Marine Outfall Systems

Transcription

1 Marine Outfall Systems Tobias Bleninger Institute for Hydromechanics (IfH), Karlsruhe Institute of Technology (KIT), Germany currently at: Departamento de Hidraulica e Saneamento (DHS), Universidade Federal do Paraná (UFPR), Brazil INSTITUTE FOR HYDROMECHANICS, ENVIRONMENTAL FLUID MECHANICS GROUP KIT University of the State of Baden-Württemberg and National Large-scale Research Center of the Helmholtz Association

2 Content Coastal Polllution Effluent and ambient interplay Water Quality Regulations Discharge systems Outfall characteristics 2

3 Coastal zone 60% of world population lives in coastal region Economic growth (industry, commerce, turisme) depends on WQ 70% of coastal WQ problems related to point sources outfall health impacts (aprox. 2 mio. death per year) environmental degradation (direct impact 13 bio. US$) Nov (high season): 78 of128 monitored beaches not approrate for bathing 3 Santos Harbout, Brazil Source: WHO, UNEP Santos, Brasil Source: Prefeitura de Praia Grande, Brazil

4 Outfalls Is dilution a solution? Examples worldwide show: Optimally blended technologies (e.g. treatment and submarine outfall) are viabel alternatives with less and controllable impacts to cheaper or moderate cost Principles often not understood by the public badly designed discharge systems Multi disciplinary: oceanography, civil and environmental engineering, construction, financing and public relations Advanced technologies: pipe materials, maritime constructions, lab and field instruments 4

5 US EPA shoreline impacts,

6 Environmental impacts plant related regional impacts -> salinity/temperature and substance concentration distributions influenced by discharge siting and induced mixing water body related impacts -> substance loads, accumulation influenced by water body characteristics, flushing and ambient mixing large scale and process differences Trade-off between different uses (e.g. sea turtle vs. economic growth 6

7 Effluent / ambient interplay RO effluent negatively buoyant, sinks down RO effluent blended with wastewater or cooling water positively, negatively or neutrally buoyant (can even change along a day) MSF/MED effluent (usually blended with cooling water) generally positively buoyant Buoyancy is dominant parameter for mixing / dilution, thus important to know Discharge calculator computes general effluent characteristics Free download under Allows for sensitity studies 7

8 Effluent calculator (RO) Flowrates & Effluent Characteristics RO annotations/limitations: - ambient characteristics (seawater) ambient temperature T a = C T = 10 to 180 C ambient salinity Sal a = ppt Sal = 0 to 160 ppt (ppt = g/kg) ambient density a = kg/m 3 allowed ranges for viscosity calculation: ambient kin. viscosity a = 9.98E-07 m 2 /s Sal = 0 to 130 ppt, T = 10 to 180 C (El-Dessouky, Ettouny (2002)) - fresh water (permeate) flowrate Q drink = 1.00 m³/s recovery rate: recovery rate r = 50 % percentage of intake water converted into permeate; intake flowrate Q in = 2.00 m³/s plant characteristic; following Lattemann: r = 40-65% - brine characteristics (effluent from desalination process) plant effluent flowrate Q desal = 1.00 m 3 /s temperature T desal = C usually ambient or 1 C above salinity Sal desal = ppt with Sal drink = 0 ppt density desal = kg/m 3 substance concentration c desal = ppm e.g. coagulants, anti-scalants,... - blended effluent - external - (e.g. waste water or others) flowrate Q effl,ex = 1.00 m 3 /s temperature T effl,ex = C salinity Sal effl,ex = 0.00 ppt (has no effect on density or mixing characteristics) density effl,ex = kg/m 3 Sal = 0 to 160 ppt, T = 10 to 180 C Coded in Excel Similar tab programmed for MSF / MED Final effluent characteristics: flowrate Q o = 2.00 m 3 /s effluent temperature T o = C mean average effluent salinity Sal o = ppt mean average effluent density o = kg/m 3 8 buoyant acceleration g o ' = m/s 2 g o ' = g?( a - o )/ a -> negatively buoyant, ok! g o ' < 0: negatively buoyant, g o ' > 0: positively buoyant kin. viscosity o = 1.02E-06 m 2 /s allowed ranges for viscosity calculation: Sal = 0 to 130 ppt, T = 10 to 180 C (El-Dessouky, Ettouny (2002)) substance concentration c o = ppm

9 Required dilution (example) Ambient (background) salinity Ca: Effluent (discharge) salinity Co: Co above ambient: 38 ppt 70 ppt 32 ppt (= Co Ca) Ambient standard Ca,max: Ca,max above ambient 40 ppt 2 ppt (=Ca,max Ca) Required dilution: Co ab. amb / Ca,max ab. amb 32/2 = 16 9

10 Required dilution (example) Ambient (background) salinity Ca: Effluent (discharge) salinity Co: Co above ambient: 38 ppt 70 ppt 32 ppt (= Co Ca) Ambient standards Rule of thumb, 10% above ambient Ca1,max: 41.8 ppt Gold Coast, 5% above ambient Ca2,max: 39.9 ppt Olympic dam or Israel, 1% above Ca3,max: ppt Required dilutions Rule of thumb: 9 : 1 Gold Coast 17 : 1 Olympic dam or Israel 84 :1 10

11 Example I: Salinity impact on seagrass Figure: courtesy Sabine Lattemann Required dilution: order of 15 11

12 Concentration [log µg/l] Toxicity of copper Source: Lattemann & Höpner ,900 µg/l: LC 50 Rangia cuneata (96 h) 100 µg/l 222 µg/l: LC 50 Crassostrea gigas (96 h) Required dilution: order of µg/l 13 µg/l: EC 50 Nitzschia closterium (96 h) 5.6 µg/l: predicted no effect concentration (EU saltwater) 5.0 µg/l: coastal water quality objective (Mediterranean) 3.1 µg/l: long-term water quality criterion saltwater (U.S. EPA) 1.4 µg/l: LC 50 Daphnia magna (21 days) Figure: Tobias courtesy Bleninger, KIT and Sabine UFPR, Germany Lattemann and Brazil

13 Concentration [log µg/l] Residual chlorine toxicity 500 µg/l 250 µg/l 440 µg/l: LC 50 Bluegill (96 h) 208 µg/l: LC 50 Coho salmon (1 h) 50 µg/l 73 µg/l: LC 50 English sole (96 h) 65 µg/l: LC 50 Herring (96 h) 40 µg/l: phytoplankton photosynthesis decreased by 80% 26 µg/l: LC 50 American oyster (96 h) Required dilution: order of µg/l: LC 50 Daphnia magna (48 h) 13 µg/l: short-term 7.5 µg/l: long-term water quality criterion saltwater (U.S. EPA) 13

14 Mixing Zone Dilution is not an instantaneous process Requires space and time to achieve required dilution Species can be in danger unless required dilution not reached Regulatory mixing zone definitions required on WHERE minimum dilutions should apply! 14

15 Mixing regulations Approach within EU regulation (WFD, 2000) ES Effluent Standard AS Ambient Standard 15

16 Mixing regulations for desalination ES and AS values: International directives National directives e.g. Chemical pollutants and wastewater regulations: Pollutant example Effluent standard ES Ambient standard AS ES/AS Copper 500 µg/l (Worldbank) 4.8 g/l (USEPA) 104 Chlorine 200 µg/l (Worldbank) 7.5 µg/l (USEPA) 27 Temperature 10 C above ambient (Worldbank) 3 C above ambient (Worldbank) 3 Salinity not existing yet (RO causes up to 35ppt above ambient) 5-10% from ambient (Spain) (e.g. for Meditteranean (36ppt) 3.6ppt) acute effects chronic effects dilution requirement 5 to 1000

17 Regulatory Mixing Zone ES - Source control: no discharge of acutely toxic substances Discharge control: Regulatory mixing zone: AS apply outside the mixing zone, restricting impact region efficient mixing (no chronic impacts, no accumulation) and no discharge near sensitive regions (e.g. coral reefs) Environmental protection: standards for specific water uses (Jirka et al. 2003, 2004) Regulatory Mixing Zone Dimension RMZ = N * H Omani regulations: circular area of 300m Outside: T< 1 C, S < 2ppt above ambient Similar regulations in US and UK Requires models and field studies H 17 RMZ = N * H

18 Regulatory Mixing Zone (Freire, IH Santander) Regulatory Mixing Zone Dimension RMZ = N * H N = (D + B + V) / 3; V = (I s + I bps + I bcs + I bs ) / 4 18

19 Local effects require high dilutions = good mixing Regional effects require good flushing or reduced loads = good siting (but still in enclosed sea) Requires Waste load allocation concepts and Coastal zone management plans estimated total: ~ 65 tons / day (based on a dosage of 2 mg/l) 20

20 Shoreline surface discharge TRADITIONAL! Example 1: RO-plant discharge, negatively buoyant density current of high stability develops, flowing down the seabed density effects strongly influence mixing characteristics H RMZ = N * H 21

21 Source: Safrai & Zask (2007) sum: approx. 70m³/s 22 Source: Google Earth

22 Shoreline surface discharge TRADITIONAL! Example 2: Combined MSF-plant+ cooling water discharge, positive buoyancy usually mixing is slow in surface plume 23

23 Single outfall channel Jeddah power & desalination plant (MSF) 24

24 Single outfall channel Hadera SWRO and power plant, Israel 25

25 Several outfall channels along coast Dubai Jebel Ali power and desalination plant (MSF), UAE 26

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27 28

28 MSF Plant Taweelah, Arabian Gulf, 1.12 mio m³/d, Source: Lattemann and Höpner,

29 Mitigation measures contaminant reduction at source: substitution of contaminants e.g. using "green" chemicals with less toxicity and higher biodegradability e.g. using steels with lesser corrosion install treatment technologies e.g. using higher level treatment improve discharge technology Blend effluent with cooling water balance with water body usage and natural assimilation processes (e.g. multiport diffuser) 31

30 Dilution systems Required (minimum) dilutions for salinity Rule of thumb: 9 : 1 Gold Coast 17 : 1 Olympic dam or Israel 84 :1 WHERE? Dilution systems performance for near-field (10s-100s of meters from outfall) Surface discharge: 3-10 Single port submerged discharge Multiport diffusers

31 Outfall types optimized siting of outfalls allows for improved operational conditions and better environmental protection optimized mixing device (e.g. submerged multiport diffuser) high mixing rates reduce local impacts considerably 33

32 Mixing devices Construction details Typical construction details for multiport diffusers in water bodies: (a) Diffuser pipe on bottom with port holes, (b) diffuser pipe buried in trench with short risers, (c) deep tunnel construction with long risers 34

33 Multiport diffusers 1. Pipeline-style diffusers nozzles arranged along a pipe instead of rosette 35 Figure: courtesy Sabine Lattemann

34 Multiport diffusers 2. Rosette-style diffusers several outlet risers above the seafloor with a small number of nozzles attached to each riser 36 Figure: courtesy Sabine Lattemann

35 Long outfall pipes 2.4 m Rio de Janeiro, Brazil, 4 km, concrete 8 m 1.6 m 37 ntalya, Turkey, 2.6 km, HDPE Boston, USA, 16 km, tunnel

36 38

37 Example: Cooling water diffuser near Vienna 39 (Courtesy: Schmid, TU Wien)

38 Multiport diffusers France France Chile 40 Turkey

39 Mixing devices Simple ports (Source: C. Avanzini, M.E.C.C.) 41

40 Mixing devices Simple port configuration 42 Riser/port configuration (Guarajá outfall, coast of Sao Paulo, Brazil, Source: T. Bleninger)

41 Mixing devices Simple port configuration Riser / port configuration Rosette like port arrangement (Boston outfall, Source: Massachusetts Water Resources Authority, Boston, USA) 43

42 Mixing devices Simple port configuration Riser / port configuration 44 Rosette like port arrangement Duckbill Valves (Source: Red Valve Company)

43 Sydney SWRO plant 45 Source: Sydney Water and Fichtner 2005

44 Sydney SWRO plant m offshore water depths m 5 risers (25 m spacing) each with several nozzles discharge jet angle: 60 from horizontal 46 Source: Sydney Water and Fichtner 2005

45 Sydney modelling study 47 Source: Sydney Water and Fichtner 2005 assumes three risers with four nozzles per riser

46 Subsurface outfalls Subsurface outfall Offshore Onshore Percolation gallery Deep-well injection Evaporatio n ponds Sewer discharge Zero Liquid Discharge 48 Figure: Tobias courtesy Bleninger, KIT and Sabine UFPR, Germany Lattemann and Brazil

47 Subsurface outfalls Subsurface outfall Offshore Onshore Percolation gallery Deep-well injection Evaporatio n ponds Sewer discharge Zero Liquid Discharge Suitable deep-well required, expensive, risk of groundwater contamination Large land area requirements, inexpensive, risk of groundwater contamination Potential effects on sewage treatment plant Energy intensive 49 Figure: Tobias courtesy Bleninger, KIT and Sabine UFPR, Germany Lattemann and Brazil

48 Evaporation pond (Ktziot plant, Negev) 50 Figure: Tobias courtesy Bleninger, KIT and Sabine UFPR, Germany Lattemann and Brazil

49 Evaporation pond (Ktziot plant, Negev) 51 Figure: Tobias courtesy Bleninger, KIT and Sabine UFPR, Germany Lattemann and Brazil

50 Conclusions Water quality protection needs careful blend of technologies source reduction and contaminant substitution treatment technologies discharge technologies Ambient standards need mixing zone definition for point source discharges Discharges optimally should be sited offshore be submerged have high initial mixing consist of multiple ports Need for intense pre- and post-operational monitoring complemented with expert modelling 52