LANDFILL LEACHATE TREATMENT USING SUBMERGED MEMBRANES AND REVERSE OSMOSIS TECHNOLOGY

The Lee/Hendry County Landfill, located on the gulf coast of Florida, was opened in 2002. At the time of construction (in 1997), a leachate collection system was installed and a conventional sand filter treatment was constructed for the removal of large suspended solids. The filtered leachate is currently stored on-site in a double-lined storage tank. The stored leachate is hauled off-site to a permitted disposal location. Due to an increased volume of leachate and the cost associated with hauling and disposal, the County directed Hazen and Sawyer to evaluate the treatment components that would eliminate the need for hauling and disposal of leachate.Based on the leachate data collected by the County, ultrafiltration (UF), a low- pressure (vacuum) membrane process, was selected as a possible option to reduce total suspended solids and organic material. This process would be followed by reverse osmosis (RO) to reduce the total dissolved solids in the leachate to acceptable discharge limits. The treated leachate must conform to primary and secondary drinking water standards in order to meet the requirements of the Florida Department of Environmental Protection's (FDEP) discharge permit.Before construction of a leachate treatment process was begun, pilot testing of the technologies was conducted. The primary objectives of this testing were to demonstrate the performance of the UF membrane and decrease the risk of RO fouling, collect performance data for the UF and RO systems, confirm the RO system effectiveness for removal of dissolved solids, and demonstrate and confirm membrane recovery rates.This paper presents the field and laboratory analytical data from the pilot testing of the UF and RO membrane technologies conducted at the Lee/Hendry County Landfill. The pilot test consisted of testing two separate membrane types and components, the UF system and the RO system. The submerged UF system tested was a Trisep SpiraSep 500. The membrane elements tested were spiral wound, negative pressure submerged UF elements constructed as immersed hollow fiber cast membranes. The flow path of the elements was outside-in, allowing the filtered material to remain on the outer surface of the membrane element. In addition, the submerged system typically requires lower feed pressures or vacuum requirements, has the ability to clean membranes in place, and experiences a lower transmembrane pressure which results in a lower probability of fouling. While UF is effective for removing suspended solids, it has little effect on dissolved ions and total organic carbon. However, the addition of pretreatment polymers and ferric chloride enhanced the removal of organic material by the UF process.The spiral wound RO membranes removed the dissolved ions in the leachate allowing the facility to meet discharge requirements. The RO membrane was tested using a single element membrane unit that utilizes recycling of the concentrate to simulate a recovery of 75 percent of the leachate feed water. The unit was loaded with one 4-inch diameter, 40-inch long membrane element provided by TriSep Inc.Physical data, flow, and pressure were collected using programmable logic controllers (PLC) for the UF module and manually collected for the RO unit. Samples were taken at eight (8) locations in the treatment process.