The Carboxylate Platform Nigel Horan Training That Makes A Difference Lecture Outline • The industry – why it should innovate • What is the carboxylate platform? • Potential benefits • Retrofitting and new build • Conclusions Training That Makes A Difference AD Industry • Now over 185 digesters (more than water industry?) • Processing 0.72 million tonnes food waste • But producing 1.44 million tonnes digestate • And >90% recycled to land • Feedstock getting more difficult to source • Security of land route? Training That Makes A Difference Gate Fee Training That Makes A Difference Transport and application cost to land We are close to a situation where the cost of digestate recycling may be greater than the gate fee! Training That Makes A Difference A Profitable Future? • To maintain income the industry needs to keep being innovative • The basic flow train offers huge opportunities due to the versatility of anaerobic organisms • Parallel advances in thermal technologies (HTC) extend innovative opportunities Training That Makes A Difference What are carboxylates? • an ester or salt of a carboxylic acid Training That Makes A Difference Why the interest in carboxylates • Metal salts are high-value oil-soluble, water-insoluble detergents (fracking) • Carboxylate platform provides a cheaper route for syngas (carbon monoxide, hydrogen, carbon dioxide) production from a range of waste feedstocks • And many high value chemicals …….. Training That Makes A Difference Most important products • Butanol (£2,400/tonne) • Succinate (£2,600/tonne) • Acetone (£1,800/tonne) • Ethanol (£540/tonne) Training That Makes A Difference A Route to Acrylamides poly(hydroxypropionate) HO OH O O 1,3-propanediol O O OH EEP H O n HO OH O 3-hydroxypropionic acid NH 2 CH2 HO OH O OH acrylamide O O CH2 O malonic acid acrylic acid Training That Makes A Difference Conventional MAD Biodegradable Organic Material (Carbohydrates, Fats, Proteins) Hydrolysis Simple Soluble Organics Acidogenesis Propionic Acid Butyric Acetic Acid Acid Long Chain VFA Acetogenesis Acetic Acid H2 + CO2 Methanogenesis Acetoclastic Methanogens Hydrogenotrophic Methanogens CH4 + CO2 Balance of microbial processes for stable conditions Hydrogen / Biomass Carbon dioxide polymers Sugars Biogas Methane / Amino acids Intermediate Carbon Carbohydrates Long chain Products Proteins fatty acids dioxide Lipids Acetate Hydrolysis Acidogenesis Acetogenesis Methanogenesis Net acid producer Net acid remover Ideal pH = 5.0 Ideal pH = 7.4 Conventional MAD at pH 7.4 is sub-optimal for acid production Training That Makes A Difference How do we Drive Carboxylate Production • Pure culture with sterile, glucose-based media (ABE) • Mixed culture on waste with: – inhibition (iodoform at 5g/m3) – Organic loading rate control of pH Training That Makes A Difference ABE Fermentation Training That Makes A Difference Organic Loading Rate (OLR) Feed rate (m3/d) x Feed VS (kg/m3) OLR = Reactor volume (m3) Dictates flow of energy through the system Low OLR encourages Methanogenesis High OLR encourages Solventogenesis Very high OLR encourage Hydrogenesis Training That Makes A Difference H2 Acetone, Butanol, Ethanol CH4 Hydrogenesis Solventogenesis Methanogenesis HRT (d) 2 -3 4 – 5 >10 pH 5.0 5.5 6.8 OLR 12 7 3 Training That Makes A Difference Products of anaerobic metabolism of pyruvate (Solventogenesis) Succinate Acetyl CoA Acetate Malate Lactate Oxaloacetate Pyruvate Ethanol Acetaldehyde Acetoacetyl CoA Acetolactate Formate CO Acetoin 2 Butanol H Butyrate Butylene glycol 2 Training That Makes A Difference Hydrogenesis Glucose C 6H12O6 2 Lactate 2 Pyruvate CH3COCOOH CH CH(OH)COOH 3 Low pH route 2 Acetyl-Co 2 Formate HCOOH Ethanol Acetat 2CO2 + 2H2 eCH COOH CH3CHOH 3 Training That Makes A Difference Ten routes of synthesis from pyruvate (a)– (i) Selected based on OLR Batch Production of VFAs Training That Makes A Difference Continuous Culture • VFA concentrations of up to 25 kg/m3 in continuous mixed waste fermentation – and rising • Waste C:N influences yield (higher C:N better) • Low alkalinity encourages low pH Training That Makes A Difference Existing Plant Feedstock (type) Pre-processing (screening, blending, pasteurisation) Biogas & CHP Digesters (long HRT) Whole digestate Whole Fibre Dewatering Liquor Easy Retrofit to a VFA Factory To Refinery VFA rich liquor (80,000 mg/l) Feedstock Short HRT (type) Fermenter Thickening/ (to produce VFAs) Dewatering Pre-processing (screening, blending, Thickened sludge pasteurisation) Biogas & CHP Digesters (long HRT) Whole digestate Whole Fibre Dewatering Training That Makes A Difference Liquor Circular Process with HTC Feedstock (type) Fuel for energy recovery or to land Pre-processing (screening, blending, pasteurisation) Liquor Solid Product Short HRT Fermenters HTC Thickening/Dewatering Thickened To Refinery sludge Liquor VFA rich liquor (80,000 mg/l) Extraction? • POD to POR approach? • Strong UK chemical industry • Refineries also need to diversify • Opportunity to move away from a petrochemical economy Training That Makes A Difference Conclusions • Thinking about the future will help secure the waste industry future • A lot can be achieved in the laboratory environment, but is this real? • Economic costing should drive research • What does the industry want ? • How can we involve the refineries Training That Makes A Difference.