Environmental Engineering Reference
In-Depth Information
TABLE 7.6
Heavy Metals from Biosolids from a Canadian
Wastewater Treatment Plant in 2007
Heavy Metals
Concentration (mg/kg)
As
6
Cd
9
Co
19
Cr
131
Cu
477
Hg
1
Mo
7
Ni
35
Pb
105
Se
9
Zn
596
These can constitute around 10% of MSW. There are numerous problems with disposal, as
it is not very biodegradable. It is a hazard in the marine ecosystem and occupies substan-
tial volumes in landills. Recycling can be achieved with generic plastic, mixed plastics
to regenerate raw materials. New products can be formed from recycled polypropylene
and polystyrene by injection molding, blow molding, and foam molding. The construction
industry uses PVC for piping, and baseboard moldings. Polyethylene can be used for trash
containers, topic binders, bags, and other household applications. Biodegradable plastics
are another alternative that is increasing in use.
Scrap tires are environmental threats (a) as mosquito hazards from accumulation of
rain water and (b) as ire hazards, since they are dificult to extinguish and can burn for
months, creating substantial contamination in the air and ground. Landilling is difi-
cult since landills (a) are not compactable, (b) require hundreds of years to decompose,
and (c) occupy substantial amounts of space. Contaminants may also leach into the soil.
Heavy metals, PAHs, and TPHs have leached out under various conditions. This has lim-
ited the reuse of tires as artiicial reefs and other environmental applications. The type of
tire shredding can substantially affect the leaching results. Various applications for reused
tires are shown in Table 7.7. Since there will be restriction for tire-derived fuel in the future,
the engineering applications for tires are the most promising. Shredded tires, known as
Tire Derived Aggregate (TDA), have many civil engineering applications such as a backill
for retaining walls, ill for landillgas trench collection wells, cover material in landills,
backill for landslide repair projects, and vibration damping material for railway lines.
Ground and crumb rubber, also known as size-reduced rubber, can be used in both paving
type projects and in moldable products.
Demolition debris and concrete are wastes from infrastructure renewal and building
demolition. It has been estimated by the U.S. Environmental Protection Agency (USEPA,
2009) that 170 million tonnes of building-related waste were generated in 2003 in the
United States (a 25% increase from 1996). Approximately 39% of this was of residential ori-
gin. It was also estimated that 49% was generated by demolition, 42% by renovation, and
9% by new construction. Approximately up to 75% of the wood, concrete, masonry, met-
als, and drywall are potentially recyclable. Overall, in 2003, 48% of C&D was recovered
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