Kirill Ukhanov, GE Water & Process Technologies, Russia, describes how advanced membrane technology is helping a Russian refinery to meet stringent wastewater requirements.
In Russia, there are strict wastewater regulations to protect water supplies and encourage water reuse. Table 1 details the maximum allowed contaminants for wastewater effluent in Russia. If requirements are not met, water users must pay significant fees, or might be asked to suspend production for non-compliant wastewater discharge. That means that water users must treat their wastewater to comply with discharge limits, avoid penalties and minimise the environmental impact. Meeting these requirements is especially difficult in the refining and petrochemical industries, as the processes used in a refinery or petrochemical plant contaminate the water with pollutants such as recalcitrant chemical oxygen demand (COD, toxicity and phenols. This water cannot be discharged into the environment without treatment. It also cannot be reused within the plant itself because it contains impurities, making it unsuitable for plant process water. There are conventional treatment technologies that help refineries and petrochemical industries to remove contaminants. As regulations get stricter, as they are in Russia, conventional technologies do not fully meet the new regulations, and require refiners to pay disposal fees. To help, GE developed a membrane bioreactor (MBR with MACarrier, which was specifically designed to treat difficult refinery
wastewaters and to produce treated effluent that meets the toughest standards, and/or can be reused at the plant. Wastewater treatment technology MBR with MACarrier technology combines three major technology components: Table 1. Russian wastewater effluent requirements Contaminant Value COD 30* (mg/l BOD 5 4* (mg/l TSS 10 (mg/l N-NH 4 0.5 (mg/l NO 3 -N 40 (mg/l NO 2 -N 0.08 (mg/l PO 4 -P 0.2 (mg/l Oil products 0.05 (mg/l Phenols 0.001 (mg/l Sulfide 0.01 (mg/l *For recreational ponds Figure 1. MBR with MACarrier process flow diagram. n MACarrier (membrane accommodating carrier: enhances the removal of COD, toxicity, phenols and other contaminates found in wastewater. n Bioreactor: provides stable biological wastewater treatment to remove suspended colloidal solids, reduce organic content and reduce concentrations of nutrients such as nitrogen and phosphorus. n Membrane filtration: delivers a physical membrane barrier as a final step to remove microorganisms found in wastewater and provide high quality effluent. Figure 1 shows the MBR with the MACarrier process, where the MACarrier is dosed into the bioreactor. The MACarrier works through adsorption and biodegradation. By adding MACarrier into the mixed liquor, it removes recalcitrant COD and toxicity. The MACarrier provides sites for adsorption of recalcitrant COD and toxic compounds, as well as attachment of biomass. The biomass degrades the adsorbed COD and then regenerates the MACarrier. At the heart of the MBR with MACarrier lies the membrane bioreactor technology. The main objective of biological treatment is to remove or reduce the pollutants concentration in the wastewater. Microorganisms can be used to accomplish these objectives in a relatively cheap way. The microorganisms convert the colloidal and dissolved pollutants into biomass, which are removed by membrane filtration. The main purpose of the membranes is to retain the solids produced by the microorganisms from pollutants. The MBR with MACarrier uses ZeeWeed membranes, which produce high quality effluent. The ultrafiltration technology provides high solids tolerance and can operate with <1.0 mg/l TSS to 50 000+ mg/l MLSS (sludge thickening. In fact, a single ZeeWeed fibre can hold over 50 kg without breaking. The outside in filtering facilitates cleaning and maintenance of the membrane, creating a continuous flow of large bubbles rising vertically along the entire length of the membrane and removing solids from the surface. Periodically, the permeate flow automatically changes the direction of backwash of the membranes from the particles accumulated in the membrane pores. Figure 2. Results for COD reduction using MBR with MACarrier. Case study: Russian refinery One of Russia s vertically integrated oil companies operates a refinery in REPRINTED FROM July 2016 HYDROCARBON
Table 2. Wastewater characteristics and treatment objectives Parameter/ion form Units Raw feed water quality Guaranteed well discharge water quality Guaranteed river discharge quality Calcium mg/l 108.0 Magnesium mg/l 20.4 Sodium mg/l 394.0 Potassium mg/l 5.0 NH 4 mg/l 40 (as N-NH 4 0.5 (as NH 4 Barium mg/l 0.01 Strontium mg/l 0.8 Iron mg/l 0.4 0.099 (as Fe Manganese/Mn 2+ mg/l 0.2 0.01 (as Mn 2 Sulfates mg/l 250 100 (as SO 4 Chlorides mg/l 300 273.9 (as Cl Fluorides mg/l 1.0 Nitrate, as NO 3 mg/l 25 40 Bromides mg/l 0.000 Phosphate, as PO 4 mg/l 0.2 0.13 Boron mg/l 0.000 Silicon dioxide (SiO 2 mg/l 10.2 Hydrogen sulfide mg/l 5.0 Bicarbonate (HCO 3- mg/l 183.0 Dry residue (TDS mg/l 1.250 20.500 1.000 ph ph units 6.5-9.5 6.0-8.5 6.5-8.5 COD mg/l 450.0 30.00 BOD total mg/l 135.0 (BOD 5 3.00 Non-ionic or mg/l 2.0 0.35 non-/anionic surfactants Phenols mg/l 7.0 0.001 Oil products mg/l 25.0 0.05 Ether-extractable mg/l 6.7 compounds Anionic surfactants mg/l 2.0 0.396 TSS mg/l 50.0 6.40 Copper mg/l 0.025 0.001 (as Cu Aluminium mg/l 0.250 0.04 (as Al Cobalt mg/l 0.010 0 (as Co Nickel mg/l 0.025 0.01 (as Ni Chromium ion, (Cr 6+ mg/l 0.007 0.006 (as Cr 6 Zinc mg/l 0.100 0.01 Vanadium mg/l 0.025 0.001 (as V Nitrites, as NO 2 mg/l 8.0 0.08 Sulfides mg/l 10.0 0 (is calculated as S Alkalinity mg-eq/l 3.0 Note: zero value targets for sulfides and cobalt are assumed to reference the lower detection limit. southwest Russia. The refinery wastewater treatment plant could not meet the strict discharge regulations and did not allow for sufficient water reuse. The development of a new wastewater treatment plant would require a comprehensive solution to address all of the plant s needs. The system needed to handle a combined refinery effluent of 84 000 m 3 /d (84 million l/d, and achieve a very low COD level less than 30 mg/l, and less than 0.001 mg/l of phenols. Additionally, there are limitations on concentrate disposal to the well; the agreed upon amount of total dissolved solids (TDS for well discharge could not be exceeded. Table 2 shows the refinery wastewater quality characteristics and treatment objectives. The refinery also needed to reuse as much treated wastewater as possible, because it would provide savings through lower river discharge payments and lower raw water consumption fees. It is anticipated that, depending on internal water use and the season, there could be periods with zero liquid discharge to the river. If the refinery did not seek a complete solution, it would face significant financial penalties for non-compliance with consumption and discharge requirements. Pilot study The refinery partnered with GE to complete a two year pilot study of GE s MBR with MACarrier technology to address the challenges. The MBR with MACarrier was trialled on 100% high COD wastewater, which mainly came from the refinery s desalting process. The average COD was around 700 mg/l, and the system was tested up to 2100 mg/l through shock-loading the system. Figure 2 shows the MBR with MACarrier, which achieved the 30 mg/l requirement for COD, despite feed COD ranging from approximately 300 mg/l to well over 2000 mg/l. The pilot also tested the MBR with MACarrier under various upset or shock-loading conditions (high COD/NH 3 -N/O&G and demonstrated much faster system recovery than without the MACarrier. The ZeeWeed membranes were also found to be highly compatible with the MACarrier, with no abrasion or damage found. Additionally, there was no clogging or HYDROCARBON REPRINTED FROM July 2016
Figure 3. A process flow diagram of the refinery s wastewater treatment plant. membrane fouling due to the use of the MACarrier during the entire testing period. Refinery wastewater treatment Based on the pilot study results, the refinery has installed a full scale MBR with MACarrier and has worked further with GE to expand the water treatment system to include additional technologies, which help the facility meet its goals for water reuse. The new MBR with MACarrier biological treatment plant includes 144 ZeeWeed 500D cassettes in 12 membrane trains. Designed to handle tough to treat water sources, the ZeeWeed 500D membranes offer one of the most robust hollow fibre membranes on the market. Used for water and wastewater applications around the world, the ZeeWeed 500D membranes help meet strict water quality requirements and allow for greater water reuse. In addition to the MBR with MACarrier, the refinery installed electrodialysis reversal (EDR systems. This is an important part of the new plant in order for it to reach its water reuse goals. Because of the polarity reversal design, EDR is a self-cleaning, durable membrane system ideal for turbid wastewater. EDR technology achieves a high water recovery of up to 94%. It also provides up to 95% TDS reduction on the water from the MBR with MACarrier. In this application, permeate from the reverse osmosis (RO system is fed back to the EDR to further increase water recovery. Following the EDR, GE supplied its PRO Series RO system, equipped with an integral concentrate recovery (ICR system and ion exchange (IX filters. The ICR will save 30-50% of the RO concentrate water. This makes the RO system operate at around 85-90% overall recovery, and greatly improves the water efficiency. The combination of the RO and ICR helps the refinery to reuse as much of the water as possible. The IX system polishes the EDR dilute by removing heavy metals using selective resins. This helps the refinery meet all of the regulations for wastewater discharge to well disposal. From the MBR with MACarrier to the IX system, the technologies work together to ensure the highest possible recovery to meet discharge well quantity and quality regulations, and the refinery is able to re-use the treated wastewater onsite. The maximum flow to discharge wells is approximately 2200 m 3 /d and the maximum river discharge flow is 36 000 m 3 /d. Wastewater treatment process flow Figure 3 shows the process flow of the refinery s wastewater treatment. All the wastewater streams enter the MBR with MACarrier after mixing and fine screening. With a capacity of 84 000 m 3 /d (84 million l/d, the MBR with MACarrier permeate is partially treated in nine EDR systems (eight plus one redundant; its concentrate is further treated in the RO units (two plus two redundant with the integral concentrate recovery system to ensure the highest possible recovery. The EDR dilute is compliant to river discharge on all the parameters, but a few heavy metals are polished with the IX filters filled with ion-selective resins. The IX regeneration flow blends with RO concentrate before discharge to the wells, and IX rinse water is recycled back to the MBR inlet. The system is designed to be flexible, easily adjusting to the refinery s operational requirements. The system is configured to reuse the maximum amount of treated wastewater, and represents a mix of MBR permeate and EDR dilute streams in a variety of ratios, not to exceed flow and TDS discharge to well limits. For the discharge to river stream, the system performs a final polish in the IX stage before discharge to ensure 100% compliance to regulations. Conclusion At the start of the MBR with MACarrier pilot project with GE, the refinery had specific goals to meet the stringent wastewater treatment requirements in Russia. Water reuse was also an important goal for the refinery to reduce potential costs. By the end of the pilot, and the subsequent completed installation of the full wastewater treatment system, the refinery has been able to: n Avoid penalties for water discharge. n Decrease payments for water consumption. n Minimise payments for well discharge of concentrate. n Reuse up to 97.3% of the wastewater in certain conditions. Using a technology provider such as GE offered an added benefit to the refinery. The project was simplified as it could work with a single source for the wide range of technologies that were needed to meet the facility s wastewater treatment and water reuse goals. REPRINTED FROM July 2016 HYDROCARBON