Submerged Membranes to Replace Media Filters to Increase Capacity 4X for a Small Community. Richard Stratton, PE HDR Engineering, Inc.

Transcription

1 Submerged Membranes to Replace Media Filters to Increase Capacity 4X for a Small Community Richard Stratton, PE HDR Engineering, Inc.

2 Main Points of this Presentation Membranes can provide 4 times the capacity in the footprint of a conventional plant Membranes provide absolute pathogen barrier and are more cost effective Removal of organics and DBP compliance achieved with proactive approach Retrofitting an operating WTP requires a well thought out plan

3 Description of Rancho Murieta Located in Sierra Foothills east of Sacramento, California Golf course community - Currently 2,000 dwelling units (DU) with room for 4,000 DU Mediterranean climate cool wet winter, dry hot summers Rancho Murieta

4 Need for Water Plant Upgrade and Expansion Original plant built in 1970s with traveling bridge filter no filter-to-waste Expansion needed to accommodate growth and obsolete Plant 1 Concern with taste and odor events in water storage lakes Plant 2 Plant 1

5 Existing Plant 1 Treatment System Pant 1 Travelling Bridge Filter Existing Sedimentation Basin

6 Existing Common Treatment Systems Chlorine Room Coagulant/Polymer Feed System

7 Raw Water Supply from Consumnes River - Stored in 3 Reservoirs

8 Cosumnes River Intake

9 Occurrence of Aquatic Weeds in Chesbro Reservoir

10 Aquatic Plants in Chesbro Reservoir Causing Elevated Organics Levels Most prevalent algae species include: Eurasion Water Milfoil Phormidium

11 Raw Water Characteristics PARAMETER UNITS RAW WATER AVERAGE MAXIMUM MINIMUM Turbidity NTU Total dissolved Mg/L <100 solids Total Hardness Mg/L as CaCO3 Alkalinity Mg/L as CaCO3 ph Color TCU TOC Mg/L MIB µg/l < Geosmin µg/l < DOC Mg/L Temperature DegC

12 Water Source and Treatment Challenges Water source is Cosumnes River, withdrawal allowed only in winter Raw water storage in 3 small lakes with low TDS and low turbidity (0.5 NTU avg.) Aquatic plants and cyanobacteria in lakes add TOC and MIB (0.084 ppb) Chesbro Reservoir stratifies causing manganese to solubilize Jar testing performed to determine possible TOC removal

13 ACH Achieved 24% TOC Removal at Dose of 18 mg/l % TOC (mg/l) TOC TOC Removal (%) 25% 20% 15% 10% 5% 0% Percent Removal Coagulant Dose (ACH, mg/l)

14 Alum Achieved 25% TOC Removal at Dose of 42 mg/l % TOC (mg.l) TOC TOC Removal (%) 25% 20% 15% 10% 5% Percent Removal 0.0 0% Coagulant Dose (Alum, mg/l)

15 Ferric Chloride Achieved 55% TOC Removal at Dose of 27 mg/l % % TOC (mg/l) TOC TOC Removal (%) 30% 25% 20% 15% 10% 5% 0% Percent Removal Coagulant Dose (Ferric Chloride, mg/l)

16 Conclusions from Jar Testing ACH required the lowest dose Ferric Chloride achieved the highest TOC removal Alum required highest dose, but costs the least

17 Summary of TOC and T&O Control Strategies Use ACH or Alum up to 40 mg/l to achieve TOC removal Add powdered activated carbon (PAC) up to 4 mg/l during taste and odor and/or high TOC events Continue proactive management of Chesbro Reservoir: Algaecide addition Weed removal Level changes to discourage weeds

18 Historic TOC Levels and Alum Doses

19 Proactive TOC Control Started in 2010 has Resulted in DBP Compliance Clearwell: TTHM Annual Max 56 ppb HAA5 Annual Max 35 ppb

20 Membrane Retrofit Selected for the Following Reasons: Small footprint 6 mgd membrane plant fits in footprint of 1.5 mgd conventional plant Absolute pathogen barrier Lower capital and operating costs Allows decommissioning of Plant 2 with addition of membranes in 4 th train.

21 Pilot Testing Performed by Memcor Confirmed Performance Able to operate at up to 30 mg/l alum and 5 mg/l PAC Flux avg. 20 gfd, peak 30 gfd 30-day CIP interval

22 Description of Selected Membrane System Design Membrane system capacity = 4 mgd (Phase 1), 6 mgd ultimate, process train includes: Automatic self-cleaning screens ACH, KMnO4, and PAC addition and 5 minutes contact time in floc basins Submerged membranes (Zenon 1000) Chlorine contact basin

23 Process Schematic PAC KMnO4 ACH Recycle Air Scour Bowers Chlorine To Distributio n System FCV Chesbro Reservoir Strainers Flow Meter Flash Mix Flocculation Basins Channel Membrane Basins Filtrate Pumps Chlorine Contact Basin Booster Pumps Future To Plant 2 Contact Basin Reject Recycle to Head of Plant BW Waste Holding Basins Inclined Plate Settler Solids Drying Beds

24 Membrane System Layout in Existing Plant 1 Footprint

25 Selected Submerged Ultrafiltration Membrane Systems Zenon ZW-1000 (v4)

26 Membrane Trailer Provides Temporary Capacity

27 Membrane System Piping/Pumps Influent/BW Drain BW Drain Pumps CIP Pumps

28 Permeate Pumps and Piping

29 Solids Handling System Backwash waste holding basins Plate Settler with polymer and coagulant for solids removal Recycle to flash mix (less than 10%) Drying beds for solids drying CIP Waste will be sent to sewer

30 Summary of Design Criteria Item Value Automatic strainer: Type Mesh Opening Capacity (each) Number Rapid Mix Detention Time Mixer motor G Flocculation Basins (3) Flow each Detention Time Mixer motor G Self cleaning 0.4 mm 6 mgd 2 18 seconds 0.5 HP 700 sec -1 2 MGD 7 min. ½ HP 47 sec -1

31 Item Immersed membranes: Material Pore size Number of trains Number of cassettes per train Modules per cassette Area per module Maximum flux (instantaneous) Firm capacity Transmembrane pressure Recovery Backwash interval Maintenance clean interval CIP interval Cleaning chemicals Value GE Zenon 1000 PVDF 0.02 micron 3 (4 future) sf 30 gfd (2 trains) 4 mgd (6 mgd future) 0-13 psi 92-95% 15 min 1 day 30 days Sodium hypochlorite Citric acid Sodium hydroxide Sodium bisulfite

32 Item Reclamation System (membrane reject water) Equalization Basins Number Volume, each (net operating) Plate Settler Number Maximum recycle rate Settling rate Chlorine Contact Basin Volume Length:Width Ratio Detention Time (max day) Baffling factor Design CT for 0.5 Giardia inactivation Value 2 23,000 gal gpm 0.32 gpm/sf 105,000 gal. 70:1 37 min (winter) 11.5 (summer)

33 Item Booster Pumps (Plant 1 and 2): Number (existing) Capacity, ea (Plant 1 and Plant 2) Number (add to Plant 1) Total Firm capacity Sand Drying Beds (common facility): Number of cells Total Area Sludge loading rate Chemical Feed Systems Coagulant Dosage Range Typical Usage Storage tank (double wall) Disinfectant Dosage Range Typical Usage Value mgd; mgd 6 mgd 4 9,600 sf 9 lb/sf/yr ACH or alum mg/l 1,150 lb/day 4,000 gal Chlorine (gas) mg/l 208 lb/day

34 Item Chemical Feed Systems (cont d) Taste and odor control Dosage Range Typical Usage Preoxidant Dosage Range Corrosion control Dosage Range Typical Usage ph Adjustment Dosage Range Typical Usage Storage tank (double wall) Value PAC 3 to 5 mg/l 200 lb/d (seasonal) Permanganate mg/l Zinc Orthophosphate mg/l 146 lb/day Sodium Hydroxide 3 6 mg/l 188 lb/day 2,500 gal

35 Project Status Project procured with CMAR - total bid amount $11.5 million Construction began in June 2014 Membrane commissioning to be completed by December, 2015

36 Submerged Membranes to Replace Media Filters to Increase Capacity 4X for a Small Community Richard Stratton, PE HDR Engineering, Inc.