At one time, a heavy rainstorm could shut us down for a week or two,” says Phil Quigley, wastewater manager with the Bell-Carter Olive Co., the world’s largest ripe black olive cannery. Although rain seldom falls during the summer in Corning, CA, home of this state-of-the-art olive processing facility, Quigley says that the winter months can bring a deluge of rain that would sometimes fill the plant’s wastewater lagoons and leave little or no capacity for treating wastewater from the plant.
Moreover, cooler winter temperatures slow the reduction of organic pollutants in the lagoons, requiring longer detention times for wastewater to achieve the permitted levels of biological oxygen demand (BOD) and total suspended solids (TSS) in the effluent. BOD and TSS are strictly regulated by the US Environmental Protection Agency and are of most concern for food processors, since effluent can contain high levels of organic waste. For example, at Bell-Carter Olive, TSS can rise as high as 6,000 mg/L. If untreated, high levels of organic pollutants can have severely harmful effects on aquatic ecosystems—depleting dissolved oxygen, raising water temperature, reducing growth rates, and even causing death in fish and other aquatic life.
“We added dissolved air flotation (DAF) to our process to help us reduce TSS to an acceptable level and shorten detention times, but we still couldn’t avoid occasional shutdowns. The DAF coagulants also significantly increased our operating costs,” Quigley says. “What we needed was an advanced membrane system that could provide tertiary filtration of treated effluent—this would accelerate the treatment process, improve effluent quality, and also significantly reduce our operating costs.”
Membrane Systems Put to the Test
Working with Carollo Engineers, of Phoenix, AZ, Bell-Carter Olive invited several membrane manufacturers to pilot test systems at the plant. Conducted during the winter, when the plant faces the most difficulty in treating its wastewater, the study evaluated flat-sheet, pressurized, and immersed hollow-fiber membrane systems. At the conclusion, the team selected a ZeeWeed packaged plant with reinforced hollow fiber membranes, manufactured by Zenon Membrane Solutions, now part of GE Water & Process Technologies.
“We were most impressed with the outside-in, low-pressure operation and performance of ZeeWeed ultrafiltration membranes, and the dramatic reduction in operating costs that the system would bring,” Quigley says. “ZeeWeed provided the best performance under tough conditions, the simplest operation, and did not foul as quickly as the other membrane systems. The effluent from the ultrafiltration system exceeds the parameters of our discharge permit which means we’re in a very good position to continue meeting any future discharge requirements.”
Difficult-To-Treat Wastewater
Olives are harvested only once per year, although olive processing and canning is a year-round operation. Ripe olives awaiting processing are stored in large vats at the 50-acre plant and are preserved in a brine that contains acetic acid, salt, sodium benzoate, and calcium chloride. Black olives also have ferrous gluconate added to the brine to preserve their color. Once the olives are sent for processing, the brine must be disposed of, accounting for the majority of wastewater from the plant. Organic matter produced during processing, largely olive pieces, is also a large component of the wastewater.
Bell-Carter Olive’s original wastewater treatment process consisted of seven ponds: three extended aeration ponds, two polishing-sedimentation ponds, and two storage-clarification ponds. The process was effective in the warmer summer temperatures, reducing BOD by as much as 99.5% in the aeration ponds; however, ammonia was often very high in the sedimentation and clarification ponds. Conversely, cooler winter temperatures resulted in lower ammonia levels; but BOD was higher in the aeration ponds, since the biological breakdown of the organic matter was not as efficient in the lower winter temperatures. The new tertiary filtration system would physically remove suspended solids from the wastewater, resulting in shorter detention time in the ponds and virtually eliminated TSS in the effluent.
Innovative Process Integration
“We decided to implement our tertiary filtration system in two phases, over two years,” Quigley says. “This would help the company spread the capital costs over a longer period of time and also give us time to fine-tune the entire process and ensure we could get the results we wanted in a full-scale system.”
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| Ultrafiltration provides solids separation by filtration rather than settling, so large sedimentation or clarification tanks are not essential for the process. |
The first 10 ZeeWeed cassettes, along with tanks and control equipment, were shipped to Bell-Carter Olive in September 2001. “Our entire system arrived on just three trucks,” Quigley says. “All the equipment for the two-train system—including tanks, controls, and chemical addition systems—was installed on a concrete pad that’s only 30 feet wide and 100 feet long.”
Five membrane cassettes were installed in each train of the two-train system. Ten more cassettes were shipped the following year and installed in September 2002. Since the tanks were already sized to accommodate the membranes, the cassettes were quickly installed and put into service.
“The modularity of the system is a real asset to us,” Quigley says. “The components were quickly and cost-effectively installed and we can easily increase our treatment capacity as our company continues to grow.”
Because of the seasonal variability in BOD reduction and ammonia concentrations, the ZeeWeed system was designed to draw wastewater from each treatment step in the ponds. In the winter BOD is high in the first three ponds, typically ranging between 100 to 150 mg/L, but low in the remaining ponds, so the membranes draw the wastewater feed from Pond 4, 5, 6, or 7. In the summer, when BOD is low in the first three aeration ponds, but ammonia is high in the others, the membrane system draws from Pond 2 or 3. By drawing wastewater from different ponds at different times of the year, Quigley says he can effectively reduce soluble BOD and ammonia from the wastewater prior to filtration.
Wastewater drawn from the ponds is pumped directly into one of two stainless steel membrane tanks. A flow-control valve regulates the amount of wastewater to each train, enabling either tank to be isolated for cleaning or maintenance. ZeeWeed membrane cassettes are immersed directly into the filtration tank. Hollow-fiber membranes are very thin, flexible strands of porous plastic fibers with billions of microscopic pores that form a physical barrier to suspended solids and colloidal material in the wastewater. Thousands of such fibers are loosely suspended in each cassette, and a slight suction is applied to the end of each fiber to create a vacuum that draws clean water inside while blocking contaminants on the outside.
Filtered water is collected in a central permeate header and flows directly into the Sacramento River without any additional treatment.
Ultrafiltration provides solids separation by filtration rather than settling, so large sedimentation or clarification tanks are not essential for the process. This makes the tertiary system inherently resistant to variations in water quality and can produce high quality effluent at all times, regardless of the settling characteristics of the particles in the wastewater.
Fully Automated Operation, Cleaning, and Monitoring
The highly automated operation of the ZeeWeed system has enabled Bell-Carter Olive to increase its wastewater treatment capacity by nearly 50% without adding operating staff. Permeation, membrane cleaning, and monitoring of membrane permeability and effluent quality are all computer controlled. A full-time operator maintains both wastewater systems at the plant, but, according to Quigley, only spends an average of 10 hours per week performing maintenance and documenting performance parameters on the ZeeWeed system.
A turbidity meter continuously monitors the clarity of the treated water from both trains, ensuring that only the highest quality effluent is discharged to the river. Should turbidity levels rise beyond a predetermined level, an alarm notifies the operator of the condition.
“We love the ability to have remote access to the system,” Quigley says. “Either our operator or someone from the Zenon Services group can connect to the system by modem and check or adjust system parameters.”
Membrane permeability is also continuously monitored, and while coarse bubble aeration is an ongoing way to scour debris from the surface of the fibers, a comprehensive range of clean-in-place procedures can be invoked to maintain optimum membrane permeability.
Membrane fibers can be automatically cleaned with a clean-in-place backpulsing process that forces permeate water back through the membranes. This dislodges any particles that may adhere to the membranes. When necessary, chemical cleaning can also be performed to restore permeability. The flexible two-train system gives Bell-Carter Olive the ability to schedule cleaning during periods of low demand, when one train can be offline, while the other continues operating.
Cost Savings
Bell-Carter Olive has nearly doubled its olive production since the ZeeWeed tertiary filtration system was added to its wastewater treatment system in 2001. Today, the facility discharges about 1.1 million gallons of treated effluent per day directly to the Sacramento River.
Although the membrane system is sized to treat 800,000 gallons per day, the effluent it produces is of such high quality that Bell-Carter Olive can blend the membrane effluent with effluent from the clarification ponds without worrying about exceeding the limits of its National Pollution Discharge and Elimination System (NPDES) permit.
“Under our old permit, we could only discharge 750,000 gallons of effluent per day,” Quigley says. “However, only 400,000 gallons were permitted to enter the Sacramento River, and the remaining 350,000 gallons had to be sent to the municipal sewer at a cost of about $250,000 per year.”
With today’s production levels, Quigley estimates that the disposal cost could have easily doubled to $500,000 annually if the facility was still required to discharge effluent to the municipal sewer.
“Our DAF system would also cost us about $250,000 per year to operate,” Quigley notes. “The elimination of that system, combined with no longer using the municipal sewer and paying associated fees has resulted in about $750,000 in annual savings and cost avoidance. We estimate that these savings could pay for the system in just four years.”
Regulations And Responsibility
Water is a primary ingredient for food processors; used for washing, preserving, and processing raw product as well as for cleaning and sanitizing equipment. Many food processors discharge wastewater to municipal or publicly owned treatment plants; however, the large volume, and high variability of the wastewater makes it difficult to treat for municipal systems, which often results in high surcharges for producers. In other cases, food producers must provide some type of onsite pretreatment of wastewater prior to discharging it to the municipal system.
Strengthening of the Clean Water Act and continued progress in establishing Total Maximum Daily Loads (TMDLs) for receiving bodies is making it more challenging for food producers with onsite systems to consistently meet the discharge requirements of their NPDES permits.
Rising costs, increasing regulatory pressure, and a desire to conserve water resources while protecting the environment are compelling many companies in the food industry to examine advanced wastewater treatment technologies.
Membrane packaged plants for tertiary ultrafiltration provide a rapid and cost-effective method to improve effluent quality from aging or underperforming wastewater treatment plants.
Membrane bioreactors are also an ideal method for greenfield or retrofit applications, providing a compact and highly efficient treatment process that combines ultrafiltration membranes with activated sludge processes into a single step—eliminating the need for large sedimentation and clarification tanks. In either case, these advanced technologies not only help a business to comply with effluent discharge regulations, but produce water of such high quality that it can be safely reused for nonpotable applications—a solution that holds appeal for environmentalists and business leaders alike.
Lawrence Novachis is vice president of industrial systems with Zenon Membrane Solutions.
OW - September/October 2006 |
