W O C H H O L Z R E G I O N A L W A T E R R E C L A M A T I O N F A C I L I T Y O V E R V I E W

Transcription

1 Facility Overview The recently upgraded and expanded Henry N. Wochholz Regional Water Reclamation Facility (WRWRF) treats domestic wastewater generated from the Yucaipa-Calimesa service area. The WRWRF consists of primary, advanced biological secondary and tertiary treatment to obtain Total Nitrogen (TN) of less than 6 mg/l. The current capacity of the facility is 6.67 mgd, with expansion to 8.0 mgd. The Tertiary process, MF/UV (Microfiltration/Ultraviolet disinfection) was selected to meet the coliform removal and turbidity requirements of Title 22 for reclaimed water. Once the reclaimed water reservoir and the reclaimed piping are put into operation, non-potable water from the facility will be used in the system. Currently the plant effluent is overflowing into the San Timoteo Creek. Figure 1: View of Upper Half of Wochholz Facility A schematic of the facility and components is provided at the end of this document. The Wochholz facility was originally placed into service in 1986 with an initial capacity of 3.0 mgd. The facility was originally designed with trickling filters and small aeration basins in order to provide treatment of wastewater. The facility was upgraded and expanded in 1992 to 4.5 mgd, at which time dentirifcation filters were incorporated in order to reduce Total Nitrogen to less than 10 mg/l. 1

2 Facility Elements A summary listing of primary components contained in the WRWRF is as follows: Headworks. Primary Treatment Secondary Treatment Solids processing Microfiltration System UV Storage and pumping Process residuals treatment Headworks Influent to the facility undergoes ¼ screening, flow measurement and grit removal before it is discharged to the primary treatment basins. Solids collected from the bar screens and grit chamber are washed, compacted and disposed. The facility is designed to operate at a peak influent flow of 26.5 mgd. The system contains 2 bar screens and a single grit removal chamber that can be by-passed for maintenance purposes. Primary Sedimentation Basins Figure 2: Bar Screens and Grit Removal Effluent from the headwork passes through the three primary sedimentation basins to remove coarse solids and floatable scum. Chain and flight sludge collectors are used to move solids and scum to the appropriate collection point. The solids and scum are sent to digestion for additional treatment. The primary sedimentation basins remove about 50 percent of the solids from the influent wastewater. Figure 3: Primary Sedimentation Basin 2

3 Primary Equalization Basin One of the unique features of the WRWRF is the primary equalization basin that is used to stabilize the diurnal flow through the facility. Flow from the primary sedimentation basin can be diverted to a primary equalization basin for processing during off peak times. An adjustable weir gate is used to determine the amount of flow that is diverted to the primary equalization basin. The primary equalization Figure 4: Primary Equalization Basin basin contains 5 mixers to keep solids in suspension during the time which is it stored. Flow from the Primary equalization basin is returned once the incoming flow drops off below an operator established plant setpoint. Return flow is varied with a VFD to maintain the target plant flow setpoint on the HMI. The mixers are turned off automatically as the level falls below the minimum level in the primary equalization basin. Secondary Treatment Splitter Boxes There are 2 splitter boxes that provide flow to the secondary system. The primary effluent splitter box contains the effluent from the primary sedimentation basins. The new mixed liquor splitter box contains flow from the following sources: MLR Pumps RAS Pumps Primary Equalization Pumps Anoxic Basins Flow from the splitter boxes flows into the anoxic basins. There are 2 anoxic basins that operate in parallel. The anoxic basins operate in a depleted oxygen environment in order to reduce the level of nitrogen in the feed. The basins are divided into 4 quadrants and each quadrant is mixed in order to Figure 5: Anoxic Basins 3

4 maintain the biological environment. The configuration of the Anoxic basins is somewhat unique. At one time these basins were operated as trickling filters, but were converted to Anoxic basins. Aeration Basins - AnoxKaldness IFAS Biological process Flow from the anoxic basins is aerated in order to convert to achieve nitrification and conversion of ammonia to nitrite-nitrate. There are four aeration basins at the Wochholz facility. Aeration and microorganisms in the mixed liquor converts soluble BOD and nutrients into biomass and increases the level of suspended solids. The system is designed to run in Automatic control based on dissolved oxygen in the aeration basins. During periods of low flow the system blowers run down to the minimum setpoint. There are 2 zones of treatment in the AnoxKalness process. The Figure 6: Aeration Basins first oxic zone operates at a higher level of dissolved oxygen, and the second zone operates at a lower concentration of dissolved oxygen. Each zone of treatment contains AnoxKaldness media. The media is used to increase the level of treatment available within the aeration basin by allowing attachment of biosolids to the media structure. After aeration, the majority of mixed liquor is recirculated to the anoxic basins while a smaller portion undergoes a post anoxic treatment. In this zone the oxygen in the mixed liquor is depleted and denitrification will occur. Methanol can be added to the post anoxic zone to enhance denitrification. Figure 7: AnoxKaldness Media that is required to maintain the media in suspension. The primary purpose for the selection of the Anox Kaldness process was associated with the space limitations of the facility. As originally constructed, the Wochhoz facility had limited aeration basins. Expansion of the facility within the available footprint was limited. The AnoxKaldness allowed the District to add the additional treatment within the available constraints of the facility, at a slight cost of additional energy 4

5 Secondary Clarification Secondary Clarifiers are manually controlled. Mixed Liquor enters a center collector and forced downward where the solids begin to settle. In each of the four clarifiers, solids settle to the bottom of the clarifier to form Return Activated Sludge. Each clarifier has a rotating sludge rake which is used to move solids to a collection sump. The sludge rake is designed operate continuously. In the sump, Return activated sludge (RAS) is drawn off. Figure 8: Secondary Clarifier Secondary clarified effluent is formed when the incoming mixed liquor passes through the solids collected on the bottom and flows outward and upward to the periphery of the clarifier. Clarified water is typically in the range of 2-10 ntu. Waste activated sludge can be taken from the effluent channel of the aeration basins, or from the RAS line. Operation of the WAS pumps reduces the concentration and mass of biosolids in the mixed liquor. WAS is pumped to the existing DAF system. Figure 9: View of Lower Half of Wochholz Facility 5

6 Tertiary Treatment The lower half of the Wochholz Facility contains the secondary equalization basins, MF/UV treatment equipment, filter press, and storage reservoir. The large pond in the middle is a storm water retention basin. Secondary Equalization Basin Water from the secondary clarifiers flows into the secondary equalization basin proportional to incoming flow. The level in the secondary equalization basin is designed to fluctuate and follow the diurnal curve of the plant incoming flow. Originally this basin was used to equalize flow to the denitrification filters, but was retained for the expansion to provide additional equalization. Pall Microfiltration System The facility plant construction incorporates six Pall MF units. The Microfiltration produces filtered water of less than 0.2 ntu, and is generally around 0.03 ntu. The system is designed to utilize the secondary equalization basin to maintain a relatively steady output from the plant while trying to minimize the time the MF system is running at full capacity. The system has a nominal capacity of 6.67 mgd, with a maximum one day treatment capacity of 10.0 mgd. Each MF unit has 95 membrane modules. In the future, the use of MF will allow the District to add Reverse Osmosis for the reduction of Total Dissolved Solids in the effluent. Figure 11: Pall Membrane Unit Figure 10: Pall Membrane Filtration System The complete Pall treatment system will normally be run with all systems operating. Of course system capacity is reduced with each MF unit out of service and it is not recommended to have the units out of service for more than 24 hours because of bacteriological growth and possible corrosion issues without preserving the membrane in a slight chlorine residual solution. The microfiltration system is designed to operate with flow generated by the six MF feed pumps provided in the feed wet well of the microfiltration system. Each feed pump is designed to deliver a maximum flow of 2.0 mgd, at a pressure of 35 psi. 6

7 Once necessary operating parameters are provided, the operator initiates an automated sequence which successively starts the designated MF Units. The MF system is designed to produce a maximum of 10.0 mgd. Reverse Flush System Backwashing of the individual MF Units will commence automatically as required to maintain membrane flux as will periodic enhanced membrane cleaning. Backwashing is accomplished through the use of an Air Scour (AS) and Reverse Filtration (RF) process by which process air and filtrate is used to dislodge particulate matter that have accumulated on the membrane surface. The MF Filtrate storage tank contains sufficient volume to accommodate the temporary interruption from the individual Membrane Unit flow during these operations. The AS/RF (backwash) water from the MF system is discharged to the Backwash Recovery Basin. Figure 12: Reverse Filtration (Backwash) Pumps EFM and CIP systems Particulate matter that is not removed by backwashing can be removed by chemical cleaning. The Pall membrane system uses 2 types of cleaning processes. The first process is termed Enhanced Flux Maintenance (EFM). EFM involves the recirculation of a chlorine solution through the membrane unit for a short period (20 to 30 minutes) of time. EFM solution is drained and flushed from the system before it is returned to service. EFM s are scheduled once every hours during the low flow period of the diurnal curve. The other type of chemical cleaning is termed Clean In Place (CIP). In this process citric acid (to remove inorganic contaminants) is heated and recirculated through the membrane unit and then drained and flushed from the system. CIP is initiated when the TMP of the unit reaches 35 psi. The citric acid CIP is generally followed by a heated solution of caustic and chlorine CIP to remove organic Figure 13: EFM and CIP System contaminants. The CIP process takes approximately 4 to 6 hours to complete. Because the EFM and CIP processes utilize a common pump and piping, the EFM process cannot occur during the CIP process. 7

8 Ultraviolet Disinfection System UV Supply Basin Filtrate from the MF system flows to the UV Supply Basin. An overflow weir from the tank provides gravity flow to the UV system. There is a control valve located at the effluent of the MF filtrate tank that is designed to maintain a relatively constant flow to the UV system. The UV Supply Basin contains sufficient volume to accommodate the temporary interruption from the individual Membrane Unit flow from a backwash operation. UV System The UV system is designed to disinfect the MF Filtrate treated waste water. The UV system consists of two UV channels that expose the microfiltered water to UV light. Based on the transmisstivity and flow of water in the UV channels the UV system will automatically determine the UV dose, the number of channels to run and the number of light banks to utilize. Typically the UV system will maintain a minimum level of water in the UV channels to keep the lamps covered. The outlet gates on the UV channels are modulated to maintain the appropriate level in the UV channels. Flow is calculated from the difference between the water level in the channel and the position of the weir gate. Effluents Storage and Pumping Figure 14: UV System The intention of the facility is to send the effluent water from the UV system to the Reclaimed Water Reservoir prior to nonpotable water distribution. Currently the piping has not been completed for the non-potable water system and therefore the plant effluent overflows into the existing outfall to the San Timoteo Creek. In the future, when the Non-potable water piping is complete the effluent will be dosed with sodium hypochlorite to provide a chlorine residual before being sent out the to the non potable distribution system. Figure 15: Not Potable Reservoir 8

9 Solids Processing DAF System The DAF system receives sludge from the WAS pumps. The DAF system uses air to lift and concentrate suspended solids that is sent to the digesters. The system pumps sludge to the digesters when a sufficient level has accumulated in the DAF sludge collection basin. Anaerobic Digesters The Anaerobic Digesters receive sludge from the primary sedimentation basins and the dissolved air flotation (DAF) system. Influent valves are controlled automatically from the existing DAF. Each digester has a recirculation pump and heater used to mix and heat the solids in the digester. Methane gas is released and flared, or used as a fuel to heat the solids. Belt Filter Press Solids dewatering from the digester flows to a holding tank outside of the belt filter press building. A polymer is added to the solids and belt filter presses are used to dewater the solids. Water that is removed from the Belt filter press is sent to the return water pump station. Solids are conveyed to a truck and taken to a local recycler for additional treatment. 9