Water Reuse Simplified by Modular Microfiltration System

By James Schaefer

Water reuse represents a practical and reliable means of extending water supplies in areas with water shortages. Typically, highly treated wastewater has been reused by industry for process water, which could justify the higher cost of treatment for reuse. Now, modular treatment units are reducing costs to make water reuse practical for irrigation of parks and landscaping, and to protect watersheds that supply drinking water.

Pall Corporation has developed a line of easy-to-operate, modular microfiltration systems that are being successfully applied to a wide range of reuse applications, as summarized in Table 1.

The Bedford Hills Correctional Facility and Toppan Electronics use Pall's small flow AriaSM units to meet tough water quality standards at low cost. The large installations for Fountain Hills Sanitary District and Sonoma County Water Agency, using Pall's standard microfiltration systems, represent new applications for water reuse to meet increasing water demands. The Sonoma County and Fountain Hills systems were also designed to meet tough standards and provide flexibility, as described below.

Sonoma County
Sonoma County, in the heart of California's wine country, is reusing water to assure adequate supplies for drinking water, and commercial and agricultural uses. The 3 mgd water reuse facility treats secondary effluent from a partially aerated lagoon treatment plant near the county airport in Santa Rosa. The reused water will irrigate fields near the airport and some of the many nearby vineyards. In the future, reused water may also replenish water in local geysers, which have recently been less active because of low water levels.

Microfiltration was chosen because it provides high quality filtered water with low suspended solids, which is required for vineyard irrigation. A detailed evaluation of capital and operating and maintenance (O&M) costs over a 20-year period showed that microfiltration, with its much lower O&M costs, was the most cost effective alternative. The Water Agency chose the Pall system based on the results of on-site pilot testing.

Fountain Hills
The 2 mgd microfiltration installation is part of a system for conjunctive use of ground water. During the fall, winter and spring, the microfilter treats an average of 1.7 mgd of tertiary wastewater effluent, which is used to recharge the district's three aquifer storage and recovery (ASR) wells. This ASR system is one of only three similar installations in the US. During the summer, tertiary effluent is used directly for golf course irrigation, and water is pumped from the ASR wells to meet peak water demands.

The Pall microfiltration system was chosen because of its excellent turbidity removals, its ability to accept high chlorine residuals, and the ability of the existing system to accept ultrafilter modules, if viruses must be disinfected without using chlorine.

Feed turbidity ranges between 0.5 and 1.5 ntu, while the filtered turbidity is consistently 0.03 to 0.04 ntu. The extremely low turbidity improves ASR well longevity by minimizing the amount of solids pumped into the aquifer by the recharged water. The system is designed for expansion to 3 mgd by adding a fifth module rack and additional modules to the existing four racks.

Summary
Water reuse is becoming more prevalent to meet increasing demands for water, especially in water-short areas. Pall offers standard and compact AriaSM microfiltration systems to meet a wide range of needs. The systems are flexible to handle a range of feed water qualities while providing consistently high filtered water quality.

James Schaefer, P.E., is Technical Director for Water Processing, Pall Corporation.

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