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CE 527 Solid Waste Management Problem Set 3 Dr. S.K. Ong Due Date: Dec. 2 Leachate Generation 1. a. Write water balance equations for a landfill cover. Terms to be included are infiltration (I), precipitation (P), evapotranspiration (ET), change in storage (ST) and percolation (PER). (One of the term may not be in the final expression) b. Use the above water balance to compute the potential percolation through a landfill cover over a six-month period. The landfill cover is 3 feet thick and is classified as clay loamy. Initial moisture content is 18%. Field capacity (FC) and permanent wilting point (PWP) for clayey loam are 27% and 12%, respectively. Assume SCS curve number is 70. Given: (i) Moisture in excess of field capacity is assumed to percolate through the cover. (ii) Maximum moisture storage capacity = [(FC - PWP)/100] x Depth of Cover (ins) (iii) Runoff may be estimated using (assume that this is the average runoff over a month period) Q= where Q S P CN (P - 0.2S)2 ---------(P + 0.8S) = runoff (ins) = maximum retention = 1,000/CN - 10 = precipitation intensity (ins) = Curve number (iv) Evapotranspiration may be estimated using a simplified Thornthwaite-Holzman equation. 0.1 (V2 -V1) E = ------------------(T + 459.4) where V2 and V1 are wind speed (mph) at height z1 and z2 from ground level T is the mean temperature (˚ F) of the layer between the lower z1 and upper z2. E = evapotranspiration (in/hr) (v) Precipitation and mean temperature Data Month January February March April May June Precipitation (ins) 6 4 4.5 3.5 4 1 Mean Temperature (˚ F) 42 44 50 55 65 70 V1 (mph) 4 4 4 3 4 3 V2 (mph) 10 12 20 15 10 12 2. Lysimeter Tests at University of Wisconsin A landfill test cell (called lysimeter) at University of Wisconsin-Madison was tested from 1970 - 1977 to evaluate the volume of surface runoff and leachate (Ham, 1980). The cell is 60 ft long and 30 ft wide as shown in Fig. 1. The depth of the refuse was 4 feet deep. Refuse was underlain with a 10 cm (4-in) layer of crushed granite over a 0.15 mm (6 mil) polyethylene barrier. Bottom slopes of approximately 3 % directed leachate to a collection box at the center of the cell, where it is periodically pumped and the volume of the leachate measured. The refuse is covered with 15 cm (6 in) of sandy silt soil with the top surfaces of the cell sloped at 3% toward one of the 60 ft walls where the surface runoff was collected and measured. Surface vegetation may be assumed to be poor grass and the evaporative depth of 20 cm (8 in.) may be assumed. The mean annual temperature is 7.2o C (45o F) with the daily minimum temperature falling below freezing on 163 days per year. The mean annual precipitation is 31 in. and the mean daily solar radiation is approximately 330 langleys or 1,380 kJ/m2. (you may use default values in the program). (i) With the HELP model, compute the 5-year runoff and drainage (leachate) production. Compare your results with the actual data (cumulative data). (Note data was obtained from several graphs and may not be very accurate - however, the data will give you an idea on what kind of results to expect). The data shown are for the last three years, i.e., compute five years of results and neglect the first two years. The first two years is assumed to be a period for the landfill to be established. Comment on your results. (ii) Repeat the above model run by assuming that you are in Las Vegas, Nevada. Comment on your results. Date Cum. runoff (in.) Cum. ET + ∂S (in.) Cum. Drainage (in.) Jan 1973 0 0 0 May 1973 1.1 10 7.5 Sept 1973 1.65 16 10 Jan 1974 2.5 20 12 May 1974 3.75 30 17 Sept 1974 4.25 38 19 Jan 1975 4.625 44 21.5 May 1975 5.25 52 24 Sept 1975 5.75 68 26 Jan 1976 6.15 70 27 Ham, R.K.. 1980. Decomposition of residential and light commercial solid waste in test lysimeters. SW - 190C, US EPA, Office of Solid Waste, Washington, D.C. ET - evapotranspiration ∂S - change in moisture content Resource Recovery and Recycling 3. Two air classifier manufacturers report the following performance for their units: Manufacturer A Recovery of heavy fraction = 80% Recovery of light fraction = 80% Manufacturer B Overall Recovery = 60% Purity of light fraction = 95% Assume a feed that consists of 85% light fraction. (i) Compare the performance of the two units (ii) Which one will you purchase. (Overall recovery = [(x1 + y1)/(xo + yo)] x 100 4. Solve problem 12-4, page 606 in the textbook 5. An approach used in the industry to assess the environmental impact of manufacturing a product is the life cycle analysis. Part of the analysis consists of an energy analysis of the raw materials to final disposal. Using the data below, calculate and compare the energy required to provide soft drinks in returnable glass bottles with soft drinks in nonreturnable glass bottles. Note that the data are based on modern throwaway glass bottle. Compute two sets of results (i) with 100% recovery of the bottles (which is not possible) and (ii) with only 30% recovery of the returnable glass bottles. Volume in liters Mass of Bottle (kg) Mass of soft drink (kg) Average number of times filled Extraction of raw materials kJ/kg Transport, extraction to manufacturer kJ/kg Manufacture of Bottle (kJ/kg) Manufacture of metal cap (kJ/cap) Transport, manufacturer to bottler (kJ/kg) Filling Bottles (kJ/liter) Transport, bottler to retailer (kJ/kg) Transport, retailer to consumer (kJ/kg) Transport, return empty bottles (kJ/kg) Waste collection and disposal (kJ/kg) Separation/washing for recycling (kJ/kg) Returnable 0.47 0.298 0.47 15 Nonreturnable 0.47 0.184 0.47 1 2,300 290 17,990 255 720 1,700 815 30 30 210 2,560 (a) Based on your calculations, comment on your results and assess which approach will be more efficient with regards to energy savings. (b) Of all the data listed above, which parameter, in your opinion, has the most impact on the success of recycling returnable bottles? State why?