ANAEROBIC MEMBRANE BIOREACTOR (ANMBR) SUCCESSFULLY TREATING HIGH-STRENGTH FOOD PROCESSING WASTEWATER FOR SEVEN YEARS. Abstract

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1 ANAEROBIC MEMBRANE BIOREACTOR (ANMBR) SUCCESSFULLY TREATING HIGH-STRENGTH FOOD PROCESSING WASTEWATER FOR SEVEN YEARS Shannon R. Grant, ADI Systems Inc., 370 Wilsey Road, Fredericton, NB, Canada E3B 6E9 / Phone: shannon.r.grant@adi.ca / (506) Dwain Wilson, ADI Systems Inc., Fredericton, NB, Canada ZaiYan Mi, ADI Systems Inc., Fredericton, NB, Canada Dale Mills, Ken s Foods Inc., Marlborough, MA, USA Abstract The Anaerobic Membrane Bioreactor (AnMBR) process incorporates anaerobic digestion and membrane filtration in one process that effectively treats high-strength and high solids wastewater and produces an anaerobic effluent of superior quality with virtually no suspended solids. AnMBR technology offers the advantage of complete retention of biomass in the reactor leading to a very stable process in a compact system footprint, which maximizes the production of biogas that can be used as a renewable fuel source. The first vendor full-scale AnMBR system installed in North America was at Ken s Foods in Marlborough, Massachusetts to treat salad dressing and BBQ sauce production wastewater. The AnMBR system at Ken s Foods is comprised of the existing anaerobic reactor plus four membranes and was designed to treat 125,000 gpd of raw wastewater with 39,000 mg/l COD, 18,000 mg/l BOD, 12,000 mg/l TSS, and 1,500 mg/l FOG (at the time of design). The required effluent discharge limits for BOD and TSS are 400 lb/d and 500 lb/d (equivalent to 380 mg/l BOD and 480 mg/l TSS at design flow) for discharge to the local POTW. The AnMBR produces a consistent, high-quality effluent with non-detectable TSS concentrations and average COD and BOD concentrations of 270 mg/l and less than 25 mg/l, respectively; corresponding to average COD, BOD, and TSS removals of 99.3%, 99.9% and approximately 100%, respectively. During the seven years of continuous operation, the AnMBR system consistently performs well, providing process stability and excellent membrane performance. Introduction Ken s Foods manufacturing company, located in Marlborough, MA, USA, has been making salad dressing, sauces, and marinades for over 60 years. Its high-strength wastewater from the production line contains high chemical oxygen demand (COD), high biological oxygen demand (BOD), high total suspended solids (TSS), and fat, oil, and grease (FOG) concentrations. With the requirement of plant production expansion, land space limitation, and the desire of renewable energy utilization, an innovative technology AnMBR technology was considered as a means to upgrade its original wastewater treatment system to handle the flow and load expansion. 1

2 An AnMBR treatment system was installed at Ken s Foods and commissioned in July This is the first vendor installed full-scale AnMBR treatment system in North America. A paper presented by Christian et al., 2010, provides a case study of the AnMBR system at Ken s Foods after two years of operation. This paper now discusses the performance of the AnMBR system after seven years of operation (July 2008 to June 2015). AnMBR Technology For industrial customers, facing more stringent discharge limits, and seeking renewable energy source and greater water recycling opportunities, the AnMBR is a solution. The process incorporates anaerobic digestion and membrane filtration in one process. The technology developed in mid-late 1980s by the government-instigated Japan s Aqua Renaissance 90 project (Liao, et al., 2006), tested in the mid-1990s, and successive commercial technologies have been used in full-scale applications in Japan since Pilot-scale AnMBR studies were carried out in North American from 2007 on different types of industrial wastewaters and showed high biogas production, low waste sludge, and a superior effluent quality (Burke et al., 2008; Landine et al., 2008; Hulse et al., 2009; and Burke et al., 2010). ADI-AnMBR Technology The ADI-AnMBR process utilizes Kubota flat-plate membrane cartridges (with an average and maximum pore size of 0.2 and 0.4 micron, respectively) that are submerged directly in the anaerobic biomass to retain the biological solids in the system and virtually block all suspended solids from escaping to the effluent. The near-absolute (zero TSS) membrane barrier performs the gas-liquid-solids separation and ensures efficient system operation and stability, even under high organic loading and intense mixing scenarios. The significant inventory of biomass in the AnMBR system makes it particularly robust and able to accommodate shock organic and hydraulic loadings. Also, due to its long solids retention time, it allows for a high degree of biomass acclimation and adaptation, and a high degree of process stability, biogas generation, and minimization of waste sludge. The technology is ideal for high strength wastewaters that contain suspended solids and oil and grease. Figure 1 presents a general process flow diagram of the ADI-AnMBR process. 2

3 Figure 1 General process flow diagram of the ADI-AnMBR process Ken s Foods Upgraded Design The original wastewater treatment plant included raw wastewater primary pretreatment (screening, oil skimming, and equalization), a 2.2 MG low-rate anaerobic (Type S ADI-BVF ) reactor, and a 0.35 MG ADI-SBR. The organic load and flow continued to increase as the production plant expanded and the anaerobic effluent TSS concentrations continued to increase, which made aerobic polishing in the existing SBR problematic, resulting in poor sludge settleability and solids management issues. An AnMBR pilot study was operated on site at Ken s Foods from September 2007 to March 2008 to evaluate the AnMBR treatment process as a means of upgrading Ken s existing anaerobic treatment system, which was space-limited. The pilot study results (Christian et al., 2008) concluded that the AnMBR process was suitable for meeting the final effluent limits on a consistent basis (without post-aerobic biological treatment for BOD/TSS removal). It would also increase operating capacity with minimal additional footprint due its ability to operate at higher biomass concentrations and organic loading rates. Based on the successful pilot study, Ken s Foods contracted ADI Systems Inc. to design and construct the full-scale AnMBR system in early Upgrading the existing anaerobic system to an AnMBR provided complete solids-liquid separation of the anaerobic effluent and a sixty percent increase in operating capacity while meeting the current effluent BOD5 and TSS limits of less than 400 and 500 lb/d, respectively. Ken s Foods wastewater is characterized as high-strength industrial wastewater with average COD, BOD, TSS, and FOG concentrations of 39,000 mg/l, 18,000 mg/l, 11,000 mg/l, and 1,500 mg/l, respectively. The high TSS and FOG concentrations ruled out granular sludge based highrate anaerobic technologies due to the significant capital and operating costs required to modify the primary systems in order to remove these constituents prior to anaerobic treatment, and the 3

4 reduction in biogas production for utilization in a combined heat and power (CHP) plant (now under commissioning at time of writing). The AnMBR design raw wastewater characteristics and effluent discharge limits (discharge to sewer) are presented in Table 1 below. Table 1 Design raw wastewater average characteristics Parameter Raw Wastewater Discharge Limits Avg Flow (gpd) 125, ,000 Peak Flow (gpd) 140, ,000 COD (mg/l) 39, BOD5 (mg/l) 18, * TSS (mg/l) 11, * FOG (mg/l) 1, ph * Discharge limit for BOD5 and TSS concentrations are calculated based on effluent BOD5 and TSS limits of less than 400 and 500 lb/d at design flow. AnMBR Process Description Figure 2 presents a process flow diagram of the AnMBR system at Ken s Foods. It consists of an existing proprietary 2.2 MG Type S ADI-BVF anaerobic reactor operated as a CSTR, biogas relief transmission and conveyance system, and four new AnMBR membrane tanks (each with a working volume of 27,300 gallons equipped with Kubota submerged membrane units. The overall system also includes sludge recycle and effluent pumps, biogas scour blowers, process piping and valving, membrane cleaning chemical system, instrumentation and controls. A retractable geomembrane cover system on each membrane tank provides a gastight seal for biogas collection. The AnMBR process recirculates biogas from the tank s headspace through the diffusers located beneath the membrane units. This scours the membrane surfaces and significantly reduces trans-membrane pressure (i.e., TMP), the rate of membrane fouling, and frequency of membrane cleaning. Membrane cleaning is currently carried out every four to eight months as a regular maintenance clean (whether it is needed or not). The raw wastewater from Ken s Foods production plant first enters a tangential screen to remove any large particles from entering the treatment system. Wastewater is then equalized and continually mixed in an equalization (EQ) tank to provide influent flow and load control to the anaerobic system. Magnesium hydroxide is supplemented in the EQ tank to provide alkalinity for ph control in the anaerobic reactor. The anaerobic reactor contents flow by gravity, splitting evenly to the four AnMBR tanks. Anaerobic sludge is continuously recycled from the anaerobic membrane tanks back to the anaerobic reactor. AnMBR permeate from each membrane tank is extracted by an effluent pump which operates on a cycle (9 minutes on during a 10-minute cycle), providing a 10 percent membrane relax period to scour the membranes when not under suction to further reduce operating TMP. AnMBR permeate is discharged to the existing ADI-SBR system, which nitrifies ammonia before being discharged to the municipal sewer. 4

5 Figure 2 Process flow diagram of the full-scale AnMBR system Each anaerobic membrane tank includes Kubota submerged membrane units and is covered with a retractable geomembrane structural cover system which is connected to a biogas scour system. Three biogas scour blowers (two duty, one standby) continuously recirculate biogas from the headspace of each anaerobic membrane tank to the diffuser case located below the submerged membrane units to scour the membrane surface. This minimizes the cake layer formation and reduces membrane operating TMP. Biogas produced in the anaerobic membrane tanks combines with the anaerobic reactor head space, from where biogas is collected under a floating, insulated, geomembrane cover system. A biogas blower conveys the biogas to a dual-fuel boiler for utilization. The boiler produces hot water to heat the treatment system (via sludge recycle through a heat exchanger) so it operates at a temperature close to 95 F (35 C), as well as building heat. Biogas is now utilized in a CHP system and any excess biogas is flared off in an enclosed flare. Figure 3 is a photo of the anaerobic membrane tanks. 5

6 Figure 3 Anaerobic membrane tanks Operating Results The AnMBR system was commissioned in July 2008, and was able to take 100 percent of flow immediately. This rapid start-up period was possible since the original anaerobic system was already taking 100 percent of the raw wastewater flow. Flow and COD Load The annual average flow and COD load during seven years of operation is presented in Table 2 below. Table 2 Average Flow During Seven Years of Operation Year Flow (gpd) COD Load (lb/d) 2008 (July Dec) 66,900 18, ,565 24, ,820 25, ,045 29, ,660 29, ,630 34, ,200 37, ,800 38,540 Overall Average 89,900 30,240 6

7 Figure 4 presents the AnMBR influent flow and COD load in seven years of operation (July July 2015). Figure 4 AnMBR system influent flow rate and COD load Figure 5 shows flow and COD load annual average values during operation. It is very clear that both flow and COD load have shown an upward trend throughout the operation years, a reflection of increased process plant production. Figure 5 Average flow and COD load during operation 7

8 Influent flow has progressively increased over the years, from 66,900 gpd in 2008 to 102,800 gpd in The COD load also increased over seven years of operation, from 18,900 lb/d in 2008 to 38,540 lb/d in The COD load increased more rapidly and consistently over the seven years of operation at an average increasing rate of 15% every year. The flow increased greatly from 2008 to 2009 by 26%; while in the later years from 2009 to 2011, the flow stayed the same due to in-plant flow minimization efforts. From 2013 to 2015, the flow increased continuously by 7.1%, 6.3% and 9.1%, respectively, while the annual increasing rate is approximately 7.5%. The overall flow rate increase per year over the seven years of operation is 7.7%. The overall average influent COD concentration throughout the seven years operation was 39,150 mg/l, with a peak COD concentration of approximately 145,000 mg/l. The annual average COD concentration has increased gradually and the average value exceeded the design of 39,000 mg/l in 2011, 2012, 2013, 2014, and 2015 by 4.2%, 5.3%, 11.1%, 10.7%, and 8.2%, respectively. Effluent Quality Table 3 lists the annual average results of the influent, effluent COD concentrations, and COD removal rates Figure 6 presents the AnMBR influent and effluent COD concentrations and percent removals throughout the first seven years of operation. As noted in Table 3 and Figure 6, the AnMBR effluent COD concentration was consistently low, with an overall average concentration of 272 mg/l, corresponding to an overall average COD removal of 99.3 percent, demonstrating the superior robustness and stability of AnMBR technology. Table 3 Influent COD, Effluent COD, and COD Removal Efficiency COD Removal Year Influent COD (mg/l) Effluent COD (mg/l) Efficiency (%) 2008 (July Dec) 32, , , , , , , , Overall Average 39,

9 Figure 6 Influent COD, Effluent COD and COD removal efficiency during operation Figure 7 presents the average results of influent TSS, effluent TSS, and TSS removal efficiency during the seven years of operation. It clearly shows that TSS in the influent wastewater also has an increasing trend. Figure 7 Influent TSS, Effluent TSS, and TSS removal efficiency 9

10 Similarly to COD concentration, the TSS concentration exceeded the design values from 2011 to 2014, while the AnMBR system still provided superior effluent quality with nearly 100 percent TSS removal efficiency. The average influent TSS concentration was 12,050 mg/l and ranged from 4,000 to 93,000 mg/l. The overall AnMBR effluent TSS concentration is 2.5 mg/l, corresponding to approximately 100 percent solids removal. One of the challenges of measuring the TSS in the permeate effluent is due to there being almost no solids present in the permeate. Therefore, large quantities must be filtered to make the test accurate, which is impractical, meaning that the effluent TSS concentration is typically higher than it would be if the test were done properly by filtering more sample. Removal of TSS is one of the key advantages of AnMBR technology. The submerged membrane units provide a near-absolute barrier to block all suspended solids from escaping to the effluent, resulting in a very high quality anaerobic effluent compared to conventional anaerobic technologies that rely on gravity settling in the reactor. The AnMBR effluent being discharged to the existing SBR contains virtually no TSS, and the SBR effluent TSS concentration is also very low, allowing Ken s Foods to meter anaerobic sludge to the sewer ahead of effluent flow proportioned sampler. This allows Ken s to confidently stay within the TSS mass discharge limit of less than 500 lb/d. This significantly reduces sludge dewatering and disposal costs. The overall average effluent BOD5 concentration throughout the seven years of operation is 23 mg/l, corresponding to 99.9 percent BOD5 removal. Christian et al., 2008, reported the AnMBR pilot study results. They observed average influent BOD5 and COD concentrations of 17,600 and 33,200 mg/l, respectively; while the effluent BOD5 ranged from 8 mg/l to 27 mg/l and effluent COD concentration ranged from 200 mg/l to 900 mg/l, respectively. The full-scale AnMBR system effluent BOD5, COD, and TSS concentrations during the seven years operation corresponded well with the effluent concentrations observed in the pilot study. The AnMBR system consistently produces a high-quality anaerobic effluent that easily meets the discharge limits. The system also provides complete digestion of the raw wastewater fat, oil, and grease concentrations, providing further biogas generation and better management of biomass and TSS concentrations. Table 4 summarizes the AnMBR system performance during the seven years operation. Table 4 AnMBR Effluent Average Characteristics Parameter AnMBR Effluent Removal Efficiency (%) COD (mg/l) BOD5 (mg/l) < TSS (mg/l) 2.5 ~100 FOG (mg/l) ph <

11 System Performance The AnMBR system operating temperature is controlled by continuous sludge recycling through a spiral heat exchanger linked to a hot water boiler burning biogas from the system to maintain a mesophilic operating temperature range. Figure 8 shows operating temperatures in each membrane tank. The operating temperature has a wide range from F (26 37 C), with an average of 92 F (33 C). The stable system operation clearly shows that the Ken s Foods AnMBR system operates well under a wide range of temperatures, and consistently provides superior effluent quality despite the variations in temperature and loading conditions. Figure 8 Temperature in each membrane tank during operation Table 5 summarizes the average of TMP during operation. The TMP for each AnMBR tank has remained between 3 and 8 inches of water column (in. w.c.) in the first two years of continuous operation, thereby suggesting a very low rate of membrane fouling during that time. The TMP data shows higher readings in 2011 and early 2012, which was due to a malfunction of the pressure transmitters. TMP stayed low below 20 in. w.c. after June 2012 until present with maintenance membrane cleaning events done every four to eight months, for each membrane tank. This demonstrates a very low membrane fouling rate. 11

12 Table 5 Average TMP (in. w.c.) in the Anaerobic Membrane Tank Parameter 2008 (July Dec) Overall ( ) Tank 1 Tank 2 Tank 3 Tank 4 Average Continuous biogas scour minimizes the cake layer build-up on the membrane surface, decreasing TMP (membrane fouling). Membrane cleaning is required when the TMP reaches 10 kpa (40 in. w.c.) or every four to eight months. Cleaning involves soaking the membranes in situ in the membrane tank for two hours in either a 0.5 1% sodium hypochlorite solution (biological fouling) or a 10 percent citric acid solution (chemical fouling). The maintenance membrane cleaning events were only performed once on AnMBR tanks 1, 2, and 3 in two years of continuous operation, and no membrnae cleaning for membrane tank 4 in the first two years of operation. Maintenance membrane cleanings are now performed every four to eight months. Biogas Generation The biogas generated in the anaerobic system is collected under a floating, insulated geomembrane cover and recirculated in the membrane tank to scour the flat plate membrane surface, minimizing the cake layer build-up on the membrane surface, and reducing the membrane operating TMP. The biogas has been utilized in a plant boiler to provide the heat source of the anaerobic system to maintain mesophilic temperatures (35 C or 95 F), as well as providing building heat and more recently in a CHP system. Christian has reported an observed biogas yield of 0.32 m 3 CH4 per kg COD removed (Christian et al., 2010) for the first two years of operation and an average daily biogas flow of 6,000 m 3. The biogas flow production continuously increased as the organic load increased during operation. In 2012, the average daily biogas flow was 6,400 m3/d, and this increased to 6,870 m3/d from April 2014 to July The observed biogas yield rate stayed the same at 0.32 m3 CH4 per kg COD removed. Reduction in Operating Costs Reduced sludge dewatering (via centrifuge) has provided a significant operating and maintenance cost reduction in polymer/chemical usage and sludge hauling and disposal costs. It was estimated that after the first year of full-scale AnMBR operation, the AnMBR system reduced operation and maintenance costs by 50 percent while handling increase loading (Christian, et al., 2010). The main method of sludge wasting for the upgraded AnMBR system is metering anaerobic solids to the sewer up to the allowable daily effluent mass TSS discharge 12

13 limit, which is very easy to control as the AnMBR provides negligible effluent TSS to the SBR, resulting in a very low effluent TSS concentration in the aerobic system effluent. The AnMBR effluent, with an average BOD concentration of less than 25 mg/l, presents a very low oxygen requirement for the downstream aerobic process (i.e., SBR), resulting in an 85 percent reduction in aeration/oxygen requirements and energy consumption after commissioning the AnMBR. The AnMBR system also decreases or eliminates the chemical addition in macronutrient, defoamer, chlorine and polymer, which are associated with improving sludge settleability in the SBR process and the hauling/disposal of skimmed FOG, further reducing the operating and maintenance costs. Conclusions The first full-scale vendor supplied AnMBR system in North American at Ken s Foods plant has been treating salad dressing and BBQ sauce wastewater successfully for seven years since being commissioned in July It clearly proved the suitability of the AnMBR process upgrading at Ken s Foods treatment system. Conclusions for the full-scale AnMBR system operation are summarized as follows: The upgraded AnMBR system provided a sixty percent increase in operating capacity over the original anaerobic system design parameters, with minimal additional footprint. During seven years of continuous operation, the AnMBR system continues to provide consistent superior system performance despite flow and load increases. The AnMBR process was able to have a rapid start-up period and treat 100 percent organic load and flow during the first week of commissioning. Granular sludge is not required for the AnMBR system, eliminating costs associated with obtaining granular seed sludge. The flow and COD load have progressively increased during operation, while the AnMBR system provided excellent performance and superior process stability on a consistent basis under variable operating temperature and loading conditions. The influent COD and TSS concentrations continue to increase with process plant production increases, while the COD and TSS removal efficiencies remain consistently stable at greater than 99% and 99.9%, respectively. The AnMBR system BOD, COD, and TSS removals all exceeded 99 percent in the seven years of operation when treating high-strength raw wastewater with average BOD, COD, and TSS concentrations of 18,000, 39,000, and 12,000 mg/l, respectively. The AnMBR provides very high effluent quality due to the membrane barrier blocking essentially all suspended solids, and retaining the biomass in the anaerobic system. 13

14 The AnMBR has low waste sludge production, and the anaerobic wasted sludge can discharge freely to the sewer to the allowable TSS mass discharge limit of less than 230 kg/d. Minimal sludge dewatering was undertaken during the operation, resulting in significant operational cost savings. The AnMBR system reduced operating cost by 50% as loading increased as a result of a significant reduction in sludge dewatering (via centrifuge), and associated polymer/chemical usage and sludge hauling/disposal costs. Very low BOD concentrations of less than 25 mg/l in the AnMBR effluent resulted in an 85 percent reduction in aeration/oxygen requirements and energy consumption in downstream SBR system. The AnMBR system operates well under a wide range of the temperatures (26 37 C), and consistently provides superior effluent quality. The membranes exhibited negligible membrane fouling. Membrane maintenance cleaning is performed every 4-8 months. Continuous biogas scour minimizes the cake layer build-up on the membrane surface, decreasing operating TMP and membrane fouling. There has been no membrane replacement or need for membrane cassette maintenance in over seven years of operation. The observed methane yield rate is 0.32 m3 CH4 per kg COD removed. Biogas generation is as expected and has increased with the flow and organic load increase over the seven years of operation, providing more favorable economics in the installation and operation of the CHP system. References Burke, D., Christian, S., Grant, S., Singh, K, Landine, R. (2008). The Anaerobic Membrane Bioreactor (AnMBR) Process for the Treatment Potato Processing Wastewater. Proceedings from the IWA Membrane Research Conference. August, Amherst, Massachusetts, USA. Burke, D., Christian, S., Grant, S., Singh, K. (2010). The Submerged Anaerobic Membrane Bioreactor (AnMBR) for the Treatment of High Strength Degradable Food Processing Wastewater. Proceedings from the ASCE EWRI Conference. January, Chennai, India. Christian, S., Grant, S., Wilson, D., McCarthy, P., Mills, D. (2008). Pilot-Scale Study of the Anaerobic Membrane Bioreactor Process for Treatment of a Salad Dressing Wastewater. Proceedings from WEFTEC Chicago, Illinois. Christian, S., Grant, S., Wilson, D., McCarthy, P., Mills, D., Kolakowski, M. (2010). The First Two Years of Full-Scale Anaerobic Membrane Bioreactor (AnMBR) Operation Treating 14

15 A High Strength Industrial Wastewater at Kens Foods Inc. Proceedings from WEFTEC Anaheim, California. Hulse, A., Singh, K., Grant, S. (2009). An Innovative Submerged Anaerobic Membrane Bioreactor for Treatment of Potato Solids and Bioenergy Production. Proceedings from WEFTEC Orlando, Florida. Landine, R., Christian, S., Burke, D., Grant, S., Singh, K. (2008). Cutting-Edge Wastewater Treatment Process Good for Potato Processing Industry. Proceedings from the 2008 International Potato Processing Convention. June 2008, Warsaw, Poland. Liao, B., Kraemer, J.T., Bagley, D.M. (2006). Anaerobic Membrane Bioreactors: Applications and Research Directions. Critical Reviews in Environmental Science and Technology, 36, pp