eg 5. 
537 
mixture. 
All of the solid waste used in the process is screened through a 2 inch 
rotary trommel; any material not passing the 2-inch screen is hanmeamelled: 
this improves uniformity of the product. The dense rock product is inert. It 
is economically useful right in the municipality generating the wastes. 
Market surveys have shown that municipal aggregate consumption for roadway 
resurfacing far exceeds the amount that could ever be produced from a 
municipality's sludge and solid waste production; all of the ECOROCK produced 
would be used in the city itself. 
Economics 
Continual updatings on the costs for the process have been made during 
the course of development. These have shown it to be less costly than land or 
even ocean disposal in most cases. Table I gives a detailed breakdown of the 
currently projected costs for a 20-ton-per-day unit, such as the demonstration 
scale plant built on a 3/4 acre site at Philadelphia's Northeast Water 
Treatment Plant. Municipal incinerator residue in this case is being used as 
the solid waste carrier, fuel and fluxing agent for the sludge. (Its small 
combustible heat content of 2,000 BTU/1b. is adequate to help dry the sludge.) 
Table 2 shows projected capital costs and complete annual operating costs 
for several levels of expanded capacity. Economies of scale drop the sludge 
disposal costs to approximately $63 per ton (dry sludge basis) for a unit 
handling 400 tons per day of sludge solids. This is less than the $90-per-ton 
cost now projected for deep ocean disposal of Philadelphia's sludge and well 
below the costs many cities now pay for land disposal of sludge. Moreover, 
these costs do not take all economic and environmental benefits into account. 
For example, a value higher than $4.50 per ton for the durable, safer, skid- 
resistant ECOROCK aggregate might actually be realized in practice. In 
addition, both monetary and health benefits to society result from sparing the 
air, land and water from the burdens of dumping these wastes. Land is also 
spared from quarrying when the ECOROCK aggregate is used in place of natural 
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