Anaerobic Fermentation of Organic Solid Wastes: Volatile Fatty Acid Production and Separation

Transcription

1 Santiago de Compostela, SPAIN June 25-28, 2013 Anaerobic Fermentation of Organic Solid Wastes: Volatile Fatty Acid Production and Separation H.Yesil, A.E.Tugtas, A.Bayrakdar and B.Calli Marmara University, Department of Environmental Engineering, 34722, Istanbul, Turkey

2 Organic Fraction of Municipal Solid Waste OFMSW PROBLEM Environmental Economic SOLUTION Composting Landfilling Anaerobic Digestion Environmental impact reduction Energy/material recovery Operational cost reduction Massive disposal avoidance 2/16

3 from Production to Separation VFA accumulation lower the ph alter fermentation process shifts ionized to undissociated inhibitory to fermentative bacteria thermodynamically unfavorable reactions changes the pathway of certain reactions VFAs should be removed to optimize the VFA production and to recover VFAs as valuable chemicals 3/16

4 Objectives Evaluation of the performance of a leach-bed reactor for the hydrolysis/acidification of organicrich municipal solid waste to produce highly concentrated VFA mixture Investigation of mixed VFA separation from the fermentation broth of the leach-bed reactor via the use of membrane contactors 4/16

5 Preparation of OFMSW Mechanically and manually sorted MSW Manual separation of inorganic components Shredded OFMSW Size reduction/shredding 5/16

6 Characteristics of Raw Waste Properties Value Total solids 37.1 ± 1.1 % Volatile solids 64.7 ± 1.2 % (of dry weight) Water content 62.9 ± 1.1 % Total COD (g/kg) ± 25.2 Total Nitrogen (g/kg) 6.10 ± 0.20 Total Phosphorus (g/kg) 0.67 ± 0.14 COD/N/P ~500/9/1 6/16

7 Leach Bed Reactor (LBR) Gas collection balloon Gas valve Distribution system Temperature = 30 ± 0.5 o C Recirculation rate = 6.3 L/day 2 kg OFMSW L tap water Operational period = 72 days N 2 Milli-gas counter Recirculation pump Leachate sampling valve Leachate collection chamber 7/16

8 Results - VFA Production Total VFAs (g COD/kg SW) ,0 6,5 6,0 5,5 5,0 ph Daily VFA Production (g VFA/kg SW) 16 Lactic acid Formic acid Acetic acid Propionic acid Butyric acid Valeric acid Caproic acid Total VFAs (g COD/kg SW) This study Cavdar et al Daily Acetic Acid Production (g VFA/kg SW) This study Cavdar et al Time (Days) Time (Days) 8/16

9 Effect of Leachate Replacement and Recycle Rate Effect of Leachate Replacement 1L of tap water 1L of tap water Total VFA 0-31 days days days Cavdar et al. (2011) gcod / kg WW gcod / kg DW gcod / kg WW This study gcod / kg DW Effect of Recycle Rate on Acetic Acid Recycle Rate 0-31 days days days Cavdar et al. (2011) Manual 1 L/d 21% 24% 24.7% This study Continuous L/d 31% 39% 43.0% 9/16

10 Membrane Contactor for VFA Separation Membrane Contactor A lab-scale membrane contactor made of acrylic plates Feed pump Counter-current flow channels Membran VFA Effluent NaOH 4 Influent Acidic feed phase (mixed VFA, ph=3) Alkaline stripping phase (1N NaOH, ph>12) Magnetic stirrer VFA 3 Influent NaOH Effluent PTFE Membrane chemical resistance poor surface hydrophilicity 10/16

11 Mass Transfer Mechanism Acid Solution Alkaline Solution No back-diffusion 11/16

12 VFA Separation Assays The highest selectivity was observed at 30 o C by using 1N NaOH as alkaline stripping solution (paper in preparation) Synthetic VFA mixture Strip: 1N NaOH Assay: Batch Membrane: PTFE Temperature: 30 o C ph: 3 Leachate Strip: 1N NaOH Assay: Integrated to LBR Membrane: PTFE Temperature: 30 o C ph: /16

13 Result - VFA Separation Assays Synthetic Feed (ph 3) Integrated LBR-membrane contactor (ph 6.6) VFAs Flux (g/m 2.h) Flux (g/m 2.h) Acetic acid Propionic acid Butyric acid Valeric acid Caproic acid Low permeation flux with leachate: 1) High ph of leachate 2) Cake-like formation 3) Other volatile species 13/16

14 CONCLUSIONS & RECOMMENDATIONS Increasing the leachate recycle rate along with integrated VFA separation increased the cumulative VFA production and the acetic acid percentage in the leachate. VFA separation via the PTFE membrane contactor can be achieved with relatively high permeation flux values at low ph. In order to optimize the integrated fermentative VFA generation and membrane separation, ph of the anaerobic fermentation system needs to be controlled and the leachate needs to be filtered to prevent cake formation on the surface of the membrane. 14/16

15 MARMARA UNIVERSITY ENVIRONMENTAL BIOTECHNOLOGY GROUP

16 Santiago de Compostela, SPAIN June 25-28, 2013 Anaerobic Fermentation of Organic Solid Wastes: Volatile Fatty Acid Production and Separation H.Yesil, A.E.Tugtas, A.Bayrakdar and B.Calli Marmara University, Department of Environmental Engineering, 34722, Istanbul, Turkey

17 Initial VFA Concentrations in Feed Synthetic Feed (ph 3) Integrated LBR-membrane contactor (ph 6.6) VFAs Concentration (mg/l) Concentration (mg/l) Acetic Acid Propionic Acid Butyric Acid Valeric Acid Caproic Acid

18 % Concentration Acetic Acid Dissociation at 30 o C ph Acetic acid Acetate

19 Anaerobic Fermentation Digestion Complex Organic Matter (Carbohydrate, protein, fats) 1. Hydrolysis Mono and Oligomers (Sugars, Aminoacids, Long-Chain Fatty Acids) 2. Fermentation H 2 + CO 2 Intermediate Products (Propionate, butyrate, valerate, etc.) Acetate 3. Acetogenesis 4. Methanogenesis CH 4 + CO 2 OFMSW high VFAproduction due to its organic-rich composition

20 Characteristics of OFMSW Properties Value Total solids 37.1 ± 1.1 % Volatile solids 64.7 ± 1.2 % (of dry weight) Water content 62.9 ± 1.1 % COD/N/P ~500/9/1 Wet Weight Dry Weight Total COD Total Nitrogen ± 25.2 g/kg WW ± 67.9 g/kg DW 6.10 ± 0.20 g/kg WW 16.4 ± 0.54 g/kg DW Total Phosphorus 0.67 ± 0.14 g/kg WW 1.81 ± 0.14 g/kg DW WW: wet weight DW: dry weight

21 Volatile Fatty Acid Separation Methods Advantages Disadvantages Precipitation Distillation Adsorption Electrodialysis Solvent Extraction Membrane Separation Well established Higher product yields Low capital costs Products of high purities Well established Highly pure products Byproducts can be used as fertilizer Well established Easily operable Concentrated carboxylate in solution Any chemical requirement to adjust ph Higher product yields Suitable for carboxylate salt production Lower costs Developing technology High product yields Suitable for a wide range of applications Low energy Economic Easy to scale up Generating solid wastes High energy High capital costs related to distillation High resin costs High energy demand due to resin regeneration Low adsorption capacities Separation is not highly selective The products have high impurities Further purification requirement Diffuculties in scaling up High energy demand Prone to fouling The feed needs to be acidified for efficient extraction Extractants needs to be regenerated by distillation or back extraction Membrane fouling and clogging Largely untried in complex waste systems

22 SYNTHETIC SOLUTION LEACHATE FROM LBR