CHARACTERIZATION OF FUGITIVE EMISSIONS OF GREENHOUSE GASES FROM A WASTEWATER TREATMENT PLANT USING THE RADIAL PLUME MAPPING TECHNIQUE

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1 CHARACTERIZATION OF FUGITIVE EMISSIONS OF GREENHOUSE GASES FROM A WASTEWATER TREATMENT PLANT USING THE RADIAL PLUME MAPPING TECHNIQUE Mark Modrak, Victor D Amato, Michiel Doorn, Ram Hashmonay ARCADIS, Research Triangle Park, NC Walter Vergara, Alejandro Deeb World Bank, Washington, D.C Carlos Suarez, Carlos Aparicio, Martin Cuevas Corporacion Autonoma Regional Para La Defensa de La Meseta de Bucaramanga, Bucaramanga, Colombia KEYWORDS OP-FTIR, Radial Plume Mapping, greenhouse gas emissions, anaerobic wastewater treatment plant INTRODUCTION An existing anaerobic wastewater treatment plant (WWTP) near Bucaramanga, Colombia is being upgraded to include nitrification/denitrification and improvements in capture and recovery of methane. The existing plant utilizes upflow anaerobic sludge blanket (UASB) reactors followed by facultative lagoons. For this project, the UASB reactors will be retrofit to maximize the collection of biogas, and the lagoons will be converted into an aerobic/anoxic activated sludge (aerated oxidation tank) process for biological nitrogen removal. It is anticipated that the upgrade will result in a reduction in odors associated with plant operation, and a net reduction in greenhouse gas emissions via the recovery of methane and the reduction in nitrous oxide emissions from the plant and the receiving river. This will result in carbon credits under the Kyoto Protocol s clean development mechanism (CDM) which would be purchased by carbon finance trust funds at the World Bank. In order to document the emissions reductions, an accurate and cost-effective monitoring of the emissions before and after the upgrades is crucial to the success of the project. The first round of emission measurements were conducted in October 2005 using a scanning Open-Path Fourier Transform Infrared (OP-FTIR) spectrometer, and a technique known as Radial Plume Mapping (RPM). The study included single-path measurements at five points along the surface of the river adjacent to the plant. The monitoring points were located upstream of the plant, near the plant discharge, and downstream of the plant. 7200

2 In addition to the measurements conducted along the river, the RPM method was used to measure emissions of methane and nitrous oxide from the facultative lagoons and UASB reactor area located at the WWTP. METHODOLOGY The RPM method involves using a novel, yet simple, configuration of non-overlapping radial beam geometry to map the concentration distributions in a plane. It requires only a single optical remote sensing (ORS) instrument that is scanned horizontally to several retro-reflecting mirrors located along different paths in a configuration (see Figure 1). Emission area Figure 1- Example of Horizontal Radial Plume Mapping (HRPM) Configuration The RPM method can also be applied to a vertical plane (see Figure 2) downwind from an area emission source to map the crosswind and vertical profiles of a plume. By incorporating wind information, the flux through the plane can be directly calculated, leading to a direct, measurement-based estimation of an emission rate for the upwind area source (Hashmonay and Yost, 1999). 7201

3 Figure 2- Example of Vertical Radial Plume Mapping (VRPM) Configuration RESULTS Measurements Along the River Measurements were made using a single optical path at five points along the surface of the receiving river. The monitoring points were located upstream of the plant, near the plant discharge, and downstream of the plant. The measurements detected nitrous oxide concentrations at 10.3 ppb above background concentrations at the plant discharge point, and 12.5 ppb above background concentrations at the farthest measurement point downwind of the plant. Nitrous oxide was not detected above background concentrations at the other measurement points along the river. The measurements detected methane concentrations at each measurement point along the river. The lowest methane concentrations were found at the measurement point located upstream of the plant. The highest concentrations (up to 1.57 ppm above background values) were found at the plant discharge point. The measured methane concentrations decreased downstream from the discharge point of the plant. Measurements of the UASB Reactor Area Measurements were also taken along the surface of the UASB Reactor area at the plant. Analysis of the data did not detect the presence of nitrous oxide above background concentrations. However, this may be due to the relatively short optical path lengths used during the survey of the reactor area, because spectral analysis of nitrous oxide is generally difficult along short optical paths. The measurements detected surface methane 7202

4 concentration values ranging from 3.52 to 26.7 ppm above background levels. Figure 3 presents a surface methane concentration contour map of the reactor area produced using the HRPM method. Figure 3- Surface Methane Concentration Contour Map from the UASB Reactor Area The figure shows the presence of two surface methane hot spots, each having concentrations greater than 15.3 ppm above background values. Measuring Emissions from the Facultative Lagoons Additional measurements were taken at the facultative lagoons at the plant. Nitrous oxide was detected along the surface of the facultative lagoon (average nitrous oxide concentration of 16.0 ppb above background values). The surface measurements also detected methane values as high as 3.95 ppm above background levels. Methane flux values downwind of the facultative lagoons were calculated using the VRPM method. The average calculated downwind methane flux was 1.7 g/s. Figure 4 presents the average downwind methane plume map. 7203

5 Figure 4- Average Methane Plume Map Downwind of Facultative Lagoons (concentrations shown in ppmv) CONCLUSIONS The current study was conducted to document emissions of methane and nitrous oxide from a WWTP prior to an upgrade to reduce emissions of greenhouse gases. The study corroborated the presence of nitrous oxide along the receiving river as well as immediately above the surface of the facultative lagoons. The study detected elevated methane emissions from the UASB reactors (concentrations as high as 26.7 ppmv above background levels), and slightly elevated methane emissions (concentrations as high as 5.5 ppmv) from the facultative lagoons at the plant. The average methane flux downwind of the facultative lagoons was 1.7 g/s. It is recommended that additional measurements be conducted using Optical Remote Sensing techniques after the plant upgrade has been completed to document any reductions in greenhouse gas emissions resulting from the upgrade. 7204

6 REFERENCES Hashmonay, R.A., and M.G. Yost, Innovative approach for estimating fugitive gaseous fluxes using computed tomography and remote optical sensing techniques, J. Air Waste Manage. Assoc., 49, ,