A Tale of Two Systems: Safe Drinking Water for State Park Users

Background

The Oregon State Parks and Recreation Department is responsible for the safe operation of state parks, including provision of reliable and sanitary drink-ing water and wastewater facilities for park users and staff. The drinking water treatment facilities at Beverly Beach and Bullards Beach State Parks were 30 years old and needed to be upgraded to meet new requirements for disinfection and to improve the overall quality of the drinking water supply. Beverly Beach State Park is located on Highway 101 about 10 miles (16 km) north of Newport, Oregon on the central Oregon Coast.The source of sup-ply is an 80 gpm (300 L/min) variable quality sur-face water. Operation of the existing package filtration equipment required proper dosing of chemicals and frequent operator attention. The new treatment facilities consisted of a microfil-tration system to remove turbidity and protozoa, such as Giardia and Cryptosporidium. Bullards Beach State Park is also located on Highway 101 about 4 miles (6.4 km) north of Bandon, Oregon on the southern Oregon Coast. The source of supply is a 50 gpm (190 L/min) well containing high concentrations of iron and manganese. The new treatment facilities includ-ed preoxidation with aeration and chemical addi-tion, and microfiltration to remove turbidity, precipitated iron and manganese, and bacterial and protozoan pathogens.

Objectives

The Parks and Recreation Department established several objectives for the new drinking water treat-ment facilities. The new equipment was to be NSF 61 certified, or approved by the Oregon Health Division,Drinking Water Program for contact with potable water. The filtered water quality objective for average turbidity over a 24 hour period was 0.05 ntu with a maximum turbidity of 0.1 ntu. The objective for average particle count was 2 parti-cles/ ml in the 2 to 10 micron (µm) range with a maximum particle count of 5 particles/ml in the 2 to 10 µm range. The required treatment capac-ity was 50 gpm (190 L/min) for Bullards Beach State Park, and 50 gpm (190 L/min) winter and 80 gpm (300 L/min) summer for Beverly Beach State Park. The design of the treatment equipment must allow for increasing the capacity by 33% with only the installation of additional membrane modules.

Raw water quality based upon available operating data is significantly different for the two parks, as summarized in Table 1.

Spencer Creek at Beverly Beach State Park is a protected,small watershed,which can experience wide variations in raw water turbidity. During storms, turbidities have been as high as 100 ntu. In addition, temperature varies significantly from winter to summer. Raw water iron and manganese are low to moderate and hardness is very low. The supply has been subject to occasional algae

Table 1. Raw Water Quality

 

growths,which can challenge any type of filtration system,and also has a moderately high total organ-ic carbon (TOC) of 5 mg/L. The well water at Bullards Beach State Park has extremely high iron levels of 15 to 25 mg/L and moderate manganese levels of about 0.1 mg/L.

After oxidation, the resulting iron hydroxide will create floc equivalent to a dosage of about 40 mg/L of a ferric coagulant. Hardness is moderately low at 50 mg/L, but dissolved carbon dioxide is extremely high at about 100 mg/L. The high car- bon dioxide concentration lowers the raw water pH. The well supply also has moderately high TOC of 5 mg/L and consistent temperature of 12 to 14° C.

The new filtration systems were designed with preoxidation to remove the iron and manganese and conservative loading rates to successfully han-dle other variations in raw water quality. More extensive treatment was required for the Bullards Beach well because of its unusual water quality.

Bid Documents

The Parks and Recreation Department working with their consulting engineer prepared an eco-nomic evaluation of alternatives for the Beverly Beach system. Based on budget cost information from membrane system suppliers, the department decided that it was economically advantageous to replace the existing package treatment plant at Beverly Beach with a membrane filtration system. Later the department decided to also install a mem-brane system at Bullards Beach. As a result, they developed specifications for procuring the two sys-tems as part of one bid package. The membrane systems were to be the same standard model for both sites, differing only in the number of membrane modules. The membrane system also had to be NSF 61 listed or approved by the Oregon Health Division, Drinking Water Program for contact with potable water. The membrane material was required to be able to operate with a continuous 1 mg/L chlo-rine residual. The minimum recovery of filtered water from the raw flow was required to be 92%.

Because of the small size of the two systems, pilot testing was not required. However, each membrane manufacturer was required to provide evidence of a successful drinking water installation at a similar site, or three months of successful pilot testing on a surface supply with water quality similar to that at Beverly Beach State Park. Four manufacturers were judged to meet these criteria and invited to bid. The specifications indicated that the new filtration system should fit inside the existing buildings. Since sanitary sewers were available at both sites, the fre-quent backwash discharges and neutralized chem-ical cleaning wastes were equalized and discharged to the sanitary sewers.

Schedule

Bids were received on November 18,1998,and the systems were scheduled to be operational for the 1999 summer park season. The first priority was to upgrade the system at Beverly Beach State Park to provide the higher levels of disinfection required by new drinking water standards. Two maufactur-ers, Pall and Koch, submitted bids. Based on a review of the bids, Pall was selected as the lowest priced,responsible, and responsive bidder and was awarded the contract to supply microfiltration sys-tems. The bid prices for the different alternatives are summarized in Section 3.3.

The Beverly Beach system was delivered in late May 1999, and became fully operational for the Memorial Day weekend, just in time for peak sum-mer park usage. The Bullards Beach system was delayed because of the greater complexity of assem-bling and installing the microfiltration system with preoxidation to remove iron and manganese. It was rescheduled for installation and start-up dur-ing November 1999,when potable water demands are low.

Bid Prices

Bid prices are summarized in Table 2.

Pall’s bid for the Beverly Beach system only and both systems supplied together were approxi-mately 10% lower than Koch’s bid. The lower prices were an important factor in awarding the contract for both systems to Pall. The average cap-ital cost of the two microfiltration systems and related process equipment was approximately $2.75 per gallon per day of installed treatment capacity, or $2.15 per gallon per day of treatment capacity if the Bullards Beach system was expand-ed to 80 gpm (300 L/min).

Table 2. Comparison of Bid Prices

System Components

The microfiltration system was designed as skid-mounted packaged units to minimize field assem-bly. The microfiltration skid includes six microfiltration modules and all required pumps, tanks, piping,valves, instrumentation,and controls required for a functional system, as shown in Figure 1. The principal components of the micro-filtration system include:

• Microfiltration modules and racks
• Backwashable strainers – continuous, self-clean-ing 40 mesh strainers (400 µm)
• Feed Pumps - horizontal pumps with variable frequency drives
• Reverse filtration controls
• Reverse filtration chlorine feed pump

Figure 1. Microfiltration System

 

• Chemical transfer pumps and storage tanks -adjustable output electric diaphragm pumps and double containment polyethylene tanks
• Clean-in-place recirculation, neutralization, and residuals pumps and tanks - horizontal end suc-tion pumps and vertical cylindrical fiberglass plastic tanks
• Valves & piping
• Instrumentation & controls – includes flow, pres-sure, and temperature sensors, turbidimeters, and pH analyzer

The microfiltration system also was designed for sim-plicity of operation. All plant operations are auto-matically controlled via a programmable logic controller (PLC). The instrumentation and controls also include equipment for continuous remote mon-itoring of critical process parameters. The equip-ment tabulates the data over time to provide trending of parameters critical to the performance of the system.

The performance data are available to process operators on-site or at remote locations via advanced communication technology.

Microfiltration Membrane

The microfiltration modules are specially designed for water processing applications. The modules use proprietary, 0.1 µm rated polyvinylidenefluo-ride (PVDF) hollow fiber membranes with high and stable flux rates and high mechanical strength. The membrane can operate successfully between pH 2 and 11 and with chlorine residuals up to 5,000 mg/L, which easily meets the department’s requirement to be able to operate with a chlo-rine residual of 1 mg/L. Microbial challenge tests using Giardia and Cryptosporidium have con-sistently demonstrated at least 4 or 5 log removal, depending upon the feed concentration of the cysts.

The microfiltration modules operate in an out-side- in mode with a small amount of recircula-tion. The membranes are placed parallel to the feed direction and only clean liquid passes through the membrane.The recirculation is a small portion of the flow returned to the feed stream. The recir-culation flow is taken from the top of the mod-ule and ensures complete utilization of the available filter area by increasing the velocities in the upper end of the module. Solids retained on the filter are removed via regular backwashing and air scrub-bing, and periodic chemical cleaning.

These microfiltration membranes provide:

• Very high filter area (538 ft 2 or 50 m 2 ) per module
• Small footprint
• Low energy requirements
• Efficient cleaning and regeneration

System Operation

Water is pumped through the backwashable strain-er into the system, then through the supply mani-fold to the rack holding the six microfiltration modules. Each module is fed an equivalent flow rate. The feed pumps are controlled to maintain a constant feed pressure. As water flows through each module, the module hollow fibers gradually foul, and the pump speed increases automatically to increase feed pressure as required to maintain the filtrate flow set point. At the same time a con-trol valve maintains a constant recirculation rate.

Periodically, the modules undergo a reverse filtra-tion (RF) cycle that cleans the membranes. Water for reverse filtration is obtained from a filtered water storage tank and is pumped at about 150% of the normal forward flow through the module hol-low fibers in the reverse direction.The reverse fil-tration flow is maintained for about 30 seconds and the spent water is diverted to the drain. As required to prevent biological fouling, 20 to 30 mg/L of chlorine is fed into the reverse filtration water as it flows into the modules. The reverse fil-tration cycle restores the modules to near clean condition.

A second type of cleaning is required once every hour to thoroughly remove solids from the mem-brane. This cleaning cycle, called air scrubbing, involves injecting instrument grade compressed air into the feed side of the module rack while main-taining feed water flow through the modules. The air scrub mode is maintained for two minutes.

Every three to four weeks, the system requires a more thorough cleaning than reverse filtration or air scrubbing. Cleaning chemicals are added to the system and recirculated as required to remove firm-ly attached foulants,such natural organic matter or mineral precipitates. Even though the clean in place (CIP) operation happens infrequently, it is designed to be an automatic operation, which is man-ually initiated by the operator when indicated by the control system. The procedure normally involves two steps – caustic/chlorine to remove biological growth and natural organic matter, and citric acid to remove mineral precipitates.

System headloss,or transmembrane pressure (TMP), and flows are constantly tracked to monitor the amount of membrane fouling and the effectiveness of reverse filtration and air scrubbing. When the TMP reaches a selected maximum, a CIP is initiated.

Integrity testing of hollow fiber membranes is con-ducted in accordance with Pall’s standard proce-dures. These procedures have been optimized for modular installations and have proven successful in detecting an integrity breach in a system con-taining over a half of a million hollow fibers.

In operation, feed and filtered water turbidity are constantly monitored to assure consistently high quality filtered water and to immediately detect a performance change at the system level. An off line pressure hold test provides the ability to isolate and identify a questionable module. These procedures ensure system reliability without adding extensive costs or maintenance burden on the operators.

Beverly Beach State Park

The new microfiltration system was installed in the existing treatment building with inside dimen-sions of approximately 18 ft by 18.7 ft (5.5 m by 5.7 m), as shown in Figure 2. The equipment was designed to fit through the existing access door, with an opening of 8 ft tall by 9.3 ft wide (2.4 m tall by 2.8 m wide). The microfiltration system con- sisted of the microfiltration skid shown in Figure 1. In addition, some space is required to store need-ed chemicals – sodium hydroxide and sodium hypochlorite in drums and bags of granular citric acid.

Filtered water is discharged to an existing 10,000 gal (38,000 L) redwood clearwell adjacent to the treatment building. Spent backwash water and neu-tralized CIP solutions are discharged to an on-site equalization basin and then pumped into the san-itary sewers for treatment with the other park wastewaters.The clarified water is returned to a local stream.

The equipment was delivered during the third week of May 1999, installed and was operational for the Memorial Day weekend (May 29 - 31) influx of campers. The unit has been operating suc-cessfully, as described in Section 6.2.

Bullards Beach State Park

The new microfiltration system and related equip-ment were installed during November 1999 because of the complexity of assembling the sys-tem and delays with other construction work at the site. The Parks and Recreation Department also rescheduled the installation to this period to main-tain water supply throughout the busy summer park use period.

The microfiltration system and related equipment included the same size microfiltration skid as sup-plied for Beverly Beach plus a preoxidation system consisting of two tanks,aeration,and potassium per-manganate feed equipment. The first tank for oxi- dizing iron aerates the water through a circulation pump and eductor. The tank has a nominal deten-tion time of 20 minutes, or 1000 gal (3,800 L). In addition to providing oxygen to oxidize the dis-solved iron,the aeration system also strips out much of the dissolved carbon dioxide,thereby, raising the pH. The second tank for oxidizing manganese and creating a filterable floc has a nominal detention time of 17 minutes, or 850 gal (3,200 L). Potassium per-manganate is fed immediately upstream of the sec-ond tank to oxidize the dissolved manganese. The fully oxidized water is pumped through the micro-filtration system which removes the precipitated iron and manganese. Filtered water flows to a clear-well located outside the building. Spent backwash water containing the iron and manganese solids are discharged to an equalization basin and then pumped into the sanitary sewers for treatment with other park wastewaters.

The new equipment was installed inside the exist-ing 19 ft by 25 ft (5.8 m by 7.6 m) building, as shown in Figure 3. Because the only access to the building is through a standard sized door, the con-tractor installed new bay doors in the building to allow the equipment to be moved inside the build-ing. All equipment was designed to fit inside the existing building.

Beverly Beach State Park

The Beverly Beach system has been operating since late May and delivering high quality drink-ing water to campers and staff in the park. Raw water turbidities averaged 2 to 3 ntu from June through October 1999. Filtered water turbidity has consistently been 0.02 to 0.03 ntu. During the sum-mer, the system typically operated at flows of 30 to 40 gpm (110 to 150 L/min). Average flows declined to about 15 gpm (55 L/min) during September and October after the peak camping season ended.

The membranes were chemically cleaned first on July 27 after two months of operation on this sur-face water. A second chemical cleaning was per- formed on August 28 prior to a performance test for the membrane. At that time, approximately 60% of the available headloss, or TMP, had been used, so that the true chemical cleaning interval would have been six to eight weeks instead of the four weeks before this second cleaning. No chemical cleaning was required during September and October because of the lower system flows. The TMP was only 14 psi at the end of October, or about 50% of the allowable TMP.

Bullards Beach State Park

No operational data were available for this paper because the system was installed during November 1999. Available data will be reported at the meet-ing in January 2000.

The Oregon Parks and Recreation Department recently upgraded water treatment facilities at the Beverly Beach and Bullards Beach State Parks. Microfiltration systems were installed to treat a small surface water supply and a well with high iron and manganese concentrations. The Beverly Beach system was installed to treat the surface supply four months after the contract was award-ed and provided high quality drinking water for park users and staff throughout the peak use peri-od during the summer of 1999. The filtered water turbidity typically was 0.02 to 0.03 ntu. Based on available microbial challenge data, the microfil-tration also provided excellent removals of Giardia and Cryptosporidium.

The installation of the Bullards Beach system was delayed until November 1999, because of the greater complexity of the system and other delays in the construction of the improvements for this site. This system includes a two stage preoxida-tion system to remove the 15 to 25 mg/L of dis-solved iron and 0.1 mg/L of dissolved manganese. Aeration and a reaction tank oxidize and precip-itate the iron while potassium permanganate feed and a second tank oxidize the dissolved man-ganese. The precipitated iron and manganese and other turbidity are removed by the microfiltration system.

Because of the small capacity of these systems, the capital cost for each unit of capacity is high - $2.75 per gallon per day of installed capacity based on 100 gpm (380 L/min) combined for the two sys-tems. New, more economical designs for small microfiltration systems are needed to meet the widespread need for adequate treatment for small water suppliers.

New standard designs for small microfiltration units are being developed to meet the needs of small water systems. Using the microfiltration module described in Section 4, standard skids would provide treatment capacities from 10 gpm (40 L/min) to 100 gpm (380 L/min). In addition, by simplifying the overall microfiltration system design, the capital cost for each unit of capacity will be reduced to less than $2.00 per gallon per day of installed capacity for systems greater than 50 gpm (90 L/min). This capital cost is signifi-cantly less than the cost of the microfiltration sys-tems installed in the Oregon parks. The capital cost for very small systems remains high at $3 to $4 per gallon per day of installed capacity.

The new standard design is based on separate skids for microfiltration equipment and controls, and chemical cleaning equipment,including chem-ical feed equipment. The skids design is based on being able to move the equipment through stan-dard size doors, to minimize the need for build-ing modifications or special designs.

Small microfiltration systems offer many advan-tages because of their automatic operation, sim-ple treatment process that reliably removes turbidity and pathogens, and little need for con-trolling chemical additions for successful opera-tion of the system. As drinking water standards, especially for disinfection, become more strin-gent, the need for high quality, easy to operate, and low cost treatment will continue to grow.

A Tale of Two Systems: Safe Drinking Water for State Park Users (PDF: 84KB)