Water Treatment

Options for industrial water reuse

By Jared Galligan, Capital Projects Manager at U.S. Water

Every day in the US, more than 355 billion gallons of water are withdrawn from surface and ground water sources to serve industry

Every day in the US, more than 355 billion gallons of water are withdrawn from surface and ground water sources to serve industry and the public, according to a 2010 report from the US Geological Survey. As the strain on water sources steadily increases, it is critical for all users to work towards water conservation.
The primary drivers towards water recycling and re-use are environmental compliance and water availability. Every 5 years, a facility that discharges to a public body of water must apply for and renew its National Pollutant Discharge Elimination System (NPDES) permit. During the renewal process, the local regulating authority may choose to impose tighter discharge restrictions on specific constituents. In states like Iowa, iron and sulfate are targeted, while in Minnesota and Wisconsin, phosphorus is under greater scrutiny. The ongoing permitting costs, costs to comply with new discharge restrictions, or the threat of not being granted a permit are driving more facilities toward minimal or Zero Liquid Discharge (ZLD) operations.
For those facilities that receive municipal water or discharge to a Publically Owned Treatment Works (POTW), water availability may become an issue. As infrastructure continues to age, and costs to replace it approach the hundreds of billions of dollars nationwide, communities may be forced to choose between supplying residents or supplying industry. Those plants that are still served may face double digit increases in costs to maintain their services. It is these costs that have companies looking at alternative water sources, installing their own intake systems (surface or well), or evaluating re-use options.
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Water re-use and recycling projects can be one of the most difficult water treatment processes to design and implement. They often require a combination of chemical and mechanical solutions. They must also be designed by someone familiar with water quality requirements, air and water permitting, and the nature of plant operational cycles. While it is easiest to design a greenfield plant to operate with a water re-use, or ZLD system, any plant in operation today must look to retrofit existing equipment. Generally speaking, the simplest and lowest cost option is to install equipment at the front end (raw water intake) to minimize waste water generation at the back end of the plant (i.e. cooling tower blowdown). 
Because there is no single design that works for all applications, it is important to find the right, integrated solution for each plant. In order to create a successful water treatment system design for a plant, it is necessary to have a thorough understanding of the chemistry and equipment aspects and plant conditions: plant design, operating conditions, available water quality and quantity, available personnel and training, capital and operating budgets, and environmental restrictions. Most water re-use and ZLD systems use one or multiple of the following water treatment technologies, in order of capital costs: chemical feed systems, membrane filtration, reverse osmosis, evaporation ponds (if climate allowable), cold lime softening and evaporation/crystallization. While evaporation/crystallization may seem like the simplest solution, its initial capital investment and ongoing energy costs greatly exceed all other technologies combined.
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As ground water sources become more limited, facilities are looking at alternative water sources to supply their plant. One of the most common sources today is municipally-treated waste water, called greywater. This low cost, or sometimes free, water source is abundant and does not strain local sources.
However, while at first attractive from a financial perspective, greywater carries many concerns, most frequently centring around its variability and nutrient content. Common constituents like phosphorus and ammonia can be costly to remove, and if left untreated can lead to scale formation on heat exchange surfaces, corrosion and other biological based concerns. The suspended solids content is usually much higher than most ground water sources and requires its own method of treatment.
A Midwestern United States ethanol facility implemented a greywater re-use system that eliminated their need for freshwater. While first designed to operate on potable water, during construction the facility learned the municipality could not supply the quantity of water required by the ethanol producer. Forced to find another water source, the municipality offered to supplement their potable water with greywater. The alternative water source changed the facility’s planned water treatment system to include microfiltration, a membrane-based filtration system excellent at removing suspended solids and other organics common to greywater, and additional reverse osmosis capacity. The plant has been operating successfully since system integration almost 10 years ago. This facility was the first of its kind to use the technologies of microfiltration and reverse osmosis together for greywater re-use.
As water re-use and recycling projects continue to take centre stage in a facility’s long term environmental plan, water related projects will become even more common. Creative engineering and treatment technologies will continue to drive their advancement and further water conservation.
Jared Galligan, Capital Projects Manager at U.S. Water, 12270 43rd Street NE, St Michael, MN 55376, USA
T: +1 866 663 7633