9420.pdf

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Two
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2
Iischarge scenarios were considered:
Discharge to a municipal sewer (assumed to be the GVS&DD)
Direct discharge to the environment
For discharge to the GVS&DD, the fee structure presently proposed by the GVRD,
$0.27/kg TSS and $0.13/kg BOD for TSS concentrations and BOD exceeding 200 mg/L,
is used. The fee to be paid for discharge to the environment was calculated based on
the method described in the Provincial Permit Fee Regulation. According to this
regulation, the maximum permitted daily discharge flow is multiplied by the TSS
concentration and BOD of the effluent. Each is then multiplied by the number of days per
year. The effluent TSS concentration and BOD are assumed to be 70 mg/L and
100 mg/L, respectively, as is the current practice for calculating permit fees if limits on
these parameters are not set in the discharge permit itself.
As operating costs of finer screens were assumed to be comparable to the costs of the
existing 600 pm screens, and the implementation of in-house modification is not expected
to result in additional operating costs, these added operational costs were assumed to
be zero. The operating costs for DAF were assumed to be $0.50/m3 based on
experience obtained from pilot plant tests. The volume of process water discharged, was
assumed to be 90% of the water consumption. Equipment costs were assumed to be
amortized in 5 years at an interest rate of 8 %
The assumptions used in the economic analysis are summarized in Table 7.4. The result
of the evaluations are shown in Tables 7.5 and 7.6 which, for comparison purposes, also
present the cost accrued if no modifications are carried out.
7.3.3 Results and Discussion
7.3.3.1 Discharge to GVS&DD
During the relatively short amortization period of five years, each of the evaluated
modifications would result in a larger annual expenditure than maintaining the status quo.
Of all modifications, the installation of 150 ~m screens would result in the lowest
expenditures followed by the installation of 500 pm screens, and in-house modifications.
The annual expenditures for these three modifications are fairly close, ranging from
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