Production of polyhydroxyalkanoates from anaerobically digested sewage sludge: the B-PLAS proof of concept. Cristian Torri, Chiara Samorì, Alisar Kiwan, Eleonora Torricelli Dipartimento di Chimica “Giacomo Ciamician”, University of Bologna, Via Selmi 2, Bologna, Italy
Wastewater treatment How Wastewater treatment sludge (WTS) is generated • Wastewater treatment converts soluble substances mainly into excess activated sludge (mostly bacterial biomass). • In best practices, excess sludge is subjected to Anaerobic digestion • >300 Mt dry /y worldwide (1.2 Gt/y), mostly dumped, applied to soil, landfilled and dried and incinerated. • Disposal cost 50-120 €/ton • Globally ≈ 0.2-0.4 Gt Chemical Oxygen Demand exploitable CO 2 200 L Wastewate 200 L 140 g 10 g biogas r 35 g DM Clean dewatered 100 g water sludge AD organics 1 k g (45 g DM) per day Sludge
B-PLAS process water WTS 55°C hydrochar S/L Acidogenic Fermentaion PHA enriched VFA ( aq ) 150-200°C bacteria 10-18 bar SBR AR S/L Pertraction Extraction VFA (aq) Slighly alkaline water PHA (>98%) Extraction residue Alkenes
B-PLAS DEMO Industrial demonstration of sludge to bioplastic pathway CAVIRO EXTRA BAU 0,5 Mton sludges 70 kton WTS Sludge from food industries CAVIRO Wastewater treatment Stillage from ethanol production AD WTS
HTC • Test on sludge as received ( 2.9% VSS , 27 g/L COD ) • From 150 to 200°C gradual increase of conversion to water soluble substances (peaks at 200°C, 60 min RT) • Mostly formed by oligomers and non GC-MS detectable compounds. • >250°C oil formation, increased production of aromatic compounds. • 150-200°C best trade of between reliability and efficiency. Water soluble organics 1 ml reactor 1 h treatment
200HTC-AD Soluble COD • 4 days HRT • 55°C • 60d test e l b a l i a v a o i B VFA yield • 35% soluble COD • 20% of total COD P to solid N to liquid (NH 3 ) n • Initial pH=7.8 o i t a r r 22% DW e • a Final pH=6.5 i p s 9.5% DW a e E s L / S
HTC energy req. 500 L/h module • Pressurized Reactor 500 L • ½ in. Airpin heat exchanger • 100 m (3 m 2 HA) • T=200°C , ΔT=12 K Sludge at 45 g/L (as received) • En. required= 3 MJ/kg COD sludge En. Required=15 MJ/kg COD VFA • 20 mm Pumpable Sludge at 90 g/L 3 keuro/m 2 En. required= 1.5 MJ/kg COD sludge • 10 mm OD • En. Required= 7.5 MJ/kg COD VFA
Pertraction of VFA Liquid membrane (LM) diluent + VFA carrier LM LM Fermenter Receiving (pH 6-7) solution (pH 7-8.5) Aerobic PHAs fermenter (MMCs) Treated water (N, P + solids) NaHCO 3 (aq)
Pertraction of VFA Receiving Feed Best Mix Screening of LM 89% Biodiesel water solubility + kinetic of phase trasfer 10% TOA toxycity toward bacteria + cost, stability 1% Palmitic acid e c a f n r u o s i s h l u g m i H e 40 mix tested VFA depleted VFA enriched Torri et al. Chemical Engineering Journal 366 ( 2019 ) 254-263,
Pertraction of VFA Receiving Feed Main effects: • LM composition • Temperature e c • Trickling mode a f n r u o • pH (especially at low T) s i s h l u g m i H e • Opt. productivity 20 m 3 90% 1 m 3 10% VFA depleted VFA enriched
Overall yields Most relevant losses -HTC (difficult to improve) -MMC (potentially halved ) • sankey Samorì et al. ACS Sustainable Chem. Eng. 201971210266-10273
Conclusions • HTC can release 50 % of organic matter in WTS with acceptable energy requrement. • HTC coupled to fermentation allows to decrease the amount of sludge (mainly due to improved dewatering) by a factor 6 . • Overall conversion of WTS to VFA =20%, no inhibition. • Pertraction of VFA using recirculated alkaline solution allows to obtain a clean VFA solution , suitable for MMC feeding. • Preliminar economics is promising: 1. Saving disposal cost: 60% revenues 2. Production of PHA: 40% revenues 3. Expected ROI>35%. • 26/07/2029 DEMO open doors
Cristian Torri Dept of Chemistry – Unibo cristian.torri@unibo.it Thank You for your attention For more information on B-PLAS please visit the B-PLAS DEMO website: https://site.unibo.it/b-plas/en
Recommend
More recommend
