Abstract : In this study, the method of using high concentrated oxygen water to depurate the bottom sediment was confirmed to be effective. The high concentrated oxygen dissolver was developed and the lab scale experiment was performed. High rate, high efficiency oxygen dissolver was developed, the optimum running condition of the equipment and the method of making high concentrated oxygen water was discussed in this study. In addition, the inhibition of phosphorus release was also studied. On the basis of the fundamental knowledge from the lab scale study, pilot scale apparatus was set up and the pilot study was carried out.
Trang 11 INTRODUCTION
Eutrophication in the closed water body, such as lake or
reservoir, is attracting more and more attention (JONES R A
and LEE G F (1982); NAKANISHI H., et al (1991); UEDA
N., et al (2000); NOMURA R and SETO K (2002)) To
prevent the eutrophication, nowadays much effort is put on
diminishing the nutrition resource from the wastewater
treatment plants For the water bodies that are already
eutrophicated, reducing the anaerobic bottom sediment
comes to be very important In this study, the method of
using high concentrated oxygen water to depurate the
bottom sediment was confirmed to be effective The high
concentrated oxygen dissolver was developed and the lab
scale experiment was performed On the basis of the
fundamental knowledge from the lab scale study, pilot scale
apparatus was set up and the pilot study was carried out
The effects of the high concentrated oxygen water on the
bottom sediment lie in the following two aspects First,
oxygen changes the anaerobic surroundings into aerobic
ones so the phosphorus release is inhibited Second, keeping
the dissolved oxygen (DO) content at a certain value (up to
3mg/L) can not only improve the quality of the bottom
sediment, but also recover or strengthen its natural
self-purification capacity
High rate, high efficiency oxygen dissolver was developed,
the optimum running condition of the equipment and the
method of making high concentrated oxygen water was
discussed in this study In addition, the inhibition of
phosphorus release was also studied
DISSOLVER
2.1 The Development of High Concentrated Oxygen
Dissolver
The high rate, high efficiency equipment of high concentrated oxygen water is shown in Fig.1 To improve the contact efficiency between gas (oxygen) and water, pressure gas is applied to contact the water film The oxygen-water mixture is ejected into the high concentrated oxygen dissolver at a tangent so a great deal of air bubbles is produced As a result, the DO content in the water can achieve a very high value immediately The surplus oxygen
is recycled at the bottom part of the high concentrated oxygen dissolver, so it is possible to use 100% of the oxygen under the proper running condition, that is, oxygen loss can
be avoided if no gas is released from the high concentrated oxygen dissolver
O 2 P
P
oxygen
gas collection deviice
collected gas
H igh concentrated oxgen w ater
oxygen +
w ater
oxygen
ejector
Fig.1 Experimental apparatus of high concentrated
oxygen dissolver
NOVEL RESTORATION TECHNOLOGY FOR PUZRIFICATION
OF WATER QUALITY IN CLOSED WATER BODY
BY HIGH CONCENTRATED OXYGEN WATER
1 Dept of Civil and Environmental Eng., Yamaguchi University, Yamaguchi, Japan
2 Dept of Chemical and Biological Eng., Ube National College of Technology, Yamaguchi, Japan
Abstract : In this study, the method of using high concentrated oxygen water to depurate the bottom sediment was confirmed
to be effective The high concentrated oxygen dissolver was developed and the lab scale experiment was performed High rate, high efficiency oxygen dissolver was developed, the optimum running condition of the equipment and the method of making high concentrated oxygen water was discussed in this study In addition, the inhibition of phosphorus release was also studied
On the basis of the fundamental knowledge from the lab scale study, pilot scale apparatus was set up and the pilot study was carried out
Key words: Closed Water Body, Eutrophication, High Concentrated Oxygen Water, Bottom Sediment
Trang 22.2 Running Condition
DO content depends on the pressure in the high concentrated
oxygen dissolver A valve is set at the outlet of the lab scale
high concentrated oxygen dissolver By adjusting this valve,
the pressure in the high concentrated oxygen dissolver can
be increased However, increasing the pressure also means
decreasing the water flow rate, so it is necessary to find the
optimum condition to keep both of them at a proper amount
Additionally, the amount of gas supply should also be
considered to prevent the oxygen loss
In the lab scale study, 2.3-liter of high concentrated oxygen
water was made and the pressure in it was kept at 0.2Mpa
Pure oxygen was supplied as the oxygen resource DO and
flow rate were measured at the oxygen supply of 300, 500,
700 and 900 mL/min, respectively
2.3 Experimental Results
Under the running condition mentioned above, the results
are shown in Fig.2 To consider the importance of oxygen
transfer, oxygen transfer rate was applied and calculated as
follows:
Oxygen transfer rate (mg/min) =
DO (mg/L) * water flow rate (L/min) (1)
From Fig.2, it was found that the oxygen supply rate at the
oxygen supply of 700 mL/min was same as that of 900
mL/min That meant the oxygen was not fully used at the
supply of 900 mL/min and surplus oxygen was released
from the high concentrated oxygen dissolver Fig.2 revealed
that 700 ml/Min was the optimum oxygen supply amount at
the pressure of 0.2 MPa With 700 mL/min oxygen supplied,
the instant DO amount was as high as 70 mg/L and 22
m3/day of high concentrated oxygen water could be made
with this high concentrated oxygen dissolver
0
2 0
4 0
6 0
8 0
0
5 0 0
1 0 0 0
1 5 0 0
concentration of dissolve oxygen（mg/L）
flow rate of effluent (L/min) O2 supply rate
flow rate of oxygen(mL/min) Fig.2 Variations of oxygen supply rate with the changes
of oxygen flow rate
Table 1 Operational conditions of Vial experiment
condition of experiment sampling analytical item
The water of bottom layer
(after the treatment by high concentrated
oxygen dissolver)+soil sediment 0,12,24hr after passing PO4-P
The water of bottom layer ＋soil sediment 3,5,7day after passing Fe 2+ ,Fe 3+
The water of bottom layer
(after the treatment of N 2 aeration)
+soil sediment
2,4week after passing
Based on these results, the pilot plant was made to produce the high concentrated oxygen water
OXYGEN WATER ON THE PHOSPHORUS RELEASE
By introducing the high concentrated oxygen water into the bottom sediment, it was expected that the phosphorus release be inhibited Vial experiment was performed to verify it The bottom sediment treated with high concentrated oxygen water was sealed into the 200 mL serum bottle and was put in a 20 oC dark incubator
0
0 1
0 2
0 3
0 4
0 5
0 6
0
0 0 2
0 0 4
0 0 6
0 0 8
0 1
0 1 2
E la p se d tim e (d a y)
F e 3 +
F e 2 +
P O 4 - P
Fig.3 Phosphorus release in the water of bottom layer
(after the treatment of high concentrated oxygen dissolver) + bottom sediment
E la p se d tim e (d a y)
0
0 1
0 2
0 3
0 4
0 5
0 6
0
0 0 2
0 0 4
0 0 6
0 0 8
0 1
0 1 2
-) P O 4- P F e 2 + F e 3 +
Fig.4 Phosphorus release in the water of bottom layer +
bottom sediment
0
0 0 2
0 0 4
0 0 6
0 0 8
0 1
0 1 2
0
0 1
0 2
0 3
0 4
0 5
0 6
E la p se d tim e (d a y)
F e 3 +
F e 2 +
P O 4 - P
Fig.5 Phosphorus release in the water of bottom layer
sediment
Trang 3Variation of dissolved phosphorus (PO4-P), dissolved ferrous
(Fe2+) and ferric (Fe3+) irons were measured with time
course, as shown in Table.1 For comparison, same
experiment was done to the bottom sediment mixed with the
bottom water sampled from the same place
Results of Vial experiments are shown in Fig.3, Fig.4 and
Fig.5 From these figures, obvious differences were found
among the different samples The inhibition of dissolved
oxygen on the phosphorus release was confirmed
4 PILOT STUDY IN THE ACTUAL CLOSED
WATER BODY
4.1 Outline
Modeled after the lab scale high concentrated oxygen
dissolver shown in Fig.1, pilot scale apparatus, shown in
Fig.6, was developed, with the production capacity of 1,000
tons of high concentrated oxygen water per day It was set in
an 18,770,000 m3 (valid volume) dam reservoir The total
volume of the reservoir was 19,570,000 m3 The high
concentrated oxygen dissolver was introduction the bottom
sediment
Though it is very difficult to depurate the lake completely,
the three-year pilot study focuses on the verifying the
feasibility of the full-scale application
P S A
P ressured S w in g A d so rption
high concentrated oxyg en w ater prod ucer
w inch
m a in cable sub
cable
sub cable
in
com pressor
A IR (O 2)
out bottom layer
bottom
sedim ent
Fig.6 Outline of experimental apparatus to prove the high
concentrated oxygen water into the dam
4.2 Pilot Scale High Concentrated Oxygen Dissolver and
Its Characteristics
The mechanisms of the high concentrated oxygen dissolver
are just the same as the lab scale one However, due to the
different water pressure at the different water depth, it is
possible to utilize the water pressure in the pilot experiment, and thus, to save the energy consumption and the running cost For example, if the high concentrated oxygen dissolver
is put at the water depth of 40 m, 0.5 MPa water pressure is exert on the high concentrated oxygen dissolver naturally With only a small pump at the outlet, 0.2 MPa can be available in the high concentrated oxygen dissolver For that purpose, the high water pressure-tolerant pump is necessary Compared with those working onshore, the submerged apparatus has some advantages First, it doesn’t need to pump, return, or transfer the substrate, so the expend on energy consumption and transferring pipelines is saved Second, the equipment doesn’t need to be cooled down when it works, so the energy consumption and device for cooling down are also no necessary And third, also the most important, in the submerged high concentrated oxygen dissolver the treated water (high concentrated oxygen water) keeps its temperature unchanged so it can keep in touch with the bottom sediment directly without any temperature control
4.3 Production of High Concentrated Oxygen Water and the Improvement Method
The pilot scale apparatus was set at a place where the average water depth was about 41 m The high concentrated oxygen dissolver was hung at the water depth of 37~38 m to avoid the bottom sediment being sucked into the high concentrated oxygen dissolver, as observed with a submerged camera In the pilot study, oxygen production device (pressure swing adsorption) used air as resource and produced 8 L-O2/min at most, so air was also supplied to remedy the inadequacy of oxygen In this way, the oxygen accounted for 30 % of the gas supplied to the high concentrated oxygen dissolver, therefore, DO concentration
in the high concentrated oxygen water was much lower than that in lab scale experiment In the pilot study, the high concentrated oxygen dissolver produced 1000 t/d high concentrated oxygen water that contained 10 mgO2/L
approx 20m approx 14m
buoy autom atic w ater
quality m easure instrum ent
T he flow direction
in the closed w ater body reservior apparatus (approxim ately 40m the depth of w ater)
T he flow direction
in the closed w ater body reservior
Fig.7 Explanation about sampling point in the dam
An YSI MODEL 58 Dissolved Oxygen Meter was used to measure the DO contents and water temperature the upper stream, the down stream and close at the high concentrated oxygen dissolver, as shown in Fig 7 Fig.8, Fig.9 and Fig.10 show the variation of DO and water temperature along with the depth at these three sites
Trang 40 5 1 0 1 5 2 0 2 5
concentration of dissolve oxygen(m g / L )
tem perature(℃)
0
1 0
2 0
3 0
4 0
concentration of dissolve oxygen tem perature
Fig.8 Variations on concentration of DO and temperature
every depth in the dam (sampling point is upper
buoy)
0 5 1 0 1 5 2 0 2 5
0
1 0
2 0
3 0
4 0
concentration of dissolve oxygen(m g / L )
tem perature(℃)
concentration of dissolve oxygen tem perature
Fig.9 Variations on concentration of DO and temperature
every depth in the dam (sampling point is under the
machine)
concentration of dissolve oxygen(m g / L )
tem perature(℃)
concentration of dissolve oxygen tem perature
0 5 1 0 1 5 2 0 2 5
0
1 0
2 0
3 0
4 0
Fig.10 Variations on concentration of DO and
temperature every depth in the dam (sampling
point is the opposition of the buoy)
From the results, a thermo cline was found at the depth of 30
m, DO concentration also decreased rapidly over the water
depth of 30 m However, at the depth of 37 m where the high
concentrated oxygen dissolver was set, higher DO was found at all the three sites, which verified that the high concentrated oxygen water didn’t destroy the thermocline
of the water body and surely made a layer of higher DO surroundings near the bottom
5 CONCLUSION
1 The production of high concentrated oxygen water was available by using the high rate, high efficiency oxygen dissolver The 2.3 L lab scale apparatus could make 0.015
m3/min (22 m3/d) of high concentrated oxygen water in which the instant DO could be as high as 70 mg/L
2 Samples were taken and pretreated in different ways to verify the effect of high concentrated oxygen water on the phosphorus release Compared with the sediment soaked
in bottom water and in nitrogen-aerated water, the sediment contacted with high concentrated oxygen water released the least phosphorus, which confirmed that the phosphorus release was inhibited when the high concentrated oxygen water was introduced into the bottom sediment
3 Pilot study was performed in an 18,770,000 m3 dam reservoir The apparatus for high concentrated oxygen water production was set at a place where the average total depth was about 41 m When the high concentrated oxygen dissolver was hung at the water depth of 37-38 m, oxygen accounted for 30 % of the gas supplied to the high concentrated oxygen dissolver, which produced 700 L/min (1,000 tons/day) of high concentrated oxygen water DO concentration in the high concentrated oxygen water achieved 10 mgO2/L
4 Measurement of DO concentration and water temperature confirmed that the high concentrated oxygen water didn’t destroy the thermocline of the water body and made a layer of higher DO surroundings that might alter the anaerobic conditions near the bottom
ACKNOWLEDGEMENT
The authors greatly acknowledge Mr Shioshige and Mr Ueyama for their excellent experimental assistance
REFERENCES
JONES R A and LEE G F (1982) Recent advances in assessing impact of phosphorus loads on eutrophication-related water quality, Water Res, Vol.16, No.5, pp.503-515
NAKANISHI H., UKITA M and SEKINE M (1991) Evaluation of primary production loads and their control
in enclosed seas, Mar Pollut Bull, Vol.23, pp.25-29 UEDA N., YAMADA M., TSUTSUMI H., HANAMOTO K and MONTANI S (2000) Impacts of Oxygen-Deficient Water on the Macrobenthic Faune of Dokai Bay and on Adjacent Intertidal Flats, in Kitakyushu, Japan, Mar Pollut Bull, Vol.40, No.11, pp.906-913
NOMURA R and SETO K (2002) Influence of man-made construction on environmental conditions in brackish Lake Nakaumi, southwest Japan, Foraminiferal evidence, journal of geology, Vol.108, No.6, pp.394-409