Mass Balance Computational Procedure in Landfill Assessment 1

Estimate the remaining site life for disposal of refuse Step 1. Develop a general indication of the solid waste specific weight Step 2. Estimate the volume of soil required to cover each day’s waste from the appropriate solid waste-to- cover ratio (e.g., 4 to 1) Step 3. Estimate the tonnage of refuse that may still be landfilled, given site volume remaining. = Refuse placed Mass leaving in leachate Mass leaving in gas Waste remaining Mass transformed to other products

 Methanogenic decomposition C a H b O c N d + 1/4(4a-b-2c+3d) H 2 O  1/8(4a+b-2c-3d)CH 4 +1/8(4a-b+2c+3d)CO 2 + dNH 3 Estimate an upper bound on the gas production relative to the quantity of substrate utilized. Because acid-phase anaerobic and aerobic decomposition gives rise to CO 2 and not to CH 4, there is a higher CO 2 content in the gas generated than predicted from eq. above. a = 60, b = 94.3, c = 32.8, d = 1, noncombustibles = 53.4, and H 2 O = 44.4  53% CH 4  520 L/kg  Theoretical: 300 to 500 L of landfill gas produced from 1 kg of municipal refuse (5 to 8 ft 3 /lb)  Full-size landfill projected: 50 ~ 400 L/kg (0.8 ~ 6.4 ft 3 /lb)  Optimum moisture content: 75 ~ 100% of the refuse dry wt. 3

 In 100 lb of solid waste, 56 lb decomposable C 60 H 94.3 O 37.8 N+18.28H 2 O → 31.96CH CO 2 +NH g g g g 17 g Specific wt: CH 4 – lb/ft 3 ; CO 2 – lb/ft 3 Solution CH 4 = 511.4/ ⅹ 56 lb = 20 lb CO 2 = / ⅹ 56 lb = 48.2 lb Volume CH 4 = 20 lb  lb/ft 3 = ft 3 CO 2 = 48.2 lb  lb/ft 3 = ft 3 4

Fraction of CH 4 and CO 2 CH 4 (%) =  ( ) ⅹ 100=53.3% CO 2 (%) =  ( ) ⅹ 100=46.5% Gas production based on dry wt. of org. material ( ) ft 3  56 lb=14.9 ft 3 /lb=0.93 m 3 /kg Gas production based on total wt. of org. material ( ) ft 3  100 lb=8.4 ft 3 /lb=0.52 m 3 /kg 5

ElementWt, g Atomic wt., g/mol Mole Mole ratio (N=1) C H O N S Ash C 60 H 94.3 O 37.8 N → C 60 H 94 O 38 N 6

 Refuse composition, age of refuse, moisture content, pH, microbial population present, temperature, and quantity and quality of nutrients  Rate of methane generation  Cumulative gas produced C = C o (1 - e -kt ) Assume that the factor limiting the rate of methane generation at a landfill is the quantity of material remaining in the landfill.  7

 The Scholl Canyon model may be used to estimate emissions using the following first-order decay equation (IPCC, 1997): G i = M i × k × L 0 × exp-(k × t i ) where: G i = emission rate from the i th section (kg CH 4 /year); M i = mass of refuse in the i th section (ton); k = CH 4 generation rate (1/year); L 0 = CH 4 generation potential (kg CH 4 /ton of refuse); t i = age of the i th section (years). IPCC (1997), Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories, Vols. 1 and 3, Intergovernmental Panel on Climate Change, Bracknell, U.K. 8

L 0 = (M c × F b × S)/2 where: M c = kg of carbon per kg of waste landfilled; F b = biodegradable fraction; and S = stoichiometric factor = 16/12. L 0 : 4.4 to 194 kg CH 4 /ton of waste (Pelt et al., 1998) EPA: L 0 = 165 kg CH 4 /ton of waste 9

 Organic portion of municipal wastes  Readily decomposable: food wastes (t 1/2 = 0.5~1.5 yrs)  Moderately decomposable: paper (t 1/2 = 5 ~ 25 yrs), wood grass, brush, greens, leaves, oils, and paint  Non-decomposable: plastics, leather, rubber, and rags  Landfill methane generation  Lag phase  Active methane generation phase  Life of methane gas generation for economic recovery: 5 to 20 years 10

11 Waste productDecomposition time Banana skin3~4 wks Paper bag1 month Cardboard2 months Wool sock1 yr Orange peelUp to 2 yrs Cigarette buttsUp to 12 yrs Plastic bags*Up to 20 yrs Polyfilm wrapping (clingwrap)*25 yrs Leather shoeUp to 45 yrs Tin cans50 yrs Plastic bottle*450 yrs Plastic 6-pack holder*500 yrs Disposable nappies550 yrs Polystyrene cups> 500 yrs Aluminum cans> 1 million yrs or forever? Glass1~2 million yrs * Even though these products break down in the times indicated they are still petrochemical products and will always remain in the environment.

 Example: Calculate CO 2, CH 4, and water consumed in the formation of landfill gas per kg of MSW. MSW empirical formula: C 68 H 111 O 50 N C 68 H 111 O 50 N + 16H 2 O  33CO CH 4 + NH 3 (1741) (288) (1452) (560) (17) Water consumed = 288/1741 = kg H 2 O/kg MSW = kg H 2 O/0.435 m 3 gas/kg MSW = 0.38 kg H 2 O/m 3 gas CO 2 and CH 4 : 95 to 99% of landfill gas 12

Typical conc. ComponentSource(% by vol.)Concern MethaneBiodegradation50~70Explosive Carbon dioxideBiodegradation30~50Acidic in GW HydrogenBiodegradation< 5Explosive Mercaptans (CHS)Biodegradation0.1~1Odor Hydrogen sulfideBiodegradation< 2Odor TolueneContaminant0.1~1Hazardous BenzeneContaminant0.1~1Hazardous DisulfatesContaminant0.1~2Hazardous OthersBiodegradationTracesHazardous or contamination 13

 Water quantity  Water present in the waste (small)  Water produced during decomposition (negligible)  Water added to the landfill - percolation through the landfill surface, horizontal flow through the sides, and upward flow through the bottom (major)  Hydrologic water balance  Formation of surface water runoff, evaporation directly to the atmosphere, transpiration to the atmosphere through vegetation surfaces, or infiltration into the cover soils and refuse at the surface of the landfill  Infiltrates may be held in surficial soil and percolate through the refuse (leachate). 14

 Cellulose is a major carbohydrate in domestic refuse.  15 Cellulose Glucose & cellobiose CO 2, H 2, ethanol, & acetic, propionic, butyric, valeric and caproic acids CH 4 & CO 2 pH increase to 7~8 Cellulose:hemicellulose:lignin = 70:15:15hemicelluloselignin

 Cellulose: A long chain of glucose molecules, linked to one another primarily with glycosidic bonds. Only a small number of enzymes are required to degrade this material.  Hemicelluloses: Branched polymers of xylose, arabinose, galactose, mannose, and glucose. Hemicelluloses enhance the stability of the cell wall. They also cross-link with lignin, creating a complex web of bonds which provide structural strength, but also challenge microbial degradation.  Lignin: A complex polymer of phenylpropane units, which are cross-linked to each other with a variety of different chemical bonds. This complexity has thus far proven as resistant to detailed biochemical characterization as it is to microbial degradation. Lignin degradation is primarily an aerobic process, and in an anaerobic environment lignin can persist for very long periods. 16

17 Aerobic decomposition High CO 2, temp. , pH , high COD, BOD, and specific conductance, high concentrations of most inorganic constituents Anaerobic acid phase Highest COD, BOD, and specific conductance Methanogenic phase pH ~7, COD, BOD, and specific conductance 

 EPA Landfill Methane Outreach Program, Program Development Handbook: tools/handbook.html tools/handbook.html  LandGEM program:  Useful reference: M_the_EPAs_Landfill_Gas_Emissions_Model_ aspx M_the_EPAs_Landfill_Gas_Emissions_Model_ aspx 18