SECTION 2.0 WASTEWATER TREATMENT PLANT AND DISPOSAL SYSTEM DESCRIPTION

Transcription

1 SECTION 2.0 WASTEWATER TREATMENT PLANT AND DISPOSAL SYSTEM DESCRIPTION Analytical Environmental Services 2-1 Jamul Indian Village Wastewater Treatment Plant

2 Analytical Environmental Services 2-2 Jamul Indian Village Wastewater Treatment Plant

3 SECTION 2.0 DESCRIPTION OF WASTEWATER TREATMENT PLANT AND DISPOSAL SYSTEM WASTEWATER TREATMENT DISPOSAL SYSTEM DESCRIPTION OVERVIEW An immersed membrane bioreactor (MBR) system is proposed to provide the highest quality of effluent for reuse or subsurface disposal. MBR facilities have been successfully used for similar Indian gaming facilities in California and elsewhere. Experience at other plants demonstrates the ability of the MBR system to consistently produce a high quality effluent. The effluent meets all requirements of California Title 22 and is suitable for all purposes approved in Title 22 such as toilet flushing, landscape irrigation and crop irrigation. Use of recycled water will save a significant amount of potable water that would otherwise be used for these purposes. The membrane bioreactor treatment system is designed for biological oxidation, nitrification (ammonia removal), denitrification (nitrate removal), and solids removal. The MBR system is planned for an average dry weather flow of approximately 170,000 gallons per day (gpd). The membranes could be operated at higher filtration rates for short durations (24-48 hours) allowing for higher peak flows. The anticipated average dry weather flow from the Jamul Indian Village is 159,000 gallons per day. The planned MBR process will be split into two separate process trains. A third process train will be available for future plant expansion should it be required. Each process train will consist of an anoxic zone, an aeration zone and membrane filters. Filtered effluent from the MBR will be sent to an ultraviolet light (UV) disinfection system. Disinfected effluent will be stored in a reservoir or pumped to a recycled water holding tank. Water pumped to the recycled water holding tank will pass through a chlorination disinfection system. Water sent to the reservoir will be stored onsite for eventual recycling or will be disposed of at an onsite leach field. A site map showing the proposed location of the wastewater treatment facilities is provided as Figure 1. The proposed site plan of the wastewater treatment plant is provided as Figure 2. A process flow diagram of the proposed MBR treatment system is shown in Figure 3. 1 Except as otherwise noted, the treatment system description included in this section is based on the November 2002 HydroScience Water, Wastewater, Recycled Water Feasibility Study; and on conversations with Dennis Sanchez, HydroScience Engineer. Analytical Environmental Services 2-3 Jamul Indian Village Wastewater Treatment Plant

4 LIFT STATION AND PLANT HEADWORKS Sewage generated onsite will be collected and conveyed by gravity to one of two sewage lift stations. The locations of the proposed lift stations are shown in Figure 4. The purpose of the lift stations is to convey raw sewage to the headworks of the wastewater treatment plant. The lift station will consist of redundant submersible solids handling pumps, odor control provisions, and associated controls, valving and mechanical equipment. Each pump will be capable of pumping 100% of the designed flow. The lift station will be designed to provide a minimum excess capacity equal to 1 hour of peak design flow. Sewage from the lift station will be transported to the wastewater treatment plant through an underground transmission pipeline. The pipeline will carry sewage approximately ¼ mile across the hilly terrain to the wastewater treatment plant, which will be at a higher elevation from the lift stations. Check valves installed in the transmission pipelines at the lift stations will prevent material from flowing from the pipeline back into the lift station. At the treatment plant headworks, the sewage will pass through an influent cylindrical sieve screen capable of handling up to the peak instantaneous flow. The screen will be provided with a bypass around the screen to act as an emergency overflow in case of mechanical or electrical failure. Following screening at the headworks, the filtered effluent will pass into one of the two MBR process trains. MEMBRANE BIOREACTOR (MBR) The MBR process will be split into two separate trains. A typical process train consists of an anoxic zone, an aeration zone and membrane filters. In addition to the two trains, an equalization basin and an emergency storage basin will provide excess storage in order to regulate flow into the MBR trains and provide emergency storage. The anoxic zone is a basin where the influent sewage is mixed with the recirculated contents of the aeration basin, known as return activated sludge. The basin is mixed without aeration to promote denitrification, which converts nitrates to nitrogen gas. The aeration basin converts dissolved Biological Demand (BOD) to a filterable solid material in a suspended growth process known as activated sludge. This basin also serves to convert ammonia into nitrates. The basin is aerated and mixed through the use of a fine bubble diffuser system. Process air blowers supply air to the aeration basins. A submersible pump recirculates the activated sludge to the anoxic zone. Two aeration blowers supply process air to the fine bubble diffuser system in the aeration basins to support the biological treatment process. Two duty blowers provide scour air to the filtration membranes. A third blower for each air system serves as a standby. Analytical Environmental Services 2-4 Jamul Indian Village Wastewater Treatment Plant

5 Water is removed from the aeration basin through membrane filters. The membrane filters consist of long, hollow, bundles of spaghetti-like fibers with a pore size of approximately microns. Suction is applied to the membranes by a low pressure permeate pump. The applied suction draws water through the membranes and filters out suspended solids. Since the membranes have such a small pore size, they also provide advanced or tertiary treatment. Several hundred filtration membrane strands are combined into a module. Several modules are installed in a cassette. A process train will typically have several cassettes, each of which can be valved on or off independently. Filtered effluent from the MBR is pumped to the disinfection system. Solids are removed from the MBR system by pumping a small amount of the MBR contents to a solids handling facility, described in Section 2.3 below. DISINFECTION SYSTEM Since a portion of the effluent will be recycled as toilet flushing and irrigation water and the remainder of the effluent will be disposed of, a dual disinfection system is required. All effluent from the MBR facility will first be disinfected by a UV disinfection system. Water which will be recycled will pass through an additional chlorine disinfection system and be stored in a recycled water holding tank. This recycled water will be used for landscape irrigation, and for toilet flushing water at the casino, hotel and tribal housing. Excess water, beyond what the recycled water storage tank can hold will be held in the reservoir or disposed of as described in Section 2.2 below. Effluent sent for disposal will be disinfected by the UV system only. The UV system will provide the same bacterial kill as chlorination, but will not produce chlorinated byproducts associated with chlorination. 2.2 EFFLUENT DISPOSAL SYSTEM To the extent possible, water will be recycled rather than disposed of. Only if there is no avenue for recycled water use will the water be disposed of. Treated water is produced by the wastewater treatment plant at the rate that wastewater is received at the plant. The wastewater treatment plant will treat an estimated 159,000 gallons of wastewater per day (average flow). The majority of that water will be recycled. The excess will be stored or disposed of. EFFLUENT RECYCLING The plans for the Jamul Indian Village include the use of a dual plumbing system at various locations. This system will use water from the recycled water storage tank for toilet flushing and landscaping irrigation. Estimations of toilet flushing requirements indicate that up to 100,000 gallons per day of recycled water will be required. Additional water will be required for landscaping. The amount of recycled water required for irrigation will vary depending on the season. During the peak irrigation season, the recycled water demand is expected to exceed Analytical Environmental Services 2-5 Jamul Indian Village Wastewater Treatment Plant

6 recycled water supplies and additional water will be needed from either the storage reservoir or the potable water system. The recycled water system will include a pump station located at the wastewater treatment plant, a recycled water storage tank, the recycled water transmission and distribution pipelines, a dual plumbing system at various facilities, and landscape irrigation systems. Recycled water will be pumped to a 1.0 MG (million gallons) recycled water storage tank. Water sent to the storage tank will be disinfected by a chlorine disinfection system in addition to the UV disinfection system. In the event of a low level in the recycled water tank, a control valve in the potable water backup pipeline will open and supply potable water through an air gap to the recycled water tank until the tank refills and the low-level condition has been rectified. EFFLUENT STORAGE Excess effluent, beyond what can be recycled will be stored in 2 unlined reservoirs located on trust land. These reservoirs will be able to store approximately 17.6 acre feet of water for either future recycling or disposal. During the dry portion of the year, water from the reservoirs will be pumped back into the recycled water tank for use. If effluent generation exceeds recycled use and storage capacity, it will be disposed of as described below. EFFLUENT DISPOSAL Excess effluent above what can be recycled or stored will be disposed at onsite leach fields. The leach fields proposed for the project are high-capacity leach fields which have much higher loading rates than conventional leach fields. The leach field system will consist of multiple separate leach fields, with a total disposal capacity of 200% of the design flow which will provide for 100% redundant disposal capacity. Each leach field will be able to be operated separately from the other leach fields. As a result, a failure in one of the leach fields can be isolated without requiring a complete shut down of the disposal system. 2.3 SOLIDS DISPOSAL To control solids in the MBR, a certain amount of biomass will be pumped out of the MBR into a solids handling facility. At the solids handling facility, solids will be dewatered using a belt filter press and will eventually be hauled off for disposal at a suitable waste handling facility. Water extracted from the solids will be reintroduced into the wastewater treatment plant headworks. 2.4 POWER SUPPLY Main power will be supplied to the wastewater treatment plant by San Diego Gas and Electric (AES, 2002). In addition to the main power line, supplemental power will be supplied by back- Analytical Environmental Services 2-6 Jamul Indian Village Wastewater Treatment Plant

7 up generators. The back-up generation system will be sufficient to power all critical systems for 1 day. Additional back-up generators will be used to provide back-up power to the lift stations. 2.5 ALARM SYSTEM Process control at the wastewater treatment plant will include the use of a supervisory control and data acquisition (SCADA) system. The SCADA system will be used to monitor essential processes and equipment and will trigger an alarm in the event that there is an excursion from accepted operating parameters. Critical alarms will activate a pager notification system to alert personnel of the alarm condition. In addition to providing alarm notification, the SCADA system will place the wastewater treatment system in standby in the event of a priority effluent quality alarm. An example of a priority effluent quality alarm is a disinfection system failure alarm. In the event of a failure of the disinfection system, the SCADA system will put the wastewater treatment system in standby, which will halt effluent discharge until the problem is addressed and the system is reset. 2.6 EMERGENCY STORAGE Emergency storage will be provided by the emergency storage basin. This basin will be located right next to the MBR basins and will provide storage for a minimum of 24 hours average flow. The emergency basin will be situated such that the MBR trains and the equalization basin will overflow into the emergency basin. Material can be returned to the MBR trains from the equalization basin using mobile pumps. 2.7 MBR EFFLUENT QUALITY All recycled water will comply with the requirements of Title 22, Division 4, Chapter 3 Water Recycling Criteria, commonly referred to as Title 22. Under Title 22, the highest level of treatment is referred to as disinfected tertiary recycled water. In accordance with Title 22 Section 60304, disinfected tertiary recycled water can be used for toilet flushing, irrigation of parks, and irrigation of crops including all edible root crops where the recycled water comes into contact with the edible portion of the crop. To meet the requirements of disinfected tertiary treatment, wastewater must be oxidized to stabilize any organic matter in a nonputrescible form. The water must then be filtered to remove solids (tertiary treatment). Finally, the tertiary treated effluent must be disinfected using either chlorine or an equivalent disinfection system capable of inactivating or removing % of plaque forming units of F-specific bacterophage. Water quality criteria for water receiving the highest level of treatment include: Analytical Environmental Services 2-7 Jamul Indian Village Wastewater Treatment Plant

8 1) Effluent daily average turbidity less than or equal to 2 nephlometric turbidity units (NTU). 2) Effluent 7-day median total coliform less than or equal to 2.2 bacteria per 100 ml. Title 22 also specifies redundancy and reliability features that must be incorporated into a reclamation plant. Features include emergency storage areas, redundant biological treatment units, failure alarms and other features necessary to ensure reliable treatment of wastewater. 2.8 PERSONNEL QUALIFICATIONS Operations of the wastewater treatment plant and associated system monitoring will be performed by qualified personnel. Personnel will have training commensurate with their responsibilities and will have the appropriate certification by the State of California or an equivalent certification from another state. Continuing education will be made available to the operations staff as necessary to maintain the required level of competency. Analytical Environmental Services 2-8 Jamul Indian Village Wastewater Treatment Plant

9 Figure 1 Analytical Environmental Services 2-9 Jamul Indian Village Wastewater Treatment Plant

10 Figure 2 Analytical Environmental Services 2-10 Jamul Indian Village Wastewater Treatment Plant

11 Figure 3 Analytical Environmental Services 2-11 Jamul Indian Village Wastewater Treatment Plant

12 Figure 4 Analytical Environmental Services 2-12 Jamul Indian Village Wastewater Treatment Plant