Toward zero liquid discharge
September 10, 2012
Animal feed recovery used to constitute best practice in food plant wastewater treatment. Technology and sustainability efforts are pushing manufacturers far beyond that.
Wastewater handling may never be a core competency in food and beverage manufacturing, but that doesn’t preclude food company involvement in some of the most advanced treatment and reuse systems in use or under development.
Take zero liquid discharge (ZLD), for example. With ZLD, all contaminants—BOD, COD, TSS, FOG (fats, oils and grease), etc.—are removed, leaving water that is more pure than the water coming into the plant. Instead of being discharged, the water loops back into the facility for processing, cleaning, boiler feed or any other application. Five years ago, only a handful of ZLD systems had been designed; today, most major water technology suppliers are promoting ZLD, though one specialist puts it in the lunar-colony category: technically feasible but financially pie in the sky.
Frito-Lay’s Arizona chip plant represents the food industry’s boldest stab yet at ZLD (see “Frito-Lay Casa Grande plant achieves near net zero,” Food Engineering, November 2011). FOG is an issue when potatoes are fried, though BOD levels are too low to support an anaerobic digester. Until Frito-Lay management gave its blessings to an effort to take Casa Grande off the electric, gas and water grids, treated wastewater was land applied. The last crop was harvested in 2010.
Since then, Frito-Lay has completed a process water treatment and recovery plant that includes screening, equalization and pH adjustment with carbon dioxide, primary clarifiers, an activated sludge bio-reactor with nutrient removal for nitrogen, a membrane bioreactor (MBR), granular-activated carbon treatment, ultraviolet and chlorine disinfection, low-pressure reverse osmosis (LPRO), water stabilization chemical addition and storage of purified water for reuse. On a typical day, the system reclaims 648,000 gallons, three-quarters of the incoming water stream. Total dissolved solids in the recycled water range from 28-40 parts per million, less than a tenth the level of incoming municipal water.
“If a plant can segregate its waste streams, water reuse is feasible,” observes Al Goodman, principal of CDM Smith Inc., the Louisville, KY engineering firm that provided design-build services in Casa Grande. Sanitary water does not enter the treatment loop, and FOG is separated prior to biological treatment to prevent fouling in the ultra filtration and MBR systems.
His firm is designing a dual-DAF (dissolved air flotation) system for another food company, with the first DAF recovering oil and returning it to production. “The key is if it can be segregated,” he says. Less ambitious than the Frito-Lay recovery system, that project should generate a return in two years.
The biological processes that occur downstream of the DAF add considerable cost, but major food companies are beginning to include increased sales attributable to sustainability efforts in their ROI calculations to help cost-justify water recovery. “It’s a huge challenge to attribute a sales increase to a green initiative, and it means bringing the marketing people into the discussion of ROI,” says Goodman. Nonetheless, it can be done, and some major customers are demanding it. “Companies like Walmart and McDonald’s are the new EPA,” he adds.
Water fetches a much lower price in Kentucky than it does in the Arizona desert. Water reuse wasn’t even part of the discussion in food plant water treatment a quarter of a century ago, when Goodman’s firm was called in to address a crisis situation at Purnell Sausage Co. “We were putting out bad water,” conceded Tim Hernden, assistant plant manager of the Simpsonville, KY manufacturer, in a presentation at Food Engineering’s 2012 Food Automation & Manufacturing Conference. The kill plant processes up to 400 sows a day, and the waste stream overwhelmed the onsite lagoon. Discharge was poor enough to result in a proposed $7 million EPA fine, which would have devastated a company with annual sales of about $25 million at the time. A screen and DAF pretreatment system staved off a shutdown in 1987. Two years later, Purnell installed what was believed to be only the 12th sequencing batch reactor (SBR) in the world. Two more SBR systems were added in 1995, and the company continues to improve its treatment system, most recently with new SCADA controls that give managers remote monitoring capabilities, an important upgrade for a treatment system that runs without staffing for one shift a day.
BOD and TSS limits are much stricter today than in the 1980s, though failure to meet the old standards would have put Purnell out of business. Instead, the firm prospered, and sales have more than doubled. The treatment plant is essentially the headwater of a creek that slakes the thirst of downstream cattle. Today’s challenge is to maintain and optimize operations. The new SCADA system is expected to help lower electricity use, treatment’s second-highest cost after labor.
Sustainable water policy
Corporate sustainability was a top consideration when Keystone Foods developed plans for a replacement plant in Gadsden, AL in 2009 (see “Keystone Foods puts its best food forward,” Food Engineering, April 2010). “Keystone wanted to pull out all the stops to make it a show facility,” and that included a significant upgrade to pretreatment, according to Paul Greene, vice president with O’Brien & Gere (OBG), the Syracuse, NY-based engineering firm that designed the treatment system and now operates it with a staff of five, including former Keystone employees. Those workers underwent additional training and earn wages commensurate with their higher skills.
Within a year of operation, the Gadsden pretreatment plant helped Keystone realize $900,000 in cost reductions. Recovered nutrients go to animal feed. SBR and a moving bed bioreactor were among the technologies considered. In the end, OBG opted for conventional activated sludge technology, followed by DAF for secondary clarification.
High-strength waste from a poultry processor like Keystone is a very attractive feed stock for anaerobic digesters, and those are destined to become popular options in the coming years, predicts Greene. States like Massachusetts and Vermont are easing the permitting process for biogas suppliers, and a number of municipal and independent projects that rely on waste from food plants are springing up. Novi Energy recently commissioned a 3 MW biogas-to-electric system in Fremont, MI, relying in part on food waste from Gerber Products to feed its digester. “There are more than 7,000 of these types of facilities in Germany,” says Greene. With their domestic market saturated, the German firms that optimized anaerobic digesters are flocking to the US.
One likely landing spot is Lowell, MI, an hour’s drive from Fremont, where enCO2 is waiting to build a codigester in a vacant factory. Sustainable Partners LLC (Spart) is heading the effort to build an 800 kW biogas-powered generator, assuming a long-term purchase agreement can be reached with the local electric utility. A key factor in the digester’s location is its proximity to Litehouse Foods. A quarter-mile pipeline would link the digester to Litehouse, which would either channel process waste or all 15 million gallons of its annual wastewater load to the digester, according to Greg Northrup, a principal in Spart. Digester upsets from CIP chemicals are a concern, however.
“There can be very positive economics to food companies in anaerobic digestion,” says Northrup, noting Litehouse currently must truck food waste 30 miles and pay tipping fees. Codigestion eliminates those costs while casting a halo over the Litehouse brand. Although European technology dominates the codigester business, Northrup is confident more innovation will occur as applications grow, and US engineers get more involved. “The technology is the easy part,” he scoffs. “It’s getting everyone to sign the agreement that’s difficult.”
Innovation already is progressing, insists Lola Arowoshola, chief author of Water for food & beverage: opportunities in water efficiency and gaining value from wastewater, a research report from Global Water Intelligence in Oxford, UK. Today’s digesters can handle FOG that used to have to be filtered out, she says, and the steel tanks favored by German firms shrink the digester’s footprint considerably, compared to the reinforced concrete tanks more typical in US systems. Based on in-depth interviews with some of the largest food and beverage companies in the world, Arowoshola concludes firms are “open to new, innovative technologies and solutions” to wastewater handling, though they “still require technologies to be proven to minimize their operational risks.” Microbial fuel cells, bioplastics and fertilizer pellets are among the technologies that enthuse food and beverage executives, but biogas digesters will account for a big chunk of the projected $6 billion food and beverage companies will spend on water technology by 2020. Emerging markets will account for much of the growth, though Arowoshola projects spending by US processors will grow to $901.3 million, up from last year’s $749.1 million.
Brand image and public pressure to address both water use and energy consumption force global food companies to take a big-picture approach to wastewater. Mainstream processors are more likely to address the issue when surcharges spike, as was the case at Gaytan Foods, a Hacienda Heights, CA maker of snacks such as pork rinds and cheese puffs.
After building a 64,000-sq.-ft. plant in 2007, Owner Rudy Gaytan was startled when wastewater surcharges jumped to $76,000 annually from $5,000. An after-the-fact pre-treatment solution had to be wedged into an area the size of two parking spaces. That limitation led him to Clean Water Technology Inc. (CWT) in nearby Los Angeles. CWT devised a modified DAF system that incorporates a series of six-headed hydrocyclones to fully aerate influent. Installation of the technology, which the firm calls GEM (gas energy mixing), lowered Gaytan’s surcharges to their original level.
Using pressurized dissolved air to create flotation bubbles requires energy, though CWT Business Development Manager Linda Mills insists energy consumption is no greater than with a conventional DAF if all components of the system are considered. Besides superior BOD removal, GEM also produces more concentrated solids, she says. Conventional DAF results in 3 to 6 percent solids, while GEM delivers 10 to 13 percent solids, “and it will continue to decant to above 20 percent,” according to Mills.
Coagulants typically are added to a DAF to help remove soluble BOD and COD, with calcium hydroxide or clay the most common polymer additive, says Stuart Davis, chief technical officer at Carmel, IN-based GenChem International. He and his brother, Robert Davis, believe powdered activated carbon is a better mousetrap. The carbon enrobes soluble elements more effectively than other chemical clarifiers, he claims. “It’s fundamentally different, and that’s why we were able to get the patent” last year, according to Davis.
“Effluent standards are getting tougher and, in some cases, are absolute,” Davis adds. “As big users of municipal systems, companies know that if the tax base shrivels, the surcharges they pay are going to increase.”
For most companies, wastewater is an ad hoc issue that is immune to long-range solutions. “New projects that don’t affect production are a low priority, and the will to devote time, energy and money to wastewater treatment is low,” concedes Glenn Cramer, technical applications director for Eco Bionics, an operating unit of NCH Corp., Irving, TX. Unless managers are aware of the cost of their plant’s surcharges, interest in Eco Bionics’ bacteria cocktail for BOD reduction will be low. On the other hand, if surcharges have ratcheted into the six-figure range, his firm’s bacteria incubation system can be an effective solution.
ZLD’s tantalizing promise
Evaporators or crystallizers are necessary end-of-line components for wastewater systems that move from high recovery to ZLD, but their energy requirements make them impractical in food and beverage, points out John Brittan, technical director-food & beverage for Siemens Water Technologies, Warrendale, PA. “ZLD is a reality now in mining, where discharging minerals is not an option, and ZLD is part of the cost of doing business,” he says. “People are starting to look at it in food, but I don’t know of any plants that are approaching ZLD.”
Besides the cost, the energy demands would undermine a sustainability program that also strives to cut energy use. “The energy and water nexus will become even more interrelated in the future,” notes Goodman, and a wastewater system that returns effluent for reuse must do so in an energy-efficient way to be viable.
GE Power & Water is moving in that direction with a non-thermal brine concentrator that sidesteps the energy expense of thermal evaporation, according to Alfredo Zepeda, product manager-food & beverage for the company’s water and process technologies division in San Diego. The system, which combines a desalination unit with a concentrator, achieved 99 percent water recovery in an ingredient room during a pilot study. “We’re actually crystallizing the salts,” says Zepeda.
Wastewater influent is another matter, however, and the company has not validated non-thermal brine concentration with a waste stream.
For now, Brittan advocates an à la carte approach to ZLD, with a focus on high recovery rates until the economics and energy consumption of ZLD can be brought in line. “Adding processes over time is the approach we’re taking,” he says.
OBG’s Greene concurs. He views ZLD as a long-term goal. For now, anaerobic digestion makes the most sense because it addresses the treatment issue while also generating renewable energy. And an anaerobic system does not preclude ZLD, making them compatible solutions for water and energy goals.
For more information:
- Al Goodman, CDM Smith Inc., 502-339-0988, firstname.lastname@example.org
- Linda Mills, Clean Water Technology Inc., 414-336-8735, email@example.com
- Glenn Cramer, Eco Bionics, 610-597-6914, firstname.lastname@example.org
- Marty Fallon, EZSoft Inc., 484-568-5040, email@example.com
- Alfredo Zepeda, GE Power & Water, 858-526-1520
- Stuart Davis, GenChem International, 317-201-3102, firstname.lastname@example.org
- Lola Arowoshola, Global Water Intelligence, 44 1865 204208, email@example.com
- Paul Greene, O’Brien & Gere, 518-951-5766, firstname.lastname@example.org
- John Brittan, Siemens Water Technologies, 724-772-1402, email@example.com
Weapons of waste management
Information is power, and a lack of timely information on the condition of its wastewater discharge threatened the future viability of a Pennsylvania manufacturing facility when stricter wastewater discharge permits were issued. Rather than more tanks, screens and other hardware, the solution was the installation of a data historian and report-generation system.
Harleysville, PA-based Colorcon makes excipients—the binders, coatings and other non-active ingredients in nutraceuticals and prescription pills. When the Township of Gwynedd upgraded its wastewater treatment plant in 2007, it put Colorcon on notice that strict pH balancing and chlorine limits would be required from Colorcon’s West Point, PA plant. Notification of any excursions beyond those limits would have to be reported within 15 minutes of the event. Fines of up to $10,000 and a possible plant shutdown were potential consequences of noncompliance.
Meters with chart recorders outside the facility proved woefully inadequate, and in 2010, the firm contracted with system integrator EZSoft Inc. to provide an automation solution. Last year, EZSoft completed the integration of a data historian and a FactoryTalk server from Rockwell Automation to generate reports of daily discharges, pH and chlorine averages and maximums, and other variables. Additional reports were generated for the company’s environmental engineer and operators who previously lacked control-room visibility to pretreatment conditions.
“They were capturing data in a very cumbersome, inexact manner, with paper-chart recorders on which each degree represented a 20-minute timeframe,” according to Marty Fallon, vice president-sales at EZSoft, Malvern, PA. Additionally, the recorders were in a remote location, making timely identification of upsets unlikely. With the new controllers, alarms to the control room and the pre-treatment manager are generated in real time.
While better effluent monitoring was a must-have upgrade, “the idea was to build the infrastructure needed to extend data collection to batching and other areas” of enterprise manufacturing intelligence, Fallon explains. Maintaining manufacturing viability was the rationale for data automation, but improving production control will deliver payback.