Municipal landfills are designed for certain types of waste, mostly solid refuse. Specially designed landfills must be created for the storage of liquid waste and hazardous materials. In South Africa, liquid waste is not always separated from the solid refuse and can end up in landfills.
This poses a threat to the environment and groundwater as the liquids can soak into the soil beneath the landfill, carrying leachate and harmful substances with it. Some of these liquids include oils, cleaning products, beverages, food sauces, beauty products and other bottled substances.
Liquid waste can create problems for landfills
A lot of these types of waste can be paste-like or solids with a high liquid content, and some can contain reactive chemicals. This is why it is important to separate liquids from solids in the waste stream and send them to different landfills. However, this is hard to achieve and control, so municipal waste landfills must try to solidify the liquid refuse where possible.
Reducing the moisture content of this refuse is important as it makes the landfill more structurally stable and minimises the potential for harmful leachates and groundwater contamination. This de-moisturisation can take place in a number of ways, depending on the type of liquid waste involved.
Two types of binding agent
Binding agents are most commonly used and fall into two categories – bulking agents and solidification/stabilisation (S/S) agents. Bulking agents reduce moisture content by physically absorbing the liquids. Common examples include sawdust, mulch and soil. They are good at absorbing water but do not provide structural integrity to the landfill or control hazardous contaminants.
S/S agents reduce moisture through a process of chemical reaction. Common examples include cement, lime or fly-ash. These agents do provide structural integrity to a landfill and can minimise the leaching of hazardous substances. However, they are more expensive and often result in a permanent structure that is hard to move (i.e. a concrete block).
A lot of care must be taken by landfill operators when using bulking and S/S agents. The right agent must be used where appropriate and landfill operators should conduct pilot tests before choosing the best agent. Controlling liquid wastes is a vital process but landfill operators must also consider the pros and cons of de-moisturising agents before using them.
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