There Is Another Flat Plate MBR - PNCWA PNCWA... · 2016. 7. 14. · Membrane Bioreactors §Flat plate §Hollow fiber §Tubular §Others Kubota, Toray, Meurer, Westech, Huber
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There Is Another Flat Plate MBR There Is Another Flat Plate MBR There Is Another Flat Plate MBR There Is Another Flat Plate MBR Evaluation of Huber's VRM Membrane Evaluation of Huber's VRM Membrane Evaluation of Huber's VRM Membrane Evaluation of Huber's VRM Membrane Bioreactor Technology Bioreactor Technology Bioreactor Technology Bioreactor Technology Henryk Melcer
There Is Another Flat Plate MBRThere Is Another Flat Plate MBRThere Is Another Flat Plate MBRThere Is Another Flat Plate MBREvaluation of Huber's VRM Membrane Evaluation of Huber's VRM Membrane Evaluation of Huber's VRM Membrane Evaluation of Huber's VRM Membrane
§Four plates stacked with defined gaps to make a modulemodule
§Four/six modules assembled into one element
The membrane is mounted on a polypropylene backing to create a membrane plate. Both sides of a plate are covered with a membrane. The membrane is capable of operating over a temperature range of 5 to 400C and a pH range of 1 to 14 and rated to produce an effluent with < 1 mg/L TSS concentration. Four plates are stacked with defined gaps to form a module, an example of which is shown in the insert of Figure.
The VRM technology consists of a flat plate membrane system that is rotated completely submerged within a tank of mixed liquor. The permeate pump withdraws permeate from the modules through permeate collectors and the hollow shaft. 6 or 8 (depending upon the disc diameter) modules are assembled in a circle to create one element or disc as indicated. Multiple discs are inserted on a hollow rotating shaft
RotationRotationRotationRotation
Drive motor
Chain
Element/disc
Chain
Scouring air lines
Varberg Pilot ProjectVarberg Pilot ProjectVarberg Pilot ProjectVarberg Pilot ProjectVarberg Pilot ProjectVarberg Pilot ProjectVarberg Pilot ProjectVarberg Pilot Project
Varberg, SwedenVarberg, SwedenVarberg, SwedenVarberg, Sweden
Oslo
Stockholm
Oslo
Stockholm
Copenhagen
Varberg
Copenhagen
Varberg
The Municipality of Varberg in Sweden is located on the west coast of Sweden, north of Copenhagen and west of Stockholm as shown in Figure
Bua WWTP AS Package PlantBua WWTP AS Package PlantBua WWTP AS Package PlantBua WWTP AS Package Plant
It operates a secondary wastewater treatment plant (WWTP) in Bua that services the northern communities in the catchment area. Built in 1971, the facility consists of a donut-type of package activated sludge system that is in need of upgrading because of age and growth. Critical discharge criteria are 10 mg/L BOD7 and 0.3 mg/L TP. Increasing flows and loads as well as the annexation of the northern Loftaskog community has increased the design basis of the Bua plant from 3,700 to 5,500 PE.
Opportunities for plant expansion are limited because the community has expanded towards the west and south boundaries of the treatment plant, and the plant is surrounded by wetlands to the north and east. The plant’s ocean outfall is subject to European Community bathing standards because of its proximity to the highly frequented beaches. To comply with these standards, a 780 m (0.5 mile) extension of the outfall would be required such that discharge would occur beyond the reach of coastal currents that would otherwise return the treated discharge to the beaches. The cost of the outfall was very high, which prompted an evaluation of alternative measures of complying with the standards. The site constraints and the desire to produce a higher quality effluent led the Municipality to consider using membrane bioreactor (MBR) technology.
Pilot PlantPilot PlantPilot PlantPilot Plant
Parameter Total System
System model VRM 20/108
Total Flow, gpd - average 9,510
- maximum 17,120
Aeration Tank Membrane Tank Volume, gal 3,700 2,640
Approx. operating depth, ft 8.2-9.5 8.2-9.5
Membranes Membranes
Disc diameter, ft 7.15
Disc speed, rpm – average 0.9
Membrane area/module, ft2 32.3
No. of modules per disc 6
No. of discs 6
Total membrane area, ft2 1,163
Fluxnet lmh (gfd) < 30 (17.4) A M C
Of the different configurations of MBRs available today, Municipality was interested in evaluating flat plate technology, specifically the new vacuum rotation MBR (VRM) technology. In November 2007, a VRM pilot plant was installed at Bua WWTP and operated to collect process design data and allow Bua WWTP staff to gain hands-on experience with this technology. The VRM 20/108 pilot plant consisted of an aeration and membrane tank with common wall construction, located adjacent to Bua AS facility as shown in Figure. It could treat up to 5% of plant influent flow. Essential characteristics are listed in Table 1. A slip stream of de-gritted and screened (6 mm step screens) raw sewage was withdrawn from activated sludge plant and directed through 3 mm perforated plate rotary drum screen to aeration cell. Figure illustrates orientation of aeration and membrane tanks, and PLC and control systems. Mixed liquor was pumped to membrane tank from which it would overflow back into aeration tank. To ensure that membranes were always submerged, the PLC controlled the sequence of influent pumping, mixed liquor transfer to the membrane tank and permeate pumping. A separate tank for anoxic denitrification was not provided; rather, this was achieved by intermittent operation of the aeration blowers and the submersible mixer in the aeration tank.
Wastewater/permeate BOD, COD, P species, TSS, alkalinity, pH
Grab Provide influent & permeate characteristics to measure loading parameters & system performance
Membrane tank parameters (flow, pressure, ML level)
On-line Measure membrane performance in terms of flux, TMP and permeability (T-corrected) in real time
MBR process parameters (temperature, MLSS, ammonia, nitrate)
On-line Provide real time process data
Figure illustrates the graphical interface that allowed the operator to monitor and adjust set points for the above characteristics. This interface also displayed real time information for the critical operational characteristics, TMP, flux and temp-corrected membrane permeability. T and DO conc probes were located in the aeration tank; an ammonia concentration probe was located in the aeration tank and a nitrate concentration probe was located in the permeate discharge stream. Process and scour air flow rates were measured, the latter to ensure that the correct air scour intensity was applied to the membranes. Head loss across the membranes was measured to compute the trans-membrane pressure (TMP). Permeate flow was measured to compute flux rates. The rotational speed of the membranes was also monitored.
SCADA Data LoggingSCADA Data LoggingSCADA Data LoggingSCADA Data Logging
Figure shows SCADA system output at 10-second intervals for essential operational parameters: the sequence of pump operations to move wastewater through the tanks, operation of RAS and WAS pumps and blowers, MLSS, DO and ammonia concentrations, temperature and side water depth in the aeration tank and MLSS concentration and side water depth in the membrane tank. This greatly facilitated the operator’s ability to maintain control of the MBR.
Test ObjectivesTest ObjectivesTest ObjectivesTest Objectives
§VRM previously subject to Title 22 test protocol–Av flux 29.3 lmh (17 gfd)–Peak flux 56.9 lmh (33 gfd) for 4 hr over 6 days–No significant increase in TMP
§These tests complementary to Title 22: §These tests complementary to Title 22: measure performance at–Operation at const flux 15.7 lmh (9.1 gfd) at low T–Operation during incremental increases in flux rate to 24 lmh (14.1 gfd)
–Peak flow testing
The VRM was previously evaluated under the California Title 22 program, which seeks to address wastewater reclamation criteria in California (MWH, 2006). The membranes were subjected to the typical flux rate regime called for in this protocol, which included operating the VRM at an average flux rate of 29.3 lmh (17 gfd) with daily peak flux rates of 56.9 lmh (33 gfd) for four consecutive hours over a six day period. The permeate characteristics were similar to those reported in this investigation. No significant increase in TMP was recorded during the peak flux testing period. In the light of complying with the Title 22 testing protocol, the opportunity was taken in this project to evaluate the VRM membranes according to a different test regime that addressed long term steady state operation, the impact of exposing the membranes to stepwise increases in flux with and without resting periods and alternative membrane rest frequencies. This alternative test program was considered to be complementary to the Title 22 testing and extended process knowledge on the VRM when operating under these conditions.
Effect of Changing Rest Period: 1Effect of Changing Rest Period: 1Effect of Changing Rest Period: 1Effect of Changing Rest Period: 1
FluxTMP
Doubling time between resting periods from vendor-recommended 240 sec permeation/60 sec rest to 540 sec permeation/60 sec rest
PermeabilityTemp
The effect of changing the frequency of the membrane resting period was evaluated on 2 separate occasions. MBRs have progressed through several different membrane management procedures that sought to minimize the decline in membrane permeation rate and extend the period between cleaning. The more recent approach of resting membranes for a short period appears to be a beneficial strategy. The real time data provided an insight into the behavior of the membrane to a change in this procedure. Figure shows the effect of more than doubling the time between resting periods from the vendor-recommended 240 sec permeation/60 sec rest to 540 sec permeation/60 sec rest. This test was conducted from 4.00 pm through 11.30 pm January 5, 2008 (Phase 2). TMP increased from 0.63 to 1.42 psi (44 to 98 mbar) over a period of 8 hr before the filtration time was restored to its original setting. The increase in temp from 9.9 to 10.10C during this period is unlikely to have had an impact on this response.
Effect of Changing Rest Period: 2Effect of Changing Rest Period: 2Effect of Changing Rest Period: 2Effect of Changing Rest Period: 2
Flux
TMP
PermeabilityTemp
In the second test, conducted over the period, 10.00 am March 18 through 7.30 am March 19, 2008 (Phase 3), the filtration time was increased from the vendor-recommended 240 sec permeation/60 sec rest to 270 sec permeation/30 sec rest. This was a minor change compared to the first test and the TMP response was less albeit evident. The TMP varied between 54 and 60 mbar (0.78 and 0.87 psi) during this period. The temperature was approximately the same as in the first test.
Minimal response to step changes in flux w/o interim rest phase until 15 lmh (8.7 gfd)
In late December 2007, flux was increased on a daily basis in increments of 1 lmh (0.58 gfd), without resting the membranes between changes, to observe the response of the membrane. Figure 7 illustrates the linear stepwise increase in TMP (0.15 psi [10 mbar]) in response to these flux increases over the period, December 27-30, 2007. However, the last step increase in flux from 15 to 16 lmh (8.7 to 9.3 gfd) resulted in a large gain in TMP from 1.23 to 2.9 psi (85 to 200 mbar), clearly showing the limitation in elevating flux rate without introducing rest periods for the membranes.
Slow linear response to step changes in flux with interim rest phase
During May 28 through June 16, 2008, effect of escalating flux rate was again evaluated although in this case, it was increased in approx 2 lmh (1.2 gfd) steps from base level of 11 lmh (6.4 gfd) to 30 lmh (17.4 gfd). Unlike the incremental increases in flux conducted during Phase 2, the membranes in this case were rested for one day at the base level of 11 lmh (6.4 gfd) after each increment. Figure 11 illustrates the response in terms of TMP and permeability. Except for the response on June 11, 2008, a relatively linear response in TMP was observed unlike the rapid escalation in TMP during the incremental flux increases without membrane resting in Phase 2.
Operation at Long Term SteadyOperation at Long Term SteadyOperation at Long Term SteadyOperation at Long Term Steady----State FluxState FluxState FluxState Flux
Flux: 15.7 lmh (9.1 gfd)
Temp: 9.2-11.20C
TMP
Permeability
TMP range = 0.78-0.87 psi
Operation at Extended High Flux Operation at Extended High Flux Operation at Extended High Flux Operation at Extended High Flux RatesRatesRatesRates
Temp
Flux: 30.4 lmh
TMP
35 lmh
Permeability
TMP
Figure illustrates system response to extended period of time at flux rate of 30.4 lmh (17.6 gfd) & extended pk day event at 35 lmh (20.3 gfd). TMP slowly increased during both periods of constant flux at approx same rate of 1.8-2.2 mbar/day (0.03 psi/day). Permeability declined quickly from approx 450 to 400 lmh/mbar (11.2 to 10 gfd/psi) at beginning of 7-day test & continued to decline to approx 300 lmh/mbar (7.5 gfd/psi) at end of test. Both TMP & permeability returned to baseline levels when membranes were returned to starting flux rates. Permeate produced during these tests continued to be of high quality w BOD, COD & TSS concs < detection limits of 3, 30, & 2 mg/L.
The permeate quality in terms of BOD, COD, ammonia, nitrate and TSS concentrations remained constant during this period as shown in Table. The low values of plant influent characteristics reflected the dilution resulting from inflow/infiltration during this time. These values increased during spring. Although N removal was not a treatment objective, it was evident from the high effluent nitrate concentrations that there was insufficient readily degradable COD to induce denitrification. Influent and effluent TKN concentrations were not measured.
The air is introduced at approximately half the water depth, which reduces scour air pressure and the scour air power requirement. Only a segment of a membrane disc is scoured as it rotates through the 12 o’clock position. Rotation ensures that the entire disc area is scoured up to 2.5 times per min. The air scouring specification calls for 0.25 m3/m2-hr (1.67 cfm/100 ft2), which is similar to that required by other MBR vendors. However, because this air is applied to only a segment of each disc at any one time, the actual scouring intensity is higher than in other MBR systems. Assuming that air fans out from the perforated pipe with a pie-shaped a 600 angle of range of application in the same dimension as the disc, the specific scouring air rate per membrane area receiving the air is likely to be up to six times the typical specific scouring rate. This may account for the relatively infrequent requirement for membrane cleaning experienced by Huber MBRs that have been in operation over the past few years at Hutthurm and Kupfer in Germany and in Arenas de Iguna in Spain.
Other Engineering IssuesOther Engineering IssuesOther Engineering IssuesOther Engineering Issues
§Power consumption–0.5 kWh/m3 at full-scale
– At pilot-scale, measured 2.0 kWh/m3
§Submerged bearings§Submerged bearings–>50 years’ history with screening technology
§Filterability–Very good: 2-6 mg/L TOC measured in dewatering filtrate
Potential cause for concern stemmed from use of submerged bearings to support rotation of membranes in ML. Bearing technology is similar to that used by Huber in their submerged rotating screens that have been in operation for past 20 years without failure if the vendor maintenance instructions are followed. Not regarded as a weakness in the design of this type of MBR. Measure of sludge filterability in terms of TOC remaining in filtrate from the TTF tests. The lower this value the better sludge filterability & the less loading transmitted to membrane. Superimposed on these data are permeate TOC data for corresp times and difference in TOC between filtrate & permeate, illustrating contribution of membrane to removing residual TOC. Values were low, ranging from 2 to 6 mg/L indicating excellent filterability for latter part of investigation.
ConclusionsConclusionsConclusionsConclusions
§Permeate BOD & TSS were < detection limits for whole trial
§Met EEC bathing standards§Demonstrated benefit of membrane relaxation§No discernable TMP increase observed over 6-wk of §No discernable TMP increase observed over 6-wk of operating at constant flux of 15.7 lmh (9.1 gfd) & low influent T of 9.2 - 11.20C.
§Continuous high fluxes of 30 & 35 lmh did not cause dramatic TMP increases nor decline in permeability
§Operators had favorable experience with VRM for 6-month period
