Special Issue on Bioreactor Landfills

Since the introduction of the concept of enhanced degradation of municipal solid waste (MSW) using liquid addition by the late Professor Pohland in 1975, MSW landfills have been designed, permitted, and operated as bioreactors for almost three decades in many developed countries including the United States. About 75% of the states within the United States allow bioreactor landfills, and the remaining states only approve bioreactor landfills on a case-by-case basis.

Although short-term benefits of bioreactor landfills have been relatively well established, long-term benefits and challenges have not been fully understood or addressed. The short-term benefits of bioreactor landfills include (1) faster settlement of the waste resulting in airspace gain; (2) reduced leachate treatment costs if leachate is recirculated to enhance the biodegradation; and (3) greater rate of landfill gas generation, which can enhance the gas to energy production. Long-term benefits of bioreactor landfills that have not been fully understood include improvement in the postclosure leachate quality and mechanical properties of MSW.

Key challenges associated with bioreactor landfills can be divided into three categories: (1) changes in mechanical properties; (2) targeting and monitoring of physical and chemical parameters; and (3) fluid management. This special issue contains 11 papers that address some of these challenges via lab-scale to field-scale experiments and using numerical models. The papers cover topics such as enhanced degradation of waste using septage and air; seismic imagining to monitor moisture content and to capture spatial changes in the dynamic properties of the waste; dual-phase flow and slope stability implications; coupled hydromechanical behavior and settlement; and seepage control.

We believe that this special issue on bioreactor landfills can benefit practitioners, educators, and researchers. The articles provide the state of the art of bioreactor landfills to design and operate more efficient and environmentally robust bioreactor landfills.