Improvement of VFA production from food waste using biological pretreatments Y . K. CHEAH 1 ; C. VIDAL-ANTICH 1 ; J. DOSTA 1,2 ; J. MATA- ÁLVAREZ 1,2 1 Departament d’Enginyeria Química i Química Analítica. Universitat de Barcelona 2 Water Research Institute. Universitat de Barcelona jdosta@ub.edu
Introduction FOOD WASTE TREATMENT (OR CO- TREATMENT) IN THE BIOREFINERY CONTEXT 2
Introduction ACIDOGENIC FERMENTATION C H O N P a b c d e PROTEINS CARBOHYDRA LIPIDS HYDROL YSI TES S Aminoacids, Fatty acids, Simple sugars alcohols ACIDOGENE INTERMEDIATE SIS & PRODUCTS ACETOGEN (propionic acid, butyric N NH 4 ESIS acid, …) 3 P PO 4 H 2 , CO 2 ACETIC ACID VFA Concentration - T ype of substrate METHANOGENESIS REGULATION OF and co-substrates VFA Composition fed CH 4 + CO 2 Ratio - Operational COD VFA /COD SOLUBLE parameters 3 - Pretreatments
Introduction BIOLOGICAL PRE- TREATMENTS Hydrolysis is usually the limiting step of acidogenic fermentation. BIOLOGICAL PRETREATMENTS are getting more attention to improve acidogenic fermentation. since they do not require reagent addition and do not require high energy demands to be applied. In this study, 2 biological pretreatments were studied to improve hydrolysis and VFA production: 1) ADDITION OF MATURE COMPOST Mature compost contains a variety of hydrolytic bacteria , by adding it into acidogenic fermenter, they will enhance solubilisation and hence, increase the rate of hydrolysis for VFA production . 2) ADDITION OF WASTE ACTIVATED SLUDGE PRETREATED AT 55ºC T reating WAS at 55 º C , the microorganisms release extracellular polymeric substances (EPS) that are contained in their own metabolic system resulting in autohydrolysis (Carvajal et al., 2013; Arias et al., 2018). 4
Materials and methods EXPERIMENTAL DEVICES FOR ACIDOGENIC Semi-continuous lab-scale FERMENTATION Batch test assays reactors (5L) Operating at 35°C Efgect of and 3.5/5d of HRT, mature pH6/7, with and compost or without compost pretreated addition WAS addition ANAL YTICAL METHODS Standard Methods for the Examination of Water and Wastewater (APHA, 2012) SUBSTRATE AND INOCULUM SUBSTRATES INOCULUM FOOD WASTE (University Canteen) Effmuent from acidogenic WASTE ACTIVATED SLUDGE fermenters treating FW (municipal WWTP) initially inoculated with anaerobic digetate MATURE COMPOST (MBT plant (mesophilic conditions) of treating OFMSW and Parks and sewage sludge gardens waste) 5
Results and discussion REFERENCE ACIDOGENIC FERMENTER TREATING FW Difgeren Features: Acetic acid and butyric acid pH t T = 35 º C V F A c o n c e n t r a t i o n ( m g V F A / L ) control concentrations were predominant collecti HRT 3.5 days --> 6.0 at pH 6.0 although FW was on VS: 4.1-6.1 randomly collected from a periods %w/w University canteen 12500 0 % compost, pH 6, HRT 3.5d Heptanoi c 10000 Caproic Isocaproi 7500 c V aleric 5000 Isovaleric Butyric 2500 Isobutyri O L R (g V S /(L .d ) c 0 OLR at HRT 3.5d 35 30 25 20 15 10 5 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 6
Results and discussion BATCH FERMENTATION ASSAYS OF FW ADDING MATURE COMPOST pH 6 Experiment carried out in duplicate. Ratio inoculum/Fresh FW : 1:1 (VS basis) pH 7 VFA VFA Compost FW Improvement Improvement added (% VS in the mixture) (%) at pH 6 (%) at pH 7 (% ST) 50 % (10d) - 0 % 44 % P e r c e n t a g e o f V F A ( % C O D ) P e r c e n t a g e o f V F A ( % C O D ) - 4.5% 2.5 % 41 % 15.0 % 1.6% 3.5 % 39 % 12.9% - 4.5 % 9.7% 100% 100% Heptanoic Heptanoic 80% Hexanoic Hexanoic 80% Isocaproic Isocaproic 60% Valeric Valeric 60% Isovaleric Isovaleric 40% Butyric 40% Butyric Isobutyric Isobutyric 20% 20% Propionic Propionic 0% Acetic Acetic 0% 0 1 2 3 4 6 7 10 0 1 2 3 4 5 6 7 10 Time (days) Time (days) 10 days , 2.5% mature 10 days , 2.5% mature compost pH 6 compost, pH 7 7
Results and discussion BATCH FERMENTATION ASSAYS OF FW ADDING MATURE COMPOST Mature compost Higher solubilisation and ammonium release Mature compost Higher butyric acid production Mature compost Higher ammonium release Mature compost Similar distribution of VFA 8
Results and discussion SEMI-CONTINUOUS OPERATION ACIDOGENIC FERMENTER A,C pH 6 VFA production Ref. A Reference A Reference A,B,C enhancement B 2.5% B 2.5% compost B 2.5% compost Ref. using 2.5% w/w compo C 3.5% compost C 1.5% compost compost. Major st impact at lower OLR 11-19% higher (%VS infm. 5.5-6.1%) 29-51% higher (% VS infm. 3.8-3.9%) Similar VFA production using 2.5% and 3.5 w/w compost Slightly lower VFA production when using 1.5% instead of 2.5 w/w compost 9
Results and discussion SEMI-CONTINUOUS OPERATION ACIDOGENIC FERMENTER pH 6 • VFA production could be boosted up in the beginning and maintained its dominance during the experiment, with compost doses between 1.5-3.5%w/w at pH 6. • Higher butyric acid proportion when compost is added (from up to 12.2% (COD basis) in the reference reactor to up to 23.5%) • Higher solubilisation expressed in terms of sCOD and NH 4 + -N release was detected in the fermenters working with mature 10 compost addition.
Results and discussion SEMI-CONTINUOUS OPERATION ACIDOGENIC FERMENTER A: No A Ref. pH 6 and 7 change A : No change B: 2.5 % compost pH B: No B: 0% compost, pH 7, 6 change TRH 5 d C: 2.5 % compost pH C: HRT to 5 C : No change 7 d High VFA production enhancement using 2.5% w/w compost at pH 7 11
Results and discussion SEMI-CONTINUOUS OPERATION ACIDOGENIC FERMENTER REACTOR A - REFERENCE • At pH 7 with addition of 2.5% mature compost, an improvement of 186% of the VFA concentration REACTOR B (on COD basis) were recorded with respect to the reference reactor. • At pH 7 , a rise in propionic (from 1.6 to 7.7%) , valeric (from 0.8 to 5.6%) acids production was observed as REACTOR C compared to 12
Results and discussion SOLUBILISATION ASSAYS WITH PRETREATED WAS AT 55 º C WAS Solubilisation at 55 ºC 30% Experiment carried out in 25% No duplicate with bottles of 1L of 240 min enhanced 20% S ( VSs/VS %) working volume. VS 15% solubilizati 10% 150 min Every 60-90 min, the T sS and on 5% VsS are analysed to determine 90 min 0% the solubilisation (SsV/SV ) of 0 60 120 180 240 300 360 420 480 540 WAS Time (min) • A growth of VS solubisation from 3% to 26% at 9h was observed. • 4h 30 min were enough time of WAS autohydrolysis with 25% of solubilisation. Food Waste Pretreated WAS + Food Waste Hydrolysis and (55 º C at 4h) VFA production 35 º C enhancement 13
Results and discussion PRETREATED WAS (55 º C AT 2.5 H) + FOOD WASTE Discontinuous assays: • Food Waste (FW) • Pre-treated WAS (Wp) • WAS (W) C O D V F A c o n c e n t r a t io n ( m g C O D - L - 1 ) • 20% FW + 80 % pre-treated WAS (in VS content) C O D V F A c o n c e n t r a t i o n ( m g C O D - L - 1 ) • 50 % FW + 50 % pre-treated WAS (in VS content) • 80 % FW + 20 % pre-treated WAS (in VS content) 20%FW+80%WAS 20%FW+80%WAS_Theoric 50%FW+50%WAS 50%FW+50%WAS_Theoric FW Wp W 18000 18000 16000 16000 14000 14000 12000 12000 10000 10000 8000 8000 6000 6000 4000 4000 2000 2000 0 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Time (d) Time (d) 14
Results and discussion PRETREATED WAS (55 º C AT 2.5 H) + FOOD WASTE Food Waste (FW) V FA (% C O D ) 80 % FW + 20 % pre-treated WAS (in VS V FA (% C O D ) content) 100% 100% 80% 80% 60% 60% 40% 40% 20% 20% 0% 0 1 4 5 6 7 8 9 12 13 14 0% 0 1 4 5 6 7 8 9 12 13 14 Time (d) (pH: 3.9 -> Time (d) V FA (% C O D ) WAS (W) (pH: 3.9 -> 3.7) V FA ( % C O D ) 50 % FW + 50 % pre-treated WAS (in V 4.6) content) 100% 100% 80% 80% 60% 60% 40% 40% 20% 20% 0% 0 1 4 5 6 7 8 9 12 13 14 0% 0 1 4 5 6 7 8 9 12 13 14 Time (d) (pH: 6.4 -> 7.9) (pH: 5.5 -> Time (d) Pre-treated WAS (Wp) 20% FW + 80 % pre-treated WAS (in VS 5.9) V FA (% C O D ) V FA (% C O D ) content) 100% 100% 80% 80% 60% 60% 40% 40% 20% 20% 0% 0% 0 1 4 5 6 7 8 9 12 13 14 0 1 4 5 6 7 8 9 12 13 14 Time (d) Time (d) (pH: 5.8 -> 7.8) (pH: 6.5 -> 7.8) 15
Conclusions CONCLUSIONS The addition of 2.5% w/w of mature compost to a semi-continuous acidogenic fermenter treating FW at mesophilic conditions (35ºC), pH 6 and HRT of 3.5 days led to an improvement of the VFA yield up to 51.2 % (on VFA basis) The mature compost dosage at pH 6 resulted in a higher percentage of butyric acid on COD basis in the fermentation broth, increasing from up to 12.2 % (0% compost addition) to up to 23.5 % (2.5% compost addition). When pH was changed from pH 6 to pH 7 , VFA production was boosted and a higher production of propionic and valeric acids was recorded with respect to the reactor working at pH 6. Regarding WAS pretreatment, solubilisation of WAS at 55 º C from 3% to 25% took place in 4h . Synergies in VFA production when mixing pretreated WAS at 55 º C during 2.5h and FW were observed for mixtures containing up to 50% VS of FW. No synergies were observed when mixing WAS at 55 º C during 1.5 and 4 h. 16
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