Efficient aeration oxygen transfer

Transcription

1 Efficient aeration oxygen transfer Prof. Dr.-Ing. habil. Martin Wagner Justus Behnisch, M.Sc. Anja Ganzauge, M.Sc Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 1

2 Structure Introduction Oxygen transfer in wastewater SOTR General requirement α-value Dimensioning an energy efficient aeration system New design approach and the EXPOVAL project Conclusions References Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 2

3 Energy demand for aeration/mixing WWTP consume large amounts of energy Consumer: POWER REQUIREMENT WWTP 5% 5% Aeration Aeration Mixing Pumps 15% 15% 60% Recirculation Sludge treatment Mechanical cleaning Other Optimization of the energy efficiency of a WWTP [DWA(2008)] Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 3

4 Objectives of Aeration provide oxygen for carbon and nitrogen oxidation maintaining minimum oxygen concentration: without nitrification nitrification > mg/l mg/l Disc Tube Plate Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 4

5 Objectives of Aeration Mixing of aeration tanks avoid settling of activated sludge provide nutrient transfer (BOD, N, P, O 2 ) to bacteria (-flocs) provide transport of metabolism products from bacteria (-flocs) provide stripping of gases CO 2 from BOD degradation (ph-value) N 2 denitrification source: Ruhrverband Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 5

6 Aeration systems 1. Mechanical/Surface aeration Water drops in the air O 2 Diffusion from air into water 2. Fine bubble Aeration source: biogest.de Gas-bubbles in the water O 2 Diffusion from gas bubble into water Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 6

7 Dimensioning an aeration system Standard Oxygen Transfer Rate SOTR [kg O 2 /h] SOTR is the mass [kg] of oxygen transferred by an aeration installation in one hour in a tank of certain size filled with clean water at DO of C = 0 mg/l, a water temperature of 20 C and normal atmospheric pressure (1,013 mbar). (ATV-M209E) Oxygen Transfer at Standard Conditions atmospheric normal air pressure (1,013 mbar -> C S ) TW = 20 C -> c S und k L a oxygen concentration C = 0 mg/l Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 7

8 Dimensioning an aeration system calculation of Standard Clean Water Oxygen Transfer Rate (SOTR) according to the DWA-M (2013): SOTR = f d β C S,20 α f d β C S,T p atm 1,013 C X θ OV T h W 20 SOTR: Standard Oxygen Transfer Rate [kgo 2 /h] OV h : Oxygen demand (OUR) [kgo 2 /h] f d : depth factor [-] c S : O 2 saturation concentration [mg/l] β: salt factor [-] f S : salt factor for α-value [-] α: alpha-value [-] Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 8

9 General requirements Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 9 source:

10 General requirements Influence of salt: Salt reduce O 2 saturation concentration: c S,wastewater = β c S β: salt factor = 0,95 to 1,0 = 1 0,01 TDS [-] TDS: Total Dissolved Solids [g/l] e.g. North Sea: β 0,8 Other effects by salt, where investigated in the EXPOVAL Project (later in this presentation) Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 10

11 Oxygen saturation concentration [mg/l] General requirements Influence of water temperature: Water temperature [ C] T [ C] C S [mg/l] 12,77 11,29 10,09 9,09 8,26 7, Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 11

12 General requirements Influence of pressure: depth factor f d C S C S, p hd 1 CS p0 2 10,35 0, 1 hd 20,7 Depth factor f d : h d : depth of submergence [m] h BB : depth of the tank [m] p 0 h d h d / Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 12

13 SOTR R [g O 2 /(m³ h)] General requirements Atmospheric pressure: 800 4,000 m a.s.l ,000 m a.s.l ,000 m a.s.l ,000 m a.s.l. 0 m a.s.l Water temperature [ C] city height Inhabitants about NN Mio. Lhasa ,5 La Paz ,9 Quito ,4 Bogota ,8 Mexico-City ,8 Sana'a ,5 Johannesburg ,9 Nairobi ,7 Ulaanbaatar ,0 Teheran ,8 source: Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 13

14 The α-value various substances in wastewater (i.e. surfactants, MLSS): k L a at operation conditions is usually lower than in clean water. k L a service conditions = α k L a clean water with k L a service conditions calculated k L a for operation conditions 1/s; 1/h α α-value - k L a clean water k L a from clean water tests 1/s; 1/h fine bubble aeration: α = 0.2 to 0.9 (average: 0.6) surface/mechanical aeration: α = 0.7 to 1.8 (0.9) Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 14

15 α-value [-] The α-value Influence of SRT 1 0,9 0,8 α-wert [-] 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 EPA [19] Groves [20] Wagner [21] Rosso [15] Gillot [22] SRT [d] Schlammalter [d] Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 15

16 α-value [-] The α-value Influence of MLSS/MLVSS MLSS and MLVSS MLSS and MLVSS [g/l] Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 16

17 The α-value for different treatment processes and load cases The α-values depends on : treatment processes cleaning objectives Treatment process α min α medium α max Denitrification-Nitrification 0,60 0,75 0,85 SBR-reactor with N-Elimination 0,50 0,65 0,80 MBR (TS ~ 12 g/l, t TS = 25 d) 0,50 0,60 0,70 aerobic stabilisation 0,70 0,80 0,90 C-Elimination 0,35 0,50 0,60 [Günkel-Lange 2012] Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 17

18 Dimensioning an aeration system Many aeration systems are oversized because: optimistic assumptions were made of future loads sized using the same forecasting as the treatment plant structures sized for unfavorable conditions and for too high loads sized with too high, and overlapping safety factors Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 18

19 Dimensioning an aeration system Systems should be sized for a range of load cases DWA M (2013) give a new approach Determination of oxygen demand (OUR) for four different cases: 1. average OUR 2. maximum OUR for the actual situation 3. minimum OUR 4. OUR for the predicted situation or expansion Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 19

20 Dimensioning an aeration system New procedure for design of a fine bubble aeration system according to DWA-M (2013) Input Parameters are determined according to DWA-A 131 New edition of DWA-M 229 are in progress and will be published in 09/ Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 20

21 Required SOTR (%) Sensitivity of the calculation of SOTR α OV ODh h TTW W c X CX hd D Change of the parameter by + 10% Change of the parameter by - 10% [Günkel-Lange 2012] α: Alpha-value (-); OV h : Oxygen demand (OUR) (kg/d); T W : wastewater temperature ( C); c X : oxygen concentration in aeration tank (mg/l); h D : depth of submergence (m) Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 21

22 General requirements Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 22 source:

23 electric conductivity (µs/cm) water level (cm) High salt concentrations in wastewater Seawater for toilet flushing (Hong Kong g/l Cl - ) Seawater intrusion into leaky sewers Industrial wastewater De-icing salt in winter electric conductivity sea-water level Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 23

24 The α-value Influence of Salt Effects of salt on oxygen transfer: Reduce the mass transfer (k L ) Increase the interfacial area (a) Results in a net increase of the volumetric mass transfer (k L a) f S = k La 20,saline water k L a 20,clean water ( ) without salt with salt Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 24

25 Project EXPOVAL: Aeration under particular framework conditions Influence of two parameters on oxygen transfer in WWTPs: Salt concentration Water temperature Measurements from Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 25

26 Project EXPOVAL: Aeration under particular framework conditions Measurement of k L a- values in clean, salty and wastewater Dosage of salt into the reactor (up to 28 g/l) Fine bubble aeration system Depth of submergence up to 6 m Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 26

27 Project EXPOVAL: Aeration under particular framework conditions (-) α f S -value describe the influence of salt and activated sludge in the aeration tank α f S -value obvious higher than 1,0 α f S there is an correlation between electric conductivity (saltconcentration) and α f S - value electric conductivity (µs/cm) Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 27

28 New design approach from the results of EXPOVAL New equation for calculation of standard clean water oxygen transfer rate (SOTR): SOTR = f d β St C S,20 f S,St (α f S,α ) f d β α C S,T p atm C X θ OV T h W 20 SOTR: Standard Oxygen Transfer Rate [kgo 2 /h] OV h : Oxygen demand (OUR) [kgo 2 /h] f d : depth factor [-] c S : O 2 saturation concentration [mg/l] β: salt factor [-] f S : salt factor for α-value [-] α: alpha-value [-] Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 28

29 New design approach from the results of EXPOVAL New equation for calculation of standard clean water oxygen transfer rate (SOTR): SOTR = f d β St C S,20 f S,St (α f S,α ) f d β α C S,T p atm C X θ OV T h W 20 Salt concentration (g/l) S TDS,St S TDS,α reduce C S (-) β St = 1 0,01 S TDS,St β α = 1 0,01 S TDS,α increase k L a (-) f S,St = 1 + 0,08 S TDS,St f S,α = 1 + 0,08 S TDS,α Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 29

30 New design approach from the results of EXPOVAL Validity of the new equation: Only for municipal wastewater For wastewater with high salt concentration as a consequence of sea water intrusion, predominant NaCl (investigation about the influence of other salts are in progress) Only fine bubble aeration systems (not for mechanical/surface aeration) Publishing of the new DWA-M in 09/ Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 30

31 Conclusions aeration systems are technically mature fine bubble aeration systems are state-of-the-art technology increasing electricity costs demand also for optimizations of: design of aeration system diffuser technology Many aeration systems are oversized: with new design approaches, the efficiency of aeration systems increase additional knowledge of oxygen transfer mechanisms necessary to further improve the efficiency of aeration systems Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 31

32 Thanks you for your attention Prof. Dr.-Ing. habil. Martin Wagner Justus Behnisch, M.Sc. Anja Ganzauge, M.Sc. TU Darmstadt, Institut IWAR Franziska-Braun-Straße Darmstadt Germany Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 32

33 References DWA-M 209, 2007: Messung der Sauerstoffzufuhr von Belüftungseinrichtungen in Belebungsanlagen in Reinwasser und in Belebtschlamm. DWA-M 229-1, 2013: System zur Belüftung und Durchmischung von Belebungsanlagen Teil 1: Planung, Ausschreibung und Ausführung. Henkel, 2010: Oxygen Transfer Phenomena in Activated Sludge; PhD Thesis; Institut IWAR TU Darmstadt Wagner u. Stenstrom, 2014: Activated Sludge 100 Years and Counting; IWA Publishing Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 33

34 References Günkel-Lange, 2012: Sauerstoffzufuhr und α-werte feinblasiger Belüftungssysteme beim Belebungsverfahren, PhD Thesis; Institut IWAR TU Darmstadt Institut IWAR Prof. Dr.-Ing. habil. Martin Wagner 34