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NOM Innovations and Applications Whaler s Inn, Victor Harbor, Adelaide, South Australia, March 2-5, NOM increase in Northern European Source Waters: Impacts on coagulation/contact filtration processes
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NOM Innovations and Applications Whaler s Inn, Victor Harbor, Adelaide, South Australia, March 2-5, NOM increase in Northern European Source Waters: Impacts on coagulation/contact filtration processes B. Eikebrokk, R.D. Vogt and H. Liltved Research Director, Dr. Bjørnar Eikebrokk, SINTEF, Trondheim, Norway 1 Acknowledgement - Coauthors Dr. Rolf D. Vogt, Associate Professor, Univ. of Oslo, Norway Dr. Helge Liltved, Research Manager, NIVA, Norway 2 Presentation outline Introduction Increasing NOM in surface waters in Europe and North America Specific examples Explanatory models Implications on coagulation/ filtration processes: Quantification of major effects of NOM increase Pilot experiments on selected raw waters Results and modeling coagulant dosage sludge production filter run length treatment capacity backwash water, ripening/hygienic aspects Summary and conclusions 3 Major negative impacts of NOM are well known NOM may complex: Heavy metals Organic micro-pollutants b Form potentially harmful DBP (THMs, HAAs, MX, OBP) b Cause taste, odor and color problems b Promote corrosion b Promote biological growth in distribution systems b Increase disinfectant dose requirements increased mobility and human exposure/intake to these substances b Form complexes with heavy metals, organic micro pollutants, etc b Affect stability and removal of particles and pathogens 4 Norway: A doubling or even tripling of color in some sources from Color increase in Oslo s water sources (Annual averages calculated from monthly measurements) Colour, mg Pt/l Skullerud Oset Langlia Alunsjøen NOM-increase in Oslo s raw waters Maximum color levels in past 10-year periods (Monthly samples) Max Raw water color (mg Pt/L) Max Råvannsfarge (mg Pt/L) Maridalsvann Elvåga Langlia Alunsjø 7 NOM status in ICP-Surface waters in Europe and North America ICP-Waters: The International Cooperative Program on Assessment and Monitoring of Acidification of Rivers and Lakes Established under the Executive Body of the Convention on Long-Range Transboundary Air Pollution at its 3rd session in Helsinki, July 1985 Results from Skjelkvåle B.L. 2003: The 15-year report: Assessment and monitoring of surface waters in Europe and North America; acidification and recovery, dynamic modeling and heavy metals. ICP-waters report 73/2003. Norwegian Inst. for Water Research, NIVA, 113 p. 8 Location of ICP Waters sites in Europe and US/Canada Skjelkvåle B.L.: ICP-Waters Report 73/2003, NIVA, Norway 9 Regional DOC-trend results for ICP water sites for the period Values are median slopes, and 90% confidence intervals of trend tests on all sites in each region. Units for DOC are mg/l/year (Skjelkvaale, ICP-Waters Report 2003) Region Continent N median lower CI upper CI p East Central Europe Europe n.s. Northern Nordic Europe .01 Southern Nordic Europe .01 UK/Ireland Europe .01 West Central Europe Europe n.s. Maine/Atlantic Canada N. America n.s. Vermont/Quebec N. America .01 Adirondacks N. America .01 Appalachian Plateau N. America n.s. Upper Midwest N. America .01 Virginia Blue Ridge N. America .05 10 Possible reasons for NOM increase (From Liltved 2002, Forsberg 1992) Økt mengde Increased amount of drivhusgasser; greenhouse CO2, gases CH4, KFK, (CO 2, etc. CH 4, N 2 O, CFC, etc) Temp increase ( C per decade) Increased Økt nedbør precipitation Increased Økt avrenning runoff Increased Økt N- nedfall atmospheric N deposition Økt fotosyntese Increased photosynthesis Økt plantevekst Increased primary production Higher ground water level Økt mengde Increased amount planteavfall of plant residues Increased rate of degradation Økt årsmiddeltemperatur, 0,2-0,7 C pr dekade Økt nedbrytningshastighet Høyere grunnvannsnivå Mer myr- og våtmarksområder More moors and peatland areas Økt produksjon av NOM Increased NOM production Økte tilførsler av NOM Increased flux of NOM Høyere fargetall og organisk karbon i elver og innsjøer Increased source water color, UV-abs and organic carbon 11 Effect of reduction in Acid rain In the 70 and 80ties reduction in the colour in lakes were reported in the regions suffering by acid rain With decreasing S-deposition one should expect an increase in NOM Oxidized sulphuric fall-out This was explained by protonation of weak humic acids making them more hydrophobic However, this cannot fully explain the NOM increase as this is also observed in areas not influenced by acid rain 12 Studies on variation in DOM properties Base flow - no high flow episodes (Vogt et al. 2004, Aquatic Sciences) NOMiNiC project: A number of classical and sophisticated characterisation methods used to explain variation in DNOM properties from 5 sites in Norway, Sweden, and Finland Correlation studies (PCA/Pearson/Hasse diagram) indicate: As the S-deposition decreases we may find More coloured and high MW DNOM with Increased adsorptive capacity for micro-pollutants Increased carboxylic acidity 13 Correlation between runoff intensity and NOM (Birkenes catchment, Southern Norway) 4Changes in precipitation pattern may explain increases in TOC 4Correlation between temperature and TOC is less clear 4The decrease in number of days below freezing and thinner snow pack may be important TOC mg C L Fall Spring Summerr Discharge L sek -1 14 Effects of precipitation on lake water quality Riise and Hongve, 2002: Mean values for 24 low ionic forest lakes in Norway Colour (mg l -1, Pt) Ca (µmol l -1 ) ph a ,4 6,2 6,0 c e Color Ca ph DOC (mg l -1 ) NO3 (µmol l -1 ) Al (µg l -1 ) 6,8 6,4 6,0 5,6 b 5, d f DOC NO 3 Al Color is well correlated to precipitation/water flow DOC not correlated to flow Colored, high MW DOC ( 10 kda) enter the lakes at high-flow conditions 5, Precipitation (mm) Precipitation Amount of precipitation (mm) 15 Variable relationships between color and DOC Riise and Hongve, 2002: Studies on low ionic forest lakes in Norway Colour (Pt mg l -1 ) Wet Reg. line DOC (mg l -1 ) 16 NOM discharge studies - Deciduous vs. coniferous litter and organic soils - D. Hongve, Journal of Hydrology, 224, 1999, Lysimeter Litter Water Soil Sample Specimen DOC (mg/l) Color (mg/l) Color:DOC ratio Deciduous Coniferous Peat O-horizon Sphagnum Accumulated values per 10 g dry weight during an annual sampling season 17 Seasonal variation in DOC and Color - Autumn peaks very common DOC D. Hongve, Journal of Hydrology, 224, 1999, % of total Deciduous litter autumn - snowmelt 50 Coniferous litter Peat O-horizon Color spring - second autumn High leaching of DOC from fresh deciduous litter in the autumn DOC from Alder leaf litter Birch (5%) Willow (35%) More evenly distributed leaching from coniferous litter and organic soils 0 Deciduous litter Coniferous litter Peat O-horizon autumn-snowmelt spring - second autumn 18 Main factors - NOM Increase Global warming and changes in precipitation patterns Milder winters, more rain, delayed freezing and extension of autumn circulation period Growth season extended by 2-3 weeks in some regions Increase in forest volume and increased deciduous to coniferous ratio Precipitation chemistry - Reduced acid rain Sulphate content reduced by % at monitoring sites in Norway during the period (Aas et al. 2001). However, increased NOM is also detected from catchments not affected by acid rain (Liltved 2002) Hydrological flow patterns Frozen/saturated soils create flow through the upper organic soil horizons of the forest floor instead of the deeper mineral horizons. Corresponding changes in the discharge and composition of several substances, including NOM/DOC (Hongve 1999, Riise 1999) 19 NOM increase: Practical consequences for the water industry Κ More plants have to start removing NOM Κ Significant process modifications - or new and more NOM tolerant technologies required at many plants Κ More severe water quality changes during distribution: increased need also for optimization of distribution system management and operation Κ Increasing need for treatment process optimization at existing plants (more stress on water quality, capacity, sludge management issues, etc) 20 Concerns and optimization needs from NOM increase Non-compliance with current regulations on NOM (color, TOC, THM, etc) Increased biological growth in distribution systems Operational challenges due to rapid changes in source water NOM content and properties (mainly small sources) Increased coagulant doses and sludge production rates Reduced filter run lengths, increased backwash water consumption, and reduced capacity Reduction in overall hygienic barrier efficiency Increased operational costs 21 NOM increase and treatability SUVA - an important parameter with respect to NOM treatability by coagulation NOM increase is associated with a corresponding increase in SUVA Pilot plant experiments with 3 Model waters with increasing NOM and SUVA levels Main Objective: To quantify the practical effects of increasing NOM on major operational parameters 22 Pilot testing of Selected Raw Waters with Increasing NOM and SUVA levels Turbidity 0.5 NTU, Fe 0.1 mg/l, No algae RW15 15 mg Pt/L 2.4 mg DOC/L SUVA 3.8 RW30 30 mg Pt/L 3.3 mg DOC/L SUVA 4.3 RW50 50 mg Pt/L 4.5 mg DOC/L SUVA Nature of NOM and Treatability evaluations based on SUVA (Edzwald and Tobiason, 1999) SUVA Composition Coagulation DOC Removals 4 Mostly Aquatic Humics, High Hydrophobicity, High MW RW30/ Mixture of Aquatic Humics and Other NOM, Mixture of RW15 Hydrophobic and Hydrophilic, Mixture of MWs 2 Mostly Non-Humics, Low Hydrophobicity, Low MW NOM Controls, Good DOC Removals NOM Influences, DOC Removals Should be Fair to Good NOM has Little Influence, Poor DOC Removals 50 % for Alum, Little Greater for Ferric % for Alum, Little Greater for Ferric 25 % for alum, Little Greater for Ferric 24 Pilot scale testing of different types of raw waters, coagulants and filters SINTEF : 1000 filter runs 6 types of coagulants 5 types of raw water 7 filter configurations pre ozonation corrosion control 3 types of mixers low temp (1 C) polymers as filter aids etc Results/experiences Models 25 NOM removal by metal coagulation-contact filtration: Norwegian experiences Κ Minimum Al- or Fe coagulant dose requirement is controlled by metal coagulant residual MCL ( 0.1mg tot-al or Fe/L) Κ Close to 90 % color and 60 % NPOC removal is normally obtained at that dosage level Κ Loose flocs and high sludge production yield relatively early filter breakthroughs and rapid head loss development 26 Empirical Models: Coagulant dose (RW 15-50, 50, Turb NTU, 2M A-S A S filters) Minimum Coagulant dose requirement: Dose D (mg Me/L) = A Raw water color (mg Pt/L) + B ALG: D AbsMin = Col (mg Pt/L) D MinPrak = Col (mg Pt/L) JKL: D AbsMin = Col (mg Pt/L) D MinPrak = Col(mg Pt/L) Model Output Minimum Coagulant koagulantdose Dose (mg Me/L) JKL ALG Raw Water Råvannsfarge Color (mg Pt/L) 28 Empirical Models: Filter Run Length (BT) (RW 15-50, 50, Turb NTU, 2M A-S A S beds, 2 m avail. head) Model A (based on solids load, no polymer): Filter Run Length t f (h) = 298 (v f D) where v f = rate of filtration (m/h) D = coagulant dosage (mg Al/L) Model B (Low alum, 1-3 mg Al/L): t f (h) = 80/v f -4.5 Al w.o./polymer t f (h) = 180/v f -4.5 Al with polymer 29 Model A Output (Al-sulphate, no use of polymer as filter aid) Filter Run Length (hrs) Filtersykluslengde (hrs) Raw Råvannsfarge water Color (mg Pt/L) (mg Pt/L) 12 t=298(filtration rate Dose) m/h 7,5 m/h 10 m/h 30 Empirical Models: Sludge Production (RW 15-50, 50, Turb NTU) Sludge Production (mg SS/L) = K Dose (mg Me/L) ALG: JKL: SS Al = 4.2 D (mg Al/L) SS Fe = 2,5 D (mg Fe/L) 31 Sludge Model output (optimum coagulation) Raw Råvannsfarge water Color (mg Pt/L) Sludge Slamproduksjon Production (mgss/l) 32 Relative effects on selected operational parameters of an increase in raw water color from 20 up to values of 25 to 50 mgpt/l Relative Verdi rel. til to verdi a value for Råvannsfarge of 1 for RW20 3,5 3,0 2,5 2,0 1,5 1,0 0,5 0,0 ## Spylinger, BW/day, Spyle- Q og Modningsvann (m3/m2)-v/7.5m/h Al-sulfatdose + Slamproduksjon BW and Q R (m 3 /m 2 ) at m/h Al-dosage and Sludge Production (mg/l) Kapasitet-m3/h pr m2 filter-v/7.5m/h Filtergangtid(GBR) Treatment Capacity (m 3 /m 2 hr at 7.5 m/h Filter run time (BT termination) 2,90 2,35 2,20 1,87 1,88 1,54 1,27 1,64 1,41 1,21 0,97 0,94 0,90 0,87 0,79 0,78 0,64 0,53 0,44 0, Source Råvannsfarge Water Color (mg ( mg Pt/L) Pt/L) # BW/day Dose+Sludge Capacity Run time 33 3-step Optimization Procedure at full scale plants A. Identify the coagulation profile for representative raw water conditions - based on model predictions and onsite testing B. Identify the filtration profile for relevant conditions, including the opt coagulation conditions obtained in A C. Calculate the obtained benefits - when compared to an initial reference situation, in terms of: Consumption of Chemicals and Energy Production of Sludge Filter Run length Treatment Capacity potential Amount of Backwash water Operational Costs 34 Plant optimization/coagulation Profile Skullerud WTP (RW25-28) Filter effluent quality - Residual Al 12ALG 14ALG 16ALG Opt-pH 18ALG 20ALG 22ALG = REF ph 35 Plant optimization/filtration Profile Skullerud WTP Turbidity/Particle count Increasing rate of filtration, increasing NOM and dose Filter run time (hrs) 36 Summary and Conclusions The color of several water sources in Norway has been doubled or even tripled during the 1990s 10 out of 11 ICP Waters sites in Europe and North America showed increasing DOC trend results of mg/l per year for the period were significant (90% CL) The NOM increase seems to be an effect of global change or variability. Increase in temperature, growing season, primary production as well as changes in precipitation patterns and reduced acid rain/s deposition seem to be relevant factors From experimental studies on raw waters with increasing NOM and SUVA levels the practical implications on coagulation and filtration processes are quantified and modeled. 37 Thank you for the attention! 38
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