Anti-fouling membrane system for industrial wastewater treatment and recovery

Transcription

1 IWC Anti-fouling membrane system for industrial wastewater treatment and recovery Joon H. Min (1), Daeik Kim (1), Young J. Eum (1), Gi T. Park (2), Sang W. Kim (2), Jang K. Kim (3), and Dae H. Rhu (3) (1) BKT United, 1225 N. Patt St. Anaheim, CA, 92801, USA (2) FMC Tamnip-Dong, Yuseong-Gu, Daejon, Korea, (3) BKT Korea, Korea Bldg. 6F, Yeoksam-Dong, Gangnam-Gu, Seoul, Korea, Keywords: Anti-fouling membrane system, vortex, anaerobic digester effluent, brewery process water, methylcellulose, material recovery, high TS (total solids).

2 IWC ABSTRACT One of the main challenges of implementing membrane technology for the industrial wastewater is fouling. An anti-fouling membrane system was developed to address these issues. This membrane system has been in full-scale operation for anaerobic digester effluent for biogas plant, methylcellulose treatment, and livestock waste treatment. The technology has also been tested in dozens of industrial and commercial sites including used motor oil waste treatment, nano silver recovery, beer fermentation process recovery, landfill leachate treatment, food waste treatment, latex manufacturing wastewater treatment, algae biomass harvesting for biogas production, wine stillage waste, or any application where conventional membranes cannot be used. This anti-fouling mechanism is based on vortex generated with uniquely designed blade between flat membrane surfaces. This system can use any membrane material including MF (micro filtration), UF (ultra filtration), or NF (nano filtration) from various suppliers. In 2004, development of a reliable anti-fouling membrane system carried out for methylcellulose wastewater from Samsung Fine Chemicals (SFC) manufacturing facility, where previous treatment systems failed due to high viscosity and high solids loading in feedwater. However, methylcellulose was recovered through this anti-fouling system. In 2009, 3 full-scale units were also installed in Netherlands to treat anaerobic digester effluent at a biogas plant owned by Mosch Thermische Installaties (MTI), where anti-fouling membrane system improved the biogas generation rate by 30% and increased stability of digester operation. Brewery process water was treated with anti-fouling membrane system to concentrate this water approximately up to 15% to sell it as an animal feedstock. These case studies and background on the anti-fouling membrane system is presented in this article.

3 INTRODUCTION FMX is a type of anti-fouling membrane technology, which is highly suitable for niche applications such as high solid, high viscous, and high turbid water treatment. In most membrane configurations, fixed boundary layers reduce performance measured as flux over time. Fouling, also known as a concentration polarization, is the major drawback associated with membrane filtration technology. As a membrane dewaters sample water, particle buildup on the membrane interface increases resistance, thereby decreasing filtration performance. Conventional membrane systems have this limited applicability and performance due to fouling and the associated maintenance cost of frequent membrane replacement and chemical usage. On the contrary, anti-fouling membrane system overcomes these hurdles using fouling prevention mechanical system and brings a revolutionary intention to beneficially alter the membrane industry. The key to understanding where anti-fouling membrane system excels is to investigate the limitations of conventional systems. Spiral wound and tubular systems are generally limited to concentrating a given sample 10 times (90% water removed) the original particle density before requiring maintenance (i.e. frequent CIP, backwashes), limiting their ability to tackle viscous (>1000 cps), or high solid (1-8% TS) water. each membrane tray (approx. 11 ft 2 /tray), is sandwiched by engineered composite plastic vortex generation blades. The blades generate Kármán vortices at the interface, without coming in contact with the membranes. Full-scale units are modular, with 20 membranes per stack (approximately 20 m 2, 215 ft 2 ) with fully built systems comprised of 10 stacks and surface area of 95 m 2 (1020 ft 2 ). Anti-fouling membrane system employs mechanical fouling prevention that allows the installed membranes to reach concentrations approximately 20 times the original amount, while significantly reducing the required frequency of cleaning procedures. Figure 1 shows a fully-assembled industrial model. Attached to the frame are the membrane module and drive motor. A drive belt connects the motor to a drive-shaft that runs the length (height) of the module. Feed water enters through the bottom of membrane module and moves up through each segment of membrane trays to the top of the module. The feed water becomes more concentrated as it moves through each segment, and finally exits from the top of the module. Permeate (or filtrate) water passes through membrane, moves laterally along stainless plates which secure the membranes in place. The filtrate moves down the inside wall of the membrane module and is collected in a single pipe. Among strong points of anti-fouling membrane system, it can have a variety of applications using different types of membrane selections such as MF (micro filtration), UF (ultra filtration), or NF (nano filtration) from many suppliers. CASE STUDY 1: MATERIAL RECOVERY Figure 1. Anti-fouling membrane system structure and membrane stacks. (Vortices prevent the buildup of suspended solids in an otherwise stagnant boundary layer). The two components that make the anti-fouling module unique are the membrane trays and the vortex generators. As illustrated in Figure 1, In 2004, a reliable anti-fouling membrane system was developed to treat and recover methylcellulose from wastewater of Samsung Fine Chemicals (SFC) manufacturing facility, where previous membrane treatment systems have failed. The vortex-generating system efficiently prevented membrane fouling in high viscosity and high solids loading in the feed waster. SFC now operates 6 full-scale antifouling systems and 2 additional units will be installed this year (Figure 2). The membranes installed in the first anti-fouling unit at SFC lasted for 5 years without being replaced.

4 Flow(m3/hr) & Pressure(kg/cm2) IWC As shown in Figure 3, for the two weeks of operating duration, the flux through anti-fouling system was identified very stable Time (day) pressure permeate Figure 3. Flux data for 2-month operation of anti-fouling system in Samsung Fine Chemicals facility. CASE STUDY 2: ANAEROBIC DIGESTER WASTEWATER TREATMENT Figure 2. Full-scale installations in Samsung Fine Chemicals (SFC). In Table 1, the operating data are summarized. In terms of flux, anti-fouling membrane system had selectively high a throughput, while the previous systems that were installed had severe fouling problems. Replaced unit was vibratingtype membrane system. In 2009, 3 full-scale units were also installed in Netherlands to treat anaerobic digester effluent at a biogas plant (6 Mega Watts) owned by Mosch Thermische Installaties (MTI), where anti-fouling membrane system improved the biogas generation rate by 30% and increased stability of digester operation, in Figure 4. Table 1. Operating data summary Items Membrane Content UF 5,000 MWCO Flux LMH (19-22 gfd) Pressure 5-7 kg/cm 2 ( psi) Recovery 65% Permeate flow m 3 /hr (19,032 22,200 gpd) Figure 4. Full-scale installations of antifouling membrane systems in Netherlands.

5 1. DIFFICULT EFFLUENT TREATMENT Even though biogas plants have merits that appeal to the public and policy makers, there are still several key issues to address that will make it more feasible and attractive. Anaerobic digestion converts solid-form carbon into methane and carbon dioxide via complex metabolic processes. The resulting effluent has high concentration of ammonia, relative to organic carbon, rendering common biological nitrogen removal process impossible. Membrane filtration is the only alternative for treating anaerobic digestate. 2. UNEXPECTED BOTTLE-NECK: MEMBRANE TREATMENT Although many articles and academic theses have dealt with digestate treatment using membranes, it is hard to find a stable-operating biogas plant that uses ultrafiltration (UF) membranes as a treatment Method. The difficulty arises from a high solid content in the digestate, which is known to contribute significantly to fouling. Although fats, oils, and grease (FOG) offer enhanced biogas production from the digester, the elevated water viscosity serves to further inhibit the filtration process. Conventional membranes face frequent fouling problems, which jeopardize the economics of the biogas production process due to disposal issues related to untreated digestate. In Figure 5, comparing anti-fouling membrane system with other membranes, anti-fouling system has more permeate flow with less fouling. Figure 5. Comparison of anti-fouling and conventional membranes. 3. ANTI-FOULING MEMBRANE SOLUTION Anti-fouling membrane filtration system was with proven installations demonstrating its ability to tackle high density, high solid, and high-viscosity application. Almost 2 years ago, three antifouling membrane filtration systems were installed for a biogas plant in the Netherlands and those are now operating in a stable state. The effluent here has a total solids concentration of more than 8.0% in the digestate, and approximately % after pre-filtration (screw press and drum screen). Further, the stream also contains a significant amount of glycerin and excess polymer from the prefiltration. This anti-fouling system has been able to treat this effluent successfully without succumbing to fouling. There are critical functions of both permeate and concentrate from anti-fouling membrane system for the operation of biogas plant. For the case of permeate, this provides solid free feed to either RO or ammonia stripping tower as a necessary pretreatment step. The concentrate, on the other hand, makes it possible to increase biogas productivity and provide stable operation of biogas plant by returning the microorganism to the anaerobic digester and minimizing ammonia inhibition. There are a number of membrane applications for anaerobic digester using UASB (Upflow Anaerobic Sludge Blanket), which requires removal of solid prior to digestion. However, in the case of CSTR (Continuous Stirred Tank Reactor) type anaerobic digester, it is rare to find full-scale membrane applications due to significant fouling issues with high solids in the digestate stream. Therefore, biogas production increase was computer-assisted modeled using full-scale data from the Netherlands installation. Many articles suggest increase in biogas production in lab-scale, but this was the first of its kind thermophilic anaerobic digestion modeling using full-scale data (Kang, 2011). 4. PROCESS FLOW DIAGRAM Figure 6 describes the flow directions in antifouling membrane system with regards to anaerobic digester system. The key point of this process is to return the concentrate from antifouling system to anaerobic digester, which resulted in higher gas production and more stable digester operation (Kim, 2011).

6 values (Chen, 2008), 20-30% higher gas production can be as equivalent as 40-50% improvement. In Table 2, the operating data were summarized. Figure 6. The process flow diagram of antifouling system for anaerobic digester. 5. SITE DATA 5.1 Stable digester operation In Figure 7, with anti-fouling membrane system, the gas production (red dot) was higher, compared to the one without it (blue dot). In addition, anti-fouling system has better stability of operation than the one without it. Anti-fouling (red dot) has a linear relation between gas production and operating day, while one without it (blue dot) has a fluctuating line. The flux through anti-fouling system was identified quite stable. Figure 8. Higher gas production of antifouling membrane system. Table 2. Operating data summary for Netherlands installation Items Content Membrane UF 150k MWCO Flux LMH (12-14 gfd) Pressure 5-6 kg/cm 2 (71-85 psi) Recovery 80% Permeate flow m3/hr (9,504-11,424 gpd) CASE STUDY 3: MEMBRANE CONCENTRATION Figure 7. The comparison of gas production of with and w/o anti-fouling system. 5.2 Increased biogas production In Figure 8, as COD loading increases, the gas production was compared. Anti-fouling system resulted in 20-30% higher gas production than one without it. The concentrate from anti-fouling system contains microorganism consortia and high contents of carbon sources, which leads to the higher gas production and stable digester operation. For considering most of digesters have lower gas production than their designed A demonstration test was conducted to concentrate the solid content of the grain wash from a brewery to use the concentrated stream as an animal feedstock. The permeate quality was not important in this application since there is a wastewater treatment plant handling this flow. The concentrate from anti-fouling membrane system will be the product for this case, which will be sold as animal feedstocks at a 15-20% solids level. 1. RAW WATER QUALITY The water stream is from the process of washing the grains used for brewing. This process water is sent to a screw press to remove as much

7 water as possible before it is transferred to trucks and hauled away for disposal. The water from the screw press is the waste stream to be treated. Raw water quality is summarized in Table 3. Table 3. Raw Water Quality Parameter Unit Value Application - ph Total Solids (TS) % 4 Electrical Conductivity ms 1400 Beer brewery process wastewater 2. CONDITIONS The temperature of the feed water is approximately ºC ( ºF). It was hard to get the feed temperature this high due to limitations in the pilot setup, but what was observed was the flux and temperature correlations. The higher the feed temperature, the higher the flux on the permeate line. This is beneficial to the process since the feed temperature is approximately 2 times higher than tested in lab. The anti-fouling system can take feed water up to 95 ºC (203 ºF). In Table 4, operating parameters are summarized. Table 4. Operating parameters Parameter Unit Value Temperature Flux normalization temperature Optimum operating pressure Membrane surface area [Pilot] ºC ( ºF) (86-119) ºC ( ºF) 70 (158) kg/cm 2 (psi) m 2 (ft 2 ) 5 (71) 0.09 (0.97) Feed water was concentrated in a batch mode for 4 h, reaching a 13% solid content. After this was completed, a hot water flush of the system took place for 10 min. After confirming the flux restore on the membrane, an additional batch of feed was processed through the anti-fouling membrane system to check for fouling problems. The procedure was stable and reproducible, and the final solids of the second batch were measured to be 12.80% as solid content. This proved the hot water flush worked to remove foulants that had build-up on the membrane surface and could be used as a primary cleaning method for the anti-fouling membrane system. Achieving a specified recovery rate is often the primary objective of any in house pilot test. Due to the nature of the equipment (i.e. surface area limitations), the only way to reach the recovery goal is to operate in a batch mode, where permeate is continually removed while the concentrated material is returned to the feed tank for additional dewatering, as seen in Figure 9. Permeate Collection FMX Concentrate Bypass Figure 9. Process flow diagram of a concentration study (Permeate is continuously removed causing the filtration to become more difficult as feed concentration increases). The concentration study immediately follows the test after trans-membrane pressure stabilizes and the membrane has equilibrated with the sample. Contrary to the initial test, the concentration test proceeds (generally uninterrupted) until the desired recovery rate is reached, or until the flux becomes prohibitively low. The concentration study relates flux to sample concentration (or recovery) and temperature. The data acquired over the duration of a concentration is used to determine the average flux over the recovery spectrum, V1 V2 Q

8 which in turn allows for preliminary system sizing. Figure 10. Recovery spectrum of wastewater using UF membrane with initial TS, 4.1%. At point A, the total solids were approximately 10%. Filtration was conducted at 5 kg/cm 2 (71 psi). Plotted in Figure 10 are flux, temperature, and recovery (% water, removed). As indicated previously, flux is a standardized measure of permeate flow rate (LMH). Temperature was maintained using a stainless steel heat exchanger to simulate the plant condition. Flux stability resulted in a near linear recovery rate, ideal for system integrations. The selected membrane recovered 77.2% of the water from the original process water. That is from the initial value of 4.1%, the total solid of the final concentrated material was 13%. The test was continuously operated, as the temperature increased, so did the flux. Once the temperature was decreasing, the flux began to decrease and stabilize. This could also be contributed to the increase of solid content as shown in point A, where the concentrate of solids approximately reached 10%. The machine was operated using clean water at 50 o C (122 ºF) until the concentrate stream was clean. When operation resumed after hot water flushing, fresh wastewater was added into the feed tank again to test reproducibility of the membrane after CIP (cleaning in place). The hot water flush had provided sufficient cleaning for subsequent test. Figure 11. Permeate & Feed (up), and Concentrate (down) of anti-fouling membrane system testing brewery process water. Anti-fouling membrane system proved to be effective in concentrating the solids in Brewery s process water stream, as seen in Figure 11. The starting solids of 3-4% were able to reach 13% with an average flux of 124 LMH (85.7 gfd). With the higher temperature feed available on-site and the observed temperature versus flux correlation, an on-site test would likely show an even higher flux. With a higher flux, batches of feed wastewater can be processed in a shorter time to decrease operating time and maintenance costs. The anti-fouling membrane system will be able to concentrate the process waste to 15% meeting the requirement of animal feed buyer. In addition, the solid loading of the wastewater treatment facility can be greatly reduced leading to less COD/solids discharge.

9 This in return would also reduce the events for surcharges imposed for the wastewater. Although a settling tank might seem convincing to forgo membrane treatment, the actual solids from a lab test was approximately 6% after settling. This is still below the targeted 15-20% as requested. OVERALL SUMMARY Anti-fouling membrane system is highly recommended to treat high viscous, high dense, and high turbid water stemming from in a variety of industries where the fouling problem is encountered with conventional membrane systems. REFERENCES Kang, S.J., Olmstead, K.P., Schraa, O., Eum, Y.J (2011). Enhanced Biogas Generation With a Novel Thermophilic Activated Anaerobic Digestion System, Accepted for WEFTEC 2011, Los Angeles, CA, USA. Kim, D., Min, J.H., Eum, Y.J (2011). BRT (Biomass Recovery Technology) and BKT s case study in Netherlands, The 21st Korean- American Scientists and Engineers Association (KSEA) South-Western Regional Conference, February 5, Norwalk, CA, USA. Chen, Y (2008). Inhibition of anaerobic digestion process: A review. Bioresource Technology, 99,