*** Compilado por RESOL Engenharia LTDA ***

 

 

 

 

 

 

 

 

Leachate Treatment Process of

China Urban Domestic Refuse Landfill Site

by

Yang Xiangping , Hang Shijun

Deputy Chief Engineer of

Beijing Municipal Engineering Bureau

 

 

 

 

 

 

 

 

 

 

 

 

 

I. General Situation of China Urban Domestic Refuse Disposal

China is now devoting itself to modernization construction. With the development of economics at high speed, the amount of urban domestic refuse increases rapidly. At present, the domestic refuse generated by per head has reached 440 kg/year, the total amount of a year is over 80 million tons. At the same time, the amount of refuse still increases at the speed of 8~10% annually. Large quantities of domestic solid wastes are carried to the suburb of city and piled in the open air, doing great damage to environment sanitation and seriously hampering the development and construction of city. On the ground of statistics, 60 trillion tons of domestic refuse are piled in the suburb over the years, 5 billion square meters of lands are seized and more than 200 cities are encircled by refuse. It is estimated that the amount of urban domestic refuse will reach 1.5 billion tons/year until the year of 2000.

According to the National Municipal Public Facilities Survey of June 30. 1996, there are 7892 transfer stations, 640 Urban Domestic Refuse Disposal Plants (Sites) in 627 cities throughout the country. The capacity of refuse disposal is 158,000 tons/day and over 10 billion tons of refuse have been treated by these plants (or sites). Table 1 is the general situation of China Domestic Refuse Disposal.

 

General Situation of China Urban Domestic Refuse Disposal Table I

 

Number of

Refuse Disposal Plants (Sites)

of

Cities

Number of Plants

Capacity of Refuse Disposal (ton/day)

Annual Amount of Refuse Disposal

 

(Sites)

Total

Compost

Landfill

Incineration

(ton/year)

627

 

240

158,054

29,719

125,178

3,157

46,050,000

 

II. Composition of Domestic Refuse

China has a vast territory, the fundamental conditions and relevant factors between cities are quite different, therefore, the composition of refuse are different. For examples, the composition of refuse from large cities is as followed: organic matter amount to over 30% of the total amount, inorganic matter is about 60%, other wastes (such as waste paper, metal, plastic, textile) is only 4~6%. The domestic refuse from small cities contain about 20% organic matter, 65% inorganic matter and the percentage of other wastes is very small. Table 2 is the composition of China Urban Domestic Refuse (%).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Composition of Chine Urban Domestic Refuse Table 2

 

Year

 

Kitchen

Garbage

Waste

Paper

 

Plastic

Textile

Wood

Peel

Metal

Glass

Earth

Sand

Others

1991 Average

33.81

3.06

3.09

1.81

2.65

11.23

1.48

2.60

29.78

19.23

1992 Average

36.04

3.19

3.40

1.96

2.89

11.66

1.59

2.29

29.63

15.52

1993 Average

34.37

3.91

29.78

2.00

3.55

10.67

1.64

2.28

30.56

14.13

1994 Average

34.28

3.81

4.34

2.07

3.09

12.67

1.60

2.45

28.44

15.59

1995 Average

33.15

3.75

28.34

2.95

3.19

12.97

1.46

2.64

27.43

12.92

1999 Average

36.04

3.79

25.95

2.69

3.14

12.79

1.41

2.85

25.48

12.83

Total Average

34.73

3.60

15.96

2.27

3.09

12.03

1.52

2.53

28.39

14.96

 

III. Generation and Characteristics of Leachate of Domestic Refuse Landfill Site

1. Generation of Leachate:

Leachate of Refuse Landfill Site is mixed liquids of which produced during the process of refuse decomposition and infiltration water from ground water, surface water as well as precipitation seeping through refuse layers.

After filling-up, the liquid in the refuse will leach out because of pressure and degradation of microorganism. The liquid produced by biological degradation and infiltration of surface water such as precipitation, except part recycle to the atmosphere by evaporation, will be kept in refuse layers. When the containing water in the refuse layers exceeding its water capacity, water will seep down by gravity and then collected by leachate collection system to drain out, that's how the leachate forms. The generation mechanism of leachate can be illustrated by water equilibrium principle of Refuse Landfill Site. See formula 1.

 

C = P - (PR + E + S) (1)

among which C ---- Total amount of water that seep into the surface land of Refuse Landfill Site (mm)

P ---- Precipitation (mm)

R---- Runoff coefficient

E ---- Evaporation discharge (mm)

S ---- Original containing water in the soil or refuse (mm)

When P~/4PR + E + S. namely C1/4 0, no leachate forms in Refuse Landfill Site.

When P3/4PR + E + S. namely C 3/4 0, leachate forms.

Obviously, precipitation (rain, snowmelt) is main source of leachate; and original containing water in wastes and liquid from decomposition is just potential source.

2. Characteristics of Leachate:

Leachate quality varies with the sorts and composition of refuse. After landfill, the biological reactions in the refuse layers are different during different periods, so the components of leachate will have relevant changes. Under normal conditions leachate can be divided into two kinds on the basis of time of refuse being buried: one is the socalled "young" leachate from refuse being buried less than five years, its traits are low pH, high COD and BOD5, and BOD5/COD value is also high; another kind is the socalled "old" leachate from refuse being buried more than five years with low COD and BOD5, pH is more than 7, BOD5/COD value is low.

For different Refuse Landfill Site, as the climate condition, hydrological condition, treatment process and capacity are various, especially different refuse sorts and composition, so the leachate component and characteristics differs from one to another. Table 3 is typical leachate components of Refuse Landfill Site.

 

 

Typical Leachate Components of Refuse Landfill Site Table 3

 

 

Components

Typical Contents

(mg/L)

Range (mg/L)

BOD5

20000

200~40000

COD

30000

300~60000

NH4+ - N

500

5~750

pH

6

4.2~7.8

Fe

500

250~2500

Zn

50

25~250

Pb

2

0.2~10

 

3. Characteristics of Quantity of Leachate:

Quantity of leachate is affected by varied factors such as precipitation, topography, refuse types and composition, treatment capacity of Refuse Landfill Site etc., among which the precipitation and evaporation discharge are two principle factors, especially precipitation has the most noticeable influence to the quantity of leachate.

Normally the more precipitation there are, the greater the quantity of leachate is. For this reason, the quantity of leachate changes with seasons. The maximum/minimum of leachate quantity is about 10:1 in snow precipitation area while the ratio is about 4:1 in no snow precipitation area. It's really difficult to accurately calculate the quantity of leachate so the average quantity is used as quantitative index.

 

The quantity of leachate is usually calculated by the following simplified formula:

 

Q= Co-eds (2)

among which Q ----- Quantity ofleachate~m3/month)

p ----- Precipitation monthly (mm/month)

e ----- Evaporation discharge of surface land (mm/month)

s ----- Area of Refuse Landfill Site (m2)

 

4. Characteristics of Leachate Treatment:

Leachate is a kind of high-strength organic waste water. Its quantity and quality fluctuate constantly. So this characteristics of leachate must be taken into account when choosing leachate treatment process.

First of all, the quantity of leachate changes abruptly and particularly changes with seasons. In order to satisfy the maximum and average quantity of leachate during operation' the Adjusting Pond is needed.

Secondly, the quality of leachate changes as the time of refuse filling-up goes on. At the beginning of landfill, its BOD5/COD value is high, namely its ability that can be biologically treated is good. But when all kinds of reactions in the refuse layers reach stable, BOD5/COD value is getting small, namely its ability that can be biologically treated is low, and the concentration of NH4+ - N is getting high.

It is clear that single treatment method can't achieve the desired treatment results, so usually adopt compost system to treat leachate.

 

IV. Leachate Treatment Process:

The leachate treatment process are many and varied. Here we just introduce some processes adopted in Urban Refuse Landfill Sites in our country.

1. Ar Suwei Refuse Landfill Site in Beijing:

BOD5 = l000 mg/L COD = 2000 mg/L COD = 2000 mg/L

S S = 600 mg/L TN = 85 mg/L TN 8 5 mg/L

BOD5 = 20 mg/L COD = 60 mg/L COD - 60 mg/E

SS = 50 mg/L TN = 30 mg/L TN - 30 mg/L



Leachate Effluent





Return Sludge


 

 


To refuse dumping

area

 

 

Figure 1. Leachate Treatment Process Flow

 

 

 

N

Name

Number

Parameter

1

Anaerobic Tank

2

Depth: 4,5m Detention Time: 8 hr

2

Oxidation Ditch

1

Depth: 4.5m Detention Time: 70 hr

3

Sedimentation Tank

2

Diameter: 6m Depth: 2.5 m

4

Sludge Storage Tank

1

Diameter: 5m Depth: 2.0m

 

2. Tian Zilin Refuse Landfill Site in Hang Zhou City:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Return Sludge Return Sludg



Leachate Effluent












 

 

 

Sludge cake to be transported out

 

 

Figure 2. Leachate Treatment Process Flow

 

 

 

 

Technical Parameter of Primary Constructions Table 4

 

N

Name

Specifications

1

Adjusting Pond

Volume: 2.343 m3

2

Primary Sedimentation Tank

BjÁL = 3j Á6m Effective depth: 2m

Detention time: 2.88 hr

3

Primary Aeration Tank

F = 42 m3 Depth: 6m Detention time: 20 hr

MLSS = 5 g/L Air supply: 22 m3/min

4

Secondary Sedimentation Tank

BjÁL=3.5 jÁ7m Depth: 3 m

Detention time: 1 .96 hr

5

Secondary Aeration Tank

F=31.5m3 Depth: 6m T=15 hr

MLSS = 2 g/L Air Supply: 8 m3/min

6

Third Sedimentation Tank

BjÁL=3 jÁ6m Depth: 2.5 m T=2.4hr

 

 

Primary Equipment Table 5

N

Name

Specifications

Number

1

Inlet Pump

50PWF Q = 10~19m3/br

H = 18~16.5m N = 4kw

2

2

Roots Blower

635LD-6000 Q = 35.5m3/min

H 6000Pa N = 55kw

2

3

Roots Blower

L43LD-4000 Q 20.14m3/min

H = 4000Pa N = 22kw

1

4

Return Sludge Pump

80WG Q = 20~53m3/hr

H = 11~10.2m N = 3kw

2

5

Return Sludge Pump

25WG Q = 3~7.25m3/h

H = 11.5~8m N 1.5kw

2

6

Filter Press

BMY730-A F= 30m2 N=1.1kw

2

7

Sludge Pump

DGB25 Q = 1.4~2. 5m3/h 8kg/cm3

N = 4kw

2

8

Double Spiral Fixed Aerator

<<Á420

48

 

  1. Lao Gang Refuse Landfill Site in Shang Hai City

NH4+ - NjÜ80mg/L

 

 

 

 

To the East

Leachate China Sea









 

 

 

 

Figure 3. Leachate Treatment Process Flow

 

4. Da Tianshan Refuse Landfill Site in Guang Zbou City

COD = 6466 mg/L BOD5 = 3502 mg/L

SS = 329.6 mg/L pH = 5~6.5

COD = 226.7 mg/L BOD5 = 1 3.3 mg/L

SS = 27.8 mg/L pH = 6.5~7.5

 

Leachate Effluent







 

 

 

 

 

 

To Refuse Landfill Site

 

Figure 4. Leachate Treatment Process Flow

 

5. Lu Quan Refuse Landfill Site in Shi Jiazhuang City:

 

 

 

 

 

 

 

 

Sprayng irrigation of

Refuse dumping area by

Leachate Effluent leachate








To refuse


dumping


area

 

Figure 5. Leachate Treatment Process Flow

 

Primary Design Process Flow

 

N

Name

Number

Parameter

1

Adjusting Pond

2

Total volume: 9000m3

Detention time: 6.9 days

2

Anaerobic Tank

2

Length: 4.5m Width: 3m Depth: 4m ~

Detention time: 4hr |

3

Oxidation Ditch

1

Length: 29m Width: 7m Depth:3.5m ~

Detention time: 1.96 days |

4

Sedimentation Tank

1

Diameter: 7m Effective depth: 2.5m ~

Detention time: 3.0 hr |

5

Sludge Storage Tank

1

Length: 5m Width: 5m Effective depth:4m

Detention time: 2 days l

 

Spraying irrigation of refuse by leachate effluent can accelerate the degradation of organic matter in refuse and the disposal period of refuse can be shortened to 2~3 years from ordinary 15~20 years. On the other hand, the quantity of leachate will decrease during the process of spraying irrigation by evaporation, meanwhile when leachate seep through the refuse layers, it can be degraded by microorganism in order to partially reach stable.

 

V. Conclusion

Most of lechate treatment process in our country achieved the desired treatment results. At the beginning of landfill, the BOD5/COD value of leachate is higher and the ability that can be biologically treated is good so various kinds of aerobic treatment process such as activated sludge, oxidation ditch, big-disk, stabilization pond, contact oxidation and so on can be adopted. But as time goes on, the concentration of NH4+ - N in the leachate increases of the quantity of aeration and consumption of energy is relevantly improved. If anaerobic process is adopted as supplementary treatment, the treatment effect can be greatly improved and can satisfy the changes of leachate quantity and quality during the whole landfill periods bringing about flexible operation.

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