.
Both are strongly consistent with the main characteristic of UASB (<2m/h) and EGSB reactors (>4 m/h).
0 1 2 3 4 5 6 7 80
20
40
60
80
EGSB
UASB
bed
expa
nsio
n (%
)
Vup(m/h)
1mm 1.5mm 2mm
4.2.2 bed with larger granules ( diameter in 3-4mm)
The mean diameter of the granules increasing from 1.5 to 3.5 mm during 1-year operation Gonzalez-Gil, et al. 2001. Cluster structure of anaerobic aggregates of an expanded granular sludge bed reactor. Appl. Environ. Microbiol. 67(8): 3683–3692.
Biobed® EGSB reactor
a patent equipment of
Biothane Corporation
资料的检索!
4 5 6 7 8 9 10 11 12 13 14 15 160
10
20
30
40
50 3mm 3.5mm 4.0mm
bed
expa
nsio
n (
%)
Vup(m/h)Vup < 5 m /h, a static bed; bed expansion is about 20% when Vup is around 10 m /h; the value is merely about 45% even when Vup is around 15 m/h;
•Now we know the reason why the reactor can operate even at so high upflow velocities. (20 ~45% vs.10~15 m/h). •All the results revealed that considerable sludge washout mainly attribute to the bed expansion in spite of high settling velocities of the granules. (For question 2)
Fig. 5 Mathematical analysis between bed expansion and Vup in a Biobed® EGSB reactor .
Ret of larger granules (60-90)
The bed expansion degree presented in full-scale UASB-like reactors should be controlled in a certain range, considering to provide a even hydraulic condition inside the reactor or outside the granules ; (For question 1)
5. Conclusions
The changes of flow regime from laminar to transition flow regime may be the hydraulic boundary between anaerobic flocs and granules, and the corresponding Ret of smaller granules (1-2mm) is 30-40 while larger ones (3-4mm) 60-90;
when the bed expansion is controlled in a suggested range of 20~40%, it also shows that the corresponding Vup is around 3~7m/h (smaller granules) and Vup is 10~15 m/h (larger granules), respectively . (For question 2)
读万卷书不如行万里路,读万卷书不如行万里路,
行万里路不如阅人无数,行万里路不如阅人无数,
阅人无数不如名师指路,阅人无数不如名师指路,
名师指路不如自己去悟。名师指路不如自己去悟。
------------ 西游记的西游记的“悟”“悟”字辈字辈
感谢各位聆听 !