MWUA 92 nd Annual February Meeting & Trade Show

Transcription

1 MWUA 92 nd Annual February Meeting & Trade Show Biological Filtration for Iron & Manganese Treatment: Operating Experience in Cavendish, VT February 7, 2018 John N. McClellan, Ph.D., P.E. Vice President Tighe & Bond, Inc.

2 Iron & Manganese Fundamentals Iron and manganese are common in groundwater Regulated under Secondary MCLs Iron: 0.3 mg/l Manganese: 0.05 mg/l Not considered to be a health threat by EPA at the SMCLs Cause discoloration/staining

3 Iron & Manganese Fundamentals Soluble iron and manganese have +II oxidation state: Fe 2+, Mn 2+ Air or oxidants such as chlorine oxidize Fe 2+, Mn 2+ to Fe 3+, Mn 3+, 4+, 5+, 6+ which form insoluble compounds Hydroxides, oxides, carbonates Precipitation-> staining

4 Iron & Manganese Treatment Basic strategies: Prevent precipitation Sequestration with polyphosphate chemicals Remove iron & manganese Convert to insoluble form and precipitate Filter out solid

5 Iron & Manganese Treatment Iron & Manganese Removal Technologies Softening processes Ion exchange Lime softening Oxidation followed by solids removal Aeration/sedimentation/filtration Chemical oxidation/filtration» Chlorine, permanganate, chlorine dioxide, ozone» Gravity filters, pressure filters, membrane filtration Biological oxidation/filtration

6 Iron & Manganese Removal Oxidation Precipitation Filtration Challenge: Oxidation reactions of Fe & Mn are slow

7 Iron & Manganese Removal Conventional Chemical Oxidation Oxide-coated media catalyzes oxidation Greensand Proprietary media In-situ oxide coated Credit: Hungerford & Terry, Inc.

8 Chemical Oxidation Iron & Manganese Treatment System Oxidant Chemical Hypochlorite Permanganate Others Untreated Water Fe Precipitation Catalyzed oxidation of Mn on oxide coated media Solids removed in filter Treated Water

9 Chemical Oxidation Iron & Manganese Treatment System Spent Backwash Water Accumulated solids removed by air scour and backwash Air Filtered Water

10 Chemical Oxidation Process Characteristics Consumes chemical oxidants Chlorine, permanganate, others Various types of filter media can be used Greensand Proprietary oxide coated media In situ oxide coated media Frequent backwashing/large amount of residuals if Fe/Mn concentration is high Permanganate can be tricky to use Overdosing->purple water Many vendors for process equipment and media Tried and true technology

11 History of Biological Iron & Manganese Removal Biological iron oxidation observed in conventional filter plants. Conditions suitable for iron oxidizing bacteria activity studied in France s First full-scale biological filtration installations in Europe 1980s First North American installations 1990s Now >20 in Canada and U.S.

12 How does biological filtration work? Conditions for bacteria optimized in filter by controlling ph and dissolved oxygen Naturally occurring bacteria form biofilm on filter media Enzymes produced by bacteria catalyze oxidation Catalyzed reaction is fast high filtration rates are possible

13 How does biological filtration work? Bacteria are prevalent in Nature - Sheath Types, i.e. Leptothrix ochracea - Spirally Twisted Stalks, i.e. Gallionella Ferruginea

14 How does biological filtration work? Manganese oxidizing bacteria (MOB) and iron oxidizing bacteria (IOB) require different conditions Two-stage process usually required to remove both iron and manganese

15 Oxidation Reduction Potential OR P (Eh-mV) Conditions suitable for bacteria MnO 2 Mn 2+ Mn 2 O Field of Biological Iron Removal 2. Field of Biological Manganese Removal Fe 2+ Fe(OH) ph After Mouchet, JAWWA, April 1992

16 Process Schematic ORP ORP Air Mixer ph Ferazur Reactor Air Mixer ph Mangazur Reactor Treated Water ph DO Raw Water ph DO Alkaline Solution Air ph control (caustic)

17 Biological Filtration Process Characteristics No chemical oxidants, process includes air injection and ph adjustment Seeding time required Media have relatively large E.S. Oxidized solids are relatively dense Must backwash with unchlorinated water 2-stage process usually required to remove both iron and manganese

18 Retention Capacity Metals retention per Cycle - kg Fe/m FERAZUR Chemical Oxidation Filters Fe 2+ in Raw Water (mg/l)

19 Seeding time Seeding time is required to build a Biomass depends on: - Temperature - Amount/type of bacteria present Iron seeding time is relatively short - 1/2 to 5 days Manganese seeding time 2 weeks to 2 months or more Times can be reduced by adding small amount of pre-seeded media

20 Advantages No oxidant chemicals Relatively high filtration rates Long filter run times Low volume of residual solids Can handle high iron/manganese concentrations

21 Disadvantages Seeding time required Two-stage process needed to remove both iron and manganese Does not remove turbidity or organic color as well as chemical processes New technology More difficult to obtain approvals Sole source procurement approval for SRF funding and variance from Water Supply Rule were required in Cavendish May need clearwell to release excess air For practical purposes, this is a proprietary process available from only one vendor

22 Factors to Consider Raw Water Quality Iron and manganese levels Turbidity and color Inhibiting substances: ammonia, H 2 S, Zinc Backwash Water Source Availability of system water Backwash water disposal Location of sewer Seasonal use

23 Cavendish, VT Case Study Groundwater Supply Black River Well Untreated water quality Fe: 3-6 mg/l Mn: 1-2 mg/l ph: Design flowrate 150 gpm Backwash water discharge to sewer

24 Pilot Testing Results Ferazur Reactor (Iron Removal) Cavendish, VT Case Study Cavendish, VT

25 Pilot Testing Results Mangazur Reactor (Manganese Removal) Cavendish, VT MANGAZUR - Iron & Manganese Removal Total Iron & Manganese (mg/l) START UP Process Stabilization after < 90 Hours of Intermittent Operation MANGANESE SMCL = 0.05 mg/l IRON SMCL = 0.3 mg/l Filtration Rate (gpm/sf) 0.0 7/4/05 7/6/05 7/8/05 7/10/05 7/12/05 7/14/05 7/16/05 7/18/05 7/20/05 7/22/05 7/24/05 7/26/05 7/28/05 7/30/05 8/1/05 8/3/05 8/5/05 8/7/05 8/9/ Iron - Final Effluent Manganese - Raw Water Manganese - Final Effluent FIltration Rate

26 Process Comparison Cavendish, VT Biological Oxidation versus Chemical Oxidation No Chemical oxidants required Longer filter run times Less backwash water Chemical Oxidation #1 Chemical Oxidation #2 Biological Oxidation 1 Maximum Filter Backwash Flowrate (gpm) Backwash Water Production Per Month (gal) ,300 99,200 6,200 Net Production per Filter Run (%) Combination of Ferazur and Mangazur Backwash Characteristics

27 Cost Comparison Cavendish VT Capital and O&M cost summary and comparison- April 2006 Item Conventional Greensand Proprietary Chemical Oxidation Biological Filtration Capital Costs Equipment purchase $215,000 $275,000 $360,000 Equipment installation 119, , ,000 Building 81,000 81,000 81,000 Engineering & Contingency 125, , ,000 Total Capital Cost 540, , ,000 Annualized capital cost 39,000 44,000 51,000 O&M Costs 28,000 34,000 10,000 Total annual cost $67,000 $78,000 $61,000

28 Three Filter Vessels 1 Iron, 2 Manganese

29 Manganese Filter

30 Blower and Compressor Process Air Compressor & Air Scour Blower

31 Filtered Water Storage Tank

32 CausticTank Caustic Tank and Metering Pumps

33 Cavendish, VT Startup May 2009 Iron seeding time <1 Week Manganese seeding time ~5 months Iron & manganese have increased since pilot testing ProControl Series 2 plus - EOS Research Ltd.

34 Cavendish, VT Process stabilization: November 2009 Filtered water quality Iron <0.1 mg/l Manganese <0.03 mg/l Filter runs ~ 1 week

35 Problems/Lessons Learned Manganese seeding time longer than expected Treating high iron & manganese concentrations requires lots of process air Excessive air in filtered water Piping and pump system modifications were made to convert backwash storage tank to filtered water tank Filtered water is now de-gassed in prior to being pumped to distribution system in filtered water tank

36 Problems/Lessons Learned Extreme raw water iron concentration caused clogging of iron filter High headloss Increased backwashing

37 Iron Clogging

38 Problems/Lessons Learned Extreme raw water iron concentration caused clogging of iron filter Solution: Reduced influent concentration to filtration system by blending Backwashing frequency back to 4-7 days

39 Concentration (mg/l) Problems/Lessons Learned 2017 Water Quality Monitoring Data: Iron Well 1 Blend Ferazur Eff SMCL Date

40 Concentration (mg/l) Problems/Lessons Learned 2017 Water Quality Monitoring Data: Manganese Well 1 Blend Ferazur Eff SMCL Mangazur Eff Date

41 Waterloo, QC Installation Flow: 1.1 MGD In Service Since: 2000 Number of Units: 2 Filtration Rate: 10 gpm/ft 2 Fe (1.7 mg/l) & Mn (0.45 mg/l) Performance: Effluent: Fe < 0.03 mg/l, Mn < 0.01 mg/l Ferazur Filter runs: 7 days Mangazur filter runs: 14 days

42 Waterloo, QC Process Schematic

43 Biological filtration take-away points Superior performance where iron and/or manganese concentrations are very high Long filter runs/low volume of residuals

44 Acknowledgements Town of Cavendish, VT Richard Svec, Town Manager (retired) Randy Shimp, System Operator

45 Questions?