" Manhattan, MT 400,000 MGD Bio-Wheel TM Wastewater Treatment Plant "

Transcription

1 MSAWWA MWEA Conference Great Falls, Montana May 15, 2008 " Manhattan, MT 400,000 MGD Bio-Wheel TM Wastewater Treatment Plant " by Donald D. Ricketts, P.E., WTI and Robert Seamons, P.E., Stahly Engineering & Associates

2 Introduction Stahly Engineering & Associates selected the Bio-Wheel process for the Manhattan 400,000 GPD wastewater treatment plant in Construction was completed in March 2008, with initial operation scheduled for May 28, Stahly determined that the Bio-Wheel offered the most economical solution based on both construction and operating costs. This paper will show how the Bio-Wheel operates, the construction of the Manhattan facility and the determination of oxygen transfer rates that show that the Bio-Wheel would offer a very efficient power utilization factor. 2

3 How the Bio-Wheel TM works The Bio-Wheel is a combination of activated sludge and fixed film into a single treatment system, with the advantages of both. Most nitrification occurs on the fixed film, as well as substantial carbonaceous BOD reduction. The fixed film provides a stable environment which resists upsets, while the activated sludge provides an efficient utilization of available biology by optimizing their environment, providing sufficient oxygen and mixing. 3

4 How the Bio-Wheel TM works The Bio-Wheel is 80% submerged in the mixed liquor and rotates at slow speed, approximately 1 RPM depending on the size of the wheel. Both aeration and mixing are provided, with no external blowers or diffusers. A simple chain drive with variable speed gearmotor regulates the speed of rotation of the wheel. The speed can be set by the operator, or can be controlled by a DO probe with a PLC. 4

5 How the Bio-Wheel TM works The individual plastic plates form cells, and as the wheel rotates air is brought down into the mixed liquor where it escapes from the cells as fine to medium bubbles. There is air remaining even after the cells have passed bottom dead center, which contributes lift to reduce the electrical power consumption. The buoyant cells reduce the effective weight of the wheels, creating less load on the bearings and eliminated shaft breakage problems. 5

6 How the Bio-Wheel TM works The plates which form the cells are polyvinylchloride with a UV inhibitor. Four 1 diameter rods hold the plates in position. The plates are joined together with tongue and groove joints to eliminate the escape of air as it is compressed through rotation. A paddle shown on the bottom of the plate retains the air in the cell as the wheel rotates, providing longer retention of the air. 6

7 How the Bio-Wheel TM works Bio-Wheel plants can be designed not only for BOD removal, but also for ammonia, total nitrogen and phosphorous removal. Some denitrification occurs on the fixed film, however a separate anoxic zone is created ahead of the aeration tank for most denitrification solutions. The system is very sturdy and reliable, simple to operate with low noise and low energy consumption. Operation is similar to an activated sludge plant, with the advantages of the fixed film. 7

8 How the Bio-Wheel TM works Advantages of the Bio-Wheel include low sludge volume indices, shock resistance to excessively high or low loading, simple operation and low operating cost. Note the amount of aeration and mixing shown in this photo, with the excellent fixed film growth on the wheel. 8

9 How the Bio-Wheel TM works Additional advantages include a thin fixed film which minimizes sloughing and reduced sludge production which is typical of a fixed film process. The constant sloughing of the fixed film helps settling and dewatering characteristics of the sludge. 9

10 How the Bio-Wheel TM works The entire Bio-Wheel can be removed from the aeration tank without dewatering the tank. Maintenance can be preformed on the bearings with the wheel removed much easier and in less time. 10

11 How the Bio-Wheel TM works A comparison of costs between the Bio- Wheel and a SBR and a conventional activated sludge system, using a basis of 100% shows that the Bio-Wheel utilizes only 45% of the energy of the activated sludge system and 52% of the footprint. An SBR is 112% of the base amount of power and 78% of the base volume, which clearly shows that the Bio-Wheel is more efficient on both energy and volume. 11

12 How the Bio-Wheel TM works This report was prepared by Wilson Fisher, P.E. of Hess & Fisher Engineers of Clearfield, PA for a study of various treatment systems for the Winburn and Grassflat wastewater treatment plants for Cooper Township, PA. The report was submitted to Pennvest which is the grant agency for low income communities. The report shows that the Bio- Wheel was considerably less cost than an AquaAerobics SBR or an Aeromod extended air plant. 12

13 How the Bio-Wheel TM works This is a summary of the results of the Cooper Township report. 13

14 Manhattan, Montana Wastewater Treatment Plant The Manhattan treatment plant is a 400,000 GPD plant in two trains, containing six BW 24 x 5.0 Bio-Wheels. It is able to nitrify and denitrify, with two anoxic basins ahead of the aeration basins. Two conventional flight and scraper clarifiers are used. Three Penn Valley RAS/MLSS pumps are located in a separate pump room. The plant is designed for a future expansion to 0.8 MGD. At this time the effluent limits are 20 mg/l for BOD5 and TSS, however the plant is designed for ultimate limits of 10 mg/l for BOD5, TSS, total Nitrogen and less than 1 mg/l for Phosphorous which may be imposed soon because of its discharge into the Gallatin River. 14

15 Manhattan, Montana Wastewater Treatment Plant The plant is of reinforced cast-in-place concrete construction. Each train is 20 wide by 14 deep. 15

16 Manhattan, Montana Wastewater Treatment Plant The general contractor was Johnson-Wilson Construction of Great Falls, Montana. 16

17 Manhattan, Montana Wastewater Treatment Plant Construction was begun in Spring 2007, with placement of the concrete walls the first priority. 17

18 Manhattan, Montana Wastewater Treatment Plant Following completion of the concrete work, the Bio-Wheels were installed in the aeration tanks. Note the patented A-Frames which suspend the wheels from the top of the concrete walls, so that the wheels may be removed without dewatering the tank or taking the train out of service. 18

19 Manhattan, Montana Wastewater Treatment Plant A side-on view of the A-Frames. Six 1 ½ stainless steel bolts hold the frames down to the top of the tank. The trunnion blocks with their UHMW bushings are preassembled in the A-Frames. Each frame is leveled in both directions before installing the wheel axle. Notice the lifting eyes on the top angles of the frames. 19

20 Manhattan, Montana Wastewater Treatment Plant Each wheel is assembled in the tank. The wheel in the center is awaiting installation of the last six rows of plates. 20

21 Manhattan, Montana Wastewater Treatment Plant Three rows of plastic plates are preassembled on the galvanized end plates, ready for installation. Each row is 2.50 meters (8-4 ) in length. The completed BW 24 x 5.0 Bio-Wheels are 6.00 meters (20-0 ) wide by 4.50 meters (14-9 ) in diameter and contain 2930 m2 (31,500 s.f.) of fixed film surface area. 21

22 Manhattan, Montana Wastewater Treatment Plant The control building, sludge aeration tank and sludge press building are almost completed by November

23 Manhattan, Montana Wastewater Treatment Plant The control panel for the Bio-Wheels is extremely simple. Each train of three wheels contains a single D.O. probe which is connected through a PLC to the wheels to regulate rotation speed and therefore the amount of oxygen in the mixed liquor. The control panel contains primarily off-on switches for each wheel, and an operator interface to manually set the speed of each wheel. 23

24 Manhattan, Montana Wastewater Treatment Plant On a clear, cold day at the end of November 2007, the wheel installation is completed and the plant is ready for initial start-up. The chains and SEW Eurodrive gearmotors are in place. 24

25 Manhattan, Montana Wastewater Treatment Plant Clean water is piped into the bio-tank for checking the operation of the wheels. Note the condensation rising from the warm water. 25

26 Manhattan, Montana Wastewater Treatment Plant A final check is made as the wheel begins its first rotation. 26

27 Manhattan, Montana Wastewater Treatment Plant The chain tension is checked and found to be proper as the wheel rotates at 0.45 RPM. The wiring for the D.O. probe is seen at the edge of the tank wall in the foreground. 27

28 Manhattan, Montana Wastewater Treatment Plant The three Bio-Wheels on the eastern train are in full operation. At this point it is necessary to install the fiberglass covers over the equalization and denitrification tanks. Notice the RAS/MLSS/WAS pump building in the background adjacent to the clarifiers. The building is heated and is convenient for the operator to check the RAS flow. 28

29 Oxygen Transfer Capability of the Bio-Wheel TM Since this was the first Bio-Wheel project in Montana, DEQ was very interested in calculated and actual oxygen transfer rates. It is not possible to directly compare the Bio-Wheel with non IFAS systems, since approximately 20% of the carbonaceous BOD5 is removed on the fixed film, along with about 85% of the ammonia nitrogen. Since no additional horsepower is required for the fixed film, this is a free ride. For a 100,000 GPD treatment plant for normal municipal wastewater, the total oxygen demand for an activated sludge or SBR system would be 215 kg/d, but with the Bio-Wheel the fixed film component would remove 94 kg/d resulting in a net requirement of 121 kg/d, or 56% as much aeration would be required with activated sludge only. This amounts to a significant reduction in electrical power consumption. 29

30 Oxygen Transfer Capability of the Bio-Wheel TM This summary page shows the results of a clean water oxygen transfer test completed by GSEE, Inc. on a BW 18 x 5.0 Bio- Wheel in Pennsylvania. The plant was new and there was no developed fixed film, therefore it was discounted in the test protocol. The average SAEmotor aeration efficiency is 2.10 #O2/Hr/HP and the observed Oxygen transfer was 5.46 #O2/Hr. This compares favorably with other mechanical aeration systems, or with fine bubble diffusers. However, this would be the aeration equivalent of 4.77 #O2/Hr/HP since the Bio-Wheel only requires 56% as much oxygen as a conventional system activated sludge. 30

31 Oxygen Transfer Capability of the Bio-Wheel TM In order to confirm the testing done on the Bio-Wheel, Robert Seamons from Stahly Engineering and Associates obtained data from a working plant and back calculated the actual dirty water oxygen transfer. The data is shown on the left. 31

32 Oxygen Transfer Capability of the Bio-Wheel TM Actual calculated clean water transfer rates from full scale data show 2.86 #O 2 /Hr/HP which is on the high end of the scale for mechanical aerators. For the Manhattan wastewater treatment plant, it was decided to perform actual testing both on clean water before raw wastewater is introduced and after the plant has been in operation for two to three months. However, due to limited water supply at the site, the treatment plant will not begin operation until the end of May 2008, too late to include the data into this report. 32

33 Summary For the Manhattan, Montana 400,000 GPD wastewater treatment plant, the Bio-Wheel system was chosen for its modest initial cost and low operating cost. The control system is simple and presents few challenges to the operator. A detailed analysis of the oxygen transfer rate indicates that the combination of the fixed film and activated sludge system is considerably more efficient that an activated sludge process alone, approximating 45% more effective wastewater treatment for the same power consumption. The Bio-Wheel provides for easy future expansion to 800,000 GPD by adding two additional three wheel trains and clarifiers. Although the current permit limits do not call for denitrification, the plant was designed to include this capability Additional testing will be conducted this year to confirm the design oxygen transfer rates. 33