Balance of Mercury in a Modern Municipal Solid Waste Landfill in China

Transcription

1 Balance of Mercury in a Modern Municipal Solid Waste Landfill in China Zhonggen Li, Xinbin Feng, et al. Institute of Geochemistry, Chinese Academy of Sciences, P R China A&WMA International Specialty Conference, Xi an, China, May 10-14, 2010

2 Background 1 Mercury (Hg)---- a toxic heavy metal

3 Background 2 Mercury---- a global pollutant

4 Background 3 Mercury can cause severely ecological disaster

5 Why concerning Hg in the MSW landfill Hg emissions from the waste incineration was one of the most important atmospheric sources. Waste incinerator 29.29% Oil boilers 8.08% Non-ferrous smelters 12.12% Wood boiler 3.03% Other sources 13.13% 34.34% Coal combustion Year 1992 (from Pirrone et al., 1996 ) How about landfill sites?

6 Why concerning Hg in the MSW landfill 1. Landfill is the major way to treat the municipal solid waste (MSW) world wide. Household waste 60% Compost 6.6% Department Industry area 10% 10% MSW 85% vehicle Transfer station landfill 87.7% 10% Business area 10% Waste selection 15% recycling Incineration 5.7% Street The flow chart of MSW treatment in China From Yang et al., 2003

7 Why concerning Hg in the MSW landfill 2.China is one of the largest MSW producer in the world. Over 150 million tonnes each year!

8 Why concerning Hg in the MSW landfill 3. A variety of Hg containing waste have entered into the landfill. Battery Fluorescence light Thermometer Switch manometer Over 100 tonnes of Hg was released into the environment from the waste products in China each year!

9 (2) Landfill studied Gao-yan landfill: Start operation since 2001; MSW treatment rate: 1300 t/day; Type : Sanitary landfill. Gao-yan (2004)

10 (2) Sampling and analytical method The Hg input and output at Gao-yan landfill was quantified, and the ecological impact was assessed based on a mass balance method. Sketch map showing the cycling of Hg in the MSW landfill site

11 (2) Sampling and analytical method 1. Surface-air Hg flux measurement: non-working face area c c FHg = Q out in A Dynamic flux chamber method Weather station

12 (2) Sample method and analysis 1. Surface-air Hg flux measurement : working face area c( x, y) Q exp ( z h) 2σ = 2 2 πσ yσ zu 2σ y z y 2 2 The Gaussian plume model (US EPA, 1995) used here to estimate the Hg surface-air emissions from the working face area at Gao-yan landfill. where C(x,y) is the atmospheric pollutant concentration at the horizontal coordinates x, y; Q is the pollutant emission rate from the source; U is the horizontal wind speed; h is the effective height of pollution source; σy and σz are horizontal and vertical dispersion coefficient respectively; x, y, z are Cartesian coordinates.

13 (2) Sample method and analysis 2. Hg species in the landfill gas Total gaseous mercury (TGM); Monomethyl mercury (MMHg) ; Dimethyl mercury (DMHg).

14 (2) Sample method and analysis 3. Hg content in the municipal solid waste, covering soil, atmosphere, and leachate was also analyzed by atomic fluorescence spectrometry (CVAFS, Tekran Model 2500, Canada)

15 (3) Results 1. Hg content in the municipal solid waste (MSW) A Hg content (mg/kg) Range: mg kg -1 ; Arithmetic mean : mg kg -1 ; Geometric mean: mg kg -1. (N=40) MSW sample ID

16 (3) Results 2. Hg in the covering soil 0.5 B 0.4 Hg content (mg/kg) Range: mg kg -1 ; Arithmetic mean : mg kg -1 ; Geometric mean: mg kg -1. (N=16) Soil sample ID

17 (3) Results Hg content in the MSW was much higher than the covering soil 0.6 Average Hg content (mg/kg) MSW Covering soil Comparison of average Hg content in the MSW and covering soil

18 (3) Results 3. Total gaseous mercury in the atmosphere over different sites of Gao-yan landfill Tot al gas eous mer c ur y /(ng m -3 ) soil covered or grass planted area soil un-covered area working face and around area Sampling locations

19 4. Surface-air Hg flux (3) Results Relative humidity (%) Non-working face area: wind speed (m s -1 ) Uncovered waste> covered area Temperature ( o C) So i l T Ai r T Solar radiation Inlet TGM (W m -2 ) (ng m -3 ) Hg flux (ng Hg m -2 h -1 ) 400 F1 F2 F :00 Covering soil : : : : :00 F4 Un-covered waste : : :00

20 4. Surface-air Hg flux Non-working face area (3) Results Relative Humidity (%) Wind Speed (m s -1 ) Temperature ( o C) Soil T Air T Solar Radiation (W m -2 ) TGM at DFC inlet (ng m -3 ) Hg air-surface flux (ng Hg m -2 h -1 ) : :00 F1 Covering soil :00 F :00 Sampling time F :00 F4 Covering soil :00 Un-covered waste :00

21 4. Surface-air Hg flux (3) Results For the working face area: Emission rate : ng Hg m -2 hr -1 ; Emission factor: 6.81 mg Hg t -1 MSW.

22 Generally, the surface-air Hg flux decreased in the following order: (3) Results Working face>>uncovered MSW>soil covered area

23 (3) Results 5. Factors influencing Hg surface-air flux Hg content in the substrate 1000 Average Hg flux(ng m -2 h -1 ) 100 Log y= log x r 2 =0.61 P< Hg in the substrate (mg kg -1 )

24 (3) Results 5. Influence factors(cont.) Meteorological factors, specially solar radiation Solar radiation (W m -2 ) Relative humidity (%) Y= x R 2 = Hg flux (ng m -2 h -1 ) Y= x R 2 = Windspeed (m s -1 ) Soil T (C) Hg flux(ng m -2 h -1 ) Y= x R 2 = Y= x R 2 = Hg flux (ng m -2 h -1 ) Hg flux(ng m -2 h -1 )

25 (3) Results 6. Hg species in the landfill gas (LFG) Rang of total gaseous mercury: ng m TGM concentration (ng m -3 ) Vent pipe No. Average TGM concentrations in the LFG of different ventpipes at G-Y

26 (3) Results 6. Hg species in the landfill gas(cont.) 6 MMHg (ng m -3 ) MMHg : Range: 0.14~6.37 ng m -3 ; Average:1.93 ng m -3 ; Around 0.5% of TGM Sample ID

27 (3) Results 6. Hg species in the landfill gas(cont.) 20 DMHg (ng m -3 ) DMHg : Range: 2.54~19.05 ng m -3 ; Average: 9.21 ng m -3 ; Around 2.0% of TGM Sample ID

28 (3) Results 6. Hg species in the leachate along different process in the on-site waste water treatment plant Hg concentration (ng L -1 ) Dissolved Hg Particulate Hg Total Hg 10 0 Raw leachate Inside the treatment plant Effluent Different sampling locations of leachate

29 (3) Results 7. Patterns of Hg emissions from different pathways at Gao-yan landfill Each year, approximately 170 kg of Hg entered into the landfill, and 3.3 kg (about 2%) was discharged into the surrounding environment, of the emissions, the working face was the leading pathway(96%). Working face(96.22%)>>leachate(2.17%)>soil cover(1.25%)>uncovered MSW(0.33%)>vent pipes(0.03%)

30 (4) Conclusion (1)Most Hg lost from the landfill was evaporated into the atmosphere through the surface (>97%), especially the working face, only a minor (<3%) was discharged through the leachate. And the soil covering was proven to be an effective barrier preventing Hg emissions from the landfill sites. (2)Unlike the MSW incinerators, Hg in the landfill was released into the environment at a relative slow rate (2% of the buried each year ). (3)From a long run, landfill will impact the ecosystem for a long time. So, to reduce the environmental risk of Hg at landfill site, it s better to ban the Hg-containing waste entering into the waste flow, and a mechanism for recycling and management the Hg-containing waste must be set up in China.

31 Thanks for your attention!