**6.5.1 Bioreactor landfills**

162 Management of Organic Waste

compacted clay. Capping has a life span of about 50-100 years, but the performance of the cap depends on the site's environmental conditions. Cracking and erosion of caps can occur due to fluctuations in air temperatures and precipitation, and if the site is prone to subsidence and earthquakes. The cap must be adequately thick to prevent frost, and

The use of temporary caps, instead of a final cap, on a filled landfill cell increases landfill space because the feet of soil typically used in a final cap is replaced with a synthetic membrane held down by removable items, like tires rather than soil. Temporary caps may be used in conjunction with leachate recirculation and active gas extraction. They are readily removable, and do not occupy much space like soil when the landfill is reopened for future landfilling activities. Some landfills are using temporary tarps to cover the waste instead of daily soil covers, increasing landfill capacity. Soil-like materials, like spray foam, can substitute soils as daily or intermediate cover material frees landfill space (NJDEP,

When a landfill reaches final elevation levels, landfill surcharging may be implemented. The surcharging of a landfill involves the placement of a large amount of weight on top of the landfill for 6-12 months. The added weight to the top of the landfill causes enhanced settlement of the waste and increased capacity, which is recognized after the surcharge material is taken away. Clean soil is usually used as the surcharge material, which may be used elsewhere in the landfill after the surcharging process is completed (NJDEP, 2006).

Soil vapor extraction (SVE) and air sparging are in-situ remediation techniques to remove vapors from polluted soil and plume, respectively (Vasudevan et al, 2003). Usually, SVE and air sparging are concurrently used in a site (EPA, 2001).Solvents, fuels (EPA, 2001), and volatile organic compounds (Vasudevan et al, 2003) are readily removed through these methods. Two types of wells are installed around the landfill, extraction wells and air injection wells. An extraction well creates a vacuum to draw the vapors to the surface, while an air injection well pumps air into the ground. The air injected stimulates the growth of aerobic microbes to enhance microbial decomposition. If the injected air is heated, the

SVE and air sparging are safe but may take years to reach full remediation depending on the size and depth of pollution, type of soil, and concentration of chemicals in the soil and groundwater. However, these methods are quicker than just relying on natural processes

**6.5 Co-treatment of landfill leachate with sewage in a wastewater treatment plant** 

Leachate management involves discharging to a wastewater treatment plant, pre-treatment before discharging to a wastewater treatment plant, or treatment onsite and following discharging to a nearby stream. The connection with a nearby sewer line is the most

accommodate vegetative roots and burrowing animals (Vasudevan et al, 2003).

2006).

(EPA, 2001).

**6.3 Landfill surcharging** 

**6.4 Soil vapor extraction and air sparging** 

evaporation of the chemicals is accelerated.

The recirculation of leachate back into filled cells is an essential step in a bioreactor landfill, in which microbial activities are intentionally enhanced. The recirculation of leachate provide moisture and/or oxygen to stimulate the microbial degradation of solid wastes and simultaneously reduce the amount of leachate needed for treatment. A bioreactor landfill may be either aerobic or anaerobic, to reclaim landfill space. Aerobic bioreactor landfills inject both air and leachate into the waste, while anaerobic bioreactor landfills only inject leachate into the waste. The aerobic bioreactor increases microbial digestion rates, thereby resulting in quicker settlement of the waste compared to anaerobic bioreactor landfills. In contrast, anaerobic bioreactor landfills generate more methane gas. Thus, it is a promising candidates for energy recovery projects. However, the recirculation is not commonly accepted practice among the waste management community or is not favored by regulations (NJDEP, 2006).
