RO System Turns Sugar Wastewater into Saleable Product

N/A East Coast sugar company had problems disposing of sugar wastewater, Minnetonka, MN-based <%=company%> helped them find a cost-effective solution. Working in partnership, Osmonics and the distributor looked at the viability of using membrane technology to concentrate a sugar waste stream into a saleable product.

The sugar company uses insulated stainless steel-lined tanker trucks to transport sugar and corn syrup to its customers. To remove the sugar syrup and combat microbiological growth, each truck is cleaned and sanitized with a hot water rinse after delivery.

Rinse from the truck wash contains 1.5 to 5% sugars, exceeding the biochemical oxygen demand (BOD) level limits by thousands of mg/L and posing a significant waste disposal problem.

Osmonics was asked to design and manufacture a cost-effective system to concentrate the sugar. Heat-intensive technologies, such as spray evaporation, were rejected because of their high operating costs and because extremely high temperatures can cause disaccharide sugars to chemically degrade.

The company needed a system that could:

• Accept a feed stream varying from 2 to 4% HFCS.
• Concentrate the dilute sugar stream to 25% HFCS.
• Withstand operating temperatures as high as 66°C (150°F)

After performing an application test and a large batch pilot run on the truck rinse water, Osmonics' engineers determined that reverse osmosis (RO) could concentrate the rinse into a 25% sugar solution and provide a rinse stream that meets discharge limits. A sugar solution this concentrated could be sold for animal feed, turning what had been a disposal problem into an extra source of income for the sugar company.

RO has been used to concentrate sugars for many years in the fruit, beverage, maple sugar and wet-milling industries. An RO machine works by pumping a pressurized fluid across a special polymer membrane. The membrane separates the fluid into two streams, one rich in dissolved solids (the concentrate) and the other largely free of the dissolved solids (the permeate). In the case of organics such as sugar, the membrane rejects organics related entirely to the size and shape of the organic molecules. An RO membrane typically will reject all of the organics over 200 molecular weight and a percentage of those between 100 and 200 MW.

After a successful on-site pilot test, Osmonics incorporated a high temperature, high pressure RO system into the sugar company's operation. The system is able to process up to 12 gallons per minute (2.7 m3/h) of the rinse water, producing a concentrated sugar solution and recycling purified water to the truck wash. By purifying the water while it is still hot, the recycled rinse water requires minimal reheating. The end result is lower operating costs for the sugar company and a creative source of additional revenue.

Osmonics' RO system concentrates truck wash
to a 25% sugar solution.

Typical Standard Components for Membrane Systems
Cartridge Filter and Housing: 304 or 316 stainless steel housing with Hytrex 5-micron, pure polypropylene depth filter.

Pump: Multi-stage Tonkaflo centrifugal pump, 304 stainless steel construction with Noryl internals; 316 stainless steel construction and 304 stainless steel internals are available.

Motor: Totally enclosed fan cooled design (TEFC); premium efficiency available.

Membrane Element: Patented, turbulent-flow Osmo thin-film, composite-type membranes or cellulose acetate (CA) in 8-inch diameters.

Membrane Housing: Four port, side-entry membrane housings in 304 or 316 stainless steel rated to 600 psi operating pressure. Endcaps are 316 stainless steel.

Skid and Frame: Welded channel steel or I-beam, epoxy-primed with corrosion-resistant phenolic overcoat. Specially welded stainless steel skid and frames are also available.

Low-Pressure Piping: Schedule 80 PVC is standard; 304 and 316 stainless steel are available.

High-Pressure Piping: 304 or 316 stainless steel are standard.

Power Requirements: Three-phase and single-phase power in 50 or 60 Hz.

Electronic Controls: Comprehensive PLC package with optional operator/machine interface. Enclosures are rated for IEC or NEMA standards.

Isolatable alarms:

Low inlet pressure
High temperature
High/low pH
High permeate or concentrate backpressure
High permeate conductivity

Instrumentation:

Pre-filter pressure gauge
Post-filter pressure gauge
Primary pressure gauge
Final pressure gauge
Permeate pressure gauge
Electronic hour-meter
Permeate conductivity monitor
pH monitor
Permeate flow meter
Concentrate flow meter
Thermometer

System Documentation: Instruction manuals and complete sets of drawings needed to support operation and maintenance.

Osmonics manufactures and markets high-technology water purification, fluid filtration, fluid separation, and fluid transfer equipment, as well as the replaceable components used in purification, filtration, and separation equipment.

For more information: Osmonics, 5951 Clearwater Drive, Minnetonka, MN, 55343. Tel: 612-933-2277; Fax: 612-933-0141.

By Pam Ahlberg