Page 375 - Materials Chemistry, Second Edition

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346 Waste Management Practices: Municipal, Hazardous, and Industrial
with heavy equipment. It may be feasible to either break open plastic bags to expose the contents
(by equipment or during emplacement) or require the use of degradable bags for optimum bioreac-
tor performance.

10.7.5.2 Daily Cover
Daily cover materials should be selected to avoid creation of low-permeability layers within the
landfill cell. For example, clay can become a barrier to leachate drainage and recirculation, while
foams, slurries, sludges, or reusable tarps will provide the benefits of daily cover without prevent-
ing infiltration and drainage (U.S. EPA, 2000).

10.7.5.3 Liquid Addition and Recirculation
A major landfill stability concern involves leachate (i.e., hydraulic head) buildup on the landfill
liner system. Ponding of liquid on the liner can be a significant source of failure as a result of the
associated hydrostatic forces. Addressing this in the initial design phase should be a straightforward
issue for bioreactor landfills because liquid levels and other variables are generally known.
Considerations in addressing liquid addition to bioreactor landfills should include:

● How to differentiate between the amounts of liquid needed by different types and sizes
of landfills
● Use of temperature to control liquid injection since wetting of the waste mass results in
the most uniform temperature
● Timing of liquid addition, e.g., at time of waste disposal, or deposit dry waste first and
add liquid later
● Determination of the desired moisture content and the amount of liquid required is nec-
essary for the design of an effective distribution system
10.7.5.4 Alternative Liquid Sources

Alternatives to landfill leachate for liquid addition include wastewater, biosludges, biosolids from
POTWs, stormwater runoff, and groundwater. Biosolids considered most suitable for bioreactor use
are those in liquid form that typically undergo land application, rather than the dewatered sludge
(U.S. EPA, 2002). Use of the liquid form could avoid dewatering costs, but will require more trucks
to transport the larger volume of the dilute wastewater. There are concerns regarding operational
health and safety issues about this material. Of particular concern is potential worker exposure to
pathogens and risks to workers and nearby residential areas from aerosols resulting from biosolids
application to the landfill surface.
As should be clear by now, the moisture content of wastes is critical for bioreactor operation.
The addition of significant quantities of liquid may be required. Some estimates (U.S. EPA, 2000)
indicate that about 50 million L (13 million gal) of liquid might be needed for 365,000 MT (400,000
3
tons) of waste; others estimate this requirement as 270 L of water/m (54 gal/yd ) of waste.
3
Landfills in states with dry conditions may require significantly larger liquid quantities. Also, more
liquid may be needed to sustain bioreactions after a low permeability cover or cap is installed
because the landfill moisture may be removed via the gas collection system. Thus, the leachate gen-
erated in the landfill should not be considered sufficient to support the bioreaction moisture needs.

10.7.5.5 Fires

Active landfill gas collection systems are a source of fires. Other fire initiators include drilling oper-
ations on the landfill and lightning strikes. Potential fire hazards during drilling are easily controlled
through safe work practices such as no smoking and the use of spark-free tools and equipment. Note
that surface fires are much easier to control and eliminate than underground fires.