San Patricio Case Study
The San Patricio Municipal Water District is located in Ingleside, Texas, about a 15 minute drive northeast from the port of Corpus Christi. In late 1997, the Water District was faced with a challenge: provide high quality, potable water for both residential users and a new cogeneration facility by June 1999. The new facility would need to be capable of removing turbidity, Giardia cysts and Cryptosporidium oocysts. If a 5.2 MGD advanced water treatment system was to be brought online on time, a fast track schedule was required.

The District and their consulting engineer, Malcolm Pirnie, went to work on a solution. The initial water source would be the Nueces River. Upon later expansion of the facility, a new raw water facility would pump blended feed from both the river and Lake Texana. The expanded water supply would adequately provide for increased demand.

Raw water quality varied. Apart from the possible presence of pathogenic cysts, bacteria and viruses, river turbidities ranged from 5 NTU to 200 NTU, averaging 25 NTU. Water temperature ranged from 8°C to 30°C, averaging 22°C. Water hardness averaged 230 mg/L as CaCO₃ and ranged from 100 to 300 mg/L. Given the variable feed water characteristics, a robust process treatment train was developed. Coagulation and flocculation, followed by sedimentation, could handle the highly variable and silt-laden turbidity.

However, with the potential presence of pathogenic cysts, bacteria and viruses, high quality standards could be better assured with an advanced membrane system. The District evaluated the feasibility of several alternatives and determined that conventional settling followed by membrane filtration would be the most effective method of achieving the treatment goals. Research had indicated that membrane flux could be maximized when preceded by settling, resulting in a process that was economically competitive to conventional treatment.

In early 1998, the District, with guidance from the engineering firm Malcolm Pirnie, conducted pilot testing of three competing membrane systems. Microfiltration and ultrafiltration membrane systems supplied by Pall Water Processing, Memcor and Hydranautics/Ionics were tested to demonstrate successful membrane performance and to select design parameters.

Pall Pilot System Used for Testing and Validation

Membrane feed water from an existing coagulation-sedimentation system averaged less than 2 NTU with TOC at 6 mg/L. All of the systems produced filtrate turbidities of less than 0.1 NTU. The specified flux for each of the systems was as follows (see Table 1).

Table 1: Design Criteria¹

Parameter/Company	Pall	Memcor	Hydranautics / Ionics
Flux*	95 gfd	80 gfd	74 gfd

*gfd is an abbreviation signifying a flux unit of gallons per square foot per day
¹Source: Project Manual for San Patricio Municipal Water District 1998 Projects. Contract 2- MF/UF System and Membrane Procurement, Addendum 1. Prepared by Malcom Pirnie, August 1998.

Upon completion of the pilot testing, the equipment procurement phase of the project began. In order to simplify procurement and maintain a tight schedule, the membrane filtration system and auxiliary equipment were bid before the rest of the project. This sequence allowed the on-site facilities to be designed to match the microfiltration equipment and the construction of on-site facilities to proceed while the membrane filtration system was being fabricated.


Installation of Pall Membrane Filtration System Racks and Vessels

The bid requested information on membrane system capital and operating costs. Operating costs included power consumption for pumping and membrane cleaning, and chemical usage for operation and membrane cleaning. The submittal information is shown below (see Table 2).

Table 2: Cost Comparison²

Cost Designation	Pall	Memcor	Hydranautics / Ionics
Capital Cost	$2,274,000	$3,075,000	$2,161,500
Annual Payment (6%, 20 yrs)	$198,258	$268,093	$188,449
Operating Cost	$200,184	$345,400	$257,548
Yearly Capital & Operating Cost	$407,442	$613,493	$445,997
Capital & Operating Cost ($/Kgal)	$0.215	$0.323	$0.235

² As published in Water Desalination Report, Vol. 34, No. 41, October 15, 1998.

Since the bid prices were lower than projected, the District used the remaining funds in the budget to increase the facility capacity from 5.2 MGD to 7.8 MGD. Both the District and their engineer also commented on the advantages they saw as inherent to the Pall design.

Pall 7.8 MGD Membrane Filtration System

Senior Project Engineer Jim Vickers, P.E. of Malcolm Pirnie, consulting engineer to the San Patricio Municipal Water District noted, "For this site, the results of the pilot study and bid evaluation indicated that the Pall microfiltration system was the most economical alternative. We also believe that it is important to exceed current as well as proposed regulatory standards, and the use of microfiltration will allow the district to provide the highest level of filtration possible within the constraints of the project."

The Pall system design allows for easy retrofit of the existing microfiltration modules by ultrafiltration modules, in the event that more stringent filtration standards be required in the future.

Don Roach of the San Patricio Municipal Water District stated, "We serve an area of rapid growth where the demand for water quality and quantity is a daily concern. The Pall system demonstrated it could give us great performance on both counts and at a cost well within our budget. We used the savings to expand the proposed capacity of the MF system to greater than 7 MGD."

Pall Water Processing brings an experienced team of scientists and engineers to partner with each customer. The team seeks to understand the customer's requirements and works closely with their engineers and consultants to develop innovative, cost-effective solutions to their water treatment problems. Pall Corporation responded to the needs of the San Patricio Water District by designing and manufacturing a filtration and separation system that demonstrated superior performance at the lowest evaluated cost of ownership.


Pall Membrane Filtration System Installation