Wastewater Strategy Is Mission-Critical for the Water-Dependent Chemical Industry
When it comes to water management and wastewater treatment, chemical manufacturers share many of the same challenges as companies in other industries.
Interestingly, some chemical companies have a dual interest in the water issue: Not only do they deploy wastewater technologies at their plants, they also make a business out of producing those same technologies. Neil Hawkins, Dow Chemical Co.’s vice president for sustainability and global EH&S (environment, health, and safety), told me that his company provides technologies in such areas as desalination and water filtration. “Water for us is a growth business and we are trying to sell ever more sustainable ways to clean water and to treat water for drinking and processing,” he said. Dow’s Water and Process Solutions business provides such products as reverse osmosis and nanofiltration solutions, ion exchange resins, ultrafiltration, fine product filtration, catalysts, and adsorbent resins.
Water Integral to Chemical Manufacturing
Industry in general is confronting the looming problem of global water stress and competition for the precious resource of freshwater. According to UN-Water, industry as a whole consumes about 20 percent of freshwater worldwide. Seventy percent goes into irrigation and 10 percent into domestic use.
Chemical production requires a lot of water, Hawkins told me. “It’s integral to our processes,” he said. “So for a large company like Dow that has water needs, we pay a lot of attention to water risk and water supply in terms of quality and quantity.”
The chemical industry is known as one of the major industrial users of water, along with steel, paper, and petroleum refining. Water is used in the chemical industry in various ways, cooling seeing the highest usage. Mark Ellis of energy consulting firm Energetics (along with colleagues) writes that “Many chemical reactions generate heat, and the reaction vessel must then be cooled so that the temperature is controlled at the desired limit and the reaction does not get out of control.” The heat “is dissipated in cooling towers before water is returned to the plant for subsequent reuse.” Water is also used for steam generation, for cleaning, and for processes such as refining chemicals.
German chemical company BASF says that it uses about 2 billion cu m of water per year as of 2012. Out of that total, 94.1 percent is surface water, 4.7 percent is groundwater, and 1.2 percent is drinking water. BASF says 88 percent of that water is used for cooling. Twelve percent is used for production, in “production processes, graywater, rinsing and purification in production.”
Dow used 2.83 billion cu m of water in 2011. Fifty-four percent of that was surface water, 40 percent was seawater or brackish water, and the rest came from other sources.
Treating Wastewater at Chemical Plants
Most manufacturing and industrial plants base their handling of wastewater on the standard three-stage treatment process of primary treatment to remove coarse solids; secondary treatment, which eliminates organic matter using biological processes; and tertiary or advanced treatment to polish the effluent before discharge into the receiving environment. Sometimes wastewater treatment is considered to have four stages, with a pretreatment stage preceding the others in order to filter out coarse substances, oil and grease, and other contaminants.
Environmental managers at chemical plants will have to apply considerable adaptation to these standard steps to manage the highly-individualized waste streams produced during manufacturing of chemicals. What I was told by Michelle Hamm, environmental manager at Monadnock Paper Mills in Bennington, N.H., applies particularly to chemical production: “In industrial treatment systems, each waste stream is different, depending on the actual chemicals used in the facility.”
Hamm’s assertion is borne out by background materials from Siemens Water Technologies, which say that “As industrial processes differ, so do their wastewater impurities,” consisting of substances such as “acid[s] from a plating process, colorings, acids, oils, and fats from food processing, or the presence of organic chemicals, such as pesticides, paints, dyes or detergents.”
Such chemical waste streams can disrupt wastewater treatment systems if they are introduced into the primary, secondary, and tertiary stages. As an example, EPA says that “chromium can inhibit reproduction of aerobic digestion microorganisms, thereby disrupting sludge treatment and producing sludge that must be disposed of with special treatment.” Chemical reactions in wastewater can cause poisonous gases to form. Dangerous acids and caustic materials can end up in effluent. Volatile organic compounds (VOCs) can even cause explosions in sewer head spaces.
To head off such problems, special chemical waste streams are often handled at the pretreatment stage employing processes customized to the facility. One such strategy might be to separate salt and sweet wastewater streams prior to wastewater treatment, as practiced by Dow at some of its facilities.
Along with other industrial firms, chemical companies are experimenting with green infrastructure, particularly constructed wetlands, as a strategy for tertiary treatment. Dow’s Hawkins told me, “In Texas, we’re using wetland restoration as part of our wastewater treatment plant. We’re saving the company many millions of dollars and providing value to nature at the same time.” Dow’s subsidiary Union Carbide elected to take this approach 15 years ago (before the Dow acquisition) at the company’s Seadrift, Texas, facility, where plastic resins and other chemicals are produced. The 110-acre constructed wetland was built at a fraction of the cost of a comparable “gray infrastructure” tertiary pond and has been EPA-compliant since day one.
Reducing the Chemical Industry’s Water Footprint
Out of the 2 billion cu m of water per year used by BASF, the company says that some is lost to evaporation — about 100 million cu m. The bulk of the company’s volume, 1.9 billion cu m, gets discharged, 90.0 percent as uncontaminated cooling water, 9.2 percent (190 million cu m) as wastewater from production and 0.8 percent as graywater.
BASF has developed goals for continuous improvement in its water management. For example, by 2020 the company plans to “reduce emissions of organic substances and nitrogen to water by 80 percent and of heavy metals by 60 percent compared with baseline 2002.” In that same time frame, BASF plans to “reduce the withdrawal of drinking water from supply sources for production by half compared with baseline 2010.” The company is investing in new monitoring and analytics technologies that will enable it to “identify any unanticipated emissions at an even earlier stage,” thus reducing the volume of contaminated wastewater from its facilities.
Chemical companies are continually refining their water recycling processes to reduce water footprint at their plants. Dow is now developing a water recycling strategy based on zero discharge for its facilities in water-stressed areas such as Seadrift and Freeport, Texas; Aruta, Brazil; Bahia Blanca, Argentina; Tarragona, Spain; Dow Central in Germany; and the Terneuzen site in The Netherlands. Hawkins told me that at his company “the trends are more toward zero discharge and ever-tightening requirements on quality of discharge” and that “in a lot of places the water we discharge is cleaner than the water we take in.”
At Dow’s Netherlands site at Terneuzen, the company is involved with the local water municipal water provider in a collaboration in which the plant accepts 9,600 cu m of wastewater for its manufacturing operations. Using Dow’s own Filmtec reverse osmosis membrane system, the plant brings the local wastewater up to the quality level needed for manufacturing steam and feed water. The water is recycled internally yet again for cooling tower supply. Then the effluent gets treated further with a membrane bioreactor before discharge. Similarly, at Dow’s Freeport, Texas, site the company is recycling 13,600 cu m daily of municipal wastewater to reduce freshwater demand.