Bioreactor landfills : Do they work ?

This paper begins by providing an outline of various waste stabilisation techniques on which the concept of bioreactor or process-based landfills is based, followed by an overview of the research and development of this alternative landfill approach. The paper then presents a summary of the Australian experience. It also reports on the current state of bioreactor landfills and discusses the difficulties and problems associated with their full-scale operations. Areas where future research should be focused are also identified. 1. INTRODUCTION Currently our municipal solid waste (MSW) landfill technology is primarily based on a permanent storage and containment or " dry cell " concept. Most of the research activities have been concentrating on the design of liner, cover, and hydraulic systems with the aim of sealing off a landfill from the external environment. The idea is to minimise the amount of water entering the waste sealed within a well-encapsulated landfill cell, and the waste can then be preserved in a relatively inactive state— discouraging the formation of leachate and landfill gas to reduce environmental impacts. While this dry cell approach may delay decomposition due to a lack of moisture, its long-term effectiveness is very much in doubt, as it has to rely on permanent encapsulating performance of a containment system, which is rather unrealistic. As a containment system ages and becomes less effective, there is a long-term risk that the suppressed biodegradation may turn active in the future. With a better understanding of landfill decomposition processes and behaviour, there has been a strong trend in recent years to shift the philosophy of landfill design from the above permanent storage concept towards a bioreactor (or process-based) approach (Krol et al., 1994; Pacey et al., 1999). The bioreactor concept, in contrast to the permanent storage approach, allows active landfill management based on an understanding of the biological, chemical and physical processes involved. It focuses on enhancing the degradation processes to stabilise waste and aims to bring forward the inert state of a landfill in a relatively short time. It utilises a landfill as a bioreactor to treat waste rather than merely as a burial ground. It offers the potential to avoid the long-term environmental risks associated with the dry cell approach. Although laboratory tests and pilot-scale studies have demonstrated its advantages over the conventional dry landfills, there are still some technical and non-technical barriers yet to be overcome before we can truly translate …