ArcelorMittal Monessen operates

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1 Technical Article 75 Full-Scale Treatment of a Coke Oven Wastewater Using Immersed-Membrane Biological Reactor Technology ArcelorMittal Monessen operates a coke production plant on the Monongahela River located in Monessen, Pa., USA. Typical coke production is approximately 1,000 tons per day derived by heating coal in the absence of air in refractory ovens. Byproducts recovered include crude coal tar, elemental sulfur, ammonium sulfate and crude light oil. Effluent from a coke oven byproducts plant contains elevated concentrations of organic and nitrogenous compounds from sources such as coke oven gas desulfurization, crude light oil recovery, ammonia still operation, coke oven gas condensates, final gas coolers and barometric condensers. The greatest volume of effluent is waste ammonia liquor (WAL), which is used to scrub coke oven gas to condense tars and moisture and is recycled at a high rate. WAL has high concentrations of BOD 5, chemical oxygen demand (COD), ammonia, cyanide, sulfide, benzene, phenols and polyaromatic hydrogen compounds (PAHs), all of which go to the facility s byproduct wastewater treatment system. Background and Objectives With the advent of more restrictive effluent categorical standards from the U.S. Environmental Protection Agency (EPA), it became evident that more technologically advanced wastewater treatment techniques to the facility s conventional activated sludge treatment system were required. Tetra Tech and GE Water & Process Technologies (GE) were commissioned by ArcelorMittal to conduct a four-month pilot study in on an immersed-membrane biological reactor (MBR) system using a prototype of commercially available equipment. The overall objectives of the pilot study were to: Determine the effectiveness of the MBR to treat coke plant wastewater in achieving effluent quality by the Effluent Limitation Guidelines for the Iron and Steel Making Industry CFR Part 420. Demonstrate the capability of the MBR to successfully perform and achieve 75 99% removals of targeted compounds, during both steadystate and spiked loading conditions. Collect necessary information (i.e., sludge retention time, sludge wasting rate, nutrient dosing, etc.) to complete the design for a full-scale MBR treatment system. To evaluate the process technical feasibility, a pilot-scale system was erected and operated at the ArcelorMittal Warren (Ohio) coke plant; this was required since the Monessen plant was non-operational in idle hot status since 2009, while undergoing repair preceding a capital rehabilitation and replacement program until mid The Tetra Tech/GE pilot-scale demonstration unit operated from September 2011 through January Since activated-sludge nitrification processing of coke plant wastewaters is a well-known technology, the primary operational and maintenance objectives of the pilot plant were: (1) demonstrate the operational feasibility of the membrane modules to resist fouling and/or chemical degradation; (2) determine the attainable membrane Effluent from a coke oven byproducts plant contains elevated concentrations of organic and nitrogenous compounds. This paper will focus on the design, seeding, start-up and operation following a successful pilot-scale demonstration on a coke plant s wastewater using an immersedmembrane biological reactor. Authors Art Kuljian senior environmental engineer, Tetra Tech, Ann Arbor, Mich., USA art.kuljian@tetratech.com Jeff Penny GE Water & Process Technologies, Oakville, Ont., Canada jeffrey.penny@ge.com Joshua Harrison ArcelorMittal Monessen LLC, Monessen, Pa., USA joshua.harrison@arcelormittal.com

2 76 Technical Article Table 1 Membrane Biological Reactor (MBR) Pilot System Performance Constituent Units wastewater flux rates; and (3) determine the membrane chemical maintenance cleaning and recovery cleaning requirements to maintain membrane flux and permeability. The pilot testing results indicated promising performance by the MBR process. Table 1 summarizes the relative removals for the critical parameters. System Description Influent avg. Effluent avg. Target Removal % BOD 5 mg/l 1,028 3 < COD mg/l 2, < TSS mg/l 20 2 < Oil and grease mg/l 8 2 < NH 3 -N mg/l 47 1 < Cyanide mg/l < Phenol mg/l 226 <0.03 < Benzo(a)pyrene µg/l 90 ldl < Naphthalene µg/l 284 ldl < ph S.U As a result of the pilot test program s success and subsequent correspondence with local and state regulators, ArcelorMittal authorized Tetra Tech in February 2013 to perform comprehensive design/supply services for Figure 1 Schematic of membrane biological reactor (MBR) system. a full-scale wastewater treatment system. It was important to the owner (ArcelorMittal) that the engineering services contractor (Tetra Tech) accept total system responsibility for the project s duration, for not only managing its subcontractor (GE) and equipment suppliers but for ensuring regulatory compliance during the start-up period and performance testing. Fig. 1 depicts a simplified flow schematic of the 150,000-gallon-per-day (100-gpm nominal) wastewater treatment facility for satisfying the overall objectives. The primary system component is the ZeeWeed ultrafiltration (UF) MBR system by GE. The system is a low-energy, immersed-membrane process that consists of outside-in, hollow-fiber modules immersed directly in the feedwater. Depending on the required capacity, a full-scale treatment facility is comprised of a given number of modular components: modules, cassettes and trains. Fig. 2 illustrates an individual membrane module, which is the building block of the filtration system. A module consists of hundreds of membrane fibers, oriented vertically between two molded plastic headers. Membrane modules are joined together to form a cassette, which is the smallest operable unit of the filtration system. Each cassette is connected to a common permeate (filtrate) header. The full-scale facility treats wastewater with two membrane trains, each comprised of 42 membrane modules. The MBR s aerobic suspended-growth environment is maintained in the bioreactor via diffused aeration and continuous mixing of the mixed liquor at concentrations of 10,000 mg/l. The net effect of the higher biological solids concentration is that the reactor size and hydraulic retention time are reduced while higher sludge ages (of 90 days or more) are maintained. The membranes are configured as small-diameter tubules that are bundled in modules and housed in a cassette for easy handling. The membrane modules are immersed in the membrane tank, whereby wastewater passes concentrically into the membranes under a small vacuum induced by pumping versus under high pressure. This results in the solids being retained in the reactor, while the treated wastewater (permeate) is discharged. Every minutes, the process pump is reversed for approximately 30 seconds to backpulse permeate back into the bioreactor; this helps to clear the membranes and thus prevent fouling while maintaining outflow.

3 77 Figure 2 (a) (b) Membrane fiber (a) and GE Membrane Module (b). Airflow is introduced at the bottom of the membrane module to create turbulence that scrubs and cleans the outside of the membrane fibers. This reduces the solids accumulation on the membrane surface and also provides mixing within the process tank to maintain solids in suspension. The immersedmembrane system can remove particles that are greater than 0.04 microns in size. Furthermore, if dissolved components can be first converted to insoluble components, the membrane will subsequently remove them as well. Fig. 3 illustrates the flow schematic for the entire wastewater treatment system. The entire system, except for the equalization storage tanks and bioreactor tank, are housed in a 4,250-square-foot metal-sided pre-engineered building. The wastewater treatment plant (WWTP) consists of preliminary treatment for oil/tar removal and the biological treatment system for treatment of excess flushing liquor (waste ammonia liquor), wastewater from coke oven gas (COG) desulfurization, byproduct wastewater (from light oil recovery) and some site stormwater. The ammonia still effluent is discharged to the equalization tanks. From here, the wastewater is cooled via spiral heat exchangers to <85 F and an oil coalescer for free oil removal to mitigate membrane fouling. Nutrient augmentation for maintaining effective biodegradation in the MBR is supplied via phosphoric acid addition. Sludge dewatering for maintaining effective mixed liquor suspended solid (MLSS) concentrations in the bioreactor is provided with a belt filter press. These filter cake solids are beneficially recycled to the coke ovens with the coal. Effluent following MBR treatment is collected, sampled and pumped to the Monongahela River. The bioreactor entails both an anoxic zone and an aerobic zone. Denitrification takes place in the anoxic zone where nitrates and nitrites are reduced to nitrogen gas with the introduction of carbon-rich (phenolic-laden) influent from the equalization tanks. This transformation, (NO COD heterotrophs N 2 + CO 2 ), (anoxic) Figure 3 Process flow schematic for full-scale wastewater treatment.

4 78 Technical Article by the denitrifying bacteria releases nitrogen gas and carbon dioxide. For every milligram of nitrate (NO 3 ) reduction, 3.57 mg of alkalinity (as CaCO 3 ) is produced. Nitrification occurs in the aerobic zone with process air addition and here the ammonia forms nitrates and nitrites via autotrophic nitrifying bacteria. Simplistically, NH 4 + O 2 nitrosonomas NO 2 nitrobacter NO 3. (aerobic) For every milligram of ammonia that is oxidized, 7.14 mg of alkalinity (as CaCO 3 ) is consumed. Therefore, the addition of caustic soda (KOH or NaOH) to maintain effective ph ( range) in the bioreactor is essential for nitrification and good microbiological activity. System Construction, Biological Seeding and Start-Up Following the system design in late August 2013, and pre-purchase of the long-lead-time delivery equipment, Tetra Tech provided technical assistance during the WWTP s construction, beginning October System start-up commissioning began in early February The wastewater was then seeded with activated sludge from the U. S. Steel Mon Valley Works, Clairton Plant beginning in March 2014 for three weeks to acclimate the MBR s bioreactor tank. Since start-up, the system has operated for nearly a year at the time of this writing and has been in conformance with all regulatory criteria. Coke oven wastewater was introduced in early April The bioreactor s seed sludge became acclimated and the MBR system began discharging effluent one week later. Following hydrostatic (i.e., clean water) testing of the Figure 4 entire wastewater treatment system for leaks and field programming verification of the automated programmable logic controller (PLC), the system was ready for commissioning on 3 February The bioreactor was then seeded with thickened waste-activated sludge for 20 days starting 3 March 2014, as shown in Fig. 4. Adequate nutrients were provided at a carbon-tonitrogen-to-phosphorous ratio (C:N:P) of 100:5:1 to Schematic of membrane biological reactor (MBR) system. support biological activity in the reactor prior to the addition of coke oven wastewater. Sucrose (C), urea (N) and phosphoric acid (P) were added to the bioreactor in addition to caustic soda for alkalinity control. During a 10-day (one-week) period, until 7 April 2014, 100,000 gallons of remaining equalization tank wastewater from 2009, as shown in Fig. 5, were introduced to the bioreactor on a batch basis (at a rate of 5 10 gpm) for confirmation that the waste was biodegradable. Bioreactor temperature, dissolved oxygen and ph were also monitored, as well as COD concentration and phosphoric acid usage rates. Following aeration of the bioreactor, an oxygen uptake rate (OUR) expressing mg/l oxygen consumed per minute (mg/l O 2 /minute) was obtained on the biosolids. These results, which showed an increase in the OUR with a decrease in dissolved oxygen (DO), demonstrated that the microorganisms were acclimating and that the waste was being biodegraded. There were both active stalked and free-swimming ciliates observed. Rotifers and nitrifiers were also observed and quite active. Table 2 presents the results of analyses for key constituents in wastewater during system start-up and up to February Start-up of the batteries (coke ovens) and coal charging followed for five days starting 11 April 2014, while generating new stripped liquor wastewater as feed to the equalization tanks and to the new WWTP. Treated effluent from the WWTP began on 16 April 2014, and flows increased to 70 gpm for the next 50 days, while the coke ovens reached full production capacity. Fig. 6 depicts the aeration pattern of the bioreactor at the time of WWTP effluent discharge. Figure 5 Schematic of membrane biological reactor (MBR) system.

5 79 Table 2 Influent Wastewater Characteristics Figure 6 Parameter Units Design value Biological System Performance Key bioreactor operational parameters such as DO, hydraulic retention time (HRT), solids retention time (SRT), MLSSs, nutrient addition, ph and sludge wasting are discussed in detail in the following sections. Observed influent characteristics Average Min. Max. Flowrate (gpd) 144, ,000 50, ,000 ph BOD 5 (mg/l) 2, COD (mg/l) 7,000 3,281 1,756 8,896 TSS (mg/l) Conductivity (µs/cm) <22,000 11,955 7,680 18,070 NH 3 -N (mg/l) ,238 Total phosphorous (mg/l) Total cyanide (mg/l) CN, free (mg/l) Oil and grease (mg/l) TKN (mg/l) Phenol (mg/l) Benzo(a)pyrene (µg/l) Naphthalene (µg/l) Thiocyanate (filtered) (mg/l) 1,000 2, ,733 H 2 S (mg/l) Temperature ( C/ F) 30/85 23/73 14/57 32/90 Alkalinity (mg/l) ,680 Bioreactor at start-up. Table 3 summarizes the key operating conditions for the bioreactor including ph, DO, MLSS, SRT, HRT and food-to-microorganism ratio (F:M). The bioreactor has operated at ambient temperature conditions, which averaged 84 F and ranged F. The DO was consistently higher than the optimal mg/l due to the desirability to maintain process blower airflow at optimal efficiencies. HRTs of 100 hours enabled effective COD/BOD 5 removal objectives. An F:M ratio of 0.11 along with an SRT of more than 200 days yielded effective organic removals and sludge solids rates. Table 3 MBR Operational Conditions Parameter Units Range Actual ph DO mg/l MLSS mg/l 8,000 16,000 11,000 MLVSS/MLSS mg/l SRT Days Yield (sludge) % HRT Hours F:M KgCOD/Kg MLVSS OLR Kg COD/M3/d lb COD/kcf/d Influent Flowrate Following charging of the coke ovens to pull production in early June 2014, the coke plant influent wastewater averaged 102,000 gpd (70 gpm) to date, at the time of this writing. Actual flows from the equalization storage tanks are shown in Fig. 7. Biocentral (river) water is required for microbiological toxicity inhibition whenever the conductivity in the bioreactor feed tank approaches a control setpoint of 10,000 MS/(µS/cm); thus up to 65 gpm of additional water can be added to the anoxic zone of the bioreactor for conductivity control. Mixed Liquor Suspended Solids MLSS and mixed liquor volatile suspended solids (MLVSS) are indicators of biomass population in the bioreactor. Generally, MLSS concentrations in an MBR are within 8,000 10,000 mg/l, while MLVSS is about 80 90% of the MLSS. The bioreactor was originally seeded with acclimated sludge, with a concentration

6 80 Technical Article Figure 7 Influent flowrate from equalization tanks. Figure 8 Mixed liquor concentrations. Figure 9 Food-to-microorganism ratio. of 12,000 mg/l MLSS, from Clairton Works existing WWTP starting in March Over the proceeding weeks, the sludge reached 16,000 mg/l. The average MLVSS/MLSS ratio during the study was 0.9. Once the belt press was commissioned in mid- May 2014, the MLSS/MLVSS concentrations in the bioreactor stabilized to a 10,000/mg/L/9,000 mg/l condition during normal operation. Refer to Fig. 8 for the MLSS and MLVSS concentrations recorded to date. Hydraulic Retention Time and Solids Retention Time HRT and SRT are key parameters in the biological design for organics removal in the MBR process. One advantage of a MBR over the conventional activated sludge (CAS) process is that the selection of HRT is no longer a compromise for adequate SRT, due to the complete liquid/solid separation provided by the ultrafiltration membrane. Therefore, a relatively long SRT can be achieved without employing huge tanks and still provide rigorous bioactivity to remove organic contaminants. The bioreactor volume selected (i.e., 550,000 gal) guaranteed sufficient hydraulic and solids retention time to achieve full biodegradation of the design influent organic load. The design bioreactor HRT of 86 hours was required to consistently meet COD/BOD 5 removal objectives. SRT was controlled by wasting excess activated sludge from the membrane tank. During steady-state operation, the SRT was maintained at 275 days. In order to maintain MLSS in the bioreactor of between 8,000 and 10,000 mg/l, it was determined that wasting 2,000 gallons of sludge per day from the 550,000-gallon bioreactor volume be attained. Food to Microorganism Ratio The F:M ratio typically relates the

7 81 concentration of influent mass loading (pounds or kilograms) of BOD 5 or COD to MLSS (mass loading in the bioreactor and membrane tanks). The F:M ratio calculated for the duration of the start-up was based on COD as the food source and MLVSS as the microorganisms, as this is a more accurate estimate of the mass of microorganisms than MLSS. Refer to Fig. 9 for the F:M ratio observed throughout normal operations. The average F:M to date is 0.08 kg COD/kg MLVSS/d. Figure 10 Influent Ammonia, Cyanide, Thiocyanate and Phenol Wastewater from the equalization tank is laden with nitrogen compounds in the form of ammonia-nitrogen (NH 3 -N) and thiocyanate (SCN), which comprise the majority of TKN loading (reported as total kjeldahl nitrogen). Ammonia-nitrogen and thiocyanate concentrations in the influent wastewater have averaged 110 and 790 mg/l, respectively. For ammonia loading purposes, this is an equivalent TKN loading of 330 mg/l in the bioreactor during average flow conditions. Phenolic compounds formed during the coal carbonization process are condensed in the coke wastewater and attributable to a majority of the organics requiring treatment in the MBR. The system was designed to handle a range of phenols from 100 to 600 mg/l. Cyanides are formed during cokemaking operation and most peak concentrations appeared during the new Table 4 coke plant re-start with new COG piping and ensuing corrosion. Parameter Complex iron cyanides (prussian blue, prussian green) formed as fixed cyanides end up in the liquor systems and made removal in the ammonia stills and WWTP difficult. The fixed cyanide concentrations eventually subsided following metal passivation and barrier films forming on the previously corroded metal surfaces. This is evidenced in late-2014, at which time normal cyanide levels (10 30 mg/l as CNT) in the wastewater influent were attained. Fig. 10 depicts the relationships for influent wastewater ammonia, thiocynate, cyanide and phenols. Influent wastewater ammonia, thiocyanate and phenol. MBR System Performance Results of Implementation MBR Effluent Characteristics Wastewater characterization data (average influent and effluent versus target values) for the treated MBR system effluent are summarized in Table 4 along with the average removal rates. Overall, the MBR produced an effluent quality for the key target compounds (BOD 5, TSS, nitrogen, phenols and PAHs with removals between 90 and 99%. All constituents met the target removal rates. The bioreactor consistently maintained a COD removal efficiency of more than 80%. Units Influent average Effluent average Target % Removal ph BOD 5 (mg/l) <10 99 COD (mg/l) 3, < TSS (mg/l) <5 98 NH 3 -N (mg/l) <5 99 Total cyanide (mg/l) < Oil and grease (mg/l) 22 <5 <20 77 TKN (mg/l) <5 99 Phenols (mg/l) < Benzo(a)pyrene (µg/l) Naphthalene (µg/l) Thiocyanate (mg/l) Temperature ( C) Alkalinity (as CaCO 3 ) (mg/l)

8 82 Technical Article COD and BOD5 Effluent COD concentrations averaged 550 mg/l, or approximately 80% removal throughout the period. The bioreactor consistently maintained a COD removal efficiency of 85%, owing to the high biodegradability of the ammonia still wastewater. BOD 5 removals were over 99% and effluent average concentrations were less than 5 mg/l. Oil and Grease (TFOG) Throughout the entire start-up and normal operating conditions the TFOG levels in the permeate averaged under 5 mg/l. Overall, a 75% reduction in TFOG was achieved and consistently below the target level of 20 mg/l. Total Suspended Solids (TSS) and Sludge Yield Average TSS concentrations in the effluent were under 1 mg/l and turbidity was <0.10 nephelometric turbidity units (NTU). Average sludge yields were lb. VSS/lb. COD consumed. It is notable that the belt press sludge dewatering operation runs intermittently (twice weekly) when sludge wasting becomes necessary (i.e., at MLSS concentrations >10,000 mg/l in the bioreactor). Filter cake solids average 20% dry solids and the highly organic dewatered sludge is transported to coal loaders for recycle to the coke batteries. Figure 11 Effluent ammonia, thiocyanate and cyanide. Figure 12 Effluent phenol. Ammonia and Thiocyanate Ammonia, thiocyanate and cyanide trending in the effluent is depicted in Fig. 11. The effluent concentration averaged 1 mg/l NH 3 -N, indicating a viable nutrient uptake via nitrification in the bioreactor by the microorganisms. Thiocyanates were present in the wastewater influent at average concentrations of 790 mg/l and following its oxidation and decomposition in the bioreactor, an effluent of under 3 mg/l was attained. Cyanide (CN Total) Total cyanide removals over the course of normal steady-state operating conditions indicate a removal reduction rate of nearly 75%. Oxidation of cyanide by air alone is limited; however, non-oxidative removal of cyanide is enhanced by a decrease in ph (to range) and in the presence of aeration. Cyanide adsorption occurs in the biomass during wasting of the MLSS and subsequent belt press sludge dewatering operations. Except for two spikes since full coke production in early June 2014, the cyanide levels in the effluent have been below the 5.50 mg/l level, as shown in Fig. 11. Phenols Phenols have shown more than 99% removal rate in the aerobic zone of the bioreactor to levels below 0.01 mg/l. Thus, the MBR has demonstrated its ability to remove phenols at concentrations well below the regulatory limit of mg/l, as shown in Fig. 12. Polycyclic Aromatic Hydrocarbons PAHs, primarily benzo(a)pyrene and naphthalene, are present in

9 83 waste ammonia liquor. Naphthalene from coke oven byproduct gas is removed by way of light oil recovery and steam in the wash oil still. Residual naphthalene ends up in the equalization storage tanks before treatment in the MBR system. The MBR showed that it could degrade these PAHs to below the 10 mg/l, or an overall removal efficiency of 99.9%. A more comprehensive listing of the MBR permeate characteristics for all constituents analyzed is depicted in Table 5. Ultrafiltration (UF) System Performance The UF performance was closely monitored throughout the full-scale program s implementation. This section includes detailed discussions regarding the operational flux, transmembrane pressure, permeability and membrane cleaning. Flux Flux is a measure of the rate at which the permeate passes through the membrane per unit of outside surface area of membrane per day. It is reported in units of gallons per square foot per day (gfd). The net flux is a calculation that takes into account the frequency and duration of backpulsing, accounting for the lost production time as well as the actual volume of permeate consumed during a backpulse. The targeted flux demonstrated throughout normal operations was 8 10 gfd. The method incorporated to maintain the design flux included operations in a backpulse mode. During start-up (April June 2014) a conservative flux of 6 gfd was used to allow the system to acclimate while coke plant production to full capacity increased. In June, the flux was increased to 8 gfd as influent wastewater volumes increased. It can be noted that the increased membrane flux had little impact on the transmembrane pressure (TMP). Transmembrane Pressure TMP is the amount of pressure (psi) required to pull permeate through the membrane pores. The UF system is designed to maintain a constant flux, therefore, as the membrane becomes fouled, the transmembrane pressure increases. The UF system is equipped with several tools for membrane fouling control. Air scouring is used to remove solids away from the membrane surface while a backwash cycle removes fine particles loosely inserted in the membrane pores. Also, chemical maintenance and recovery cleanings are used to remove organic and inorganic membrane fouling and reduce operational TMP. Although the GE UF system has a maximum TMP control setpoint of 8 psi, the average operational TMP observed during normal operations was much lower at under 1 psi. Since start-up, the UF system is able to successfully operate under 1 psi and well within the TMP range. An N-1 test was conducted on one membrane train to demonstrate that one (of the two) membrane trains could produce 150 gpm (maximum wastewater Table 5 Effluent (MBR Permeate) Characteristics Parameter Units Observed effluent characteristics Average Min. Max. Temperature ( C) Alkalinity (mg/l) ph Conductivity (µs/cm) 8, ,420 TSS (mg/l) BOD 5 (mg/l) COD (mg/l) ,174 NH 3 -N (mg/l) NO 2 -N (mg/l) NO 3 -N (mg/l) Total phosphorous (mg/l) Total cyanide (mg/l) Oil and grease (mg/l) TKN (mg/l) Phenols (mg/l) Thiocyanate (mg/l) Benzo(a)pyrene (µg/l) Naphthalene (µg/l) flowrate) for 24 hours. A TMP of <3 psi was observed during the N-1 test, but was restored to <1 psi following a return to normal flow conditions. Overall, the test was successful and produced the required flow and met effluent discharge criteria. For the entire 8-month duration since start-up, the operational TMP was at less than 10% of the maximum allowable TMP. A minor step-up in TMP was observed from 22 September to 29 September, where the TMP reached 40% of the allowable range but with only one of the two trains operating. Through regular operations with both membrane trains operating, the TMP observed is <10 psi. Backwash Properties The backwash is used as a method of cleaning in the process. Typically, every 12 minutes, flow is reversed through the membrane (backpulsed) for 30 seconds, pushing clean water from the inside of the membrane lumen to the outside. The water used for the backpulse is permeate that has been collected in the backpulse tank. Backpulse flux refers to the rate at which the backpulse water (permeate from the backpulse tank) passes through the membrane per unit of surface area of membrane. The backpulse flux is typically set to equal the permeate flux. During normal operations, the backpulse flux is maintained at 10 gfd.

10 84 Technical Article Membrane Chemical Cleaning The chemical cleaning strategy used to maintain UF membrane permeability consists of two different types of cleans: maintenance and recovery cleans. Maintenance cleans can be performed on a regular basis and use lower concentrations of cleaning chemicals. The objective of a maintenance clean is to reduce the membrane permeability decline and maintain UF membrane performance. Recovery cleans are performed less frequently, using a higher concentration of cleaning chemicals. The objective of a recovery clean is to recover the UF membrane permeability to a baseline condition observed after the initial break-in period for the membrane. Two different cleaning agents are used for maintenance and recovery cleans. Sodium hypochlorite at a concentration of 250 mg/l was used to remove membrane fouling caused by organic compounds that have not been biodegraded in the activated sludge system as well as the biofilm that develops due to microorganism growth on the membrane surface. Citric acid was used to remove inorganic scaling that forms on the membrane surface. Maintenance cleans are scheduled once every two to four weeks, or more frequently whenever the filtration output declines by 10 15% or the differential pressure increases by 15%. Due to low TMPs, a recovery maintenance clean was deemed not necessary to maintain UF membrane TMP. It is planned for a recovery cleaning to be performed after one year of operation with a 1 g/l solution of bleach and a 2 g/l solution of citric acid. Summary and Conclusions Once the bioreactor tank microorganisms were acclimated, the effluent quality except for cyanide demonstrated that the MBR consistently exceeded the permeate requirements. By the end of start-up, an HRT of 100 hours versus the design HRT of 86 hours consistently met the removal targets. During steadystate operation, the SRT was maintained at 275 days. Good to excellent removal of all primary target compounds was attained, with 80 95% removal of BOD 5, COD, TSS and soluble FOG; 95 99% removal of ammonia, thiocyanates, phenols, benzo(a)pyrene and naphthalene; and 75% removal of cyanide. The bioreactor s performance appeared to be most vulnerable to low-ph, low-alkalinity wastewater conditions (i.e., below 6.85 ph). However, removal efficiencies appeared to improve quickly in response to ph adjustment via the addition of sodium hydroxide. Optimum bioreactor performance appeared to be in the ph range of 7.0 to 7.5. The UF membrane system treatment capacity is successfully maintained through the use of inorganic and organic fouling removal methods. Maintenance chemical cleanings utilizing sodium hypochlorite and citric acid were implemented to further improve the membrane condition. To date, no irreversible loss of permeability has occurred. Flux rates of 8 gfd were maintained throughout operations. This accounts for losses due to backpulsing of permeate via reverse pressure cleaning of the membranes to prevent organic fouling of the membranes while maintaining outflow. Permeability rates of 80 gfd/psi can be maintained during steady-state conditions. TMP of psi before backwash were achieved, and considered to be well within industry standards for a UF. Membrane maintenance cleaning of the UF membranes was induced every two to four weeks with a 250 mg/l solution of sodium hypochlorite to remove any non-biodegradable organics. Citric acid was administered with a 1,000 mg/l solution to remove inorganic scaling that forms on the membrane surface. Also notable is that the MBR demonstrated an ability to withstand relatively short periods of insufficient oxygen supply such as could be encountered during a severe shock load or emergency shutdown from a power outage. The response to this short-term anoxic condition was primarily a reduction in biological activity, but one which appeared to recover upon return to aerobic conditions. Periodic microscopy of microbiology showed a viable population present since start-up. The operation supports the following process design criteria: a dissolved oxygen supply of >4.0 mg/l, an HRT of four days and an OLR of 40 lbs. COD/day/kcf reactor volume. Overall, the effluent quality is well within categorical standards for Coke Making Subcategory 40 CFR 420 and is able to consistently comply with all discharge requirements. No irreversible loss of membrane permeability has occurred throughout normal operations. Acknowledgments To nominate this paper for the AIST Hunt-Kelly Outstanding Paper Award, visit AIST.org/huntkelly. The authors gratefully acknowledge the cooperation and dedication of ArcelorMittal Monessen s Paul Champagne and Brian Bartels, and ArcelorMittal Warren s Joe Magni for their efforts throughout the project s implementation. The authors also acknowledge the technical sales support, system commissioning and start-up assistance provided by GE s Water & Process Technologies Bob Brazier and Glenn Conners. F This paper was presented at AISTech 2015 The Iron & Steel Technology Conference and Exposition, Cleveland, Ohio, USA, and published in the Conference Proceedings.