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 !