COST TRENDS OF MBR SYSTEMS FOR MUNICIPAL WASTEWATER TREATMENT

Transcription

1 COST TRENDS OF MBR SYSTEMS FOR MUNICIPAL WASTEWATER TREATMENT James DeCarolis*, Samer Adham **, William R. Pearce***, Zakir Hirani**, Stephen Lacy**, Roger Stephenson** *MWH Americas, Inc Farnham Street, Suite 300 San Diego, CA **MWH Americas, Inc. ***City of San Diego ABSTRACT Cost estimates were developed for full-scale (1 and 5 MGD) MBR facilities designed to treat municipal wastewater. These estimates included both capital and operational / maintenance (O&M) costs related to the headworks, MBR process (biological process and membrane system), chlorine disinfection and effluent storage. The costs associated with the membrane systems were developed from budgetary cost quotes provided by suppliers which have recently introduced newly developed MBR products into the U.S. market. Each of these products offer unique design features aimed towards the reduction of capital and/or operation costs. All other costs associated with the MBR facilities were developed from previous conceptual designs performed by the project team and updated using current standard engineering cost indices. Total estimated capital plus annual costs ($/1000 gal treated) for the newly developed MBR systems (1-MGD capacity) ranged from $2.02-$2.58. The range in costs directly reflects the range in membrane system and membrane replacement costs provided by the participating MBR suppliers. Evaluation of cost estimates for 1 and 5 MGD capacity MBR facilities revealed an average economy of scale of 16.5% for the non-membrane components (i.e. headworks, process basins, buildings etc.) of the MBR facility and 23.6% for the membrane system only. Comparison of the current MBR cost estimates to historical costs estimates (adjusted for inflation) suggest that a steady decrease has occurred in the membrane system cost of MBRs between However, an opposite trend was observed over the same time period for costs associated with the non-membrane components of the MBR facility. The drop in membrane system costs are attributed to advancements in manufacturing and increased competition in the market place while the increased costs of facility components are attributed to the increased cost of concrete and other raw materials used for plant construction. Results from this analysis shows these opposing trends have resulted in the overall total cost of MBR facilities to be fairly level (i.e. < 10% increase) between 2000 and KEYWORDS Membrane Bioreactor, MBR, Wastewater Reclamation, Water Reuse, Wastewater Treatment 3407

2 INTRODUCTION Membrane bioreactors (MBR) are a leading-edge technology being applied worldwide for municipal wastewater treatment. The municipal MBR market has grown dramatically over the past decade with facilities increasing in number and capacity. During this time, the number of suppliers offering MBR systems within the municipal wastewater market has also sky rocketed. Though the technology has become established within the municipal wastewater treatment sector, little published information exists related to the cost of MBR systems (Churchhouse and Wildgoose, 1999; Davies et al., 1998). Due to the vast growing nature of the MBR market, it is important for the industry to have current cost information of these systems for budgeting and planning purposes. An evaluation of the historical cost trends of MBR systems would also provide useful information on how technological advancements and increased competition are impacting costs. Lastly, insight on specific applications where the implementation of MBR may be economically favorable over conventional treatment alternatives would be valuable for those considering the technology to meet their wastewater treatment goals. The project team has been evaluating MBR technology related to municipal wastewater treatment for nearly a decade. This included the completion of four consecutive projects focused on the development of various MBR systems (Adham et al., 1998, 2000, 2004; DeCarolis et al., 2007). The scope of each project also included rough order cost estimates of MBR technology based on various scenarios. Upon completion of the most recent project, focused on newly developed MBR products, the project team thought it would be useful to compare the cost information from the four projects to identify possible general trends in MBR costs for the given time period. It should be emphasized the cost estimates provided in this paper represent budgetary estimates for municipal MBR facilities based on certain assumptions; however site specific factors can significantly alter MBR costs and must be considered when performing budgetary planning. The objectives of this evaluation were: Perform total cost estimates (capital and annual) of new developed MBR systems recently introduced in the U.S. market for various capacities (1 and 5 MGD). Assess the economy of scale of associated with 1 and 5 MGD MBR facilities. Compare cost estimates of MBR facilities prepared between to identify possible cost trends related to the membrane component as compared to other facility system components (i.e. biological basins, pre and post treatment). METHODOLOGY Costing Approach Cost analyses were performed to estimate the capital and operational costs of full-scale MBR water reclamation facilities for treatment capacities of 1 and 5 MGD (4,000-20,000 m 3 /day). Costs were estimated for MBR facilities consisting of headworks, process basins, membrane system, mechanical equipment, blower and pump building, chlorination system and effluent storage. All costs except those related to the membrane systems were derived from previous estimates (Adham et al., 2004) and updated using current Engineering News Record 3408

3 Construction Cost Index (ENRCCI) and Chemical Engineering Plant Cost Index (CEPCI). Costs associated with the membrane systems (i.e. membranes, pumps, blowers and miscellaneous equipment along with installation) were based on recent budgetary costs estimates provided by suppliers of the newly developed MBR systems including Koch Membrane Systems, Huber Technologies Inc., Kruger Inc. and Parkson Corporation. Table 1 provides a brief description of each of these MBR products including their unique design features which may impact capital and/or operation and maintenance (O&M) costs. In order to get comparable quotes from all suppliers, a memo was created and given to each supplier, which provided specific information related to the cost request. The cost estimates of the newly developed systems were compared to historical MBR cost estimates prepared from budgetary estimates provided by establsihed MBR suppliers including Zenon, Kubota and Memcor (Adham et al., 1998, 2000, 2004). Conceptual Design Criteria Table 2 provides the MBR design criteria used for all cost estimates. The raw water quality was assumed typical of medium strength municipal wastewater with BOD 5, ammonia, and TSS of 290 mg/l, 30 mg-n/l and 320 mg/l, respectively. The membrane operating conditions and reactor design criteria were based on previous conceptual MBR designs and pilot testing conducted by the project team (Adham et al., 2004; DeCarolis et al., 2007) and consultation with participating MBR manufacturers. As indicated, the instaneuous membrane flux rates ranged from gfd for submerged systems and 30 gfd for external systems. The higher flux value used for external systems is due to membrane scouring which results from high recirculation of MLSS across the membrane surface which prevents accumulation of solids on the membrane surface. As shown in Table 2, cost estimates were based on MBR systems designed for complete oxidation of biodegradable organic matter (BOD 5 <2 mg/l), complete nitrification (ammonia<1.0 mg-n/l), partial denitrification (nitrate<10 mg-n/l) and biological phosphorus removal (total phosphorus <0.2 mg-p/l). For costing purposes, it was also assumed that all MBR facilities were sewer mining or scalping plants built on a clean plot of land. Such facilities differ from end-of-pipe systems because raw wastewater is withdrawn at a controlled rate from the collection system and all residuals (screenings, grit, WAS, etc.) are returned to the same pipe which eliminates the need for sludge handling and disposal. In addition, MBR scalping plants require much less (or no) redundancy compared to end of pipe facilities. The participating manufacturers were requested to provide membrane system cost estimates based on the ability to operate at average conditions with two filter units out of service (OOS). One OOS to accommodate routine relaxation / backwashing and an additional membrane filter OOS for chemical cleaning. Lastly, costs were based on the design capacity without peaking. 3409

4 Table 1 Description of Newly MBR Systems used in Cost Analysis Supplier Membrane Type / Configuration Key Design Feature(s) Description Intended Purpose Potential Cost Impact Koch Membrane Systems hollow fiber / submerged Sealed fibers (one end) Prevent loss of membrane active area; minimize fiber breakage lower membrane replacement costs Huber Technologies Inc. flat sheet / submerged Rotating membranes, universal air scour Reduce membrane air scour lower energy costs Parkson Corporation tubular/external Side stream external membranes; Airlift System Reduce membrane air scour / increase operating flux lower energy costs; reduce capital cost of membranes for given production capacity Kruger Inc. flat sheet / submerged Uniform membrane pore size Enhance effectiveness of membrane cleaning reduce cleaning costs / lower membrane replacement costs 3410

5 Table 2 MBR Design Criteria used in Cost Analysis Desgin Criteria Units Value Raw Water Quality BOD 5 mg/l 290 COD mg/l 630 TSS mg/l 320 VSS mg/l 260 Ammonia-N mg/l 30 TKN mg/l 60 Total Phosphorus-P mg/l 2 TDS mg/l 1200 Alkalinty mg/l 245 Temperature Deg C 20 Membrane and Reactor Design Conditions Flux 25 Deg C (submerged) 30 (external) MLSS g/l 8 F/M day HRT hr 6 SRT days 10 Effluent Water Quality BOD 5 mg/l <2 Ammonia-N mg/l <1.0 Nitrate-N mg/l <10 Total Phosphorus-P mg/l <2.0 RESULTS AND DISCUSSION Cost Estimates of Newly Developed MBRs Captial Costs. Table 3 provides capital cost estimates for the various MBR facilites designed for 1 and 5 MGD capacities. The table includes total capital costs ($K) and amortized capital costs ($K/year) assuming a 5% interest rate over a 30 year period. As shown, the total capital cost estimate for the 1.0-MGD installations ranged from $7,990,000 $9,850,000, while the amortized cost ranged from $520,000-$641,000. The range in capital costs directly reflects the range of membrane system costs acquired from the four participating MBR suppliers. Each supplier was requested to provide membrane costs to include a 5-yr non-prorated warranty. In addition, the suppliers were requested that the costs include adequate membranes to produce the desired capacities at flux rates demonstrated during pilot testing. The values of instantaneous flux during pilot testing ranged from gfd for the submerged MBR systems and 30 gfd for the external MBR system. Net flux differs from instantaneous flux as it accounts for downtime due to relaxation/backwashing and product water used for backwashing/maintenance cleans. In general such losses amount to about 10% of daily production. Each supplier was requested to account for these losses when estimating membrane costs. Operation & Maitenance Costs. Table 4 provides the estimated annual and total O & M costs (5% interest rate over a 30-year period) for all MBR installations considered. As shown key O&M costs included labor, equipment repair and replacement parts, chemicals 3411

6 (membrane cleaning and disinfection), membrane replacement, and electricity. Membrane replacement costs were provided by the participating suppliers and are based on an 8-yr membrane life. All other unit cost assumptions are provided elsewhere (DeCarolis et al., 2007). As provided in Table 4, the annually O&M cost ($K/yr) for the 1-MGD ranged from $218-$302. The range in values is reflective of differences in membrane replacement costs ($K/yr) provided by the participating MBR suppliers, which ranged from $40-$106. Table 3: Capital Cost Estimates of MBR Facilities Item 1.0 MGD Capital Costs, $K 5.0 MGD Headworks $516 $2,064 Basins $503 $2,346 5-ton bridge crane $56 $69 1 Membrane System $1,419-$2,330 $5,803-$7,750 Mechanical $480 $2,766 Blower and Pump building $274 $962 Chlorine Dosing System $248 $1,242 Subtotal $3,441-$4,352 $15,183-$17,130 Electrical, 15% $525-$661 $2,222-$2,700 Mechanical/ Plumbing/HVAC, 13% $455-$573 $1,926-$2,340 Sitework, 9% $315-$397 $1,333-$1,620 Subtotal $4,791-$6,039 $20,295-$24,659 Contractor Overhead and Profit, 15% $719-$906 $3,044-$3,699 Subtotal-Construction Cost $5,509-$6,945 $23,339-$28,357 Land $825 $1,925 Contingency, 15% $826-$1,042 $3,501-$4,254 Engineering/Legal/Administration, 15% $826-$1,042 $3,501-$4,254 Total Capital Cost, $ $7,990-$9,850 $32,270-$38,790 Interest Rate 5% 5% Number of Years P/A Factor Amortized Capital Cost, $/yr $520-$641 $2,099-$2,523 1 Costs based on proposals received from MBR vendors in July/August

7 Table 4: O&M Cost Estimates of MBR Facilities Item O & M Costs, $K/yr 1.0 MGD 5.0 MGD Electrical power for process/miscellaneous $88 $438 Equipment repairs/lubricants/replacement $38-$57 $159-$223 Chemical Cleaning $9 $46 Chemical Cost for Disinfection $5 $26 Diffuser Replacement $3 $14 1, 2 Membrane Replacement $40-$106 $193-$478 Labor $35 $98 Total O&M Costs in First Year, $ $218-$302 $974-$1,323 Interest rate 5% 5% Number of Years P/A Factor Total Estimated O&M Costs, $ $3,350-$4,649 $14,974-$20,344 1 Membrane Replacement cost estimates based on 8-yr life; annual costs shown would fund account annually. 2 Costs based on proposals received from MBR vendors in July/August Figure 1 provides a visual representation of the percent contribution each O&M component has on the total annual cost associated with a 1-MGD MBR facility. These costs were based on average membrane replacement costs provided by the participating suppliers. As shown the two largest components of the O&M cost includes membrane replacement (28%) and energy (34%). The two main energy demands of the MBR system include that required by air blowers to provide process air and scour the membranes. Judd, 2006 reported that these demands make up 35% and 38%, respectively of the total energy demand associated with a 1.5 MGD MBR system. 13% MBR O & M Costs Energy 34% Equipment Repair / Replacement Chemicals Membrane Replacement 28% Labor 6% 19% Figure 1: Breakdown for O&M Costs for 1-MGD MBR Facility 3413

8 Interestingly, pilot data collected from 10 different MBR systems between at the Aqua 2030 Research Center (San Diego CA) suggests that the membrane air scour requirement for MBR systems has shown improvement in recent years. A summary of this data is provided in Table 5. As shown the specific air demand per membrane area (SADm) and specific air demand per permeate volume produced (SADp) requirements (as defined by Judd 2006) for System A and B were lower duirng testing conducted in 2003 as opposed to testing conducted in In additon, due to its high flux rate, the external membrane tested in 2006 had the lowest SADp (with the exception of System A which used cyclic aeration) of all systems tested. Though this data is useful to make general comparisons of air scour requirements from different types of MBR systems it is important to also consider the required cleaning frequencies of the systems. For example a system operating with lower SADp or SADm value may require more frequent membrane cleaning and therefore increased costs associated with chemicals and possible reduced membrane life. The project team is currently incorporating this information into a more detailed cost model to compare the energy costs of the various MBR systems. Table 5: Membrane Air Scour used for MBR Systems MBR System ID Year Tested Configuration Instantaneous Target Permeate Flux (gfd) SADm (scfm/ f 2 ) SADp (ft 3 air / ft 3 permeate) 1 A 1998 immersed HF B 1998 immersed HF C 2002 immersed FP D 2002 immersed HF A 2003 immersed HF B 2003 immersed HF E 2006 immersed HF F 2006 side stream MT G 2006 immersed FP H 2006 immersed FP ) used cyclic aeration 2) required pumping energy for MLSS recirculation. Total Costs / Economy of Scale. Table 6 provides a summary of the capital and O&M cost estimates for complete MBR facilities based on 1 and 5 MGD capacities. The total capital costs and estimated O&M costs were summed to provide present worth values of each installation. The present worth values shown are based on a 5% interest rate over a 30-year period. The present worth ($K) for the 1-MGD and 5 MGD was estimated between $11,260- $14,429 and $47,064-$58,954, respectively. Table 7 provides total costs ($/1000 gal) for each capacity. These costs were derived from the amortized capital cost and the annual O&M cost associated with each capacity. The table shows the total cost ($/1000 gal) for the 1-MGD capacity ranged from $2.02-$2.58. An economy of scale analysis of the costs associated with the MBR facility components (excluding membrane system costs) and the membrane system only was conducted for 1 and 5 MGD capacities. The total costs ($K/MGD) (based on the average values of the four systems analyzed) associated with these two capacities was determined to be $12,844 and $10,602 respectively. A comparison of 3414

9 these estimates reveals an economy of scale exists for both the MBR facility components (16.5%) and the membrane system only component (23.6%). The former would be expected as the cost of construction and raw material decreases with size and bulk quantity. The latter would indicate savings associated with purchasing larger quantities of membranes. Table 6: Summary of Capital and O&M Cost for MBR Facilities Capacity (MGD) Capital Costs, $K Total O&M Costs, $K Present Worth Value, $K 1 5 $7,990-$9,850 $3,350-$4,649 $11,260-$14,429 $32,270-$38,790 $14,974-$20,344 $47,064-$58,954 Table 7: Summary of Costs, $/kgal for MBR Facilities Capacity (MGD) Amortized Capital Costs, $K/yr O&M Costs, $K/yr Total Cost, $K/yr Total Cost, $/1000 gal 1 5 $520-$641 $218-$302 $738-$943 $2.02-$2.58 $2,099-$2,523 $974-$1,323 $3,073-$3,846 $1.68-$2.11 MBR COST TRENDS The capital cost estimates of the newly developed MBR facilities were compared with previous cost estimates made by the project team in 2000 and The estimates of the membrane systems were obtained from original budget proposals provided by Zenon and Kubota, in the given years (Adham et al., 2000 & 2003) and budget proposals received from the suppliers of the newly developed MBR systems in All previous budgetary cost estimates of the membrane systems were adjusted to current dollars using the consumer price index (CPI) published by the U.S. Department of Labor (U.S. Department of Labor, Bureau of Labor Statistics Data, 2006). Membrane system costs include costs associated with the membranes, pumps, blowers and miscellaneous equipment along with installation. Capital costs for all other MBR facility components (i.e. headworks, process basins, blower/pump building, chlorine dosing system and effluent storage) were based on original estimates (Adham et al., 2003) and adjusted using ENRCCI and CEPCI for the desired years. As shown in Figure 2 there has been a steady increase (~24%) in costs associated with MBR process components (excluding membrane system) between Interestingly, as shown in Figure 3 the opposite trend was observed for membrane system costs, which actually have decreased by approximately 33% over the same time period. The rise in nonmembrane costs associated with the MBR facilities is due to the increased cost of concrete and other raw materials used for plant construction. The drop in membrane system costs maybe attributed to advancements in manufacturing and increased competition in the market place. These trends have resulted in the overall total cost for 1-MGD MBR systems to be fairly level (i.e. < 10% increase) between 2000 and

10 MBR Process Components Cost $8,000 1-MGD capacity $6,000 Capital Cost, $K $4,000 $2,000 $ Membrane system costs not included in estimates Year Figure 2: Capital Cost Estimates of 1-MGD MBR Facility Components ( ) Membrane System Cost Capital Cost, $K (2006 Dollars) $4,000 $3,000 $2,000 $1,000 $0 1-MGD capacity Costs for 2000 and 2003 were determined by adjusting Year orginal estimates using 2006 Consumer Price Index Figure 3: Capital Cost Estimates of 1-MGD MBR Membrane Systems 3416

11 CONCLUSIONS The following conclusions were made from this evaluation: Capital cost ($K) estimates of 1 MGD capacity MBR systems (membrane systems only) varied from $1,419-$2,330 based on budgetary proposals received from the four participating suppliers. Total cost estimates ($/1000 gal) for 1 MGD MBR facilities (headworks, biological process, membrane system, chlorine disinfection and effluent storage) ranged from ranged from $2.02-$2.58. Membrane replacement (28%) and energy costs (34%) were the largest components of the O&M cost estimates associated with the MBR systems. Cost estimates of 1 and 5 MGD MBR systems showed an economy of scale for both the MBR process components (16.5%) and the membrane system only component (23.6%). Comparison of the current cost estimates of the newly developed MBR systems to historical costs estimates (adjusted for inflation) suggests a steady decrease (total decrease ~33%) in the membrane system component cost has occurred between Comparison of the current cost estimates of the newly developed MBR systems to historical costs estimates (adjusted for inflation) suggests a steady increase (total increase ~ 24%) in the MBR process components costs (not including membrane systems costs) has increased by ~24% between Results from this evaluation has shown the overall total cost for 1-MGD MBR facilities has been fairly level (i.e. < 10% increase) between ACKNOWLEDGMENTS The project team would thanks the following groups for making this project possible. United States Bureau of Reclamation (USBR) Technical Service Center Water Treatment Engineering and Research Group for funding Agreement No. 01-FC Larry Wassermann and Neil Tran of the City of San Diego Metropolitan Wastewater Department for assisting with MBR evaluations. 3417

12 Participating Vendors for supplying budgetary cost estimates of their MBR systems: Koch Membrane Systems, Huber Technologies Inc., Kruger Inc. and Parkson Corporation. Dr. Simon Judd (Cranfield University) for providing information on normalizing MBR energy requirements. REFERENCES Adham, S., et al., (1998) Membrane Bioreactors for Water Repurification- Phase I, Desalination Research and Development Program Report No. 34; Bureau of Reclamation. Adham, S., et al., (2000) Membrane Bioreactors for Water Reclamation - Phase II, Desalination Research and Development Program Report No. 60; Bureau of Reclamation. Adham, S., and DeCarolis, J., (2004) Optimization of Various MBR Systems for Water Reclamation-Phase III, Final Report Project No. 103; Bureau of Reclamation. Churchhouse, S.J., Wildgoose, D., (1999) Membrane Bioreactors hit the big time from lab to full-scale installation. Inlt Meeting on Membrane Bioreactors for Wastewater Treatment, University, Cranfield, UK. Pg. 14. Davies, W.J., Le, M.S., and Heath, C.R., (1998) Intensified activated sludge process with submerged microfiltration. Wat. Sci. Technology. 38 (4-5), DeCarolis, J., Adham, S., Hirani Z., (in-print 2007) Evaluation of Newly Developed Membrane Bioreactor Systems for Water Reclamation Phase 4. Final Report, Project No. 01-FC , United States Department of Interior, Bureau of Reclamation. Judd, S., (2006) The MBR Book. Elsevier Publishing. U.S. Department of Labor Bureau of Labor Statistics Data (2006),