HEAVY INDUSTRY PLANT WASTEWATER TREATMENT, RECOVERY AND RECYCLE USING THREE MEMBRANE CONFIGURATIONS IN COMBINATION WITH AEROBIC TREATMENT A CASE STUDY

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1 HEAVY INDUSTRY PLANT WASTEWATER TREATMENT, RECOVERY AND RECYCLE USING THREE MEMBRANE CONFIGURATIONS IN COMBINATION WITH AEROBIC TREATMENT A CASE STUDY ABSTRACT Francis J. Brady Koch Membrane Systems, Inc. 850 Main St. Wilmington, MA In the late 1990 s a major diesel engine manufacturing plant began evaluation of wastewater treatment technologies that would improve the quality of wastewater discharge, would produce treated effluent of reduced oil and grease, BOD and COD load suitable as feed to their sanitary waste biological treatment plant, and eliminate the costs and risks associated with the use of hazardous chemical/physical treatment chemicals used to traditionally treat industrial waste. Several waste management options were examined, including waste reduction via production modification within the plant, pointsource, and end-of-pipe membrane separations technology. This study led to the commissioning of a UF (Ultrafiltration) pilot study using full scale membrane modules with the objective of economically specifying the correct membrane type and configuration to reduce oil and grease, suspended solids, and total solids contaminants. It was found, based on cost, technical, and operating (labor, chemical cost, variability in effluent quality) considerations, that UF met those objectives. The commercial scale membrane system specified was an open-channel tubular UF system. Permeate off the UF contains less than 30 mg/l oil and grease, less than 0.5 mg/l Cu and Zn, and less than 10 mg/l suspended solids. In 2005, with increased water demand in the plant, and pressure from the authorities to reduce water usage, additional membrane systems (UF and RO) were designed and installed as post treatment to the activated sludge process for recovery and recycle of wastewater back into the plant. The UF system is a hollow fiber configuration. The RO design is spiral wound membrane. This paper describes the performance of membrane systems of three configurations. Productivity, filtrate quality, and operating costs on this installation are presented and show that membrane filtration, in combination with biological treatment, is an economically viable and accepted technology for closing the loop and recovering water for reuse in heavy industry facilities. 3256

2 KEYWORDS Membrane Waste Water Treatment, Tubular UF, Hollow Fiber UF, Spiral RO, Activated Sludge, Waste Water Recovery, Waste Water Recycle, Membrane System Design INTRODUCTION The metalworking industry can be a major consumer of water. Water is used for processing, cutting and machining, and for cleaning raw materials and parts used in engine fabrication. Typically the wastewater portion from an engine production process contains: Suspended Solids Settleable Solids Fats, Oil, and Grease Petroleum Hydrocarbons Heavy Metals Biological Oxygen Demand Chemical Oxygen Demand ph swings Microorganisms These constituents of oily wastewater are at levels unacceptable for direct discharge to sewer so they are treated on site, or hauled away for treatment by others. Membrane systems are designed to treat waste to significantly reduce the volume of concentrate that is hauled away from the plant. Ultrafiltration systems produce an effluent that is low in fats, oils, grease, metals, and suspended solids allowing direct discharge to the drain. An ultrafiltration membrane can reduce BOD by up to 90-95%, suspended solids to < 5 mg/l, oil and grease to < 50 mg/l, and true petroleum hydrocarbons to <10 mg/l. Heavy metals, once precipitated by hydroxide precipitation, are typically measured in the 0.5 mg/l range. The permeate from an ultrafilter is sometimes further treated with reverse osmosis membrane if additional reduction in TDS, BOD or COD is required. RO permeate is of such high quality in these cases that often it is saved and reused in the plant rather than wasting it to drain. These membrane systems operate from 7 to 14 days or more without cleaning and can result in as much as 90% of the waste water being converted to water suitable for recycle. 3257

3 Some of the major factors supporting membrane processing of waste include: Lower operating costs A positive barrier between the waste concentrate and the discharged permeate Simple operation Reduced labor Reliability Consistent and high quality effluent Minimal chemical treatment Adaptability to waste variability MEMBRANE CONFIGURATIONS Membrane configurations used in waste treatment include spiral elements, hollow fiber cartridges, and tubular modules. The specification of one configuration over another is driven by its suitability in meeting treatment objectives, and its comparative cost where pretreatment requirements, capital and operating costs are taken into consideration. The choice is often dependent on the type of waste stream, final concentration factor or yield, and final concentrate solids. Hollow Fiber cartridges are thin channel membranes used in high volume applications like municipal potable water processing, and in industrial applications like cooling tower blowdown treatment. Compact by design these configurations carry significant membrane area in a relatively small system footprint. Hollow fibers have diameters ranging from 35 to106 mil and are densely packed in 5, 8 and 10 diameter housings of 43 and 72 lengths. The fibers are spun polymer not requiring a support backing and so can be back flushed during operation to maintain high permeate production at relatively low cross flow rates and energy consumption. Spiral elements allow too for membrane systems that are compact and efficient in design. Spirals are used in many applications from sanitary design food and dairy and seawater desalination to waste water treatment. Spiral elements are flat sheets of membrane rolled around a central permeate collection tube. Spacers between the membrane sheets are used to maintain the thin channel opening. Spirals come in varying lengths and diameters with the larger diameter elements being used on the larger flow applications. Elements are packed into housings of FRP or stainless steel in a spiral membrane system. Tubular membrane modules are open channel designs. Although fluxes are relatively high with the tubular configuration their use cannot be justified on the more dilute process and waste streams. Advantages of tubular membranes include the ability to process streams with significant suspended solids which are then concentrated to very 3258

4 high solids levels repeatedly without plugging. Tubular systems do not require the prefiltration other configurations need. Another advantage of the tubular product is its ability to be mechanically cleaned with spongeballs. Spongeballs are used to remove flux-reducing accumulations from the surface of the membrane, either while processing feed or while cleaning the membrane. MEMBRANE SYSTEM OPERATION Membrane systems are designed in either of two fundamental operating modes, batch or continuous. Batch modes include simple batch and modified batch. Continuous operation can comprise a single membrane system or multiple membrane units staged-in-series. The simple batch mode requires the least membrane area but the largest process tank. The tank is first filled with the entire quantity of feed to be concentrated, then, as feed circulates through the membranes, concentrate flows back into the tank. The feed is concentrated by small amounts with each pass through the membranes, and the overall concentration in the feed tank increases as water is removed by permeation through the membrane. Batch systems are straightforward in operation and design. They are used in wastewater treatment applications mainly on smaller systems processing typically less than 1,000 gpd. Simple batch is also seen in the chemical process industries where batch operation is more commonplace. Modified batch mode offers the advantage of minimal membrane area, but with less process tank volume. As permeate is removed, an equal volume of fresh feed is added to the process tank to keep it topped off. After a predetermined concentration, flux or time is reached, fresh feed is no longer transferred from the feed tank to the process tank, and the remaining fluid in the process tank is further concentrated as batch. When final concentration is reached, the system is shut down and cleaned, while the concentrate in the process tank is disposed of. The process tank is then refilled and processing begins again. Compared to simple batch, modified batch mode allows larger volumes of feed to be processed before disposal of concentrate and system cleaning is required. Modified batch is particularly useful and is usually the preferred mode of operation for industrial applications where maximum concentration is the objective. The single stage continuous operation mode requires the least tankage but requires more membrane area than the other modes. In this mode, the feed tank is always at initial concentration, while the concentrate within the membrane stage is always at final concentration. Because fluxes are generally lower at higher concentrations, this membrane system runs at a lower flux than a batch or modified batch system. Feed rate from the tank is dependent on the permeate rate and the final concentration desired. Flow ratio control is used to adjust the retentate (concentrate) flow out of the system. An advantage of this mode is the short residence time in the system for the fluid being 3259

5 concentrated. This is important when processing liquids susceptible to decay or biological degradation. Continuous systems are specified when equipment up and/or downstream is also continuous. ENGINE PLANT MEMBRANE SYSTEMS SUMMARY Tubular UF System: UF 96 Membrane: FEG HFP 276, MWCO 120,000 Design: 8,000 gpd feed Mode: Modified Batch Hollow Fiber UF System: HF 6 Membrane: HF PM100, MWCO 100,000 Design: 46,000 gpd Mode: Continuous Spiral RO System: RO 2S6 Membrane: TFC 8832 XR 575 Design: 38,000 gpd Mode: Continuous ENGINE PLANT MEMBRANE SYSTEMS PERFORMANCE Performance of a membrane system is measured by repeatable permeate productivity, consistent permeate quality, and cost to operate where membrane system costs include utilities, membrane replacement, labor, cleanings, maintenance, and capital investment. Tubular UF Productivity: Six years now on the original membrane tubes this UF is consistently producing an average 7,937 gpd permeate from 8,000 gpd heavy oil and grease feed resulting in a concentration factor of 127X equivalent to a yield of 99.2% conversion of waste water feed to UF permeate. 8,000 gpd of waste water is reduced to 63 gpd concentrate which is hauled. System operates on a 24 hour per day basis in modified batch with process runs of two weeks duration. Mid-run two hour cleanings with spongeballs are conducted every four days. 3260

6 Permeate Quality: Permeate quality is clear with slight color (coolant dye) at <30 mg/l oil and grease, and <0.5 mg/l Cu and Zn. TSS reported at <10 mg/l. Since UF retains suspended solids, colloids and dissolved solids above 120,000 molecular weight, the UF permeate is less than 2 NTU turbidity. The heavy metals are predictably retained by UF once the metals are hydroxide precipitated via simple ph adjustment with NaOH. Economics: Tubular UF cost is $0.02 per gallon of wastewater treated where costs include UF capital, membrane replacement estimated at 8 years life, labor, cleanings, maintenance, power, and concentrate disposal. The plant has realized significant savings by replacing their chemical based system with ultrafiltration. Savings include reduced labor by a factor of four. Chem/phys sludge production with higher cost of disposal has been eliminated. Also eliminated are the cost and safety concerns associated with the significant use of chemicals by the other technology. Hollow Fiber UF Productivity: Feed to the HF UF is effluent from the activated sludge system treating waste from 2,200 employees including kitchen waste. Since start up the hollow fiber system is treating an average 65,000 gpd feed producing 60,000 gpd permeate. The high productivity is maintained with enhanced back flush during processing and cleanings every 1 to 2 weeks as needed. Currently 38,000 gpd average HF UF permeate goes forward to the RO system. The balance is discharged from the plant. HF concentrate meets discharge limits and is sent to the city sewer. Permeate Quality: Permeate quality is excellent at <0.3 NTU. Economics: HF UF cost is <$0.002 per gallon of wastewater treated where costs include UF capital, membrane replacement estimated at 5 years life, labor, cleanings, maintenance, and power. Spiral RO Productivity: Feed to the RO is HF UF permeate. The RO is producing 19,000 gpd of permeate for recycle back into the plant. RO concentration factor is set at a current 2X with plans to increase permeate rate and yield to recycle more water back into the plant as logistics permit. RO concentrate is discharged from the plant. The RO system is cleaned on a 2 week schedule. Permeate Quality: Permeate quality is excellent reported at <2 mg/l BOD, < 5 mg/l COD and <5 mg/l Total Hardness. 3261

7 Economics: RO cost is <$0.002 per gallon of wastewater treated where costs include capital, membrane replacement estimated at 2 years life, labor, cleanings, maintenance, and power. CONCLUSION Membrane separation technology is proven and reliable. The ease of operation, low operating costs, and consistent and high quality filtrate places membrane technology as a leading waste water process technique in the worldwide effort to improve environmental water quality. Water demand is increasing. Water availability is becoming limited. Although regulations and supply vary between areas and countries, overall the need for advanced waste treatment methods to reduce water consumption and preserve the environment has become apparent. Cross flow membrane processes such as Ultrafiltration and Reverse Osmosis are providing cost-effective methods to treat wastes and recover water. Membrane technology within the plant and at the end of pipe to treat effluent for recycle is a reality. This technology was recognized by the decision makers at this progressive engine plant. Their goal to recycle 50% of the total wastewater leaving the facility will soon be achieved. 3262