I leave a like on all sections for your assistance, thank you.WATER TREATMENT PLANT PROCESS COSTSInformation: (Please see the attached image depicting the schematics + Text) The results obtained from the four operating modes showed that the hardness decreased by 4.7% when both processes were in operation (i.e., sludge recirculation and aeration). When only sludge was recirculated, the reduction was 3.8%. There was no reduction due to aeration only, or when there was neither aeration nor recirculation. For turbidity, the reduction was 28% when both recirculation and aeration were used. The reduction was 18% when neither aeration nor recirculation was used. The reduction was also 18% when aeration alone was used, which means that aeration alone was of no benefit for turbidity reduction. With sludge recirculation alone, the turbidity reduction was only 6%, meaning that sludge recirculation alone actually resulted in an increase in turbidity-the difference between 18% and 6%. Since aeration and sludge recirculation did cause readily identifiable effects on treated water quality (some good and others bad), the cost-effectiveness of each process for turbidity and hardness reduction was investigated. The calculations are based on the following data:- Aerator motor = 40 hp- Aerator motor Efficiency = 90%- Recirculation pump efficiency = 90%- Electricty cost = 9 cents ¢/kWh (previous analysis) - Lime cost = 7.9 ¢/kg - Lime Required = 0.62 mg/L per mg/L hardness- Coagulant Cost = 16.5 ¢/kg - Days/ month = 30.5Aeration cost:40 hp x 0.75 kW/hp × 0.09 $/kWh × 24h /day /0.90 = $72 per day or $2196 per monthSludge recirculation cost:5 hp x 0.75 kW/hp × 0.09 $/kWh × 24h /day /0.90 = $9 per day or $275 per monthThe estimates appear in columns 1 and 2 of the cost summary in Table 13-1. (See 2nd attached image) Costs associated with turbidity and hardness removal are a function of the chemical dosage required and the water flow rate. The calculations below are based on a design flow of 53 m^3/min.(Please see attached image with chart + Text)When sludge recirculation was discontinued, there was no hardness reduction through the clarifier, so that the extra lime cost would be $1380 per month. Obviously, the optimum condition is represented by "sludge recirculation only." This condition would result in a net savings of $1089 per month, compared to a net savings of $622 per month when both processes are discontinued and a net cost of $1574 per month for aeration only. Case Study Exercises3. If the cost of lime were to increase by 50%, would the cost difference between the best alternative and second-best alternative increase, decrease, or remain the same?4. If the efficiency of the sludge recirculation pump were reduced from 90% to 70%, would the net savings difference between alternatives 3 and 4 increase, decrease, or stay the same?5. If hardness removal were to be discontinued at the treatment plant, which alternative would be the most cost- effective? TABLE 13-1 Cost Summary in Dollars per MonthSavings fromDiscontinuation ofAlt. I.D.AlternativeDescription1 Sludge recirculation andExtra Cost forRemoval ofTotalTotalExtraNetSavingsCostSavingsAeration Recirculation(3) = (1) +(1)(2)(2)Hardness Turbidity(4)(6)=(4) (7) = (3) -(5)+(5)(6)Normal operating conditionaeration2 Aeration only27527513804691849-15743 Sludge recirculation only2196-21962628451107+10894 Neither aeration nor2196275247113804691849+622sludge recirculationCosts associated with turbidity and hardness removal are a function of the chemical dosage required and the water flow rate. Thecalculations below are based on a design flow of 53 m³/min.As stated earlier, there was less turbidity reduction through the primary clarifier without aeration than there was with it (28% vs. 6%).The extra turbidity reaching the flocculators could require further additions of the coagulating chemical. If it is assumed that, as aworst case, these chemical additions would be proportional to the extra turbidity, then 22% more coagulant would be required. Sincethe average dosage before discontinuation of aeration was 10 mg/L, the incremental chemical cost incurred because of the increasedturbidity in the clarifier effluent would be(10 x 0.22) mg/L × 10-6 kg/mg x 53 m³/minx1000 L/m³ x 0.165 $/kg x 60 min/hx24h/day = $27.70/day or $845/monthSimilar calculations for the other operating conditions (ie., aeration only, and neither aeration nor sludge recirculation) reveal that theadditional cost for turbidity removal would be $469 per month in each case, as shown in column 5 of Table 13-1.Changes in hardness affect chemical costs by virtue of the direct effect on the amount of lime required for water softening. Withaeration and sludge recirculation, the average hardness reduction was 12.1 mg/L (ie., 258 mg/L × 4.7%). However, with sludgerecirculation only, the reduction was 9.8 mg/L, resulting in a difference of 2.3 mg/L attributed to aeration. The extra cost of Page 378lime incurred because of the discontinuation of aeration, therefore, was2.3 mg/L x 0.62 mg/L lime × 10-6 kg/mgx 53m³/min x 1000 L/m³ x 0.079 $/kg× 60 min/h × 24h/day = $8.60/day or $262/month Aeration and sludge recirculation have been practiced for many years at municipal and industrial water treatment plants. Aeration isused primarily for the physical removal of gases or volatile compounds, while sludge recirculation can be beneficial for turbidityremoval and hardness reduction.When the advantages of aeration and sludge recirculation in water treatment were first recognized, energy costs were so low that suchconsiderations were seldom of concern in treatment plant design and operation. With the huge increases in electricity cost that haveoccurred in some localities, however, it became necessary to review the cost-effectiveness of all water treatment processes thatconsume significant amounts of energy. This study was conducted at a municipal water treatment plant for evaluating the cost-effectiveness of the pre-aeration and sludge recirculation practices.InformationThis study was conducted at a 106 m³/min watertreatment plant where, under normal operating circumstances, sludge from thesecondary clarifiers is returned to the aerator and subsequently removed in the primary clarifiers. Figure 13-12 is a schematic ofthe process.ChemicaladditionsFlashmixFlocculationPrimaryclarifierSecondaryclarifierAeratorFilterCanalTo clearwell

Discontinuing aeration saves $2196 per month on electricity if the cost remains at 9…

WATER TREATMENT PLANT PROCESS COSTS Information: (Please see the attached image depicting the schematics + Text) The results obtained from the four operating modes showed that the hardness decreased by 4.7% when both processes were in operation (i.e., sludge recirculation and aeration). When only sludge was recirculated, the reduction was 3.8%. There was no reduction due to aeration only, or when there was neither aeration nor recirculation. For turbidity, the reduction was 28% when both recirculation and aeration were used. The reduction was 18% when neither aeration nor recirculation was used. The reduction was also 18% when aeration alone was used, which means that aeration alone was of no benefit for turbidity reduction. With sludge recirculation alone, the turbidity reduction was only 6%, meaning that sludge recirculation alone actually resulted in an increase in turbidity-the difference between 18% and 6%. Since aeration and sludge recirculation did cause readily identifiable effects on treated water quality (some good and others bad), the cost-effectiveness of each process for turbidity and hardness reduction was investigated. The calculations are based on the following data: - Aerator motor = 40 hp - Aerator motor Efficiency = 90% - Recirculation pump efficiency = 90% - Electricty cost = 9 cents ¢/kWh (previous analysis) - Lime cost = 7.9 ¢/kg - Lime Required = 0.62 mg/L per mg/L hardness - Coagulant Cost = 16.5 ¢/kg - Days/ month = 30.5 Aeration cost: 40 hp x 0.75 kW/hp × 0.09 $/kWh × 24h /day /0.90 = $72 per day or $2196 per month Sludge recirculation cost: 5 hp x 0.75 kW/hp × 0.09 $/kWh × 24h /day /0.90 = $9 per day or $275 per month The estimates appear in columns 1 and 2 of the cost summary in Table 13-1. (See 2nd attached image) Costs associated with turbidity and hardness removal are a function of the chemical dosage required and the water flow rate. The calculations below are based on a design flow of 53 m^3/min. (Please see attached image with chart + Text) When sludge recirculation was discontinued, there was no hardness reduction through the clarifier, so that the extra lime cost would be $1380 per month. Obviously, the optimum condition is represented by "sludge recirculation only." This condition would result in a net savings of $1089 per month, compared to a net savings of $622 per month when both processes are discontinued and a net cost of $1574 per month for aeration only. Case Study Exercises 3. If the cost of lime were to increase by 50%, would the cost difference between the best alternative and second-best alternative increase, decrease, or remain the same? 4. If the efficiency of the sludge recirculation pump were reduced from 90% to 70%, would the net savings difference between alternatives 3 and 4 increase, decrease, or stay the same? 5. If hardness removal were to be discontinued at the treatment plant, which alternative would be the most cost- effective?

WATER TREATMENT PLANT PROCESS COSTS Information: (Please see the attached image depicting the schematics + Text) The results obtained from the four operating modes showed that the hardness decreased by 4.7% when both processes were in operation (i.e., sludge recirculation and aeration). When only sludge was recirculated, the reduction was 3.8%. There was no reduction due to aeration only, or when there was neither aeration nor recirculation. For turbidity, the reduction was 28% when both recirculation and aeration were used. The reduction was 18% when neither aeration nor recirculation was used. The reduction was also 18% when aeration alone was used, which means that aeration alone was of no benefit for turbidity reduction. With sludge recirculation alone, the turbidity reduction was only 6%, meaning that sludge recirculation alone actually resulted in an increase in turbidity-the difference between 18% and 6%. Since aeration and sludge recirculation did cause readily identifiable effects on treated water quality (some good and others bad), the cost-effectiveness of each process for turbidity and hardness reduction was investigated. The calculations are based on the following data: - Aerator motor = 40 hp - Aerator motor Efficiency = 90% - Recirculation pump efficiency = 90% - Electricty cost = 9 cents ¢/kWh (previous analysis) - Lime cost = 7.9 ¢/kg - Lime Required = 0.62 mg/L per mg/L hardness - Coagulant Cost = 16.5 ¢/kg - Days/ month = 30.5 Aeration cost: 40 hp x 0.75 kW/hp × 0.09 $/kWh × 24h /day /0.90 = $72 per day or $2196 per month Sludge recirculation cost: 5 hp x 0.75 kW/hp × 0.09 $/kWh × 24h /day /0.90 = $9 per day or $275 per month The estimates appear in columns 1 and 2 of the cost summary in Table 13-1. (See 2nd attached image) Costs associated with turbidity and hardness removal are a function of the chemical dosage required and the water flow rate. The calculations below are based on a design flow of 53 m^3/min. (Please see attached image with chart + Text) When sludge recirculation was discontinued, there was no hardness reduction through the clarifier, so that the extra lime cost would be $1380 per month. Obviously, the optimum condition is represented by "sludge recirculation only." This condition would result in a net savings of $1089 per month, compared to a net savings of $622 per month when both processes are discontinued and a net cost of $1574 per month for aeration only. Case Study Exercises 3. If the cost of lime were to increase by 50%, would the cost difference between the best alternative and second-best alternative increase, decrease, or remain the same? 4. If the efficiency of the sludge recirculation pump were reduced from 90% to 70%, would the net savings difference between alternatives 3 and 4 increase, decrease, or stay the same? 5. If hardness removal were to be discontinued at the treatment plant, which alternative would be the most cost- effective?

ENGR.ECONOMIC ANALYSIS

14th Edition

ISBN:9780190931919

Author:NEWNAN

Publisher:NEWNAN

Chapter1: Making Economics Decisions

Section: Chapter Questions

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I leave a like on all sections for your assistance, thank you.

WATER TREATMENT PLANT PROCESS COSTS
Information: (Please see the attached image depicting the schematics + Text)

The results obtained from the four operating modes showed that the hardness decreased by 4.7% when both processes were in operation (i.e., sludge recirculation and aeration). When only sludge was recirculated, the reduction was 3.8%. There was no reduction due to aeration only, or when there was neither aeration nor recirculation. For turbidity, the reduction was 28% when both recirculation and aeration were used. The reduction was 18% when neither aeration nor recirculation was used. The reduction was also 18% when aeration alone was used, which means that aeration alone was of no benefit for turbidity reduction. With sludge recirculation alone, the turbidity reduction was only 6%, meaning that sludge recirculation alone actually resulted in an increase in turbidity-the difference between 18% and 6%. Since aeration and sludge recirculation did cause readily identifiable effects on treated water quality (some good and others bad), the cost-effectiveness of each process for turbidity and hardness reduction was investigated. The calculations are based on the following data:

- Aerator motor = 40 hp
- Aerator motor Efficiency = 90%
- Recirculation pump efficiency = 90%
- Electricty cost = 9 cents ¢/kWh (previous analysis)
- Lime cost = 7.9 ¢/kg
- Lime Required = 0.62 mg/L per mg/L hardness
- Coagulant Cost = 16.5 ¢/kg
- Days/ month = 30.5

Aeration cost:
40 hp x 0.75 kW/hp × 0.09 $/kWh × 24h /day /0.90 = $72 per day or $2196 per month
Sludge recirculation cost:
5 hp x 0.75 kW/hp × 0.09 $/kWh × 24h /day /0.90 = $9 per day or $275 per month

The estimates appear in columns 1 and 2 of the cost summary in Table 13-1. (See 2nd attached image) Costs associated with turbidity and hardness removal are a function of the chemical dosage required and the water flow rate. The calculations below are based on a design flow of 53 m^3/min.
(Please see attached image with chart + Text)

When sludge recirculation was discontinued, there was no hardness reduction through the clarifier, so that the extra lime cost would be $1380 per month. Obviously, the optimum condition is represented by "sludge recirculation only." This condition would result in a net savings of $1089 per month, compared to a net savings of $622 per month when both processes are discontinued and a net cost of $1574 per month for aeration only.

Case Study Exercises

3. If the cost of lime were to increase by 50%, would the cost difference between the best alternative and second-best alternative increase, decrease, or remain the same?
4. If the efficiency of the sludge recirculation pump were reduced from 90% to 70%, would the net savings difference between alternatives 3 and 4 increase, decrease, or stay the same?
5. If hardness removal were to be discontinued at the treatment plant, which alternative would be the most cost- effective?

TABLE 13-1 Cost Summary in Dollars per Month
Savings from
Discontinuation of
Alt. I.D.
Alternative
Description
1 Sludge recirculation and
Extra Cost for
Removal of
Total
Total
Extra
Net
Savings
Cost
Savings
Aeration Recirculation
(3) = (1) +
(1)
(2)
(2)
Hardness Turbidity
(4)
(6)=(4) (7) = (3) -
(5)
+(5)
(6)
Normal operating condition
aeration
2 Aeration only
275
275
1380
469
1849
-1574
3 Sludge recirculation only
2196
-
2196
262
845
1107
+1089
4 Neither aeration nor
2196
275
2471
1380
469
1849
+622
sludge recirculation
Costs associated with turbidity and hardness removal are a function of the chemical dosage required and the water flow rate. The
calculations below are based on a design flow of 53 m³/min.
As stated earlier, there was less turbidity reduction through the primary clarifier without aeration than there was with it (28% vs. 6%).
The extra turbidity reaching the flocculators could require further additions of the coagulating chemical. If it is assumed that, as a
worst case, these chemical additions would be proportional to the extra turbidity, then 22% more coagulant would be required. Since
the average dosage before discontinuation of aeration was 10 mg/L, the incremental chemical cost incurred because of the increased
turbidity in the clarifier effluent would be
(10 x 0.22) mg/L × 10-6 kg/mg x 53 m³/min
x1000 L/m³ x 0.165 $/kg x 60 min/h
x24h/day = $27.70/day or $845/month
Similar calculations for the other operating conditions (ie., aeration only, and neither aeration nor sludge recirculation) reveal that the
additional cost for turbidity removal would be $469 per month in each case, as shown in column 5 of Table 13-1.
Changes in hardness affect chemical costs by virtue of the direct effect on the amount of lime required for water softening. With
aeration and sludge recirculation, the average hardness reduction was 12.1 mg/L (ie., 258 mg/L × 4.7%). However, with sludge
recirculation only, the reduction was 9.8 mg/L, resulting in a difference of 2.3 mg/L attributed to aeration. The extra cost of Page 378
lime incurred because of the discontinuation of aeration, therefore, was
2.3 mg/L x 0.62 mg/L lime × 10-6 kg/mg
x 53m³/min x 1000 L/m³ x 0.079 $/kg
× 60 min/h × 24h/day = $8.60/day or $262/month

Aeration and sludge recirculation have been practiced for many years at municipal and industrial water treatment plants. Aeration is
used primarily for the physical removal of gases or volatile compounds, while sludge recirculation can be beneficial for turbidity
removal and hardness reduction.
When the advantages of aeration and sludge recirculation in water treatment were first recognized, energy costs were so low that such
considerations were seldom of concern in treatment plant design and operation. With the huge increases in electricity cost that have
occurred in some localities, however, it became necessary to review the cost-effectiveness of all water treatment processes that
consume significant amounts of energy. This study was conducted at a municipal water treatment plant for evaluating the cost-
effectiveness of the pre-aeration and sludge recirculation practices.
Information
This study was conducted at a 106 m³/min watertreatment plant where, under normal operating circumstances, sludge from the
secondary clarifiers is returned to the aerator and subsequently removed in the primary clarifiers. Figure 13-12 is a schematic of
the process.
Chemical
additions
Flash
mix
Flocculation
Primary
clarifier
Secondary
clarifier
Aerator
Filter
Canal
To clear
well

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6. If the cost of electricity decreased to 8 ¢/kWh, which alternative would be the most cost-effective?
7. At what electricity cost would the following alternatives just break even? (a) Alternatives 1 and 2, (b) alternatives 1 and 3, (c) alternatives 1 and 4.

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