Water management of open cell landfill lysimeters, Open Cell No.2 and 3, was carried out by considering in situ moisture content of MSW in landfill, experiment on leachate recirculation and model application. Figure 3.5 illustrates the details of Task II.
Figure 3.5 Flowchart of methodology of Task II
3.3.1 In situ Moisture Content Measurement Using an Electrical Resistance Sensor
Electrical resistance technique was selected and applied for indicating in situ moisture content of MSW of Open Cell No.2 and 3. The resistance measurement historically observed good co-relation between moisture content and electrical resistance (Gawande et al., 2003; Grellier et al., 2005; Guérin et al., 2005).
Task II
Determining water management for open cell landfill lysimeters
1) Estimating in situ moisture
content of MSW in landfill 3) Reviewing the HELP model and its application
Data collection and analysis 2) Experiments on leachate
recirculation
Determining the necessity of leachate pre-treatment option
Output
Determining the water balance of Open Cell No.2 and 3 lysimeters
4) Comparison the results between experiment and model and applying for water management
Output
Determining the suitable leachate recirculation cycle
The electrical resistance moisture content sensor was designed to measure the electrical resistance occurring between two electrodes embedded in dry clay. Water moved from the surrounding waste to the sensor body. Changing resistance readings reflected the changes in moisture content of the sensor’s media.
This sensor body was locally made from geotextile. The body of sensor had cylindrical shape with diameter 5 cm and 10 cm in height. Seven centimeters long piece of stainless steel rods were inserted through the center of the sensor body. Two electrodes were connected to the resistance conductors via copper wire. Resistance across the sensor electrodes was measured using resistance meter. Figure 3.6 shows the details of the electrical resistance moisture content sensor.
Figure 3.6 Electrical resistance moisture content sensor
The relationship between moisture content and electrical resistance of this sensor were obtained from experiment in laboratory. After that, the sensors were installed into Open Cell No.2 and 3 by drilling vertical holes. Both lysimeters had two moisture sensors. One
5 cm 10 cm 7 cm Dry clay Geotextile material Electric wire
Stainless steel rod Electric insulator (wrapping stainless steel rod)
Connecting for reading resistance value
Moisture content sensor Resistance meter Tighten up
with plastic rope
sensor was installed at depth 0.3 m which was assumed as representative moisture content at the top level of lysimeter. Another sensor was installed at depth 1 m which assumed as representative moisture content at the middle level of lysimeter. The resistance values were obtained by resistance meter converting to estimate moisture content of MSW in landfill lysimeters.
3.3.2 Experiments on Leachate Recirculation
Determining suitable leachate recirculation cycle
At the beginning of operation, leacahte generation from Open Cell No.2 and 3 was pumped and collected into separate storage tanks. Whenever, the moisture content of MSW in landfill was not enough, leachate was recirculated on both lysimeters. Control of moisture content was conducted from the results of moisture content sensors, ambient condition data (e.g. temperature, rainfall, evaporation, etc.) and experiment at site. All of these investigations can provide the suitable leachate recirculation cycle (leachate recirculation rate and its frequency).
Determining water balance of Open Cell No.2 and 3 lysimeters
The main water inflow into lysimeters was precipitation and recirculated leachate. Water outflow was leachate production. Initial moisture content of MSW, water stored in the body of lysimeter and evapotranspiration were other factors to influence water balance. Climatic data and experimental data were collected and water balance was calculated by using water balance equation, as referred in Chapter 2 (section 2.4.1).
Determining the necessity of leachate pre-treatment
Leachate recirculation was provided by directly pumping it from the storage tanks into selected lysimeters. The storage tanks were the open tank, which allowed rainfall and evaporation. Therefore, the amount of water in these tanks was leachate adding precipitation and subtracting water loss as evaporation. The excess water needs further treatment before discharge.
Sampling and analysis of leachate recirculated in terms of TSS, pH and conductivity were determined. The results of analysis were investigated for balancing system and protection of clogging of leachate collection and recirculation system. The necessity of pre-treated leachate before recirculation was considered too. The flow charts of leachate management shows in Figure 3.7.
Figure 3.7 Flowchart of leachate management
3.3.3 The HELP Model and Its Application for Open Cell Landfill Lysimeter
The HELP model version 3.07 was selected for simulation water balance of open landfill lysimeters. Significant inputs were collected and assessed for model procedure.
Data collection and analysis
• Weather data was recorded by AIT Meteorological Station. Five years (2001-2005) daily rainfall, temperature, solar radiation, etc. were collected. These data were illustrated in Appendix A (Table A-1 to A-5). The other significant data for HELP model was obtained from the previous experimental data, literature review and available data from model.
• Soil and landfill design data were followed the specific design and operation of open cell landfill lysimeters. Using the default data from model was considered.
Modeling procedure
A comprehensive review on HELP model and its application was performed. The procedure followed the HELP model user’s guide Version 3 (Schroeder et al., 1994). The water balance of Open cell No.2 and 3 lysimeters were modeled. Figure 3.8 presents the model flowchart. Lysimeter Leachate collection tank Submersible pump
Leachate storage and evaporation tank Leachate Leachate recirculation Sprinkler Rainfall Evaporation Rainfall Evaporation Further treatment of excess leachate
Figure 3.8 Model flowchart
3.3.4 Comparison of Water Balance from Experiment and HELP Model
A comparison on the model output for water balance components was done with the results of lysimeter experimented. The application of model for water management of open cell landfill lysimeters was considered in this study.
Weather data
» Precipitation à Temperature
¶
Solar radiation EvapotranspirationSoil and design data
Landfill general information
Landfill profile design and layer
Runoff curve number information Output (daily/monthly/annual)y Precipitation
y Runoff
y Evapotranspiration
y Leachate generation
y Change in water
storageExecutive simulation Program input
Chapter 4
Results and Discussion