Pilot-scale Study of River Sewage Treatment by Aerobic-anaerobic

Reactor

Zhu Haiyan

Department of Chemical Engineering, Inner Mongolia Vocational College of Chemical Engineering,

Huhhot, Inner Mongolia, 010010

Keywords: River Sewage, Kaldnes Carriers, Fixed-bed Bioreactor, Sludge Reduction.

Abstract: The work conducted a pilot-scale study of sewage treatment of a certain river in the Yuquan District of

Huhhot by aerobic-anaerobic fixed-bed bioreactor constructed by Kaldnes carriers. After the reactor started

off to work, the biological film on the stuffing increased the thickness to about 1 mm a week later. It is

shown from the results after a continuous operation of 30 d that the ammonia nitrogen will become 5-10

mg/L when the water ingress COD is 60-150 mg/L and will get lower than 2 mg/L when the effluent COD

is under 40 mg/L. If the concentration of effluent suspended solid without precipitation is below 10 mg/L

and the chroma is inferior to 1,00 after the device is of stable operation, it can be indicated that the reactor is

effective for the removal of organic matter, ammonia nitrogen and chroma. The pilot-scale experiment in

the work verifies the feasibility and advantages of river sewage treatment in use of this reactor, which

proposes the new concepts and methods for the river sewage treatment.

1 INTRODUCTION

At present, the seven largest rivers of China are all

facing pollution of different degrees. Especially in

the 138 urban rivers, the vast majority that flow

through the prosperous areas are polluted in varying

levels, among which 38% are under the national

surface water quality standard V grade. Thus, it

clearly reflects based on the facts above that China is

now suffering severe water pollution and obvious

deterioration trend. Currently, there are mainly three

kinds of river sewage control technologies already in

use or tested both at home and abroad: physical,

chemical and biological methods. But the chemical

methods are not applicable here due to the large

amount of waste water and relatively low pollutant

concentration. With regard to river purifying

technology, so far in China, only physical methods,

such as water dilution and desilting, have been put

into realistic application. However, physical

methods are always palliatives that treat the

symptom but not the underlying problems.

Biological methods are the mostly studied by the

reasons that the organic matter, nitrogen and

phosphorus can be effectively dislodged from the

waste water by this method. Thereinto, most of the

research aims at the biofilm technology, but the

disadvantage is that the excess sludge produced in

the process of waste water treatment is easy to cause

secondary pollution. In particular, the excess sludge

will increase the sediment quantity. Prolonged

pollutants degradation is bound to exert a potential

adverse effect on the function of rivers. In order to

remove pollutant and reduce sludge, it is effective to

add stuffing into the aeration tank, or enhance the

biomass and the residence time of microorganism.

One of the most common biofilm technologies is the

Moving Bed Biofilm Reactor (MBBR). Kaldnes

stuffing is added to the aeration tank and anaerobic

tank so as to enhance the biomass and reduce the

sludge. On account that the carrier, having a cutting

effect on bubble, is added to the reactor, the aeration

rate will be inferior to that by the conventional

biological methods. For this reason, it can finally

increase the unit concentration of microorganism

and decrease the construction and operation costs.

MBBR has been widely adopted in the upgrading

and rebuilding of sewage treatment plants in Europe.

While in China, the method is only experimented in

the Lucun Wastewater Treatment Plant in Wuxi and

has achieved satisfactory results.

With the accretion of population, the Heihe

River in the Yuquan district of Huhhot suffers

severe contamination. Most parts of the river are

classified under V grade or worse than V grade 1,

with the pollution characteristics as synthetic

organic pollution. Ammonia nitrogen and total

phosphorus are the main pollutants, and the

214

Haiyan Z.

Pilot-scale Study of River Sewage Treatment by Aerobic-anaerobic Reactor.

DOI: 10.5220/0006022502140217

In Proceedings of the Information Science and Management Engineering III (ISME 2015), pages 214-217

ISBN: 978-989-758-163-2

domestic runoff is the primary pollution source,

followed by industrial waste, poultry and stock farm,

farmland and surface runoffs. The research utilized

aerobic-anaerobic biointerval moving bed reactor

(hereafter referred to as reactor) to dispose the

sewage. In this way, it is conducive to maintaining

microorganism inside the reactor in high

concentration and enhance the unit processing load.

There is no need of nitrification liquid reflux to cut

down energy consumption. Moreover, the diverse

aerobic and anaerobic environment inside the reactor

can reduce the productivity of excess sludge in the

process of sewage treatment. Thus, the goal can be

achieved that the excess sludge is decreased or even

eliminated at the same time of treating the waste

water. This reactor adopts the Kaldnes carrier that is

extensively used in the market. The Kaldnes carrier

is known for the characteristics of large specific

surface area, big quantity of biofilm formation and

fast biofilm forming speed.

In order to further explore the effects and

feasibility of the reactor on removing the organism

and nitrogen in the water courses of Huhhot, the

pilot-scale test was carried on to study the process of

river sewage treatment. This, as a result,

accumulated abundant engineering data for the

popularization and application of this technology.

2 TEST MATERIAL AND

METHOD

2.1 The Water Samples Were Collected

in the River near Yuquan District

in Huhhot.

The quality of waste water was tested with pH

between 7.0 and 8.2, ammonia nitrogen between 5

and 10 mg/L, TP between 0.2 and 1 mg/L, COD

between 60 and 150 mg/L and chroma between 200

and 500. The water temperature during this period

was between 18 and 24.

2.2 Testing Apparatus and Process

Flows

The pilot plant and process flows in the sewage

treatment are shown as follows. The pilot plant has a

height of 1.2 m (effective height of 1m), width of

0.33 m and length of 3 m. Interrupted by the

clapboard, the plant can be divided into nine zones.

The volume of the whole reactor is 1 m3. Inside the

reactor, there is 65% of Kaldnes stuffing, with a

diameter of 2 cm, thickness of 1 cm and specific

surface area of 450 m2/m3, placed in the reactor.

The void fraction of the reactor is 95%. Through

placing perforated aerator pipe at different positions

inside the reactor, the aerobic zone and anaerobic

zone are alternatively formed. The gas water ratio is

kept within 15:1 and the residence time of waste

water in the reactor is 10 h. By this method, the

sewage is pumped into the reactor from the river

with no need for primary settling tank or regulating

reservoir. Besides, the waste water can directly be

drained after reactor processing with no use for

secondary settling tank and can flow in the way of

baffling in the reactor. The amount of daily water

treatment reaches 2.4 tons.

2.3 Test Methods and Plant Operating

Conditions

Before the test, the activated sludge by filter

pressing should be collected from the nearby sewage

treatment plant and inoculated to the reactor in the

front. The inoculum concentration should be

controlled within the range between 10% and 15%

of the reactor volume. At the back of the reactor,

two aerobic zones should inoculate microorganisms

domesticated in the lab to remove the nitrogen-

containing compounds. Such microbial populations

contain quite a few nitrifying and denitrifying

bacteria, by which they can effectively remove the

nitrogen-containing compounds. Then the inoculated

reactor begins to input water continuously. After a

week, the microorganisms inside gradually adapt to

the characteristics of river sewage. The biofilm on

the carrier has a thickness of 1 mm and is khaki in

color. Owing to the aeration that makes the Kaldnes

stuffing keep tumbling, the internal biofilm of

Kaldnes stuffing at the aerobic zone gains a higher

thickness than the external surfaces. While in that

the Kaldnes stuffing at the anaerobic zone stays

static, the sludge stacks between the inner side and

outer side interspaces and is black in color. When

the reactor can outlet water stably, it is time for data

detection. Samples should be collected in both the

entrance and exit of reactor. During this period, the

test mainly explored the effects of reactor under a

certain residence time on the removal of organism,

ammonia nitrogen, SS, turbidity and phosphorus as

well as the variations of dissolved oxygen (DO)

inside. Based on a series of laboratory research on

the residence time for river sewage of different

concentrations, the pilot-scale test controls the time

within 10 h.

2.4 Analysis Methods

The test adopted the analysis methods including

potassium dichromate method for COD

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measurement, Nessler's reagent colorimetric method

for chroma measurement, ammonium molybdate

spectrophotometric method for determination of

ammonia nitrogen content and laws of weight for

determination of suspended sludge (SS) and the

concentration variations of microorganisms on the

stuffing. Portable dissolved oxygen instrument

(Hash DO6+) was used to test the concentration of

dissolved oxygen (DO) at different positions of the

reactor.

3 RESULTS AND DISCUSSION

3.1 Removal Efficiency of Reactor on

the Organism

After a week or so, the reactor can perform stably

after some debugging. With a continuous operation

for 30 days, the reactor is able to effectively remove

the organism from the waste water. Even if the

concentration of organic pollutants fluctuates wildly,

the exit COD of reactor can still keep stable, all

under 40 mg/L. This reflects that the reactor can

steadily wipe out the organic pollutants from the

river sewage. The main reason lies in the biofilm

suspended on the Kaldnes carrier that enhances the

monolithic microorganism concentration. By

weighing the microorganism on the stuffing after

elution, the concentration can reach 6 to 8 g/L,

which is conspicuously higher than that with the

conventional activated sludge method.

3.2 Removal Efficiency of Reactor on

the Ammonia Nitrogen

It is shown that the concentration of ammonia

nitrogen is approximately 8 to 10 mg/L from the

variation of ammonia and nitrogen in the entrance

and exit of the reactor. This indicates that the river is

suffering very serious pollution and eutrophication.

After treating the waste water through the reactor,

the concentration of ammonia nitrogen in the exit

becomes lower than 2 mg/L and the plant keeps a

stable performance in removing the ammonia

nitrogen. The reactor constructed in this research

contains a repeated alternation from being aerobic to

being microaerobic, then to being anaerobic. On this

account, the nitrate and nitrite produced at the

aerobic zone can be used for denitrification at the

next anaerobic zone. In this case, there is no need of

nitrification liquid reflux to accomplish

denitrification, which is quite helpful to save energy.

Compared with the A20 technology frequently used

in the urban sewage treatment plants at present, this

reactor makes it easier to operate and saves the

transportation expenses since nitrification liquid

reflux is no longer required.

3.3 Variation of Phosphorus in the

Reactor

The removal efficiency on phosphorus is not

apparent because the excess sludge production is not

sufficient in the operation process. But the

concentration of phosphorus is rather low in the

river, basically around 0.8 mg/L. After being treated

by the reactor, the phosphorus concentration in the

exit can reach 0.5 mg/L or so. With regard to other

water courses, if the phosphorus content is pretty

high in the river, then there is a need to add medical

flocculation precipitation at the exit of the reactor to

wipe out the phosphate so as to reach the discharge

standard.

3.4 Removal Efficiency of Reactor on

It can be seen from the SS variations at the entrance

and exit of the reactor that the SS of water inflow is

about 30 to 60 mg/L while the SS of the exit is lower

than 10 mg/L with mean of 5 mg/L. This reveals that

the reactor has a very good effect on sludge

reduction. The main reason lies that the porous

Kaldnes stuffing placed in the reactor can effectively

intercept the SS at the anaerobic zone. Then the

intercepted SS can resolve at the anaerobic zone and

the organism released can be used as the carbon

source of denitrification. Studies have shown that

the aerobic, microaerobic and anaerobic alternative

environment in the reactor is prone to separate the

anabolism from catabolism of microorganisms and

drop down the productivity of sludge. Therefore, it

is believed that the environment which is

collectively aerobic, microaerobic and anaerobic can

reduce the SS in its favor, especially conducive to

the sewage treatment in the heavily polluted rivers.

In addition, after analyzing the concentration of

dissolved oxygen (DO) at different positions by

means of DO instrument, it can also be discovered

that the DO concentration at the aerobic zone is 3 to

4 mg/L and goes up as the travel distance increases

while the DO concentration at the anaerobic zone is

only 0-0.5 mg/L. This result can explain that the

alternation phenomenon of being aerobic and

anaerobic happens at the direction of reactor

horizontal flow.

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3.5 Removal Effect of Reactor on

Chroma

The original chroma of the river is dark and

seriously polluted. Seen from the appearance, the

water is almost black with peculiar smell. The

chroma of sewage tested is between 200 and 500.

And after being treated through the reactor, the

muddy water gets transparent with the chroma

reduced to 50 to 100. This manifests that the reactor

is able to steadily and efficiently clear the pollutant

and chroma in the sewage.

4 CONCLUSIONS

(1) It can be concluded that the aerobic-anaerobic

repeatedly alternative moving bed biofilm reactor

(abbreviated as the reactor) is able to treat the river

sewage effectively according to the results gained

from the continuous sewage treatment after the

stable operation of the reactor in 30 days. When

water inflow is between 60 and 150 mg/L and the

hydraulic retention time is 10 h, the exit COD can be

maintained at about 40 mg/L.

(2) This technology has a certain resistance to

COD impact and a strong adaptability to the

concentration variations of organism in the waste

water. Thus, there is no need of regulating reservoir

and secondary settling tank. The exit SS is inferior

to 10 mg/L.

(3) The resistance to COD impact is displayed in

this technology. The Kaldnes stuffing inside the

reactor enhances the concentration of

microorganisms to the twice of biomass with the

normal activated sludge method. Moreover, the

plug-flow reactor is conducive to blending the

sewage and microorganism so that the reactor shows

a stronger adaptability.

This reactor can form an aerobic and anaerobic

environment in the flow direction. This environment

can effectively remove the ammonia nitrogen in the

waste water. When the concentration of ammonia

nitrogen at the entrance reaches 8 to 10 mg/L, the

concentration of ammonia nitrogen at the exit will

drop down to less than 2 mg/L. After the reactor

performs steadily, the SS of the water outlet keeps

below 10 mg/L with a mean concentration of 5

mg/L. This reflects that the coefficient of sludge

production in the reactor is pretty low, so no

secondary settling tank is needed for sewage

treatment. Such is also regarded as one of the

remarkable advantages of this technology.

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