Sourcebook of Alternative Technologies for Freshwater Augumentation in Some Countries in Asia


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<Sourcebook of Alternative Technologies for Freshwater Augumentation
in Some Countries in Asia>

5.3 Use of Reclaimed Water - Hindustan Petroleum Corporation Limited, India

Introduction

The Hindustan Petroleum Corporation Limited (HPCL) uses seawater for cooling and fire protection purposes at their refinery. The seawater is pumped, by means of pumps located in a salt water pump house situated on a jetty, through a 36-inch diameter cement-lined pipe, to the refinery. The refinery is switching over, in phases, from once through cooling systems to circulating cooling systems to minimize dredging frequency, effluent generation and interruptions to their operations due to pump failures. Concurrent with this change in cooling system operations, the Corporation plans to switch their cooling systems from seawater to reclaimed water from nearby sewage plants. Once this is achieved, the jetty pumps will be exclusively for fire protection service. The reasons for switching to reclaimed water for cooling purposes were principally due to changes in the pollution control regulations, and to operation and maintenance problems related to the use of the seawater.

Blow down from cooling towers, when using salt water for cooling purposes, is very high in total dissolved solids (TDS is more than 15%), and more frequent blow downs are required if the effluent from this process is to contain TDS at the level required to meet the Central Pollution Control Board's Minimal National Standards (the MINAS regulations). Use of reclaimed sewage for cooling enables the refinery to reduce the frequency of blow downs from the cooling towers and thereby reduce the volume of effluent requiring treatment to MINAS to manageable quantities.

Likewise, seawater places an undue strain on heat exchangers due to its high salt content. Switching to treated wastewater may be expected to improve the life of the heat exchangers. However, it is important that the wastewater be domestic in nature to ensure that it does not contain any industrial chemicals. Using reclaimed wastewater is expected to reduce the cooling system make-up water requirement from 4 500 m3/hour (or 108 000 m3/day) to about 625 m3/hour (or 15 000 m3 /day).

Technical Description

The design of the project entailed extensive engineering evaluations to identify the most appropriate source from which to obtain the treated wastewater. These investigations considered not only the location and infra structural requirements for conveying the treated wastewater to the refinery, but also the quality of the effluents. Four different sites from which to obtain treated sewage were studied before deciding on a site near the Ghatkopar-Chembur fly-over. This site was chosen because the source of the wastewater was purely domestic in nature (whereas other sources had some industrial loading to the treatment works), of adequate volume (not less than 15 MLD throughout the year, with an average flow of 50 MLD), and had available space in which to site a pump house without causing any outside disturbance. Sewage obtained from this source would be pumped 5.4 km to a 15 MLD sewage reclamation plant at the HPCL factory (expandable to 23 MLD, if required). Of the three possible routes between the fly-over and the plant, the route along Chembur-Govandi Road, Maharishi Dayanand Saraswati Marg Road, Golf Club Road, and Koliwada-Kurla Road, through the RCF colony to the Ashish Theatre, and along Corridor Road to the HPCL refinery site was chosen for the rising main. This route was selected because it passed along wide roads with relatively little traffic where pipe-laying work will be easier and faster. This route also facilitates future maintenance. Cast iron pipes were selected for conveyance of the sewage because of their ability to withstand heavy external pressure and resist corrosion.

Tertiary treatment of the wastewater will be provided by chemical treatment of secondary treated sewage. An alum solution will be dosed in a chamber upstream of the flash mixers and conveyed to clari-flocculators for the removal of fine suspended matter and colloidal turbidity. Clear liquid overflows the weir at the top of the clari-flocculator andflows into the launder, while the particulate sludge is collected on the bottom of the clari-flocculator and conveyed to sludge sump. The clarified effluent from the launder is then routed to four twin bed rapid sand filters containing a layer of quartz sand and a layer of graded gravel. The underdrainage system includes air blowers and water wash lines for backwashing the filters. The filtered water will be pumped from a storage reservoir, routed through four identical ion-exchange softener units, and chlorinated prior to use as cooling water. Each softener unit will have adequate cation exchange capacity so that regeneration will not be required more frequently than once in 12 hours. The chlorination system will consist of two vacuum type chlorinators.

Extent of Use

The project is being implemented by HPCL.

Operation and Maintenance

The wastewater reclamation plant uses proven technologies for treating water and wastewater. No extraordinary requirements are anticipated. The primary operation and maintenance requirements include replenishment of chemicals, maintenance of pumps and dosing equipment, monitoring of inflow and outflow effluent quality, and general plant supervision. Skilled staff are required.

Level of Involvement

This technology is being implemented at the industry level.

Costs

The operation and maintenance costs are broken down into the costs of human resources, chemicals, energy, and related costs, including the repair and replacement of equipment. These costs are summarized in Tables 27 through 29.

TABLE 27. Annual Human Resources Costs.

Category	Cost per month ($)	Number of staff	Amount per year ($)
Superintendent	$150	1	$ 1 800
Operators	$120	10	$14 400
Helper	$ 60	10	$ 7 200
	Total		$23 400

TABLE 28. Annual Chemical Costs.

Chemical	Anticipated dosage (mg/l)	Quantity required for 15 MLDplant (kg/day)	Cost per kg ($/kg)	Total cost for 15 MLD planta ($)
Alum	20	300	$0.06	$ 18
Polyelectrolyte	1	15	$4.50	$ 68
Chlorine	5	75	$0.12	$ 9
Common salt	-	4330	$0.03	$131
	Total cost per day in $ Total cost per year in $			$226 $82 730

aFirst stage = 15 MLD, Second stage = 30 MLD.

TABLE 29. Annual Operation and Maintenance Costs.

Operation and Maintenance Item	Total cost for 15 MLD plant ($/year)
Electricity
Conveying and treating sewage: 615 Kw or 14 750 Kwh @$0.03/Kwh	$178 000
Maintenance and repair
Civil engineering and hydraulic works @ 1% of capital cost	$ 20 150
Mechanical and electrical works @ 2% of capital cost	$ 16 500
Depreciation
Civil engineering and hydraulic works @ 2% of capital cost	$ 40 300
Mechanical and electrical works @ 5% of capital cost	$ 41 450
Insurance
Insurance costs @ 0.5% of capital cost	$ 14 200
Property rental and other costs
Lease costs for siting a pumphouse on MCGB lands under the Ghatkopar-Chembur Flyover	$ 18 200
Nominal cost of acquiring 23 MLD sewage from MCGB system	$ 1
Total Operation and Maintenance Costs	$328 801

TABLE 30. Total Operating Cost of the Treatment Plant.

Item	Annual operating cost for 15 MLD plant ($)	Annual operating cost for 30 MLD plant ($)
Manpower	$ 23 400	$ 23 400
Chemicals	$ 82 730	$165 460
Electricity	$178 000	$297 000
Maintenance and Repair	$ 36 650	$ 54 400
Depreciation	$ 81 750	$109 000
Insurance	$14 200	$ 18 200
Property rental and Other expenses	$ 18 201	$ 18 201
Total	$434 931	$685 661

From the Table 30, the annual operating cost per unit of flow of the 15 MLD plant will be $0.08/m3. The comparative cost of municipal freshwater supplied to industries in Bombay is $0.45/m3 in 1996. Hence, HPCL can achieve a substantial savings in operational expenditure in addition to the savings in freshwater achieved.

A breakdown of the capital and engineering costs of the various components of the project is given in Table 31.

TABLE 31. Capital and Engineering Costs of the Reclamation Project.

Item	Total Cost ($)
Pumphouse at Ghatkopar-Chembur Flyover	$ 240 000
Force main	$1 130 000
Sewage water reclamation plant	$1 350 000
Off site facilities like storage and pumping facilities at Refinery	$ 523 000
MCGB supervision fee (Tentatively estimated at 15% of the total cost of work done on municipal roads)	$ 153 000
Architectural design fees including detailed engineering and other owner expenses during construction phase (9% of total cost)	$ 305 500
Engineering fees and consultancies (10% of total cost)	$ 373 000
Design change allowance and contingencies	$ 303 000
TOTAL	$4 377 500

Effectiveness of the Technology

The use of reclaimed wastewater is expected to reduce the cooling makeup water requirement from 4 500 m3/hr or 108 000 m3/day to about 625 m3/hr or 15 000 m3/day, with a concommitant cost savings over acquiring this makeup water from municipal sources.

Advantages

Reclamation of sewage for cooling water use has three advantages for HPCL; namely:

the problem of high TDS that arises from the use of seawater is eliminated
the demand for freshwater from the municipal supply is reduced, making more water from municipal sources available for use as drinking water in Bombay.
the cost of municipal water to HPCL is reduced, providing a financial advantage to the Corporation in light of an increasing tariff structure for freshwater supplied to industrial users in Bombay.

Disadvantages

This technology requires a significant capital expenditure and is technology intensive, requiring skilled staff to install, operate and maintain.

Future Development of the Technology

The technology of sewage reclamation is an established technology that may be attractive to industries like HPCL who have large water requirements and who depend on (diminishing) water supplies from municipal corporations. The technology is transferable and can be used by other industries.

Information Sources

AIC Watson, Consulting Engineers, Bombay, India.

Hindustan Petroleum Corporation Limited (HPCL), India.

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