Waste not, want not
Not one wastewater treatment solution is suitable for every application, so it’s essential to find the one that fits your budget and future water and energy needs.
Depending on where you are in the world, you may or may not have a water sourcing problem. But if you do, you need a strategy to cut excessive use and find methods to reuse water when possible. With the right strategies, you can also decrease wastewater surcharges from your publicly owned treatment works (POTW) and maybe even recoup some energy out of your wastewater.
For at least five years now, improving the water-use ratio has been a very integral part of food and beverage companies’ sustainability goals. For example, the Coca-Cola Company achieved its goal to reduce the water-use ratio in its manufacturing operations by 20 percent from a 2004 baseline, according to its 2011-2012 Sustainability Report.
An average water-use ratio for a carbonated soft drink producer might be in the neighborhood of 2:1, which means that for every liter of product, two liters of water are used, according to Michael McDonald, GE Power & Water—Water & Process Technologies global business leader, food and beverage systems group. For a brewery, the ratio could be as high as 3.8:1—meaning for every liter of beer produced, 2.8 liters of water go down the drain. To get better ratios, producers are altering production processes to minimize water usage and are considering onsite treatment of reuse water to an appropriate quality for utility water. Cleaning up used process water for reuse also means sending less to the POTW and decreasing POTW surcharges for high-strength wastewater.
Many processors already have onsite treatment plants, but face the problem of increasing production, which means increasing wastewater—which could also mean increasing the size of the treatment center where there may be no more available space. The Long Tail Brewing Company, located in Bridgewater Corners, VT, faced this problem as its wastewater volume increased along with its BOD (biological oxygen demand) to approximately 10,000mg/l. With no space to add tanks, the company installed a Siemens BioMag system to increase treatment capacity from 500 to 1,300 lbs./day of BOD, without a plant expansion.
When FAGE built its new yogurt plant in Johnstown, NY (see “Fabulous Food Plant: FAGE Yogurt,” FE, December 2009), the local POTW was underutilized and eager to take on the new waste stream. Now that FAGE is doubling its size, it will increase its wastewater flow from 127 million gallons in 2012 to 286 million gallons by 2017, according to The Leader-Herald (November 18, 2012). The expansion calls for a $25 million whey pretreatment plant to be built on two nearby acres to handle the extra wastewater. An existing agreement with the POTW, which was extended for two years, allows for an input of 500,000 gallons of whey per week to the POTW, and the rest is hauled off the FAGE site.
The amount of discharge concentration processors are allowed can change over time. For instance, in 2006, Kan-Pac LLC’s manufacturing facility in Arkansas City, KS received new sewer discharge requirements of <300mg/l BOD. To meet the new limits, the processor installed a single-stage ActiveCell bioreactor from HeadworksBIO, which reduced BOD by 80 percent to meet the new discharge limits. The aerobic system combines the processing of production, sanitary and cooling wastewater before sending it to the POTW.
Cut if you can—otherwise recycle
The cost of building an onsite wastewater pretreatment center needs to be carefully considered, since for some processors, the center may not be necessary. “Is it more cost-effective for the processor to pretreat or to pay the surcharge to the POTW?” asks Al Goodman, CDM Smith associate. Goodman reminds processors that once the capital expenditure is out of the way, there are ongoing operational and maintenance costs—not to mention that in many locales, state-certified operators are required to run an onsite, pretreatment center.
Usually, a processor doing some form of pretreatment or segregation to minimize its loading to the POTW is more cost-effective than paying for the POTW to expand just for the processor’s waste load, according to Jeff VanVoorhis, Symbiont director of marketing. VanVoorhis recommends some basic methods of reducing effluent to the POTW. “Look at your losses and yields, minimize your waste and maximize your yield so production and sanitation processes are not creating losses that go down the drain. If losses can’t be prevented, look at alternative disposal methods—like animal feed or composting or a nearby digester that needs high-strength waste. If all those fail, then look at forms of pretreatment.”
For certain internal systems, segregation can help reduce effluent to the POTW. Cooling water blow-down is a significant component of the wastewater stream in most food and beverage facilities, according to Garth Morrison, VRTX Technologies CEO. A cooling water treatment solution can recycle water within the system, often saving processors 20 percent of the makeup and cutting surcharges as the wastewater is chemical-free.
“Our experience indicates that for typical medium- to low-strength wastewater, it is less expensive to discharge to a POTW and pay surcharges than to install an onsite treatment system,” says Reinaldo González, Burns & McDonald/Water Group associate environmental engineer. Reuse is always encouraged. However, the level of treatment is high and can be very expensive. Also, FDA regulations put a limit on the potential for reuse. “Install wastewater treatment systems only if economically viable or if the local POTW can’t take the load generated at the facility,” adds González.
Often the drive to install a pretreatment system comes from the processor’s sustainability goals, says Burns and McDonald Project Manager Jeff Keller. Reuse is site-specific, and in some areas, water is priced so low it doesn’t make sense to reuse. The degree of treatment also determines the ease of implementation and costs.
“Processors may be located in areas where water supply is not plentiful or water costs are escalating,” says Scott Christian, ADI Systems vice president of business development. These situations drive processors to seek alternative ways to reduce water usage in their plant or determine how they might reuse treated effluent.
“Nobody could have predicted some of the drought we’ve seen in Georgia, Tennessee and Virginia recently,” says Goodman. “It’s made a lot of the larger food industries start to think about the ‘what if’ we had a dry spell or ‘what if’ we didn’t have a dependable water supply?”
Getting started on water reuse
The starting point for planning a pretreatment system is to gather as much data as possible. Processors must have a clear understanding of their flows and loading relative to municipal ordinances, contracts and sewer user fees, according to Jason Duff, Stellar vice president, design and engineering. A significant factor to consider is whether sanitary waste is comingled with process waste. This will determine what treatment options may be viable. It’s also important to look down the road five or 10 years to plan for flexibility and adaptability, possible expansions and product mix changes. Consider all potential costs including the sewer connection fee, flow rate, surcharge and penalty rate, as well as any hauling charges. Realistic cost projections (capital and operating) are crucial to effective evaluation of various levels of treatment, says Duff.
Water treatment technology for reuse has improved to the point that systems can be designed to reliably treat water to any desired quality at a high volumetric recovery, says McDonald. “The problem, if one can call it that, is more high-quality reuse water can be returned to the production facility than there is for use as utility water. Since this water cannot be used as production water, the plant’s water flow and use-points often dictate the minimum water-use ratio, not the available technology. We see this as more acute when countries or regions impose zero liquid discharge or near-zero liquid discharge mandates on production facilities.”
At Setton Pistachio’s growing and processing facility, working to reduce the amount of water recirculated into public waterways is a major priority. Located in Terra Bella, CA, Setton’s processing plant uses up to 75,000 gallons of water per day during the busy harvest season. To lessen this impact, Setton implemented a system to filter and recycle the water so it can be pumped back into the orchards for irrigation. “We are making huge efforts to use and reuse all resources responsibly before, during and after harvesting our pistachios,” says Mia Choen, Setton COO. “Reusing water is one of the easiest and cleanest ways we can do that.”
Aerobic, anaerobic or both
Aerobic, anaerobic or a combination of both systems may be used to remediate wastewater. Though it will have a higher overall operating cost, an aerobic system is typically lower in capital cost and a better choice for smaller processors or those with lower-strength wastewater, according to Ian Page, Global Water & Energy LLC vice president. There are many types of aerobic systems, but essentially all consist of some form of an aerobic biological stage followed by a method of solids/liquid separation. Additional components, biological or otherwise, might be included to remove nitrogen or phosphorus, if required.
In an aerobic process, typically 70 percent of the BOD is converted to cell mass (sludge), which needs to be separated, according to Kristopher Olson, Nalco global industry development manager. The various technologies differ in how the aeration is performed— whether as a bulk liquid or as a film on media—as well as how the sludge is separated, merely by settling or floatation or by membrane technology.
“Aerobic systems can do the job on many waste streams, but for high-strength waste, the economics of aerobic treatment don’t add up,” says Keller. According to McDonald, aerobic treatment produces better-quality recovered water (lower BOD and COD, fully nitrified) than anaerobic technology, but carries higher operating costs due to the required energy to run blowers and other support equipment.
Anaerobic treatment of food and beverage wastewater generates biogas (typically 60-75 percent methane), which can be utilized in plants for boilers or to produce electricity, according to Christian.
Benefits of standalone anaerobic treatment include reduction in BOD/COD concentration, low energy input and waste solids that have added value as fertilizer. Depending on the wastewater strength, anaerobic systems tend to be less efficient at removing BOD to meet typical POTW discharge regulations, but will generate considerably less new biomass compared to aerobic-only treatment.
Is anaerobic treatment in itself enough to clean up wastewater for the POTW? “Definitely,” says Page. “Depending on the type and characteristics of the wastewater and type of anaerobic system utilized, removals of over 90 percent of the COD and BOD are achievable, often allowing single-stage pretreatment with anaerobic alone to meet the required sewer discharge limits.”
But is that good enough? “It is imperative to consider the full impact of the anaerobic effluent on the municipal sewer system and treatment facility when looking at anaerobic-only treatment,” says Henry Probst, partner, The Probst Group. “Elevated ammonia loading, sulfur content, odor potential and anaerobic solids content can all impact the municipal system adversely. Failure to consider the resultant ammonia loading to the POTW can be a costly omission.”
The presence of sulfates alone in the raw wastewater can make anaerobic technology unattractive, says Charles H. Caban, senior process engineer at The Austin Company. Removing the sulfur (hydrogen sulfide) from the gas stream would be necessary and is sure to be costly. Also, it’s important to know the raw wastewater chemistry, flows and strengths before coming to a final decision to implement an anaerobic system.
In addition, each POTW has different permit limits on BOD. “It is possible to convert sufficient BOD to methane and fall within [POTW guidelines] with just an anaerobic process?” asks Nalco’s Olson. “Often, it would be necessary to follow the anaerobic system with an aerobic. This way, the anaerobic unit takes the brunt of the load, leaving about 10 percent of the raw BOD in the water, and the aerobic unit can polish that.”
“As a rule of thumb, the only time we add that aerobic treatment step is if the facility is going to direct discharge to a waterway—like a stream, river or lake,” says Symbiont’s VanVoorhis. For processors lucky enough to be situated near a waterway, using both anaerobic and aerobic treatments and avoiding the POTW discharge entirely may be something to consider. However, VanVoorhis says this step isn’t without its risks. For example, if the equipment fails, an upset occurs, or a flood causes contaminated water to enter the waterway, processors might expect a knock on the door from the EPA.
Goodman points out his company has projects where process wastewater is being converted back to drinking water standards, beating EPA primary and secondary standards. Processors use the water to wash corn, potatoes and incoming food and sanitize the equipment. In essence, it’s used anywhere city water can be used. It’s just not put in a bottle—mainly because of consumers’ perceptions. The water also meets all the FDA requirements.
Why not get a little more back?
Many food plants produce a high-strength waste—beverage plants, juice plants, dairy production, meat packing—and can treat wastewater to generate gas to run basic functions within the plant, says Stellar’s Duff. Areas that typically generate suitable high-strength waste streams include whey and milk separators, first rinse of processing equipment, off-spec products, grease traps and DAF (dissolved air flotation) pretreatment float/sludge. All of these are excellent sources of methane gas to power boilers or cogen systems.
Dairies, large juice manufacturers and breweries have wastewater that is considerably high in chemical oxygen demand (COD) content, and has a significant energy content, says GE’s McDonald. When the total COD in a wastewater stream exceeds 5,000 kg per day, it then makes economic sense to convert the waste into useful energy.
“Anaerobic digestion converts this COD to methane and biogas that can be fed to a Jenbacher combined heat and power [CHP] engine which produces electricity that offsets plant power usage, provides useful heat for the plant and generates carbon credits in some regions,” McDonald states.
Not all projects deliver enough gas to run the really large reciprocating engines that can produce anywhere from 330kW to 3 megawatts, says VanVoorhiz. It depends on the size of the project. Smaller projects with less gas volume use a small micro-turbine like the Captsone units, which can produce up to 1 megawatt in a self-contained system. Larger projects that have several hundred up to 1,000 cfm of gas can run large reciprocating engines—Caterpillar or Jenbacher.
According to David McCallum, business development leader at GE Engines, a 330kW system could be supported by wastewater up to about 13 million gallons per day depending on BOD levels, and could be much less for high-strength effluents.
Where one processor may not have enough wastewater to support a cogen system, a new trend is to combine the effluents of several processors in a relatively close geographical area to produce power. For instance, one project in the Midwest has waste from 10 cheese plants feeding one very large-scale digester with a gas output that powers reciprocating engines, producing 3.2 megawatts of power around the clock.
Recently Stellar completed a wastewater treatment plant for an expanding dairy production facility. The system includes an anaerobic pretreatment for high-strength wastes (acid whey) and diverts high-strength waste from the process stream. A multi-mode bio-gas recovery system provides electric power generation and fuel for plant boilers.
While energy recovery may not be in the cards for your facility, a pretreatment system may be very likely in your future. Stellar’s Duff provides three points for consideration:
- Maintain a system-wide perspective with regard to wastewater treatment alternatives.
- Beware of the “one-size-fits-all” approach—each application should be considered thoroughly to ensure the best possible fit.
- Make allowances for process variability and ample future growth; the project will be less expensive if planned properly from the start.
For more information:
Michael McDonald, GE Power & Water, 952-988-6664, Michael.McDonald@ge.com
Al Goodman, CDM Smith, 502-339-0988, email@example.com
Reinaldo González, Burns & McDonald, 816-333-9400, firstname.lastname@example.org
Jeff Keller, Burns & McDonald, 816-333-9400, email@example.com
Scott Christian, ADI Systems Inc., 506-452-7307, firstname.lastname@example.org
Jeff VanVoorhis, Symbiont, 414-291-8840, email@example.com
Jason Duff, Stellar, 904-260-2900, firstname.lastname@example.org
Ian Page, Global Water & Energy, LLC, 512-697-1901, email@example.com
Kristopher Olson, Nalco, 630-305-1000, firstname.lastname@example.org
Henry Probst, The Probst Group, 262-264-5665, email@example.com
David McCallum, GE Gas Engines-NA, 360-693-0117, firstname.lastname@example.org
Garth Morrison, VRTX Technologies, 210-651-7402, email@example.com
Charles H. Caban, The Austin Company, 404-564-3950, firstname.lastname@example.org