Weighing all the options in wastewater treatment
Whether your plant is located in a drought-stricken area or where water is plentiful, building a wastewater treatment center on site may be cost effective for several reasons.
With the Sun Belt states experiencing serious droughts and the cost of processing wastewater escalating in many municipalities, conserving and reusing water at food and beverage processing facilities just makes plain business sense. There are two ways to cut expenses on water: conserve it and pretreat wastewater before sending it off to publicly owned treatment works (POTWs) since many of them charge extra for untreated sewage or may not take it at all.
- What’s your raison d’être for wastewater treatment?
- Dry times
- Aerobic digester systems
- Anaerobic systems produce energy
- MBR: A good polishing step
- BNR protects the environment
- Have it both ways: Clean water and a good ROI
You can, of course, conserve water throughout your plant by preventing wasteful amounts from going down the drain, because the more you process it (e.g., create steam or hot water, pump or filter it, etc.), the more valuable a loss it is.1 Many processors are already up to speed on pretreatment systems and have found these systems can evolve into a larger-scale processing facility where wastewater can not only be pretreated, it can be recycled as clean or even potable water for other uses within the facility. Processed wastewater also can produce energy.
Although some food and beverage processors have discovered onsite pretreatment or further polishing (i.e., refining) of wastewater for use within the facility ultimately saves money, local municipalities are just catching up with the concept of wastewater reuse, and this is mostly in the states affected by ongoing drought. Only 6.4 percent of municipal wastewater flows in the US are reused for industrial, irrigation or municipal purposes, according to the Bluefield Research report, “US Municipal Wastewater & Reuse: Market Trends, Opportunities & Forecasts, 2015-2025.”2
Though processors often place different priorities on setting up an onsite wastewater pretreatment—or complete treatment—system, altruism is usually not the first reason. CDM Smith Associate Al Goodman lists four typical reasons for setting up a wastewater treatment system:
- Compliance with discharge requirements. High BOD (biological oxygen demand) or TSS (total suspended solids) in wastewater generally needs treatment to comply with city or stream discharge requirements.
- Reduction of sewer surcharges for excessively strong wastewater.
- Recovery of useful products for resale, e.g., onsite solids used as animal feed or compost production.
- Recovery of water for reuse. This involves more extensive wastewater treatment, but is becoming a significant driver to industries in water-stressed areas.
While these reasons are certainly practical, it may be harder to put a value on “social pressures,” as Lisa Schilling, marketing manager at Veolia Water Technologies notes. “With the social ‘right to operate’ a plant in a community, manufacturers are doing everything they can to retain or develop a positive local reputation to protect their brand. Installation and operation of effective onsite wastewater treatment is one way a manufacturer can ensure it will be viewed positively by the local community it operates in.”
Having the right kind of waste stream also allows processors to recover energy, according to Scott Christian, ADI Systems vice president, business development. “Food and beverage processors can generate high-strength wastewater that is amenable to anaerobic digestion. Employing anaerobic digestion wastewater treatment onsite not only drastically reduces the COD [chemical oxygen demand] and TSS concentrations of the wastewater, it also generates biogas that can be used onsite in boilers and/or dryers, or to generate electrical power.”
Specific compliance issues besides BOD and TSS include a processor’s inability to meet wastewater limits for pH; fats, oil and grease (FOG); and excess nutrients such as nitrogen and phosphorous, which have been problematic in many areas with ground water contamination, says Stephen Schulte, manager, environmental, health & safety, Hixson Architecture & Engineering. Schulte also points out that in some areas, there just isn’t a POTW to handle processors’ wastewater, so having one onsite is a necessity.
Not every food and beverage plant has all the water it needs, and many states are feeling the pinch of decreasing water supplies as the climate changes. States with POTWs that have been active in setting up water reuse systems include California, Florida, Texas, Arizona, Colorado and Nevada, according to the Bluefield study.
“In a drought-stricken area, the cost of water can be a significant operational expense or limitation,” observes Jeff Cumin, GE Water and Process Technologies senior product manager. “Wastewater reuse provides an opportunity to avoid local limits of water consumption and maintain or increase production without exposure to increasing freshwater costs.”
But, it’s not just availability or local limits on water use that cause operational problems for processors. “Drought-stricken areas are being regulated more heavily than wet areas,” says CDM Smith’s Goodman. “These new regulations protect the pressures put on groundwater use and include parameters for total dissolved solids [TDS], nitrogen and phosphorus. Hence, more advanced wastewater treatment processes for biological nutrient removal [BNR] and membranes such as reverse osmosis [RO] for TDS removal are necessary.”
In drought-stricken areas, wastewater is valued as a potential water supply source. Additional treatment technologies such as filtration, membrane filtration, ultraviolet disinfection, carbon filtration and/or chlorination may be employed to reclaim all or a portion of the wastewater flow, says Schulte. Then, this reclaimed water can be used for evap-condenser makeup, boiler makeup, flume water and “gray” water for toilets, landscape drip irrigation and cooling water.
A wastewater treatment plant can process water for reuse to industrial standards, and its output stream can be upwards of 40 percent or more, according to Darren Gurney, senior process & business development, applications technology & innovation water treatment, Linde Gases. A system can provide tertiary treatment and even produce potable water by applying further refinement techniques such as ultra-filter (UF) membranes, RO and ozone/UV treatment. “Some plants may invest in techniques to get ‘zero discharge,’ where they recover effluent water from RO, sludge drying and dewatering. This is practiced in some Persian Gulf States where water is very expensive,” adds Gurney.
In some cases, water turnaround can be greater than 40 percent. For instance, utilizing a membrane bioreactor (MBR) system with Mitsubishi Sterapore hollow fiber membrane units, Branston, a potato product producer in Somerset, UK, has realized a 52 percent reduction in mains water usage. This was accomplished by recycling process water through the system, which includes extremely tight control of its 25 closed loops and 50 analog measuring points, according to Heiko Gramsch, Branston development project manager.
Aerobic wastewater treatment is a process where a mixed population of bacteria uses oxygen to degrade organic matter—generally quantified as BOD—and other pollutants, says ADI’s Christian. “To facilitate the biochemical reactions, the biomass [activated sludge] requires oxygen, nutrients [e.g., nitrogen, phosphorus] and the adequate environmental conditions [pH, temperature, etc.]. The digestion of the wastewater organic material by the activated sludge primarily generates carbon dioxide [CO2] plus additional biological cells.” While the CO2 escapes into the atmosphere, the biological cells are wasted from the system at the rate they’re generated to maintain a stable concentration of biomass within the activated sludge system, adds Christian.
“There are several types of aerobic configurations, with the most common being activated sludge, sequencing batch reactors, MBRs, trickling filters [bio-towers] and moving bed biofilm reactors,” explains Rick Molongoski, CDM Smith Industrial Services Group, food & beverage division vice president. The effluent from an aerobic treatment can vary, based on the influent and type of treatment, but can generally produce an effluent with BOD, COD and TSS concentrations less than 30 mg/l (≈30 ppm). “While this water is suitable for discharge to a public sewer or for stream or land application, it would need additional treatment to be reused,” adds Molongoski.
“Modifications to conventional activated sludge systems, such as MBRs that rely on physical membranes for solids retention as opposed to gravity clarification, can further improve final effluent quality [free of suspended solids and containing BOD concentrations less than 3 mg/l],” says Christian.
“With subsequent unit operations after the aerobic treatment, the wastewater can be cleaned sufficiently to allow direct discharge to the environment,” says Bill Guarini, Kusters Water industrial sales manager, food and beverage. Typical post-aerobic operations include dissolved air flotation (DAF), clarification, screening and filtration.
By combining aerobic technology with membrane filtration or MBR, solids- and organics-free effluent can be produced, which can be reused for non-food contact applications or further polished by RO treatment, offers Jeff Peeters, GE senior product manager.
Effluent from activated sludge systems is known as secondary effluent, says Christian. It is suitable for reuse in grey-water industrial applications such as makeup water for cooling towers or wash water for tanks and equipment. “However, tertiary treatment [such as nano-filtration and disinfection] is typically required to further polish the secondary effluent to meet potable water standards,” continues Christian.
“There is no usable byproduct from an aerobic system,” says Ariel Lechter, president and CEO, Clean Water Technology, Inc. “The drawbacks are that [it] is more expensive to operate and generates a lot of sludge compared to an anaerobic system.” However, the aerobic system can be designed to make the effluent stream as clean as necessary, according to Lechter.
While aerobic treatment is less susceptible to upset or toxicity compared to anaerobic treatment, large pollutant load swings can upset the balance of the overall system, says Hixson’s Schulte. In addition, aerobic treatment requires high energy use for aeration, produces a high biosolids-to-sludge yield and does not remove TDSs, he adds.
So why not combine an aerobic system with an anaerobic system to handle really large applications? After all, nearly all food and beverage plants generate wastewater that is amenable to aerobic treatment. “However, for some of these plants, the operating costs associated with mixing and aeration, sludge dewatering and disposal, and chemical addition [nutrients, polymer, etc.] can prove to be very high, particularly for those that generate a high-strength wastewater stream and/or a large organic load,” says ADI’s Christian.
In some cases, the wastewater organic load generated by a single food or beverage plant can be comparable to that of a small town or city. When evaluating onsite wastewater treatment at a food or beverage plant, anaerobic pretreatment followed by aerobic polishing often provides a more attractive ROI than a system consisting solely of aerobic pretreatment.
“Anaerobic digestion is a complex biochemical reaction carried out in a number of steps by several types of microorganisms that require little or no oxygen to live,” states Greg Parks, World Water Works VP of technology. During this process, a combined gas product composed mainly of methane [CH4] and CO2, also referred to as biogas, is produced. The amount of gas produced varies depending on the amount of organic waste fed to the digester; temperature influences the rate of decomposition and gas production, adds Parks.
“Anaerobic treatment produces biogas, which is typically 65 to 75 percent methane and can be used as a renewable energy source,” says CDM Smith’s Molongoski. A reliable and fairly consistent loading to the anaerobic treatment process provides a more dependable supply of CH4 biogas. However, the biogas will generally require some pretreatment to remove water vapor, sulfides and perhaps siloxanes prior to reuse, according to Molongoski.
Since an anaerobic system needs a constant supply of “rich” input, it can be a good option for a dairy operation. For example, the DVO Inc. two-stage mixed plug flow anaerobic digester installed at Alliance Dairies (Trenton, FL) delivers enough biogas to run a 1,000 kW generator, supplying more than 70 percent of the dairy’s electricity. The digester also protects the community and the quality of its water by reducing nutrient runoff, odors and greenhouse gas emissions, according to Steve Dvorak, DVO president.
Anaerobic treatment is generally not as effective at removing TSS, says Molongoski. “It will not reduce nutrients. Plus, it requires higher organic loading than aerobic [i.e., BOD>2,000 mg/l] to be cost effective, produces an effluent BOD typically in the 400 to 500 mg/l range and may require heating of the reactor if wastewater temperature is low.” On the other hand, anaerobic systems require no oxygen, so energy costs are lower than with aerobic treatment. Disposal and dewatering costs also are significantly reduced as a result of low sludge production. Consequently, anaerobic treatment is typically the first step in reducing high-strength wastewaters.
Anaerobic treatment is well suited to the food and beverage industry. “It can be used to treat solids and high-strength biodegradable organic wastes, such as sugary wastes and fats, and waste produced in sugar beet, dairy or meat processing,” says AT&I Water Treatment’s Gurney. Disadvantages include an effluent that needs further polishing, potential odor problems and the risk of the sensitivity in the process itself. For instance, to maintain a medium- to high-operating pH, the process needs a continuous supply of influent substrate.
“An anaerobic treatment system is typically energy positive,” says Mike Theodoulou, GE senior product manager. “In other words, the system generates more energy than it consumes. As [biogas] is a byproduct of the treatment of organic waste, [an anaerobic system] also reduces or eliminates disposal costs of organic wastes.”
If a processor already has an aerobic or anaerobic—or combined—system, but needs further polishing, an MBR can be added. “An MBR is the combination of a membrane process like microfiltration or ultrafiltration with a suspended growth bioreactor. MBRs are now widely used for municipal and industrial wastewater treatment with plant sizes up to 80,000 population equivalent [i.e., 48 million liters per day],” explains Ola Wesstrom, Endress+Hauser senior industry manager, food & beverage. “An MBR separates clean water from the activated sludge using membranes that act as a filter.”
Fresh Del Monte Produce Inc. is one processor that uses an MBR to treat process wastewater. Installed at the company’s new plant in Oshawa, ON, the ALTECH HydroKleen system treats 40,000 gallons of wastewater per day for BOD, suspended solids, pH and phosphorus to levels below city sewer surcharge limits.
“An MBR system works by combining aerobic treatment with ultrafilters to remove the bacteria and other suspended solids,” says Jim Lewis, president, Complete Water Systems, LLC. This process produces a very high-quality effluent and can offer many other benefits including reuse-quality water, smaller footprints and reduced chemical usage. An aerobic MBR doesn’t produce energy byproducts, but it does require periodic cleaning of the membranes. (Although not common, there are also some anaerobic MBRs.) The MBR’s biological system must be maintained like any other aerobic system.
“Among the three major types of systems, membrane bioreactors have the highest rates of BOD, suspended solids and phosphorus removal,” says Hixson’s Schulte. These membranes create a positive barrier at the end of the treatment process. In addition, they can pretreat process water for reuse in the plant or for irrigation, require a smaller footprint versus conventional aerobic systems and create a lower biosolids-to-sludge yield than conventional aerobic systems. However, membranes are generally more expensive than conventional aerobic systems and are much more complex because of the pumps and controls required to operate them. More aeration is also needed than with conventional systems, according to Schulte.
“Aerobic MBR is becoming more common in the industrial wastewater market,” observes ADI’s Christian, although it does have some limitations with influent FOG. Aerobic MBR systems produce very high-quality effluent (nondetectable BOD and TSS), and extremely low levels of nitrogen (<4mg/l total nitrogen [TN]) and phosphorus (<0.05 mg/l total phosphorus [TP]) are achievable. Aerobic MBR effluent alone can be used for water reuse in some applications and provides ideal feed water quality to RO systems for tertiary treatment, according to Christian.
A number of MBR plants in the US currently treat raw wastewater or anaerobically pretreated effluent. These include beverage (juice and sports drink), dairy processing (yogurt), potato processing, breweries, snack foods and sauce processing facilities, adds Christian.
Anaerobic or AnMBR technology is ideal for treating high-strength wastewater with high concentrations of TSS and FOG that conventional anaerobic systems don’t handle well. It also produces a very high-quality anaerobic effluent, free of TSS and low in COD/BOD. (In some cases, effluent BOD has been <25 mg/l from an AnMBR). In addition, AnMBR generates biogas and maximizes the amount of its production compared to other anaerobic technologies, says Christian. Like aerobic system membranes, AnMBR systems require membrane cleaning.
AnMBR systems are now operating at a variety of food and beverage processing sites for salad dressing/barbecue sauce production, confectioneries, breakfast foods and food waste-to-energy applications. AnMBR technology can be used to upgrade existing anaerobic systems that need additional treatment capacity and/or require better effluent quality. Anaerobic systems can be retrofitted to AnMBR systems by adding membrane filtration and control systems, says Christian.
In some wastewater effluents, nitrogen and phosphorus may be inherent. “Depending on the required use or disposition of the treated effluent, the inherent nutrients may need to be removed to meet discharge requirements, so the receiving municipal treatment facilities or watersheds are not overloaded,” says GE’s Theodoulou. BNR is an aerobic process that is commonly coupled with MBR treatment.
“BNR systems are used for nitrogen and phosphorus removal before discharge,” says Veoila’s Schilling. Aerobic BNR systems convert nitrogen compounds and ammonia to nitrates (known as nitrification), followed by a denitrification process that converts the nitrates to nitrogen gas, which is given off to the atmosphere. The phosphates in the wastewater are typically removed through precipitation and settling and/or filtration and remain in the sludge produced by the process—along with any minute amounts of nitrogen compounds that may not have been completely converted to nitrogen gas, according to Schilling. Sludge containing phosphates may have economic value as enriched bio-solids for fertilizer.
Using BNR combined with the membranes in an MBR can make effluent as clean as needed. Additional biomass can be processed by adding more oxygen to the system, adds Theodoulou. This can make the solids in the effluent negligible and reduce total nitrogen to under 10mg/l. Phosphorus concentrations are dependent on how much chemical is added, but if needed, can be below 1mg/l, estimates Theodoulou.
“A conventional activated sludge system can be upgraded to a BNR process by adding the appropriate tanks and recycle arrangement,” says ADI’s Christian. However, some activated sludge technologies have an inherent ability to achieve BNR. For example, in a sequencing batch reactor (SBR), a series of process events (fill, mix, aerate, settle, decant or a combination of multiple events) occur in a single vessel. The sequence and duration of event times can be arranged so that BNR is achieved with SBR technology, eliminating the need to have multiple tanks dedicated for single-process reactions. Furthermore, SBR technology provides a higher level of process control, as the sequence and duration of events can be changed by the operator on the fly to quickly respond to process requirements.
Incorporating MBR technology into an activated sludge system capable of achieving BNR results in complete control of solids retention time and eliminates problems with poor sludge settling, adds Christian. Conventional BNR systems may experience problems with sludge settling, causing biomass washout, which can result in process upsets while the biomass recovers, particularly a slow-growing nitrifying population. However, membranes provide complete retention of suspended solids, eliminating the problems associated with sludge settling. Additionally, membrane barriers provide an effective means of preventing the chemical phosphorus precipitate from being discharged into the effluent.
Many processors must implement an onsite wastewater treatment system to keep costs under control, reuse water, meet regulatory requirements and/or keep up a good public image. But, can an ROI be expected soon after implementation?
“Each wastewater stream has to be considered separately,” says Veolia’s Schilling. Some streams require little or no treatment, so they may be the first candidates for reuse. Water reduction can be achieved by charting the process for water usage and minimizing excessive use before employing water treatment methods. Keep in mind that most water recycling applications require a combination of treatment approaches.
AT&I’s Gurney has seen MBR applied to brewery, malting, salad, vegetable, dairy and other food operations. Some of them recycle wastewater back to the process. “The number of plants is not huge, but there is an increasing trend in water reuse being driven by the ‘turnaround cost’ of water.”
It’s important, however, to look carefully at all the potential costs of setting up a system. “We have found four operating cost factors that are typically underestimated when ROIs are performed: labor, chemicals, maintenance and disposal,” says Hixson’s Schulte. The hiring and licensing of operators can be another significant factor. Licensed operators are typically certified by the state in which they work. There are several classes of operators, with each certified for a certain level of treatment type and complexity. If the wastewater treatment system discharges directly to surface water, an onsite licensed operator will be required by the state. If the wastewater treatment system discharges into a sewer system, an onsite licensed operator may or may not be required by the state or the local sewer district, explains Schulte.
The potential costs of power, restrictions on manufacturing capacity, steam and external funding also should be considered. Speaking of external funding, it doesn’t hurt to check in with local, state and federal authorities to see what money may be available to aid in the implementation of a wastewater treatment system. Most A&E/C firms and wastewater treatment equipment suppliers can help with this determination. For a more detailed checklist of factors to be considered in determining the ROI of a system, see box, “ROI wastewater treatment system development cost factors,” on page 78.
ROI wastewater treatment system development cost factors
The following factors (where applicable) should be considered when determining the ROI for onsite wastewater treatment:
• Planning and design cost
• Environmental compliance (e.g., reporting)
• Permitting costs
• Capital cost for the wastewater treatment plant
• Operating costs, including:
-- Electrical power required to operate the treatment plant
-- Maintenance costs, including allowance to replace large equipment, membranes, etc. at the end of their serviceable lifetime
-- Manpower to operate the treatment plant
-- Hauling dewatered sludge or out-of-spec product not suitable to be discharged to the wastewater treatment plant
-- Chemicals for operating the wastewater treatment plant (nutrients, polymer, cleaning chemicals, etc.)
• Savings or elimination of POTW surcharges
• Reduction in volume of waste product to haul off site
• Value of water that can be reused
• Value of biogas energy that can be recovered
• Value of granular anaerobic sludge generated in a high-rate anaerobic digester
• Incentive programs for instituting onsite wastewater treatment, green energy production, water recovery, etc.
Additionally, the following factors, which may not be easy to quantify in an ROI analysis, should be considered when weighing the choice to conduct onsite wastewater treatment:
• Threat of lost production days for severe discharge violations
• Installing water reuse technology serves as a form of insurance against a future restriction of water supply. Water reuse serves as a form of risk management by facilitating internal management of the plant’s water supply needs.
• Positive publicity from instituting green energy production or water recovery systems, showing the production plant’s environmental responsibility
• Improved relationships with neighbors, suppliers and vendors.
Source: ADI Systems.
Wayne Farms upgrades existing system to MBR
Anticipating increases to production, the Wayne Farms Pendergrass, GA facility wanted to update its existing SBR, lagoons and land application system (LAS) wastewater treatment system. The single-tank SBR and LAS had reached capacity and couldn’t handle significant additional flow. Wayne Farms applied for and was issued a National Pollutant Discharge Elimination System (NPDES) permit for direct discharge to Allen Creek, a tributary of the Middle Oconee River watershed.
To meet the NPDES limits, Wayne Farms had to upgrade the existing wastewater treatment plant to provide higher removal efficiency. Considering the potential water shortage and drought issues within Georgia, the processor wanted to recycle and reuse the treated effluent in non-food contact areas within the plant.
The facility’s existing activated sludge (AS) system used a 1.6 million-gallon SBR and aerated lagoon. Effluent from the production facility was screened and had limited equalization (EQ). From the EQ, the wastewater flowed to a DAF unit, then an aerated lagoon, the SBR and a series of lagoons for further treatment and storage. Treated effluent flowed through the lagoons and was discharged through the LAS. Waste-activated sludge (WAS) was stored in the sludge lagoon.
As part of the new system design, the processor instituted a multiple-polymer system for the existing DAF. The table shows the influent design parameters following the DAF upgrade.
To meet the three main objectives for the wastewater treatment system upgrade, Complete Water Services LLC recommended an MBR system with de-nitrification, phosphorus removal and ultraviolet (UV) sanitation. Since MBRs don’t rely on conventional settling and clarification, the concentration of biomass can be increased, therefore, decreasing the overall size of the system while increasing the amount of loading the system can handle. Ultra-filters separate the mixed liquor suspended solids (MLSS), providing a high-quality effluent as permeate.
With the MBR, Wayne Farms’ existing SBR tank was converted to a bioreactor. The existing towers are sufficient to maintain the biomass. The wastewater is intercepted after the DAF, keeping the existing screen, limited EQ and DAF in service. De-nitrification and phosphorus removal add to the recyclability of the treated wastewater, which meets and exceeds USDA FSIS requirements for reuse in poultry plants.
Key pluses/minuses of aerobic/anaerobic systems
+ Can achieve very low levels of BOD, NH3 and TN
+ Simultaneous N and P removals possible
+ Minimal odor when properly maintained
+ High-rate options allow for very small footprints
+ Dissolved oxygen in effluent reduces immediate O2 demand on receiving waters
+ Less susceptible to load variations/upsets; quick recovery
+ Best for low-concentration effluents
+ Best option for colder climates/wastewaters
+ Low to medium capital cost
+ Good for all sizes of plants
+ Discharges from aerobic systems are often suitable for beneficial reuses
+ Depending upon the type of aerobic treatment technology, operations can range from very simple to relatively complicated
- Higher energy cost (compared to anaerobic treatment)
- Higher sludge production (compared to anaerobic treatment)
- May require nutrient supplementation
- Maintenance costs associated with blowers/mixers, aeration systems
- Require continuous operations; long shutdowns not suggested.
+ Ideal for heavily loaded systems
+ Produce biogas
+ Very low sludge production
+ Low operating costs
+ Minimal nutrients required
+ Seasonal operations possible
+ Generally low maintenance costs.
- May need to be constantly fed sodium bicarbonate to keep them basic for methane formers
- Highly susceptible to toxic events
- Medium to high operating cost
- Not ideal (economically) for smaller plants
- May need to heat system—an issue in colder climates
- No significant N or P removal
- Low effluent values achieved only with aerobic post-treatment
- May require Class I, Div. 1 buildings for ancillary systems/equipment/buildings
- Higher capital costs (depending upon system/design)
- Effluent needs additional treatment (aerobic) prior to any potential reuse.
- “Water Recovery and Reuse: Guidelines for Safe Application of Water Conservation Methods in Beverage Production and Food Processing,” ILSI Research Foundation, Washington, DC, 2013, www.ilsi.org.
- “US Wastewater Market to Total $11.0 Billion Through 2025,” Bluefield Research, July 2015, www.bluefieldresearch.com.
For more information:
Ariel Lechter, Clean Water Technology Inc., 310-380-4648, www.cleanwatertech.com
Jim Lewis, Complete Water Services, LLC, 678-355-9270, email@example.com