Waste Manage Res 2002: 20: 172–186 Copyright © ISWA 2002 Printed in UK – all rights reserved Waste Management & Research ISSN 0734–242X The bioreactor landfill: Its status and future The bioreactor landfill provides control and process Debra R. Reinhart optimisation, primarily through the addition of leachate College of Engineering and Computer Science, University of Central Florida. PO Box 162993, Orlando, FL 32816-2993, USA or other liquid amendments. Sufficient experience now exists to define recommended design and operating prac- Philip T. McCreanor tices. However, technical challenges and research needs School of Engineering, Mercer University, 1400 Coleman Ave. remain related to sustainability, liquid addition, leachate Macon, GA 31207, USA hydrodynamics, leachate quality, the addition of air, and Timothy Townsend cost analysis. Assistant Professor, Department of Environmental Engineering and Science, PO Box 116450, University of Florida, Gainesville, Florida 32611, USA Keywords – Landfill, bioreactor, leachate, recirculation, sustain- ability, wmr 341–2 Corresponding author: Debra R. Reinhart, College of Engineering and Computer Science, University of Central Florida. PO Box 162993, Orlando, FL 32816-2993, USA Received 29 September 1999, accepted in revised form 21 February 2002 Introduction of the barriers if the landfill is designed and operated as a Today integrated management of municipal solid waste bioreactor. results in recycling, composting, incineration, or landfilling The bioreactor landfill provides a similar approach and of waste. A landfill is an engineered land method of solid treatment as is utilised in organic solid waste digestion. waste disposal in a manner that protects the environment. The bioreactor landfill provides control and process Within the landfill biological, chemical, and physical optimization, primarily through the addition of leachate processes occur that promote the degradation of wastes or other liquid amendments, if necessary. Beyond that, and result in the production of contaminated leachate and bioreactor landfill operation may involve the addition of gas. Thus, the landfill design and construction must biosolids and other amendments, temperature control, include elements that permit control of landfill leachate and nutrient supplementation. The bioreactor landfill and gas. The inclusion of environmental barriers such as attempts to control, monitor, and optimise the waste landfill liners and caps frequently excludes moisture that is stabilization process rather than contain the wastes as essential to waste biodegradation. Consequently, waste is prescribed by most regulations. contained or entombed in the modern landfill and remains The bioreactor landfill has been defined by a Solid practically intact for long periods of time, possibly in excess Waste Association of North America working group as of the life of the barriers. However, waste stabilisation can (Pacey et al. 1999): be enhanced and accelerated so as to occur within the life “…a sanitary landfill operated for the purpose of 172 Waste Management & Research The bioreactor landfill: Its status and future transforming and stabilizing the readily and moderately 1997 that identified over 130 leachate-recirculating land- decomposable organic waste constituents within five to fills (Gou & Guzzone 1997). The number of recent litera- ten years following closure by purposeful control to ture references has also increased dramatically. In a 1998 enhance microbiological processes. The bioreactor landfill article, a large solid waste engineering consulting firm significantly increases the extent of waste decomposition, reported that over 25% of their clients have experimented conversion rates and process effectiveness over what with leachate recirculation but many chose to discontinue would otherwise occur within the landfill.” this process (Wintheiser 1998). There are four reasons generally cited as justification for These historical facts suggest that attempts to optimise bioreactor technology: (1) to increase potential for waste landfill degradation processes are usually restricted to to energy conversion, (2) to store and/or treat leachate, leachate recirculation. In addition, it appears that the (3) to recover air space, and (4) to ensure sustainability. percentage of bioreactor landfills is still small, perhaps This fourth justification for the bioreactor, sustainabili- 5–10% of landfills, although the number of landfills ty, has the greatest potential for economic benefit due to recirculating leachate is increasing. Reluctance to employ reduced costs associated with avoided long-term monitor- bioreactor technology can be attributed to several factors ing and maintenance and delayed siting of a new landfill. including a perception that the technology is not well A sustainable landfill would meet the following criteria; demonstrated, technical impediments, unclear cost impli- contents of the landfill are managed so that outputs are cations, and regulatory constraints. released to the environment in a controlled and accept- In the US, landfill regulations under Subtitle D of the able way, residues left should not pose unacceptable Resource Conservation and Recovery Act, permit environmental risk, the need for post-closure care is not leachate recirculation at lined landfills, but restrict it to passed on to the next generation, and the future use of the return of liquids that originate in the landfill. A recent groundwater and other resources are not compromised rule interpretation expands moisture input to uncontami- (IWMSLWG, 1999). This paper discusses the current nated water, although liquid wastes are still excluded. The status of the bioreactor landfill as it relates to design and US Environmental Protection Agency has expressed cer- operating concepts. The bioreactor landfill has developed tain concerns associated with bioreactor landfills that over the past three decades from a laboratory concept to include the long-term fate of metals, the lack of data that its present status as a viable waste management tool. The demonstrate the reduction of environmental risk and lia- complete history of its development is beyond the scope of bility, and increased operational requirements during the this paper, but may be found elsewhere (Reinhart & active phase of landfilling (Fuerst 1999). Technical issues Townsend 1998). that must be addressed include landfill gas capture, leachate treatment and storage, landfill space and capaci- ty reuse, greenhouse gas abatement, bioreactor design, Current technology implementation status solid waste density considerations, settlement, waste pre- The benefits of landfill bioreactor operation were well treatment, cover, and management of amendments. proven in the laboratory during the early 1970’s (Pohland In the 1997 SWANA survey (Gou & Guzzone 1997) 1975 and Pohland 1980), with pilot and full-scale demon- only six US states allowed bioreactor landfills, although stration occurring in the 1980’s (Natale & Anderson 1985 most states approved of leachate recirculation. However, & Pacey et al. 1987). By 1988, over 200 US landfills were several states have clearly embraced the technology, for practicing leachate recirculation, although with little engi- example, the New York Code of Regulations (360-2.9) neering input to design and operation. A survey of US states the following: states completed in 1993 found that full-scale leachate “…active landfill management techniques to encourage recirculation was occurring in twelve states. A review of rapid waste mass stabilisation and alternate energy the literature at that time identified less than twenty full- resource production and enhanced landfill gas emission scale leachate-recirculating landfills located in the US, collection systems are encouraged and should be Germany, United Kingdom, and Sweden (Reinhart & addressed in the landfill’s engineering report and in the Townsend 1998). However, the Solid Waste Association of operations and maintenance manual.” North America (SWANA) conducted a US survey in In addition Florida, California, Delaware, and Iowa have Waste Management & Research 173 D. R. Reinhart, P. T. McCreanor, T. Townsend Table 1. Description of Recent Full-Scale Bioreactor Landfill Tests Location Size Start Up Leachate Bioreactor Comments Date Recirculation Cost Technique Kootenai Co., 2.83 ha 1993 (landfill Surface spray $1 035 000 First lined landfill in Idaho. Idaho operation) (summer only) amortized + (Miller & Emge 1995 (leachate trenches 24.4 m operating costs = 1996) recirculation) spacing Wells $449 600 yr–1 Bluestem SWA, 0.20 ha 1998 Trenches 4.6 m $959 000 Experimenting with bag Linn Co. Iowa 7700 tons waste spacing (cell construction) opening, biosolids addition. (Hall 1998) divided into 2 10 670 l d–1 subcells. Milwaukee 61 m x 12.2 m 1999 trenches NA No compaction, shredded, (Viste 1997) biosolids added. Keele Valley LF Pilot 1990 Vertical wells - NA Well water added to adjust Toronto, Canada 1.2 wells ha–1 moisture content not leachate. (Mosher et al. ~ 190 - 400 lpm 1997) Eau Claire, WI 720 tpd landfill, 1998 Trenches 7.6 m spacing NA Tire chips acceptable in trenches, 7 Mile Creek SL (Phase I at 180 tpd) 73 lpd m–2 gas production increased (Magnuson 1998) by 25% in wells near recirculation. Yolo County, CA Two 930 m2 cells 1995 14 infiltration $563 000 Enhanced gas production, (Yolo Co. 1998) 4080 kg MSW each trenches at surface. (cell construction) settlement. Shredded tires 12 m deep. successful in LFG collection.