Recirculated leachate

Anaerobic. Moisture is added to the waste mass in the form of recirculated leachate and from other sources to obtain optimal moisture levels. Biodegradation occurs in the absence of oxygen (anaerobically) and produces landfill gas. Landfill gas, primarily methane, can be captured to minimize greenhouse gas emissions and for energy projects. 

Biodegradation can be accelerated in a prepared bed reactor with forced aeration. These reactors (Figure 1.2) are used at many Superfund sites for bioremediation of PAHs and BTEX (benzene, toluene, ethylbenzene, and xylene) (Alexander, 1994). This method, with recirculating leachate, was used to reduce the average total petroleum hydrocarbon concentration in a diesel-contaminated soil from 6200 mg/kg dry soil to 280 mg/kg in approximately 7 weeks (Reynolds et al., 1994). A bed reactor with forced aeration was also used to treat 115 000 m3 of soil contaminated with bunker C fuel oil (Compeau, Mahaffey Patras, 1991) and 23 000 m3 of soil contaminated with gasoline and fuel oil (Block, Clark Bishop, 1990). 

Decrease of pollutant concentrations in the leachate. Positive effects in the reduction of leachate strength in a full-scale bioreactor landfill were observed at Sea Carr Landfill. The COD in the leachate from the area with recirculation was always lower than in the control area (without recirculation). The differences became more apparent with time. After three years of observation the COD values in the recirculated leachate were approximately 15 g dm while in the control they exceeded 50 g dm . A similar trend was observed in the case of chlorine, and ammoniacal-N. During three years of observations concentrations of these substances decreased in both cells, but the lower values and a more pronounced drop were noticed in the cell where leachate recirculation was applied. After three years, the chlorine and ammoniacal-N concentrations in the recirculated leachate was about 1,600 and 500 mg dm" respectively, while in the leachate from the control cell they were about 2,100 and 800 mg dm, respectively (Bioreactor Landfill for Sustainable..., 2004). Recirculation of leachate from an active or closed landfill cell can be considered as an in situ leachate treatment method. It minimizes the hazard to the environment and reduces the leachate treatment costs (Reinhart et al. 2002). Due to the continuous recirculation of leachate the operator does not bear the costs associated with its pre-treatment and transport to the treatment plant. 

Control of ga.s movement by recovery. The movement of gases in landfills can also be controlled by instadhng gas-recovery wells in completed landfills (see Fig. 25-74b). This is considered an active venting system. Clay and other hners are used when landfill gas is to be recovered. In some gas-recovery systems, leachate is collected and recycled to the top of the landfill and reinjected through perforated lines located in drainage trenches. Typically, the rate of gas production is greater in leachate-recirculation systems. 

The use of a drain system permits the quick construction of a collection/removal system which also serves as a barrier for leachate from large, shallow sites. At the Sylvester hazardous waste site in Nashua, New Hampshire, a groundwater interception and recirculation system was installed as a method to retard further spread of the leachate plume until a remedial cleanup action could be implemented. The system was operated for 1 year until a containment wall and cap were constructed over the 20-acre site (McAneny, 1985). 

Leachate can also be degraded biologically in situ at the landfill site. Conditions within the landfill are controlled to encourage microbial activity, and leachate is recirculated through the... 

Aerobic. Leachate is removed from the bottom layer, piped to liquids storage tanks, and recirculated into the landfill in a controlled manner. Air is injected into the waste mass, using vertical or horizontal wells, to promote aerobic activity and accelerate waste stabilization. 

Modrak, M., Hashmonay, R.A., Varma, R., and Kagann, R., Measurement of Fugitive Emissions at a Landfill Practicing Leachate Recirculation and Air Injection, U.S. Department of Commerce, National Technical Information Service, Springfield, VA, 2005, 58 p. 

The United States Environmental Protection Agency (EPA) requires all new landfills to include a leachate collection system. Recirculation of leachate accelerates the decomposition of solid waste. Another alternative use of landfills is to capture the methane gas produced during decomposition to generate electricity. For example, in Yolo County, California, a landfill releases 1.4 million cubic feet of gas a day used to generate electricity. 

Changes to landfill operation, such as operating under wet conditions through leachate recirculation or other liquid additions, will result in generating more gas at a faster rate but with this software such operations were not considered [7],... 

For effective co-disposal, the draft document for consultation (DoE, 1994a) states that "flushing bioreactor conditions are needed. This leads to a separate requirement for containment and possibly recirculation" (see Chapter 7). Under enlumced conditions of gas generation (and hence microbial activity) the potential for effective co-disposal will be enhanced accordingly. Although at the moment very few landfill sites undertake leachate recirculation, it is a concept that is receiving a great deal of attention and one that appears to facilitate both codisposal practice and more sustainable landfill development. 

Figure 12 High rate leachate recirculation concept (Knox and Gronow, 1993) Reproduced with permission...

Doedens, H. and Cord-Landwehr, K (1989) Leachate recirculation. In Sanitary Landfilling Process, Technology and Environmental Inqtact (Christensen, T.H., Cossu, R. and Stegmann, R. eds.) Academic Press, London. 

Pohland, F.G. (1989) Leachate recirculation for accelerated landfill stabilisation. In Sardinia 89 Proceedings of the second international landfill symposium. Porto Conte. XXX, ppl-8, CIPA, Milan... 

If it is desired to speed up decomposition in a landfill environment, leachate recirculation can be used. In such systems, instead of pumping out, treating, and discarding any liquid effluent which reaches the top of the landfill liner, the liquid which is pumped out is reintroduced... 

Biodegradation. Current studies have shown that wet systems, or landfills that use leachate recirculation, are becoming the favored option when considering solid waste stabilization as a priority for the landfill. Since most biodegradation results from... 

Depending on the similarity theory, two laboratory simulation experiment devices were developed. Both devices I and II consist of a cover layer, a waste layer, a drainage layer, a compacted clay layer, a leachate recirculation system, as well as a few test instruments (Fig. 1). The seepage characteristics of leachate in compacted clay layers were determined through simulation experiments. 

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