Asphalt is a mixture of aggregate, sand, filler, bitumen and occasionally a number of additives. Asphalt is primarily used for road construction. In an increasing number of countries old asphalt or demolition waste is recycled to replace virgin aggregate and part of the binder.
Average asphalt manufacturing facilities can product between 50 and 800 tonnes of asphalt per hour. Production takes place in a fixed or mobile mixing plant. There are two main production processes namely in batch plants and in continuous mixing or drum mixers. After production, trucks are used to transport the asphalt to its final installation. When trucks return to the plant they are sprayed and cleaned using release agents before they are filled with another batch of asphalt.
Pollution in water effluent from washing trucks can be minimized by:
- Spraying trucks with biodegradable release agents
- Spraying trucks in a segregated area that contains its own wastewater separator
Biodegradable release agents, such as rapeseed oil, are less toxic than traditional chemical release agents. In addition, wash water from spraying trucks needs its own wastewater collection facility due to its heavy concentration of detergents. If allowed to mix with other wastewater from the facility, the detergents will allow oils to emulsify and pass unhindered through a conventional skimmer in the wastewater treatment system.