6.2 Impact of Bioreactor Activities on Leachate Quality and Waste Stabilization

Transcription

1 VOLUME 6 Deliverables to meet work plan objective 5: Monitor the bioreactor in a manner to measure the impact of bioreactor activities and to allow control of the waste treatment process 6.1 Work Plan Objective and Deliverables Objective 5 of the project work plan was: Monitor the bioreactor in a manner to measure the impact of bioreactor activities and to allow control of the waste treatment process (e.g. leachate and gas composition and generation, waste characteristics, settlement) The work plan identified the following methodology to meet objective 5: The landfill will be monitored to measure the impact of bioreactor operations on the treatment of the landfilled waste, as well as a mechanism to control the treatment. Leachate quality will be routinely measured to address the impact of operation on leachate quality and potential leachate treatment costs. The composition of gaseous emissions will be routinely measured, as will the settlement of the waste mass and the degree of biological stabilization of the solid waste. The parameters measured will be used to control the waste treatment process. For example, temperature and gas concentration will be measured using the monitoring probes as a means to control the rate of air injection into a given area of the landfill. The deliverables identified in the work plan included: Models for use in generating protocols for controlling the waste treatment process Protocols for controlling the waste treatment process. Methodology for quantifying settlement Presentation of data in periodic reports 6.2 Impact of Bioreactor Activities on Leachate Quality and Waste Stabilization An ultimate goal of bioreactor landfills is rapid stabilization of landfilled waste. Various manners to estimate the progress of the waste stabilization are used for the Florida bioreactor demonstration project. Monitoring the NRRL bioreactor also was planned in the Permit, including characterizing leachate, gaseous emissions, solid waste, and landfill settlement. Table 6.1 provides more details on the monitoring activity. In this volume, results of monitoring simulated bioreactors and full-scale bioreactors are described. The sections for leachate quality, gas quality, solid waste, landfill settlement, and summary and conclusions are included in Volume

2 Table 6.1 Summary of Monitoring Monitoring Activity Description Leachate Samples of leachate will be collected from each manhole on a routine basis. The leachate will be analyzed for the following parameters: ph Conductivity Dissolved solids Biochemical oxygen demand Chemical oxygen demand Organic carbon Nutrients (NH 3, TKN, TP) Common ions (Cl -, NO 3-, NO 2-, SO 2-4, Na +, K +, Ca 2+, Mg 2+ ) Volatile fatty acids Organic priority pollutants Heavy metals Gaseous Emissions Gas emissions from the landfill will be measured routinely as part of the operation of bioreactor for CH 4, CO 2, O 2, and N 2. Samples will also be collected at times to measure nonmethane organic compounds (NMOCs), H 2 S, and N 2 O. Solid Waste Solid waste samples will be collected to directly assess the degree of stabilization. Parameters to be evaluated included the following: Moisture content Volatile solids Methane yield Cellulose Lignin One occasion, the waste samples will be analyzed for organic priority pollutants and heavy metals (total and leachable). Landfill Settlement The bioreactor landfill will be surveyed routinely to measure the degree of waste settlement (an indicator of biological decomposition) Cited from Operational Plan in Permit Modification Application, Landfill Bioreactor Demonstration, New River Regional Landfill Cells 1 and 2, Union County, Florida. DEP Permit No.: SC , in Appendix A. 6-2

3 6.3 Monitoring Leachate Quality The chemical characteristics of leachate from a bioreactor landfill are usefully assessing the status of the landfill. Leachate quality of simulated bioreactors and full-scale bioreactor was monitored in the Florida bioreactor demonstration project. Figure 6.1 shows cross-section view of the NRRL bioreactor and the locations of manholes. Most moisture was add into area where designed as an anaerobic bioreactor and a smaller amount of moisture was added to the test area for the aerobic bioreactor. Figure 6.2 shows a leachate sampling pump merged in leachate of V- weir box in a manhole. Typical leachate monitoring parameters as shown Table 6.1 are analyzed. All leachate quality data were submitted in the biannual report of 2004 and As a part of CRADA, leachate sampled monthly at the Polk county north central landfill, Leachate was sampled at four segregated leachate sumps of the Phase II bioreactor and one sump of Phase I (Conventional MSW landfill). Figure 6.3 and Figure 6.4 shows the leachate sampling practice on the Polk county bioreactor. Also, leachate quality of the bioreactor in Alachua County Southwest landfill was included in this section. Boundary of bioreactor area Injection well cluster Landfill Surface 10 ft Safety zone ft bottom liner 2 ft thick bottom liner 100 ft Figure. 6.1 Cross-section view of NRRL vertical injection wells and leachate manholes from one to seven. The arrows on the injection wells indicate that the area with a great amount of moisture addition. 6-3

4 Figure 6.2. Leachate sampling pump installed at V-weir box in a manhole at NRRL. 6-4

5 Figure 6.3. Leachate sampling at (Phase II) of Polk north central landfill. Figure 6.4. Measuring field parameters (ph, conductivity, and temperature) of leachate sampled at Phase II. 6-5

6 6.3.1 Leachate quality of simulated bioreactors Using simulated bioreactor lysmeters, impacts of bioreactor operation on the leachate quality have been studied as parts of the Florida bioreactor demonstration project by Kim (2005) and Spalvins (2006). Kim (2005) studied using six-foot tall stainless steel simulated landfill lysimeters compacted complete with fabricated wastes. In his study, leachate quality was compared between simulated bioreactors aerobically and anaerobically. In aerobic operation, more than 90% of the maximum COD, BOD and TOC concentrations decreased within 100 days. During the methanogenic phase in the anaerobic condition, concentrations of ammonia increased by an amount four times greater than the initial concentrations. A large change of ammonia was not observed from the aerobic lysimeters. For metal leaching, As, Fe, Mn, and Zn in the anaerobic lysimeters proved significantly greater in concentration than observed in the anaerobic lysimeters. Al, Cu, Cr, and Pb in the aerobic lysimeters were leached more than those in the anaerobic lysimeters. Spalvins (2006) simulated impacts of E-waste on leachate quality using lysimeters that were built in holes excavated in an operating MSW landfill in Polk, Florida. Figure 6.5 shows the ph change over the experimental period indicating acidic and methanogenic phases of the simulated bioreactors. The concentrations of lead from the control and E-waste lysimeters were statistically different. The total mass of lead leached from the E-waste lysimeters was on average 22% greater than from the control lysimeters. However, the increase in the mass of lead leached from the E-waste lysimeters was less than 0.018% of the total mass of lead in the E-waste lysimeters. Table 6.2. Results of statistical analysis of metal leached between aerobic and anaerobic lysmeters (Kim, 2005). 6-6

7 ph /1/04 12/1/04 4/1/05 8/1/05 Lys 1 Excavated Waste Lys 2 Control 1 Lys 3 Control 2 Lys 4 E-Waste 1 Lys 5 E-Waste 2 Lys 6 E-Waste 3 Date Figure 6.5. Leachate ph versus time. Ranges for the acidic and methanogenic phases reported in landfills are indicated by arrows. Spalvins (2006) compared the amount of lead leached from the E-waste lysimeters to the lead concentration that reported from landfill leachate and lysimeter studies as shown in Figure 6.6. He found that landfill leachate lead concentrations are decreasing over time as well. The amount that the lead concentration was increased by the E-waste was insignificant compared to the decline of lead concentrations in leachate from eliminating lead from the waste stream. 6-7

8 Figure 6.6. Lead concentrations from historic landfill leachate and lysimeter studies compared the Spalvins study Leachate quality of full scale bioreactor At the NRRL bioreactor, leachate from each manhole was sampled and analyzed for a number of parameters. Since leachate recirculation started, leachate quality of some manholes showed a large variation. Leachate data of NRRL presented in this section were collected since October One of benefits from segregated manholes over an integrated leachate sump in terms of leachate monitoring is that those enable to investigate the status of the bioreactor specifically. This section provides only few example parameters, more date can be found in Appendix F Raw Data and Appendix G Periodic and Technical Report. Figure depict the changes in ph, and strength of typical organic parameters over a period of time such as TDS, TOC, COD, and BOD. The ph distributions over each manhole are also presented by the box plots. A line across each box indicates the median, and the top and bottom of each box (upper and lower hinges) represent 75 and 25 percentile of the data value, respectively. The ph of leachate collected from the manhole 7 was dropped to below 5.5 on May, 2004 while the ph of other manholes was remained in the range of 6.5 to 7.5. With the changes in the ph, changes in organic strength. The ph of the manhole 7 had increased and stayed around 6.9 to 7.0 for more than a year. As ph of manhole 7 increased above 7.1since August 2006, the organic strength decreased rapidly. 6-8

9 ph MH1 MH2 MH6 5.5 MH3 MH7 MH4 MH8 MH5 MH9 5.0 Sep/03 Mar/04 Sep/04 Mar/05 Sep/05 Mar/06 Sep/ ph Manhole # Figure 6.7. The changes in ph of the manholes over time and the distribution of ph of all manholes 6-9

10 MH1 MH2 MH3 MH4 MH5 MH6 MH7 MH8 MH9 Total dissolved solids (mg/l) Sep/03 Mar/04 Sep/04 Mar/05 Sep/05 Mar/06 Sep/ Total Dissolved Solids (mg/l) Manhole # Figure.6.8 The changes in total dissolved solids (TDS) of the manholes over time and the distribution of TDS of all manholes 6-10

11 18000 Chemical Oxygen Demand (COD), mg/l MH1 MH2 MH3 MH4 MH5 MH6 MH7 MH8 MH9 0 Sep/03 Mar/04 Sep/04 Mar/05 Sep/05 Mar/06 Sep/06 Figure. 6.9 The changes in chemical oxygen demand (COD) of the manholes over time and the distribution of COD of all manholes 6-11

12 25000 Biological Oxygen Demand (mg/l) MH1 MH2 MH3 MH4 MH5 MH6 MH7 MH8 MH9 0 Sep/03 Mar/04 Sep/04 Mar/05 Sep/05 Mar/06 Sep/ Biological Oxygen Demand (mg/l) MH1 MH2 MH3 MH4 MH5 MH6 MH7 MH8 MH Manhole # Figure The changes in biological oxygen demand (BOD) of the manholes over time and the distribution of BOD of all manholes 6-12

13 6000 Total Organic Carbon (mg/l) MH1 MH2 MH3 MH4 MH5 MH6 MH7 MH8 MH9 0 Sep/03 Mar/04 Sep/04 Mar/05 Sep/05 Mar/06 Sep/ Total Organic Carbon (mg/l) MH1 MH2 MH3 MH4 MH5 MH6 MH7 MH8 MH Manhole # Figure The changes in total organic carbon (TOC) of the manholes over time and the distribution of TOC of all manholes 6-13

14 Long-term leachate quality monitoring suggested that nonbiodegradable and persistent pollutants are increasing in leachate of bioreactor landfills. For example, ammonia-nitrogen in leachate increased in manhole 7 at NRRL bioreactor over time as shown in Figure This phenomenon is often seen other bioreactor sites. Figure 6.13 shows ammonia concentration of Phase I (a conventional MSW landfill) and Phase II Polk bioreactor for two years. Figure 6.14 and Figure 6.15 show temporal trend of ammonia and COD in Alachua county bioreactor for almost two decades. 6-14

15 MH1 MH2 MH3 MH4 MH5 MH6 MH7 MH8 MH9 Ammonia (mg/l) Sep/03 Mar/04 Sep/04 Mar/05 Sep/05 Mar/06 Sep/ Ammonia Concentrations (mg/l) MH1 MH2 MH3 MH4 MH5 MH6 MH7 MH8 MH Manhole # Figure The changes in ammonia of all manholes over time and the distribution of ammonia of all manholes 6-15

16 Phase I Polk 1 Ammonia (N-mg/L) Polk 2 Polk 3 Polk 4 0 5/06 9/06 1/07 5/07 9/07 1/08 5/08 Figure Ammonia concentrations of leachate samples over time at Polk county north central landfill. Phase I is referred to conventional landfill and Polk 1-4 are referred to as Phase II bioreactor. Date 6-16

17 Figure Temporal trend of ammonia concentration in leachate of Alachua county landfill. Figure Temporal trend of COD in leachate of Alachua county landfill. Although operating bioreactor landfills enhance biodegradation of organic matter in leachate, persistence pollutants in leachate likely remain or will be accumulated in the leachate during leachate recirculation. Ammonia-nitrogen in the leachate is one of the persistent pollutants. The leachate monitoring results suggested ammonia-nitrogen accumulation in leachate. Berge et al. (2005) reviewed the fate of nitrogen in bioreactor landfills. In addition, Berge et al. (2007) and Berge (2006) studied the kinetics of in situ ammonia removal in both acclimated and unacclimated wastes to aid in developing guidance for field-scale implementation. Further information on leachate quality of the bioreactors and simulated bioreactors that were studied as parts of the Florida bioreactor demonstration project can be found in the following references. 6-17

18 Appendix C. Theses and Dissertations Berge, N. (2006). In-Situ ammonia removal of leachate from bioreactor landfills. Ph.D. Dissertation. University of Central Florida, Orlando, FL. Spalvins, Erik E. K. (2006). Leaching of lead from electronics waste using simulated municipal solid waste landfills Master's Thesis, University of Florida, Gainesville, FL. Kim, H. (2005). Comparative studies of aerobic and anaerobic landfills using simulatedlandfill lysimeters. Ph.D. Dissertation. University of Florida, Gainesville, FL. Appendix D. Peer-reviewed Journal Articles and Conference Proceedings Berge, N., Reinhart, D., Dietz, J., and Townsend, T. (2007) The impact of temperature and gas-phase oxygen on kinetics of in situ ammonia removal in bioreactor. Water Research, 41, Berge, N., Reinhart, D., Dietz, J., Townsend, T. (2006) In-situ ammonia removal in bioreactor landfill leachate. Waste Management, 26, Appendix H. Periodic Reports New River Regional Landfill Bioreactor Demonstration Project Biennial Report, 2006 New River Regional Landfill Bioreactor Demonstration Project Biennial Report, 2004 Research and Data Report for the Alachua County Southwest Landfill prepared for Alachua County Public Works Department, The Second Annual Report for Cooperative Research and Development Agreement between U.S. EPA and Hinkley Center for Solid and Hazardous Waste Management, Gas Quality and Gas Generation Gas quality of aerobic and anaerobic bioreactors Gas quality is an important measure as an indicator of performance, safety, and fuel quality. The major components of bioreactor gas are methane, carbon dioxide, nitrogen, oxygen, and water vapor. Trace gas components in the gas also are important for the regulatory respect such as hydrogen sulfide (H 2 S), carbon monoxide (CO), nitrogen oxide (N 2 O) and nonemethane organic carbons (NMOCs). An aerobic operation of bioreactor results in different composition of gas emission from that of an anaerobic bioreactor. Kim (2005) compared the composition of the exhaust from aerobic bioreactor to that from anaerobic bioreactor using lysimeters. Figure 6.16 and Figure 6.17 show gas composition of the aerobic and anaerobic bioreactors. Gas composition of well-controlled lysimeters shows the clear differences between aerobic and anaerobic bioreactors: ignorable percent of methane in the aerobic bioreactor and oxygen in the anaerobic bioreactor. However, gas composition measured at the NRRL bioreactor after air injection shows coexistence of aerobic exhaust and anaerobic landfill gas (Figure 6.18). 6-18

19 Figure Gas composition of aerobic lysimeter with air injection rate. Figure Gas composition of anaerobic lysimeter. 6-19

20 Figure Typical gas compositions before and during air injection experiment at the NRRL bioreactor Trace components of aerobic and anaerobic exhausts from the bioreactor In addition to CH 4, CO 2, and O 2, the trace components of aerobic exhaust were investigated included volatile organic compounds (VOCs), nitrous oxide (N 2 O), carbon monoxide (CO), and hydrogen sulfide (H 2 S). The results for VOCs in the exhaust suggest that neither compound class changed with a change in CH 4 /CO 2. A statistically significant difference in BTEX (Figure 6.19) or chlorinated VOC concentration (Figure 6.20) before and during air injection was not found at any of the eight monitoring locations. No apparent correlation between CH 4 /CO 2 and N 2 O concentration was observed (Figure 6.21). Four samples taken from other areas of the portion not impacted by air addition had a mean N 2 O concentration of approximately 400 ppm, similar to the levels found in monitoring wells during air injection. However, H 2 S and CO concentrations are varied by air injection. A total of 168 samples were collected and analyzed for H 2 S and CO before and during air injection testing. Figure 6.22 depicts the H2S concentrations measured for three different ranges of CH 4 /CO 2. The figure suggests a trend of decreasing H 2 S concentration with decreasing CH 4 /CO 2. Statistical analysis of the data found a significant decrease in H 2 S concentration during air injection at 6 of 12 monitoring wells compared to initial levels. Figure 6.23 presents the CO concentration as a function of CH 4 /CO 2 for all locations. As CH 4 /CO 2 decreased (i.e., as aerobic conditions predominate), CO concentration increased. Nine out of 12 injection well monitoring points were found to have a statistically significant increase in CO concentration during air 6-20

21 injection. More discussion can be found in Powell (2005) in Appendix C and Powell et al (2006) in Appendix D. Figure BTEX concentration before and during air injection experiment at the NRRL bioreactor. 6-21

22 Figure Chlorinated VOC concentration before and during air injection experiment at the NRRL bioreactor. Figure N 2 O concentration before and during air injection experiment at the NRRL bioreactor. 6-22

23 Figure H 2 S concentration before and during air injection experiment at the NRRL bioreactor. Figure CO concentration before and during air injection experiment at the NRRL bioreactor. 6-23

24 6.4.3 Gas production in the NRRL bioreactor Faour (2003) estimated first-order gas generation model parameters using the USEPA LandGEM model. Based on the estimation, methane generation rate of NRRL was predicted. Figure 6.24 shows the estimated methane generation rate of the NRRL. Figure 6.25 show methane generation in the NRRL bioreactor. As moisture addition began at NRRL, methane generation rate started to increased. Comparing the predicted methane generation peak, methane generation at the field showed a blunt peak as shown in Figure Gas production of a bioreactor is a function of many site-specific variables including waste composition, climate, nutrient availability and moisture content of the waste. In addition to the factors, maintenance of the gas collection system is critical to capture and collect good quantity and quality gas. Figure Estimated methane generation rate of the NRRL. 6-24

25 Methan Flow (SCFM) /03 7/03 1/04 7/04 1/05 7/05 1/06 7/06 1/07 7/07 1/08 Figure Methane production of the NRRL bioreactor. Appendix C. Theses and Dissertations Kim, H. (2005). Comparative studies of aerobic and anaerobic landfills using simulatedlandfill lysimeters. Ph.D. Dissertation. University of Florida, Gainesville, FL. Powell, J. (2005). Trace gas quality, temperature control and extent of influence from air addition at a bioreactor landfill. Masters Thesis, University of Florida, Gainesville, FL. Faour, A. (2003). First-order kinetic gas generation model parameters for wet landfills. Masters Thesis, University of Central Florida, Orlando, FL. Appendix D. Peer-reviewed Journal Articles and Conference Proceedings Powell, J., Jain, P., Kim, H., Townsend, T., Reinhart, D. (2006) Changes in landfill gas quality as a result of controlled air injection. Environmental Science and Technology, 40(3), Appendix H. Periodic and Technical Reports New River Regional Landfill Bioreactor Demonstration Project Biennial Report, 2006 New River Regional Landfill Bioreactor Demonstration Project Biennial Report,

26 6.5 Solid Waste Characterization Solid waste sampling Solid waste samples at the NRRL bioreactor were conducted before and after operating the bioreactor. The first solid waste samples were collected during well construction in To directly asses the degree of waste stabilization in the bioreactor, the second sampling was conducted in August Figure summarized the sampling activities in the NRRL bioreactor. Solid waste sampling was also conducted at Phase II of Polk county bioreactor during gas well construction as shown in Figure The collected solid samples were analyzed for moisture content, volatile solids, biochemical methane potential (BMP) assay. Figure Locating a drill rig for solid waste sampling at the NRRL bioreactor. Sampling locations were determined based on the amount of moisture addition and air injection, degree of waste settlement, and distribution of sampling points on the bioreactor. 6-26

27 Figure Collection of solid samples retained on a continuous-flight auger bit. 6-27

28 Moisture levels increased with increasing depth of sampling hole. Bubbling in a hole drilled In the wet region where a large amount of leachate was added, waste samples were very wet and leachate also was squeezed out. Figure Waste samples with different depths. Typically moisture content increased with increasing depth. 6-28

29 measuring moisture ph BMP 0-5ft 5-10ft 0-10ft 10-15ft 15-20ft 20-25ft Samples for BMP Assays (0-10, 15-25, and ft) 15-25ft 25-30ft 30-35ft 35-40ft Samples for ph measurement (5-10, 20-25, and ft) 30-40ft Figure Solid samples collected from deferent depths for moisture content, volatile solid, ph, and BMP assay. 6-29

30 Figure Drilling at Phase II of Polk County North Central Landfill using Bucket Auger driller. 6-30

31 Figure water vapors come from drilled solid waste. Figure Solid samples collected from drilled solid waste. 6-31

32 6.5.2 Solid waste characterization Solid waste characterization at NRRL was conducted in 2001 and In this section, the results of moisture levels, volatile solid and biochemical methane potential (BMP) were compared. Figure 6.33 shows the moisture levels of waste in the NRRL bioreactor with different depths. Before adding moisture into the bioreactor in 2001, moisture levels are ranged around 20% and the difference of moisture content was relatively constant with depth. In 2007, after operating the bioreactor around 5 years, moisture levels increased to over 60%. In addition, moisture distribution showed the levels likely increased with depth. This is because moisture was not added into the most top of the bioreactor (a challenge for bioreactor operation). In contrast to moisture content, the amount of volatile solid in the waste samples decreased as shown in Figure The volatile solid analysis was conducted after sorting the samples to paper, fine and retained fractions. The decrease of volatile solids is noticeable in the paper fraction compared to the other fractions. BMP assay results provide better indication of on the status of the waste compared to volatile solids. The methane generation results of the BMP assay were markedly reduced by through the addition of leachate at NRRL as shown in Figure More discussion on the solid waste characterization can be found in Volume

33 Moisture Content (%) ft ft ft ft ft 0-10 ft ft ft ft ft Figure Comparison of moisture content of solid waste samples collected in 2001 and in

34 0.8 Volatile Solids in % Paper Fine fraction "Retained" fraction Year 2007 Year 2001 Year 2001 Year 2007 Figure Comparison of volatile solid of solid waste samples collected in 2001 and in

35 Biochemical Methane Potential (L/g VS) Figure Comparison of BMP of solid waste samples collected in 2001 and in Landfill Settlement Measurement of the surface elevation of a landfill provides a method of estimating airspace used, landfill density, and waste settlement. One of the objectives of running bioreactor landfills is to achieve rapid settlement of the landfilled waste, so as to potentially reuse the landfill airspace recaptured due to the biostabilization process. The other benefit expected out of achieving accelerated biostabilization is to reduce the settlement related problems such as cover damage. The settlement of the NRRL top surface and injection wells installed at different depths has been monitored since June Settlement measurements were performed periodically. Ninety-four points were marked across the top of the landfill to assess the settlement of the landfilled waste. Points chosen to survey the landfill surface include a concrete mogul fixed near each cluster of injection wells and monitoring wells for rigorous settlement analysis. For monitoring settlements of injection wells, the points marked on tees fixed to top of the leachate injection wells were also 6-35

36 surveyed. Figure 6.35 schematically illustrates all the points at the cluster wells that were surveyed. Figure 6.36 shows the settlement behavior along with the leachate recirculation trend. Among the four points measured a degree of waste settlement, surface show the greatest settlement. Settlement of the shallow well followed that of the surface. The settlement at the deep well was the lowest. This result may be explained by increasing density of waste with depth. Waste in deeper areas is more dense because of overburden pressure. With this reason, waste in the deeper area has less pore space than that in the upper areas. Figure 6.37 shows field observation of different degree of settlement. Figure 6.38 shows a water pond formed by waste settlement during operating the bioreactor. Concrete Mogul Well head point Surface of EGC Figure Location of different survey points for a cluster 6-36

37 Settlement (ft) ft Deep Wells 40-ft Deep Wells 20-ft Deep Wells Landfill Surface Moisture Added Moisture Added (million gallons) Time (in days) Day 1 = 06/24/02 Figure The settlement trend of the landfill surface, and three injection wells with respect to the leachate recirculation (CM3) 6-37

38 Figure Waste settlement of the NRRL bioreactors around injection wells. 6-38

39 Figure Water pond formed around an injection well cluster by waste settlement (CM3). In addition to the routine settlement monitoring, certain specific short term settlement data were also collected. The radius of influence of leachate recirculation around a well cluster was investigated over a period of time. Figure 6.39 suggests that settlement of waste occurred greatly at around a well cluster and decreased with increasing distance from the well cluster. The three wells in this well cluster were injected with leachate simultaneously at the rate of 500 gallons per day each over a period of ten weeks starting July 22, The settlement was measured around this well cluster for over 69 weeks. Figure 6.40 provides comparison of surface elevation of the NRRL bioreactor before (June 2002) and after operating bioreactor (April 2007). 6-39

40 0 1 Settlement (ft) 2 3 Settlement before Moisture Addition Settlement after 69 weeks of moisture addition Distance from well (ft) Figure The settlement behavior around well cluster before moisture addition and after 69 weeks of moisture addition 6-40

41 (a) (b) Figure Waste settlement of the NRRL bioreactor landfill measured sing GPS survey. (a) on June 2002 and (b) April

42 6.6 Summary and Conclusions The bioreactor landfills (NRRL, Polk County, and Alachua County) were monitored to measure the impact of bioreactor operations on the treatment of the landfilled waste. Leachate quality, gas quality and generation, characterizing solid waste samples, and waste settlement were monitored and compared before and after operating the bioreactor. The monitored results are summarized below. Leachate quality Leachate quality of simulated bioreactor lysimeters show rapid degradation of biodegradable pollutant in leachate such as COD, BOD and TOC concentrations, particularly by operating aerobic bioreactors. In a simulated anaerobic lysimeter, the increase of ammonia concentration was observed by an amount four times greater than the initial concentrations but did not increase in the aerobic lysimeters. For metal leaching, As, Fe, Mn, and Zn in the anaerobic lysimeters proved significantly greater in concentration than observed in the anaerobic lysimeters. Al, Cu, Cr, and Pb in the aerobic lysimeters were leached more than those in the anaerobic lysimeters. Long-term leachate quality monitoring at the Alachua bioreactor and the Polk bioreactor revealed that nonbiodegradable and persistent leachate constituents accumulated over time. Gas quality and gas generation Gas composition of well-controlled lysimeters shows the clear differences between aerobic and anaerobic bioreactors: small amounts of methane in the aerobic bioreactor and oxygen in the anaerobic bioreactor. However, aerobic and anaerobic gases were mixed in gas samples at the NRRL bioreactor during air addition. Trace components of aerobic exhaust such as VOCs, N 2 O, CO, and H 2 S were investigated by comparing their concentration in landfill gas before and during aeration. VOCs and N 2 O in aerobic exhaust were not significantly deferent from those before air injection. However, H 2 S decreased and CO concentrations increased by air injection. Methane generation rate increased by adding moisture into the NRRL bioreactor. However, Good maintenance of the gas collection system is needed to capture good quantity and quality gas. Solid waste characterization Moisture levels increased by moisture addition and the deeper waste sample had higher moisture content. Volatile solids in the waste samples reduced, in particular, in the paper fraction. The reduction of BMP in samples in 2007 suggested active biodegradation occurred during operation of the bioreactor landfill. 6-42

43 Waste settlement Settlement of waste occurred faster in waste located at shallow depth than that of deep. The most waste settlement occurred near injection wells and the degree of settlement decreased with increasing distance from the wells. 6-43