Effective Uses for Reclaimed Effluent: Under­stand­ing if Water Reuse Makes Sense for Your Facility

There are many reasons to consider reuse at your facility from concerns about regional water scarcity or limited municipal supplies, to address regulatory issues, or as a way to meet corporate Envi­ron­men­tal, Social, and Governance (ESG) goals.  However, turning municipal wastewater or your process wastewater into a reusable input can present some engineering challenges.  

Let’s consider some of the potential uses for reclaimed water in your facility:

Cooling Towers: Evaporative cooling systems require significant volumes of make-up water to replace water lost through evaporation. Addi­tion­ally, some water must be peri­od­i­cally discharged, referred to as “blow-down water,” so that dissolved solids concen­trated during evaporation do not build up in the cooling water and damage equipment. When using reclaimed water for cooling towers, you must control biological regrowth (i.e., when nutrients are present and a disin­fec­tant residual is not maintained) and scaling due to the presence of minerals (partic­u­larly calcium, magnesium, sulfate, alkalinity, phosphate, silica and fluoride).

Irrigation of Landscaping Features or Agriculture: This is often a “low-hanging fruit” in terms of water reuse.  In the past the standard for reusing domestic wastewater for irrigation was referred to as “Title 22”, named for the California State standard that defined treatment standards.  While it is no longer on the books, it is used as a standard for reuse water for irrigation and typically requires filtration and disin­fec­tion before discharge.

Prepared food manu­fac­tur­ing: Reuse water is utilized within food production facilities for various uses from initial washes to conveyance.  CDM Smith has worked with several firms to reuse process water within these facilities including J.R. Simplot Company and Frito-Lay. 

High-tech water reuse: Reclaimed water is used in high-tech manu­fac­tur­ing, such as the semi­con­duc­tor industry for microchip and circuit board manu­fac­tur­ing. Water quality for circuit board manu­fac­tur­ing is similar to that of high pressure boiler make-up water, requiring extensive pre-treatment. Some facilities use ultrapure water, which requires additional treatment processes, beyond potable water standards.

Plant washdown and utility water: Many plants have uses for “non-potable” water for washing down facilities or equipment, or for other uses that don’t require the water to be treated to drinking water standards.

If you have these use cases and are ready to take the next step, ask yourself these questions:

How should we use the water?

Some of the cases above may seem applicable to your facility, or a combination of several uses. 

What are the water flows at my facility?

Facilities should start with a water audit that considers daily and seasonal use variations, assesses current and future water use (both quality and quantity), and determines potential combined uses of recoverable water. Reuse for cooling and irrigation, for example, will vary consid­er­ably depending on the season and weather conditions.

What are future water demands?

Reuse consid­er­a­tions should include a water study to predict future demands, understand conser­va­tion oppor­tu­ni­ties and determine water reuse oppor­tu­ni­ties on a site-wide basis. This will help predict total treatment needs and capacities for design purposes and help determine your return on investment.

What is the public perception and acceptance of the type of reuse?

The reuse of treated water will rely on acceptance of the end-user of the quality and reliability of the treatment technology, plant operations and continuity of “guaranteed quality,” including removal of unknown constituents that may be harmful. This is a critically important consid­er­a­tion and needs a business-based approach as well as employee and stakeholder education and program­matic methods to confirm acceptance—before imple­men­ta­tion or construc­tion of reuse tech­nolo­gies.

What is in the wastewater?

Sampling and analytical testing are needed to determine minimum, maximum and average loadings on the treatment system. These may include nontra­di­tional analytical parameters such as PFAS compounds, salinity, hardness, alkalinity, silica, cations and anions, especially if membrane treatment systems are considered. These process streams can vary consid­er­ably in biochemical oxygen demand; chemical oxygen demand; fats, oils, and grease; total suspended solids; pH; temperature; and salt concen­tra­tions.

What waste disposal options are available?

Water reuse must be compared to traditional discharge options. In reuse scenarios that use reverse osmosis and other membrane-based processes, the concen­trated reject brine stream must be carefully managed and disposed. If this stream cannot be discharged into the publicly owned treatment works or surface water, then onsite evaporation or further concen­tra­tion of the reject may be necessary, signif­i­cantly increasing costs and the space required.

What are the potential costs and savings?

Reuse scenarios should be considered from a life-cycle cost perspective. Costs may include those for capital and operating and maintenance (with labor, electric/energy, chemicals and residuals disposal being the primary ongoing operational costs). Water reuse treatment costs depend on the water quality required. As the quality increases, the costs increase, and the level of technical sophis­ti­ca­tion required of facility operators increases likewise.