Title: Recirculation of Leachate within the Landfill for the Leachate Treat

Duration: 1997 - August 1, 1998

Critical Water Problems
Most of the treatment processes for water and wastewater treatment may be for leachate treatment. However, the aerobic treatment for the reduction of high concentration of organic in the leachate, will be to expensive. Anaerobic treatment technology will be more suitable for leachate treatment. The other leachate treatment technology is the recirculation of leachate over the landfill. This technology is attractive because it is simple and economical. Essentially, the landfill itself is used as a giant anaerobic reactor for the treatment of leachate.

This project examined the suitability of the leachate treatment recirculation. Gas production, COD and other variables were monitored during the recirculation. The specific objectives of the project were to characterize the organic matters (COD) and the inorganic matters (heavy metals) in the leachate during the recirculation, and to monitor the gas production rate during the recirculation.

Methodology
Cabo Rojo landfill is a relatively new facility of just three years old. The facility is divided into 20 cells. Each cell is a square entity with an area of 9,000 square feet and a depth of solid wastes of 90 feet. It is sufficient for receiving the city solid waste for a period of two years. At present, the first cell is completed. In each cell there are two specially constructed gas vents and a manhole with a depth of 90 feet located near the center of the cell. Cabo Rojo's landfill is located in a dry area of Puerto Rico. There is about 20 feet of leachate accumulated over the past two years in the bottom of the cell. The procedure followed to achieve the project objectives were to install the recirculation facilities and the gas meter at the gas vents, analyze the leachate sample from the recirculation flow twice a week, and monitor the gas production rate on a daily basis.

Principal Findings and Significance
The principal findings and conclusions of this project were that gas production increases after each recirculation. The principal cause seemed to be the microorganisms feeding on the organic material in the recirculated leachate. Also, the recircualted water wets the buried solids wastes and may speed up the decomposition process of the organic materials within the landfill. Also, the recirculation water does wash down the organic material within the landfill. This results in the increase of the COD concentration in the recirculation leachate. However, the COD in the leachate will be eventually reduced if the application of the recirculation continues for a long time (one or two years). Further research is needed to verify this hypotheses. It was also determined that the surface of the landfill needs to be sealed to prevent rainwater entering as the new leachate. Otherwise, it is difficult to evaluate the experimental data. Finally, the process offers an alternative route for leachate treatment because it is simple and economical. The cost for the recirculation facilities was approximately $2,000. The cost of energy for the operation is minimal because only one hour per week is needed.