United States National Risk Management Environmental Protection Research Laboratory Agency Research Triangle Park NC 27711 Research and Development EPA/600/SR-97/071 September 1997 Project Summary Biodegradative Analysis of Municipal Solid Waste in Laboratory-Scale Landfills M. A. Barlaz, W. E. Eleazer, W. S. Odle, III, X. Qian, and Y-S. Wang The objective of this research was to to the relatively low concentration of characterize the anaerobic biodegrad- food waste in MSW. ability of the major biodegradable com- Most probable number (MPN) tests ponents of municipal solid waste were conducted to identify the compo- (MSW). Tests were conducted in qua- nents of refuse that carry refuse-de- druplicate in 2-L reactors operated to composing microorganisms into obtain maximum yields. Measured landfills and to evaluate the significance methane (CH4) yields for grass, leaves, of two typical cover soils as carriers of branches, food waste, coated paper, refuse-decomposing microbes. Grass, old newsprint, old corrugated contain- leaves, and branches were the major ers, and office paper were 144.4, 30.6, identifiable contributors of refuse-de- 62.6, 300.7, 84.4, 74.3, 152.3, and 217.3 composing microbes to landfills, while mL CH4/dry g, respectively. While there the cover soils tested did not typically was a general trend of increasing CH4 contain populations with the activities yield with increasing cellulose plus required for refuse methanogenesis. hemicellulose (carbohydrate) content, This Project Summary was developed many confounding factors precluded by EPA’s Air Pollution Prevention and establishment of a quantitative relation- Control Division of the National Risk ship. Similarly, the degree of lignifica- Management Research Laboratory, Re- tion of a particular component was not search Triangle Park, NC, to announce a good predictor of the extent of bio- key findings of the research project that degradation. is fully documented in a separate report In parallel with the decomposition ex- of the same title (see Project Report periments, leachate from the decom- ordering information at back). position of each refuse constituent was analyzed for toxicity using a modified Introduction anaerobic toxicity assay. Leachate tox- Approximately 62% of the municipal icity was not found in association with solid waste (MSW) generated in the U.S. the decomposition of any refuse com- is disposed of by burial in a sanitary land- fill. The production of methane (CH ) from ponent other than food waste. How- 4 ever, substantial toxicity was measured sanitary landfills is well documented, and in leachate from the food waste reac- there are about 119 landfill gas recovery tors. This toxicity was consistent with projects currently (January 1997) in op- the behavior of the reactors but could eration in the U.S. and Canada. While the not be simulated with high concentra- production of CH4 from landfills is well tions of carboxylic acids and sodium. established, there is large uncertainty in- The toxicity associated with food waste volved in estimating the amount and rate leachate is not likely to inhibit anaero- of CH4 production. This uncertainty is in- bic decomposition in U.S. landfills due creasing as the composition of the MSW buried changes due to increased recy- cling. Development of integrated solid waste mixed residential refuse was also charac- more extensive cellulose biodegradation management programs, which include re- terized. (MC decreasing) in the less lignified sub- cycling and in some cases, combustion, Tests were conducted in 2-L laboratory strates [(C+H)/Li increasing] e.g., food and have led to a decrease in the use of reactors in quadruplicate. Each refuse office paper (r2 = 0.28). However, the quan- landfills. However, there is a limit to the component was seeded with well-decom- titative relationship is weak because the types of waste that can be recycled, and posed refuse to initiate refuse-decomposi- office paper (C + H)/Li is well above any combustion has not been the solid waste tion. CH4 yield data have been corrected of the other components tested. The trend management alternative of choice for many for the background CH4 produced from towards increased cellulose loss with a communities. Thus, landfills will be a sig- the seed. In the case of food waste, two decreasing degree of lignification is most nificant part of MSW management for the sets of reactors were tested. In the first definite among the four paper components. foreseeable future. (F) series, there was insufficient seed, 30% There is not a linear relationship be- Both CH4 and carbon dioxide CO2 are by volume, and the reactors remained in- tween (C+H)/Li and the extent of decom- greenhouse gases that contribute to glo- hibited. A second set of food waste reac- position (r2 = 0.02). However, it is bal climate change. CH4 traps about 20 tors (SF) was then initiated with 70% seed interesting to note that grass, which is times more infrared energy than CO2 on a by volume, and these reactors produced highly lignified, underwent nearly complete volume basis. Consequently, although measurable CH4. decomposition as measured by either MC landfill gas contains approximately equal The test conditions were designed to or the extent of decomposition (Table 1). proportions of CH4 and CO2, CH4 is more measure the maximum CH4 production This suggests that the lignin concentra- significant with respect to atmospheric cli- potential of each component. This included tion does not always reflect the degree to ° mate change. Data on the amount of CH4 shredding, incubation at about 40 C, and which lignin inhibits cellulose bioavailabil- that can be expected from refuse already leachate recycle and neutralization. All re- ity. Apparently, the lignins in grass are not buried, as well as CH4 that will result from actors were monitored until they were no as restrictive to microorganisms as the the decomposition of refuse buried in the longer producing measurable CH4, except lignin in other components such as future, are needed to better assess the for the old corrugated container reactors branches. This result is consistent with a impact of landfills on global climate change. in which the CH4 yield increased by less report that stated, “. .the chemistry of The overall objective of this research than 2% over the final 80 days of monitor- grass lignocellulose varies considerably was to develop information on the anaero- ing. At the termination of the monitoring from that of wood.” bic decomposition of refuse that will im- period, reactors were destructively The solids decomposition (MC and MH) prove our ability to assess the impact of sampled for analysis of the residual sol- and CH4 yield data document the biode- sanitary landfills on global CH4 accumula- ids. gradability of even the most lignified sub- tion. Three sets of experiments were con- The CH4 yield, solids composition, and strates, leaves and branches, as well as ducted to meet this objective: (1) extent of cellulose and hemicellulose de- all other components of MSW tested. The measurement of the CH4 potential of the composition for each MSW component and absence of good linear relationships is major biodegradable components of MSW; mixed MSW are presented in Table 1. As likely because a number of factors influ- (2) assessment of whether leachate toxic- summarized in Table 1, there was sub- ence CH4 production and solids decompo- ity, associated with whole refuse or some stantial variation in the range of CH4 yields sition. The biodegradation of newsprint individual constituent, inhibits the onset or (30.6 to 300.7 mL/dry g) and the extent of measured here is in contrast to reports on rate of CH4 production; and (3) identifica- decomposition (28 to 94%) among the the excavation of readable newsprint that tion of solid waste constituents that carry components tested. In previous research had been buried in landfills decades ear- the anaerobic bacteria required for refuse with mixed refuse, carbohydrates ac- lier; however, these reported data did not methanogenesis. The results of each set counted for 91% of the stoichiometric CH4 represent average values, but rather ob- of experiments are summarized separately. potential of MSW. Carbohydrates were the servations during an archaeological exca- major organic compounds analyzed in the vation. The presence of readable newsprint Experiment 1: Measurement of waste components tested here, and the that had not undergone biodegradation the CH4 Potential of the Major relationship between carbohydrate concen- may be due to its isolation from other Biodegradable Components of tration and CH4 yield is presented in Fig- factors required for biodegradation such MSW ure 1. While the data in Figure 1 show a as bacteria, moisture, and nutrients. The The anaerobic biodegradability of the relationship, the relatively low correlation biodegradability of a newspaper buried in major biodegradable components of MSW coefficient (r2 = 0.49) and failure of the a bag that did not break during waste was characterized by measurement of their regression line to pass through zero, sug- compaction would differ from the biode- gest that factors in addition to carbohy- gradability of newsprint exposed to other CH4 yield and the biodegradation of cellu- lose and hemicellulose. The components drate concentration influence CH4 yield. refuse components. that were tested were grass, leaves, Lignin decreases carbohydrate bioavail- Based on the CH4 yields presented in branches, food waste, and four types of ability and is expected to confound the Table 1, a model was constructed to esti- paper—newsprint (ONP), old corrugated relationship presented in Figure 1. The mate CH4 yields based on assumed com- containers (OCC), office paper (OFF), and components with the lowest yields are the positions of buried refuse. These results coated paper (CP). These are the most two sets of seed reactors and leaves. are summarized in Table 2. The actual common types of paper in MSW and also These are also the components with the methane yield per wet kg of refuse buried represent the range of biodegradability that lowest carbohydrate to lignin [(C+H)/Li)] decreases by only 10% between the base could be expected from paper.