Environmental Engineering Reference
In-Depth Information
working days of the week. Therefore, the weekly
water consumption is:
Water consumption = 300 + 5 x 100 = 800 m
3
/
week.
In addition, as calculated previously, it is also
known that 124.46 kg/day of caustic will be used
instead of 87.35 kg/day CaO. Since no experiment
could have been performed using real wastewater
to find out the amount of NaOH for adjusting the
pH to about 8.5, the comparison of costs of lime and
caustic was made based on theoretical calculation
of the amounts of chemicals with the assumptions
made. The prices of the pure CaO and NaOH are
76.25 $/tone and 562.5 $/tone, respectively. The
unit cost of water is 2.21 $/tone. The cash flow
analysis of the using caustic instead of lime is
compared with the current system in Table 4. As
it is seen from Table 4, even though the unit cost
of caustic is greatly higher than lime, this alter-
native gives lower costs because it significantly
reduces the water consumption by allowing the
reuse of the refined wastewater. A high cost sav-
ing is obtained with the use of this alternative.
The net present values of the current system and
the suggested alternative are calculated for one
year, as seen in Table 4. The costs are assumed to
derive at the end of each month and the monthly
interest rate is taken as 1.6%. When comparing net
present values, it can be seen that the suggested
alternative decreases costs by 45% compared to
the current system.
Comparison of Alternative
Waste Management Solutions
Table 5 shows the suggested alternative waste
management solutions and the environmental
and economical benefits that can be obtained by
using them in the company. As seen in Table 5,
it was demonstrated that the formation of dross
which is the biggest waste problem of the company
could be decreased by 30% by using a flux during
dross collection. Since the waste was reduced at
the source, the waste and recycling costs could
be significantly decreased, and most importantly,
a very big quantity of lead (Pb) raw material
could be recovered consequently. The reuse of the
treated wastewater was also a good alternative for
the company since a very high quantity of water
is used and wasted every day due to production
requirements. By using caustic instead of lime, the
company could reduce its weekly water usage up
to 44%, which would make a considerable decrease
in environmental impacts and operating costs.
Table 6 shows the difference in waste manage-
ment costs when quantity of wastes are decreased
according to the suggested alternative waste
management solutions. It can be seen in Table 6
that a cost improvement of 63% is achieved by
Table 5. Suggested solution alternatives and advantages
Wastes
Alternative
Environmental Advantages
Economic Advantages
Dross, excess parts and re-
jected grids from grid casting
Addition of Excess Parts and
Rejected Grids in Batch Mode
Waste reduction at source
Cost Reduction: 94,631
$/year.
Recovery of 70,848 kg Pb/year.
Separate Pure Lead From Dross
With Vitaflux
Waste reduction at source. Recovery of raw
material from the waste at source.
Cost Reduction: 27,812
$/year.
Recovery of 44,280 kg Pb/year.
Recovery of 1,934 kg Pb/year.
Refurbished battery from bat-
tery closing
Change the Production Sched-
ule
Waste reduction at source.
Cost Reduction: 197,231
$/year
Treated wastewater from the
wastewater treatment facility
Use Caustic Instead of Lime
Usage of water decreased by 52,000 m3/year. Cost Reduction: 79,456
$/year.
