Page 137 - Materials Chemistry, Second Edition

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108 Waste Management Practices: Municipal, Hazardous, and Industrial
address the types of containers to be used, the segregation of recyclables or other wastes for separate
collection, how frequently materials are collected, and where residents are to place materials for
collection.

5.3.3 WASTE SEPARATION
Many communities have arranged to collect some portions of solid waste separately; for example,
recyclable materials or yard wastes may be collected on a different day from ordinary MSW.
Residents will therefore be required to separate wastes before collection. Residents may be expected
to separate recyclable materials such as paper, cardboard, glass, aluminum, and plastic; similarly,
yard waste, bulky items, and household hazardous wastes may have to be segregated for separate col-
lection. Bulky items such as white goods (e.g., large appliances) and furniture are usually placed at
the same point of collection as other solid wastes. Some U.S. communities have tested the so-called
wet and dry collection systems, in which “wet” organic wastes suitable for composting are collected
separately from “dry” wastes, which may be sorted for the recovery of recyclables (U.S. EPA, 2003).

5.3.4 FREQUENCY OF COLLECTION
The greater the frequency of collection in a community, the more costly will be the collection system.
Factors to consider when establishing collection frequency include total cost, desires of the residents,
storage limitations, and climate. Collection once or twice per week is common for most U.S. munici-
palities, with collection once per week being prevalent. Crews collecting once per week can collect
more tons of waste per hour, but make fewer stops per hour than the twice-a-week collection vehicles.
Some communities in hot, humid climates use twice-per-week service due to health and odor concerns.
In one study, once-per-week systems were found to collect 25% more waste per collection hour while
serving 33% fewer homes during that period. Personnel and equipment requirements were 50% higher
for once-per-week collection (U.S. EPA, 1974a). In Montgomery County, Maryland, one part of the
county received weekly MSW pickup, while other areas received twice-per-week pickup. Twice-per-
week collection was almost 70% more costly than once-per-week collection (U.S. EPA, 1999).

EXAMPLE 5.1
In the town of Livengood, Ohio, it is determined that the per capita waste generation rate is 1.4 kg
(3.1 lb) per person per day. Collection is conducted once per week by the municipality. If the den-
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sity of MSW in a typical trash container is 150 kg/m , how many 120 L (30 gal) containers would
be needed for a family of four?
1.4 kg/person/day 7 days/week 9.8 kg MSW
9.8 kg lb/person 4 persons 39.2 kg/family
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39.2 kg / 150 kg/m 0.26 m 3
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0.26 m 1000 L/m 260 L
Thus, three 120 L containers are required.
EXAMPLE 5.2

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From the above example, collection trucks have a capacity of 11.5 m (15 yd ), which can compact
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the waste to a density of 420 kg/m . How many customers can a truck handle in a single run, before
departing for the transfer station?
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11.5 m 420 kg/m 4830 kg capacity
4830 kg / 39.2 kg/household 123 households