Two MBR Case Studies

Lessons Learned During Startup, Testing and Optimization of MBR Systems for Enhanced Nutrient Removal Vince Maillard1*, Kristi Perri1, Jason VerNooy1 1GHD, Bowie, Maryland. * Email: [email protected]. ABSTRACT Membrane bioreactors (MBRs) are known for producing high quality effluent from wastewater treatment facilities in order to meet stringent regulatory requirements (Fleischer et al., 2005), accommodate growth (Vadiveloo & Cisterna, 2008), provide opportunities for water reuse (Schmidt et al., 2011), and achieve other operational goals for various municipalities, utilities and industries (Cummings & Frenkel, 2008). The process of testing, starting up and optimizing an MBR process for enhanced nutrient removal at the end of a construction project is often overlooked. Even a well-designed MBR can fail to meet expectations if the system is not properly configured during the startup phase, making this a critical step in any successful implementation of membrane technology. The startup phase of two municipal MBR plants were compared to demonstrate the importance of various strategies for initial process optimization, with a focus on lessons learned, techniques and performance expectations that can be applied to future projects. KEYWORDS: MBR, nutrient removal, startup, testing, optimization. INTRODUCTION Membrane bioreactors (MBRs), which consist of an activated sludge process and a membrane filtration system (MFS), offer several benefits which have led to their widespread application in the treatment of municipal and industrial wastewater (Cummings & Frenkel, 2008). MBR technology allows for greater flexibility in both design and operation, as they are compatible with a broad range of process configurations, physical layouts, influent characteristics, operating conditions and control strategies (Pellegrin et al., 2012). MBRs are also ideal for expansion to accommodate growth or meet increasingly stringent effluent requirements within a relatively small footprint (Ferraris et al., 2009). Perhaps one of the most significant advantages of MBR technology is its ability to consistently produce high quality effluent, including effluent total nitrogen (TN) concentrations of 3 mg/L and total phosphorus (TP) concentrations of 0.3 mg/L, with the possibility of even lower concentrations following process optimization (Fleischer et al., 2005). The selection of MBR technology is often based on the benefits associated with the production of such high quality effluent, such as more efficient utilization of available discharge limits, a reduction in the facilitys environmental impact and the potential to implement water reuse.

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However, selection and design are only the first steps towards capitalizing on these benefits. In order to take full advantage of the advanced treatment capabilities and maximize the value of the MBR system, it is also critical for each component to be properly installed and operated to avoid costly inefficiencies, underperformance or even process failures (Ellsworth & Riddell, 2007). The successful startup and optimization of any new biological treatment process can be jeopardized by a wide range of potential setbacks, including schedule delays, equipment deficiencies, inadequate feedback or data collection, and lack of coordination between the parties involved. Standard contract specifications and other construction phase documents, such as inspection checklists and report forms, have been established over time to help manage these general types of issues. Yet these standard resources are often developed based on conventional wastewater facilities and may not adequately address the unique challenges associated with implementing MBR technology, including:

The large number of interconnected components operating as a single system; Reliance on complex automatic controls and interlocks with risk of costly failures; Use of proprietary terminology, configurations, operational schemes, testing protocols,

etc., by different system suppliers; and A relatively wide range of potential operating conditions, control strategies and

performance targets.

As such, an additional degree of planning and execution is required to bring MBR systems from installation to successful operation. A project-specific startup plan is essential for meeting the goals set for each individual installation, which can vary considerably based on the details of the application and the reasons for selecting MBR technology. The best approach to startup and optimization will depend on several factors, including the features of the proposed MBR system, recommendations of the MFS supplier, time or budget constraints and owner preferences. In order to document the impact of different strategies for bringing an MBR plant online, two municipal MBR wastewater treatment plants located in Virginia (United States) were studied during startup, performance testing and initial operation. Results and lessons learned from both case studies are documented herein. The first plant (Plant A) is a new 0.95 ML/d (0.25 mgd) facility owned and operated by a small, seasonal town of about 1,000 permanent residents on the Eastern Shore of Virginia. Plant A was built on a greenfield site to replace the Towns existing plant, which consisted of aging contact stabilization units. The new plant includes headworks, four-stage Bardenpho reactors, MFS, ultraviolet (UV) disinfection, and provisions for water reuse. The second plant (Plant B) is a 2.65 ML/d (0.70 mgd) facility owned and operated by a town of about 4,000 residents in Northern Virginia. The MFS at Plant B was added as part of a major upgrade project on the same site as the existing lagoon treatment plant. The upgrade project also added new headworks, 2.65 ML (0.7 mgd) of flow equalization, four-stage Bardenpho reactors, and UV disinfection. Both plants were designed to meet enhanced nutrient removal (ENR) level effluent concentrations of 4.0 mg/L TN and 0.3 mg/L TP. A summary of each plant is shown in Table 1.

Table 1. Plant design criteria. Parameter Plant A Plant B Current Average Flow 0.4 ML/d (0.1 mgd) 1.1 ML/d (0.3 mgd) Design Average Daily Flow 0.95 ML/d (0.25 mgd) 2.65 ML/d (0.70 mgd) Design Peak Flow 2.84 ML/d (0.75 mgd) 7.95 ML/d (2.10 mgd)

with flow equalization Peaking Factor for MBR 3:1 3:1 Design Average Influent Concentrations

BOD TSS

TKN TP

206 mg/L 226 mg/L 39.7 mg/L 6.1 mg/L

290 mg/L 270 mg/L 45 mg/L 6.5 mg/L

Flow Equalization No 2.65 ML (0.7 mil gal) Influent Pumping Operation Constant Speed Variable Speed Biological HRT 14 hours 24 hours Type of Membranes Hollow Fiber Hollow Fiber No. of Membrane Trains 2 4

METHODOLOGY The contract specifications for both plants required an extensive testing sequence as shown in Figure 1. Each step in the testing sequence had its own milestones or goals which must be completed before the next step could begin. Many of the steps also had minimum durations that would be extended in the event that the performance goals were not met.

Figure 1. Specified testing sequence for MBR system startup. The testing procedures were organized to balance the need to be thorough and verify the functionality of the installed system with the need to be concise and minimize unnecessary delays to the construction schedule. The MFS suppliers own testing procedures were considerable, so extra coordination was necessary to integrate these testing activities into the startup plan for each facility. The MFS suppliers standard testing routine was supplemented by the engineers specified testing requirements, which were adjusted during design to account for the unique features of the MBR system. Initial Planning and Coordination The first step in the startup process began while the new equipment was still being installed at each plant. The engineer and contractor worked together to create template documents that would be used during the various stages of testing, including inspection checklists, report forms and summary tables listing the applicable milestones for each step in the testing sequence. These documents were based on the contract specifications for the project and provided a consistent means of tracking progress and communicating results to the project team. On-site meetings, phone calls and other correspondence were also utilized to help plan the startup process and keep key parties informed.

During this same time, a comprehensive startup plan was developed for each facility with input from the owner, engineer, contractors, suppliers, and all other parties that would be involved in the startup process. The startup plan was used as a detailed guide that would supplement the contract specifications and the contractors construction schedule, providing additional information and recommendations such as:

Roles and responsibilities for each party during the startup period; Review of sequencing constraints; Evaluation of the proposed timing for key events, including activities not specifically

covered by the contractors schedule (delivery of chemicals, transfer of activated sludge inoculum, coordination with regulatory agencies, etc.);

Details of flow transfer and splitting (including closed loop clean water testing and the introduction of raw wastewater);

Plans for seeding the MBR (source, transfer, handling, target solids concentration, required volume, etc.);

Milestones or other trigger events to help focus efforts and determine sequencing; Summary of any available data applicable to the startup process (including recent flow

rates and influent characteristics); Sampling and monitoring protocols for each stage of testing and optimization; and Other applicable input or feedback from parties involved.

The startup plan served as a single, consolidated resource for collecting relevant information and using it to determine a practical approach to the startup process, resulting in better coordination during the critical steps of the startup process. Preliminary Equipment Checks As equipment at each facility was installed, the contractor was responsible for verifying that each component was properly set and capable of operating. Preliminary tests were conducted, including point-to-point electrical testing, infrared testing, and vibration testing, and operator training began on the new equipment. The preliminary equipment checks also served as a final opportunity to confirm that the new facilities were ready to proceed to online testing and operation, which meant collecting all product information, warranty documents, tools, test materials and lubrication equipment on site. MFS Clean Water Testing Separate clean water testing was required for the MFS at each plant as a prerequisite to clean water testing for the rest of the new facilities, as multiple components of the MFS must be operating successfully under automatic control in order to hydraulically pass flow through the treatment facility. The MFS supplier for both plants preferred the use of potable water for clean water testing to protect the membranes, and stressed the importance of thoroughly cleaning the process tanks before filling them with water. The MFS supplier also requested that all work in the area of the MBR tanks be completed before the membrane filtration equipment was installed for protection of the membranes.

Once the process tanks were cleaned and filled the membrane filtration equipment was installed and clean water testing began. For Plant A, the clean water testing loop started in the membrane tanks, where the potable water was drawn through the membrane fibers by the permeate pumps. The permeate pumps discharged the clean water into the backpulse (BP) water storage tank for the MFS, which overflowed to the downstream UV disinfection structure and adjacent plant water well. The permanently installed plant water pumps were then used to pump the clean water back into the membrane tanks, as shown in Figure 2. A separate loop was established with the mixed liquor suspended solids (MLSS) recirculation pumps, which discharged at the distribution box upstream of the biological reactors and flowed by gravity back into the membrane tanks.

Figure 2. MFS clean water testing loop for Plant A. For Plant B, the clean water testing loop for the MFS initially consisted of the MLSS recirculation pumps transferring potable water from the membrane tanks to the biological reactor tanks, which flowed by gravity downstream to the membrane tanks. Once the permeate pumps were placed online, the potable water from the membrane tanks was drawn through the membrane fibers and discharged into the backpulse water storage tank, which was able to flow by gravity back to the raw sewage pump station (RSPS) at the head of the plant. The clean water loop was then expanded to flow through most of the new facilities, as shown in Figure 3.

Figure 3. MFS clean water testing loop for Plant B. The contract specifications for both facilities required a minimum of one week of successful clean water testing with the MFS prior to plant-wide clean water testing, which would be extended as necessary if the system failed to meet the specified performance requirements. The MFS suppliers own standard clean water testing routine required two weeks for system configuration and testing, which coincided with the engineers specified testing period. During the clean water testing phase the installed equipment ran under automatic control and was inspected to verify proper function in each available operational mode. In particular, preliminary clean water testing of the MBR system was utilized to check the automatic programming developed for each facility, including data transfer and recording, alarms, interlocks, alternate control modes and operator interface. Any discrepancies observed during the clean water testing period were tracked with project-specific checklists until they could be suitably resolved.

Plant-wide Clean Water Testing After the successful completion of clean water testing for the MFS, the rest of the new facilities at each plant went through a similar clean water testing routine. The control systems for each equipment package (including the MFS) were integrated with the process control system (PCS) for the entire plant to allow for the specified remote monitoring and control functions. Any outstanding issues identified during the clean water testing phase were recorded and tracked until they were adequately addressed, at which time the plant was considered ready for wastewater operation. MBR Seeding and Introduction of Wastewater The potable water used for clean water testing was drained out of the process tanks to allow for the addition of activated sludge inoculum to the MBR system at each plant. The activated sludge inoculum was obtained from a nearby operating MBR facility in both cases, as previous studies with ultrafiltration membrane systems have shown that seeding from an existing facility can reduce membrane fouling during initial operation and help to speed up the development of higher MLSS concentrations (Di Bella et al., 2010). Seeding with activated sludge also helps the MBR system to achieve the maximum design solids concentrations during the specified testing period. Plant A initially seeded the new MBR with activated sludge at about 7,000 mg/L MLSS concentration to obtain a starting MLSS concentration goal of over 2,000 mg/L, and utilized additional 120,000 L (32,000 gal) of seed sludge to accelerate solids accumulation after the introduction of wastewater. The activated sludge inoculum for Plant A was delivered using septic hauling trucks, which introduced small amounts of mixed debris into the sludge. The high solids concentration of the seed sludge caused it to clog up the fine screens installed upstream of the MFS, so the seed sludge had to be discharged directly into the biological reactor tanks and the debris was manually screened out. Plant B seeded the new MBR with activated sludge at about 3,000 mg/L MLSS concentration for a starting MLSS concentration goal of about 900 mg/L, and did not utilize additional seed sludge following the introduction of wastewater. As a result, MLSS concentrations were significantly higher at Plant A throughout the startup period, as shown in Figure 4.

Figure 4. Startup phase MLSS concentrations. Raw wastewater flow from the collection system was diverted to each plant after initial activated sludge addition. Based on the construction schedule for the respective projects, the introduction of wastewater occurred in January 2012 for Plant A and in September 2012 for Plant B. The diversion of raw wastewater to the new MBR systems proceeded in accordance with the startup plan developed specifically for each facility. For Plant A, the startup plan recommended that the Towns existing wastewater plant remain in operation until the new MBR facility was consistently producing high quality effluent. This allowed for a gradual increase in flow to the new MBR plant and a prolonged flow split between the old and new treatment facilities. The new MBR system at Plant A began receiving 100% of the Towns raw wastewater flow two months after the initial startup date. The MBR system at Plant B was constructed as part of an upgrade to the Towns existing treatment plant, so all of the raw wastewater flow was immediately diverted from the existing treatment process to the new MBR facilities. Influent flow rates for each plant are shown in Figure 5.

Figure 5. Startup phase influent flow rates. Final Performance Testing and Optimization During the performance testing period, operating conditions and effluent quality were closely monitored at each facility to assist with process optimization. A combination of on-site laboratory testing and off-site, third party laboratory analysis were used to monitor concentrations of nutrients and suspended solids in the raw influent, mixed liquor and plant effluent. At both plants, online instrumentation was utilized to continuously measure influent and effluent flow rates, as well as dissolved oxygen (DO) and nitrate (NO3) concentrations in the biological tanks. Instrumentation provided as part of the MFS for each facility was used to monitor plant feed (raw influent) flows, permeate (filtered effluent) flows, wastewater temperature, effluent turbidity and trans-membrane pressure (TMP). Both Plants A and B were designed to use Micro C-GTM for supplemental carbon and aluminum sulphate (alum) as a metal coagulant. The startup plans for both plants called for the chemical feed systems, supplemental carbon and alum, to be started up sequentially to provide adequate time to establish dosing rates for the first chemical before starting addition of the second chemical. Full denitrification was listed as an initial milestone in the startup plan for Plant A, so the supplemental carbon feed system was brought online first. Supplemental carbon addition began 22 days after the introduction of wastewater at Plant A, followed by alum addition after 38

days of wastewater treatment. Plant B started with relatively high (> 7 mg/L) effluent TP concentrations in the first month of performance testing, so the alum feed system was started first after 40 days of wastewater treatment and the supplemental carbon feed system followed at 54 days of wastewater treatment. RESULTS AND DISCUSSION Influent Characteristics The raw influent wastewater characteristics during the startup phase of each plant are listed in Table 2. The influent characteristics at Plant B remained relatively consistent throughout the 90-day startup period. Influent wastewater characteristics at Plant A showed significant variation as a result of the Towns sewage collection system. Table 2. Startup phase average influent wastewater characteristics. Parameter Plant A

Average (Min-Max) Plant B

Average (Min-Max) BOD 142 mg/L (64-223 mg/L) 362 mg/L (209-536 mg/L) TSS 91 mg/L (30-256 mg/L) 125 mg/L (32-448 mg/L) TKN 30 mg/L (14-44 mg/L) 55 mg/L (47-59 mg/L) TP 3.7 mg/L (1.7-5.4 mg/L) 7.4 mg/L (1.7-5.4 mg/L) The collection system for Plant A consists of two main raw wastewater pump stations: one serving a gravity sewer system in the Towns historic district and the second connected to a vacuum sewer system serving primarily new development. The influent wastewater from the gravity sewer system was relatively dilute due to generally older construction and higher inflow/infiltration (I&I) rates in the collection system. In contrast, the vacuum sewer system has relatively high strength wastewater coming from the area of new development where there are more low-flow plumbing fixtures and less I&I. Both pump stations cycled on and off throughout the day, producing significant variation in the influent wastewater characteristics. This was particularly noticeable during the colder months of the year when Plant A began wastewater treatment (before the seasonal residents arrived in Town). The cyclic operation of the raw wastewater pumps also produced rapid fluctuations in the influent flow rate, as shown in Figure 6. This caused the MFS to frequently transition between production and standby mode throughout the day.

Figure 6. Screen shot of the influent flow chart for Plant A showing significant fluctuations over a two hour period during routine plant operation. Flows are displayed in units of million gallons per day (mgd) and range between 0 and 1 mgd. Nitrogen Removal Full nitrification occurred rapidly at both MBR facilities (within 7 days for Plant A and 14 days for Plant B), and as expected the time required to achieve nitrification did not appear to be significantly impacted by the volume of activated sludge inoculum utilized (Di Bella et al., 2010). As shown in Figure 7, Plant A was able to achieve partial denitrification until the addition of supplemental carbon. Full denitrification was achieved shortly after startup of the supplemental carbon feed system. Plant B was able to achieve nearly complete denitrification without the addition of supplemental carbon addition; however, as shown in Figure 7, the startup of the supplemental carbon feed system provided stable and complete denitrification.

Phosphorus Removal Plant A demonstrated significant phosphorus removal due to biological treatment after startup of the supplemental carbon system, as shown in Figure 7. Alum addition was required to maintain effluent TP concentrations below 0.3 mg/L as the plant flows and influent loads increased. Effluent TP concentrations at Plant B decreased below the target concentration of 0.3 mg/L after the addition of alum on day 40 of the performance testing period.

Figure 7. Startup Phase Effluent Total Nitrogen (TN) and Total Phosphorus (TP) Concentrations. Chemical Addition At Plant A, the supplemental carbon system started up on day 24 of the performance testing period, and the effluent TN concentrations quickly decreased from approximately 25 mg/L on day 22 to less than 3 mg/L by day 29. Supplemental carbon (Micro CGTM) was initially dosed in manual control while the automatic control programming for the plant was finalized. While under manual control, the supplemental carbon was over-dosed at approximately 142 mg/L to ensure consistent denitrification, resulting in an average effluent TN concentration of 1.2 mg/L. After the automatic controls became available the dosing rate was flow-paced using the influent flow signal, allowing the feed rate to be adjusted to achieve the desired effluent quality. After a temporary increase in effluent TN concentration following the implementation of the automatic control programming, the effluent TN concentration was again maintained below 2 mg/L for the

remainder of the performance testing period with typical supplemental carbon dosing rates of approximately 130 mg/L. At Plant A, the initial alum dose was approximately 20 mg/L and was increased to 40 mg/L by the end of the performance testing period. During startup, Plant A tested for effluent TP using a 0.2 mg/L detection limit; however, more recent laboratory testing with a detection limit of 0.02 mg/L has shown that the MBR system is able to consistently produce at or below 0.02 mg/L with an alum dosing rate of approximately 30 mg/L. This effluent TP concentration is approaching the current limit of technology (deBarbadillo et al., 2010; Bott, 2009). The alum feed system for Plant B was started on day 40 and resulted in a significant decrease in the effluent TP concentration from 7.7 mg/L on day 27 to 0.2 mg/L on day 48. Plant B continued to maintain alum feed rates for the remainder of the startup period to achieve an effluent TP concentration of 0.3 mg/L or less. Laboratory results for Plant B indicated TN concentrations as low as 4.3 mg/L without supplemental carbon addition, likely as a result of the favorable influent BOD/TKN ratio of about 6.6:1 (Fleischer et al., 2002). However, the supplemental carbon feed system for Plant B was started in automatic control on day 54 of the performance testing period to achieve the target effluent TN concentration of less than 4 mg/L. MFS Performance Both plants maintained average effluent turbidity levels below 0.1 NTU throughout the startup period, as shown in Table 3. The average pressure differential across the membranes (i.e. trans-membrane pressure, or TMP) was minimal for Plant A and well below the maximum allowable TMP of 55 kPa for Plant B. Permeability data was also monitored for both plants as a relative indicator of membrane fouling and system efficiency, with higher permeability values generally representing decreased fouling and increased efficiency. The permeability of the membranes, reported in units of litres per square meter of membrane surface area per day per kPA of TMP (Lm2d/kPa), was approximately 40% higher for Plant A during the 90-day performance testing period. The lower average permeability value for Plant B may have been a result of the limited volume of activated sludge inoculum used to seed the MBR system, as the biomass in the MBR system typically forms a protective layer around the surface of the membranes that can enhance filtering and reduce certain types of fouling (Di Bella et al., 2010). Table 3. Startup Phase MFS Performance Data.

Parameter Plant A

Average (Min-Max) Plant B

Average (Min-Max) Wastewater Temperature (oC) 15.5 (9.6 20.5) 12.4 (7.3 19.8)

Turbidity (NTU) 0.06 (0.04 0.80) 0.06 (0.00 0.76) Trans-Membrane Pressure (kPa) 0.4 (-3.5 9.8) -2.0 (-7.2 2.1)

Permeability (Lm2d/kPa) 256 (5 296) 182 (6 295) System performance was also maintained during extreme conditions, including periods of low/sporadic flow caused by cyclic operation of the raw wastewater pumps upstream for Plant A and high flow events such as Hurricane Sandy at Plant B.

CONCLUSIONS There are many different ways to start up an MBR, and each will yield different results, as evidenced herein. The milestones, durations, and sequencing associated with each phase of testing and optimization were especially important for the selected case studies. In the case of Plant A, the Town expressed interest in maximizing nutrient removal through the new MBR facility to take advantage of available nutrient credits. In response to this objective, a significant volume of activated sludge inoculum was utilized for seeding to quickly increase the MLSS concentration in the biological tanks and achieve the desired performance. The chemical feed systems were also started up earlier to enhance nutrient removal during the preliminary stages of plant operation. As a result, Plant A achieved ENR-level effluent concentrations of 4.0 mg/L TN and 0.3 mg/L TP approximately 2-3 weeks earlier in the startup process when compared to Plant B, likely as a result of the increased seeding volume and earlier chemical feed (Manninaa & Di Bella, 2012). The larger volume of sludge inoculum also appears to have reduced fouling of the membranes at Plant A during the first 90 days of operation. By maintaining conservative dosing rates for supplemental carbon and alum Plant A has consistently achieved effluent concentrations below 2.0 mg/L TN and 0.05 mg/L TP following the completion of performance testing on the new MBR facilities. Plant B took a different approach to startup of the new MBR facilities, choosing instead to develop MLSS concentrations gradually instead of relying on large volumes of activated sludge inoculum. This ultimately reduced the cost of the startup process, but delayed subsequent milestones related to chemical addition and solids processing that were dependent on reaching target solids concentrations in the MBR system. Plant B demonstrated the ability to meet ENR-level effluent concentrations within the 90-day performance testing period even with limited seeding. Plant B has averaged effluent concentrations of approximately 2.6 mg/L TN and 0.2 mg/L TP since the completion of startup testing. The two case studies demonstrated the importance of developing a project-specific startup plan early in construction, which could then be utilized as a valuable resource for coordinating between multiple parties, guiding on-site personnel, identifying and preparing for possible setbacks, and addressing variations in startup conditions. The detailed, step-by-step organization of the startup plan helped to identify what additional information was required to prepare for the startup process, and also provided a central location to document the information once it was collected. Following the logical, sequential order of the startup plan raised key questions, such as:

Do the characteristics of the raw influent wastewater match previously collected data and design criteria?

How much influent flow is expected at the time of plant startup? How much seed sludge is required? How will it be delivered into the MBR system? How long will it take before wastewater reaches each process tank? When is operator

action required? What initial set points should be used for process control? What information is required to track performance during initial operation?

When should chemical addition and sludge wasting begin? What are the operational goals for the plant owner?

For the selected case studies, the answers to these questions were not emphasized in the contract specifications or construction schedule but proved to have a significant influence on the startup process. In the case of Plant A, the actual influent concentrations and raw wastewater flows at the time of plant startup were considerably different from the values estimated during the preliminary design phase of the project due to changes in growth projections and seasonal variations in the local population. The owners of each plant also had different preferences regarding the use of activated sludge inoculum and the treatment objectives for the plant, which resulted in different approaches to the startup of each plant. Documenting these critical factors in the startup plan helped to minimize miscommunication, delays and unexpected results. In particular, details of the MBR seeding plan, from the source and delivery method of the activated sludge inoculum to the amount used, can have a major impact on plant startup in terms of process performance, scheduling, and potential risks to installed equipment. Depending on the source of the seed sludge and the method of delivery, screening of the activated sludge inoculum should be considered for protection of the MBR equipment. Utilizing larger volumes of activated sludge inoculum can increase project costs and possibly create logistical issues, but can also improve treatment and accelerate the plant startup process based on the results of the selected case studies. The condition of the sludge (age, MLSS concentration, solids retention time of the seed plant, etc.) should be checked for each batch to avoid process upsets during initial operation. In order to function as an effective tool for on-site personnel and other decision makers, the startup plan should establish intermediate milestones or goals for each phase of testing, startup and optimization. The minimum performance requirements and durations for the various stages of testing should be included in the contract specifications for the project, but the startup plan should account for possible delays due to unfinished work or equipment failures. Once wastewater is introduced to the facility the milestones may be linked to certain events or conditions, such as adding seed sludge until a target MLSS concentration is reached, waiting to start chemical addition until full nitrification is observed, adjusting chemical feed systems after receiving a certain number of consistent laboratory results or observing a specific change in effluent quality, or beginning to waste sludge when the MLSS concentration in the MBR process reaches a certain level. These goals and milestones helped to communicate objectives, assess priorities, track progress and focus efforts during startup. Extensive clean water testing is recommended for future MBR installations. Thorough clean water testing procedures can take multiple weeks to complete, but can potentially eliminate costly delays or shutdowns during wastewater operation. Point-by-point testing of the automatic controls for the MBR process during clean water testing was especially valuable for the selected case studies, and also served as a helpful training exercise for plant operators. Issues related to the automatic system controls at Plant A, including missing steps in the membrane cleaning sequence and failure to automatically re-start the system after a power outage, were successfully identified and corrected before they resulted in critical failures by utilizing project-specific checklists during clean water testing. Other automatic control issues, such as missing logic for

the operation of RAS pumps under bypass conditions at Plant A and excessive opening and closing of flow control gates at Plant B, were not identified until after the introduction of wastewater, which resulted in programming changes late in construction as well as additional costs for repairing equipment. The clean water testing protocols should cover the entire range of specified operational modes, alarm conditions and control features, with a focus on any project-specific modifications to the suppliers standard design. Extensive laboratory testing and data collection is important for accurately monitoring performance of the new MBR for a successful startup. Frequent testing can add cost and increase labor, but the benefits include faster response to changes in the MBR process, reduced risk of making key decisions based on inaccurate or marginal data, and a better understanding of the system response to various operating conditions. Plant A collected multiple samples for laboratory testing each week of the startup period, and utilized the additional data to fine-tune chemical dosing rates and plant performance early in the startup phase. Plant B opted for less frequent testing, and achieved ENR level treatment later in the startup period. On-site testing is recommended for obtaining test results as soon as possible, with packaged reagent test kits offering a relatively low cost option for checking plant performance on a regular basis. Another important consideration for the successful startup of a membrane filtration system is how to best integrate and train the plant operators to run the new process and associated facilities. Membrane filtration technology can represent a significant operational change from the treatment processes it replaces in various ways, including increased automation, different performance indicators and process variables to monitor and control, and unfamiliar equipment and terminology. This was especially true for the operators at Plant A, as limited staffing required them to work full-time at the existing treatment plant until almost all of the influent wastewater flow was diverted to the new membrane filtration plant. This resulted in a rapid transition from an aging contact stabilization plant with minimal automation and no nutrient removal to a state-of-the-art facility equipped with a high level of automation and ENR level nutrient removal. Special considerations were made to gradually familiarize the operators from Plant A with the new membrane filtration system both before and after startup, including on site meetings with the engineer and MFS supplier and review of the plant-specific computerized operation and maintenance manual (COMM) for the MFS. This was in sharp contrast to the operators at Plant B, who were on-site while the new membrane filtration system was constructed, tested, and started up, allowing for much more exposure to the new technology and more familiarity with system operation before they had to take the reins. In both cases, communication with the MFS suppliers support staff after the completion of plant startup helped continue the process of system optimization and operator training. These and other valuable lessons from the case studies can be applied to the startup phase of future projects. ACKNOWLEDGEMENTS The authors of this paper would like to thank Bob Panek, Dave Fauber and Patrick Christman (Town of Cape Charles); Dave Tyrrell (Town of Berryville); the staff of the Cape Charles and Berryville WWTPs; Shawn Addison and Jeny Chacko (GE Power and Water); Greg Jablonski and Sebastian Smoot (GHD).

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CONCLUSIONSACKNOWLEDGEMENTS