From waste to fuel: bioconversion of domestic food wastes to energy carriers

Transcription

1 From waste to fuel: bioconversion of domestic food wastes to energy carriers M. Alexandropoulou 1,2, N. Menis 1, G. Antonopoulou 2, I. Ntaikou 2, G. Lyberatos 1,2 1 School of Chemical Engineering, National Technical University of Athens, Zografou Campus, GR 15780, Athens, Greece 2 Institute of Chemical Engineering Sciences, Foundation for Research and Technology, GR 26504, Patras, Greece 5th International Conference on Sustainable Solid Waste Management, June 2017, Athens, Greece

2 Food Waste (FW) Uneaten food and food preparation leftovers from residences, commercial establishments and institutional sources. Domestic FW (DFW) is considered an ideal substrate for the production of various biofuels via microbiological processes, due to their high content in readily fermentable carbohydrates, and the necessary nutrients. Food wastes used in this study DFW was collected at municipality level twice a week from 230 houses of the Municipality of Halandri, Greece. Upon collection, DFW was subjected to simultaneous heat-drying at o Cand shredding.

3 Halandri s Pilot

4 Ethanol Ethanol (C 2 H 5 OH) is a potential alternative to fossil fuels It is an alcohol generated by sugar, starch or cellulose fermentation. If starchy or cellulosic feedstock is used, a hydrolysis step is required to convert them into sugars. Microbes such as yeasts and bacteria are essential for ethanol fermentation. Key factors affecting ethanol production are: Substrate concentration Temperature ph etc

5 Methane Anaerobic digestion is one of the most important biochemical processes for biomass conversion CH 4 and CO 2 are produced from organic substrates via mixed microbial consortia under anaerobic conditions Reaction Organic substrate + H 2 O CH 4 +CO 2 +NH 3 + new cells

6 Methane - Hydrogen It is directly related to the acidogenic stage of anaerobic digestion process. composite polymers proteins carbohydrates lipids hydrolysis amino acids, sugars fatty acids, alcohols acidogenesis Intermediate products (propionic butyric,etc) acetogenesis Acetic acid Η 2,CO 2 methanogenesis CH 4, CO 2 It is well known, that carbohydrates are the main source of hydrogen during fermentative processes.

7 Aim of this study The aim of the present study was to develop sustainable processes for maximum recovery of energy from Domestic Food Waste (DFW) via their bioconversion to energy carriers i.e. the biofuels bio ethanol, bio hydrogen and methane.

8 Substrate characterization Characteristic Value Total Solids (%) 91.28±0.75 Volatile Solids (%) 92.34±0.73 Total Carbohydrates (g/g TS) 0.43±0.03 Soluble Carbohydrates (g/g TS) 0.21±0.01 Starch (g/g TS) 0.16±0.01 Total Kjeldahl Nitrogen 1.63±0.17 (g/ 100g TS) Proteins (g/g TS) ± 1.06% Ideal substrate for the production of biofuels

9 Process approaches 1 st approach: DFW was initially subjected to extraction using water resulting to a liquid fraction (extract) and a solid residue. 2 nd approach: the water suspended DFW was directly used as substrate The effluents in all cases were subjected to A.D.

10 Optimization of extraction Parameter tested values o C, 30min 35 o C, 30 min 25 o C, 60 min 35 o C, 60min Sugars conc Solids loading (100 TS w/v) 5, 10, 20 Sugars/DFW (% w/w) (/w) C sugars (g/l) Solids loading (% TS w/v) 25 o C, 30min 35 o C, 30 min 25 o C, 60 min 35 o C, 60min Solids loading (% TS w/v) Sugars recovery Time of extraction (min) 30, 60 Temperature ( o C) 25, 35 no significant differences in neither sugars concentration nor yields the mean yield of sugars was estimated to be ± 1.46 %, indicating that the whole amount of the soluble sugars contained in the DFW can be recovered even using the lowest temperature and extraction time and the highest solids loading. Extraction protocol 20 % wts/v, 25 o C, 30 min

11 Substrate: whole DFW EtOH production from DFW at different solids loading Materials and methods C initial of carbohydrates and soluble sugars Solids loading : 10 and 20 %TS w/v. Microorganisms: Saccharomyces cerevisiae (Sc) 10 % TS w/v : ~43g/L and ~21 g/l 20 % TS w/v : ~86g/L and ~42 g/l Pichia stipitis (Ps) Pachysolen tannophilus (Pt) mono and co cultures of them Enzymes : Celluclast 10 FPU/g TS and Novozyme 188 (1:3) Inoculation : ~15% culture at late exponential phase Salts : KH 2 PO 4 and MgCl 2.6H 2 O

12 EtOH production from DFW at different solids loading Results EtOH (g/l) FW 10 FW20 Sc Ps Pt Sc/Ps Sc/Pt Maximum EtOH concentration ~25g/L was achieved for 20 %TS w/v for Sc-Ps and Sc-Pt co-culture Co-cultures exhibited higher C EtOH than monocultures when loading was 20 %TS w/v Y EtOH (g/g DFW) 0,16 0,12 0,08 0,04 0,00 FW 10 FW20 Sc Ps Pt Sc/Ps Sc/Pt Yields were high for both solids loadings Lower solids loading leaded to better yields for all microorganisms (mono- and co-cultures) tested Maximum yield was g EtOH/g DFW and was achieved by Sc-Pt co-culture and loading 10 % TS w/v.

13 EtOH production from the extract of DFW Materials and methods Substrate: extract of DFW (liquid) Loading : ~42 g/l sugars Microorganisms: Saccharomyces cerevisiae (Sc) Pichia stipitis (Ps) Pachysolen tannophilus (Pt) mono and co cultures of them Inoculation : ~15% culture at late exponential phase Salts : KH 2 PO 4 and MgCl 2.6H 2 O

14 EtOH production from the extract of DFW Results EtOH (g/l) extract Y EtOH (g/g DFW) 0,16 0,12 0,08 0,04 extract 0 Sc Ps Pt Sc/Ps Sc/Pt 0,00 Sc Ps Pt Sc/Ps Sc/Pt Maximum EtOH concentration g/l was achieved for Sc-Pt co-culture Co-cultures exhibited higher C EtOH than monocultures Yields were much lower than those obtained from the whole DFW Better yields were achieved from co-cultures Maximum yield was g EtOH/g DFW achieved Sc-Pt co-culture.

15 EtOH production from solids after extraction of DFW at different solids loading Materials and methods Substrate: solids after extraction of DFW Solids loading : 10 and 20 %TS w/v. Microorganisms: Saccharomyces cerevisiae (Sc) Pichia stipitis (Ps) Pachysolen tannophilus (Pt) mono and co cultures of them C initial of carbohydrates 10 % TS w/v : ~28 g/l 20 % TS w/v : ~55 g/l Enzymes : Celluclast 10 FPU/g TS and Novozyme 188 (1:3) Inoculation : ~15% culture at late exponential phase Salts : KH 2 PO 4 and MgCl 2.6H 2 O

16 EtOH (g/l) EtOH production from solids after extraction of DFW at different solids loading solids 10 solids 20 Sc Ps Pt Sc/Ps Sc/Pt Maximum EtOH concentration g/l was achieved for Sc-Ps co-culture Co-cultures exhibited similar C EtOH to monocultures Results Y EtOH (g/gdfw) 0,16 0,12 0,08 0,04 0,00 solids 10 solids 20 Sc Ps Pt Sc/Ps Sc/Pt Yields achieved were a little lower than the respective obtained from direct SSF of DFW in all cases Lower solids loading leaded to better yields for all microorganisms (mono- and co-cultures) tested Maximum yield achieved was g EtOH/g DFW for Sc-Ps co-culture

17 Comparison between direct SSF of DFW and separate fermentations of solids (SSF) and extract 0,16 FW 10 FW20 0,16 solids 10 extract Y EtOH (g/g DFW) 0,12 0,08 0,04 0,00 Sc Ps Pt Sc/Ps Sc/Pt Y EtOH (g/g DFW) 0,12 0,08 0,04 0,00 Sc Ps Pt Sc/Ps Sc/Pt In all cases the separate fermentation of DFW fractions after extraction led to higher EtOH yields The maximum yield achieved was 0.16 g EtOH /g DFW for the cocultures of S.c-P.s and S.c-P.t

18 Biohydrogen production potential (BHP) experiments Biogas measurement Hydrogen content Headspace Were carried out in duplicate, at 35 o C, at batch reactors Inoculum: Anaerobic sludge from the anaerobic digester of Athens wastewater treatment plant heat treated at 100 o C, for 15min (Chen and Lin, 2001) 20 % (v/v) inoculum + feedstock + synthetic medium (NaH 2 PO 4 *2H 2 O 8.98g/L, Na 2 HPO 4 *2H 2 O 5.2g/L yeast extract 0.625g/L) For some experiments with solids were also added enzymes : Celluclast 10 FPU/g TS and Novozyme 188 (1:3)

19 Biohydrogen production potential (BHP) experiments Substrate: whole DFW Solids loading : 1, 2, and 5 % TS w/v. Results Enzymes : Celluclast 10 FPU/g TS and Novozyme 188 (1:3) (only for SSF concept) Cumulative hydrogen production, ml DFW _1% DF W_1%, SSF DFW _2% D FW _2%, S SF DFW _5% D FW _5%, S SF time, h Only for the 1 and 2% TS the addition of enzymes had a positive effect on the hydrogen cumulative volumes and yields Hydrogen yield, LH 2 / kg TS DFW DFW, SSF Solids loading (% TSw/v) Maximum hydrogen yield equal to ± 4.37 L H 2 /kg TS (mean value)

20 Biohydrogen production potential (BHP) experiments Substrate: extract and solid fraction from the extraction of DFW Solids loading: 1 % TS w/v Liquid loading: ½ and ¼ of the total volume (17 and 8.5 g/l initial concentration of sugars ) Enzymes : Celluclast 10 FPU/g TS and Novozyme 188 (1:3) (only for SSF concept) Cumulative hydrogen production, ml solids solids, SSF extract (1:2) extract (1:4) time, h yield LH 2 /kg TS Solids (1% wts/v) No enzymes 10 FPU/gTS 64.18± ± C sug 17g/L 47.63± 2.64 Extract C sug 8.5g/L 49.85± 0.69 The addition of enzymes, strongly enhanced the hydrogen yield from the solid fraction obtained after the extraction process the extract under two different dilutions showed that the different initial concentrations of sugars had no effect on the maximum hydrogen yield

21 Biochemical Methane Potential (BMP) tests Biogas measurement Methane content Headspace Were carried out in duplicate, at 35 o C, at batch reactors Inoculum: Anaerobic sludge from the anaerobic digester of Athens wastewater treatment plant 20 % (v/v) inoculum + 2 g TS of feedstock/l (for solids) or 2 g COD/L (for liquids) + trace elements

22 Biochemical Methane Potential (BMP) tests Results Substrate Methane yield Methane yield (L CH 4 /kg TS DFW) DFW ± ± 2.66 Solid fraction ± ± 0.94 Extract ± ± 7.59 Effluents from DFW fermentation 4.20 ± ± Effluent from solid fraction 4.32 ± ± fermentation Effluent from extract fermentation 9.61 ± ± 5.65 Cumulative methane production, ml a DFW solids extract time, d Cumulative methane production, ml b effluent of DFW fermentation effluent of solids fermentation effluent of extract fermentation time, d 1 expressed in L CH 4 /kg TS DFW 2 L CH 4 /kg TS solids 3 L CH 4 /L extract 4 L CH 4 /L effluent the extraction process and the separation of liquid and solid fractions did not influence the methane yield of DFW The same happens when the effluents were used

23 Estimation of energy recovery via different approaches Taking into account the maximum yield of each biofuel generated from different handlings, the maximum recoverable energy from DFW was estimated for the two main approaches

24 Estimation of energy recovery via different approaches (*) in case EtOH and CH 4 are produced, (**), in case H 2 and CH 4 are produced Biofuel produced from DFW Stored energy per biofuel TOTAL recoverable energy KJ /kg TS of DFW EtOH 3374± ±542* H ± ±470** CH 4 from 16613±1404 effluents CH 4 from direct AD 17024±105 Biofuel produced Stored energy per biofuel TOTAL recoverable energy Stored energy per biofuel KJ /kg TS of DFW TOTAL recoverable energy Biofuel Energy density (kj/g) Ethanol 26.4 Hydrogen 142 Methane 55.5 In all cases the extraction process and separate bioconversion of the extract and the solid fraction led to higher yields of biofuels and consequently to higher energy recovery. TOTAL recoverable energy from solids from extract from solids+extract EtOH 2938± ±307* 1301± ±113* ±568* H ± ±412** 632±9 5399±89** ±458** CH 4 from 12493± ±224 effluents CH 4 from direct AD 13071± ± ±168

25 Conclusions Co-cultures of S. cerevisiae with either of the C5 consuming yeasts led to higher ethanol yields in all cases. The extraction process was shown to be beneficial for alcoholic fermentation, since higher ethanol yields were obtained during separate fermentation of the soluble sugars and the residual solids. Hydrogen production was significantly enhanced when enzymatic hydrolysis of the DFW was applied, but only for the lowest solids loadings i.e. 1% and 2% TS w/v Direct AD of either the whole DFW or each fraction separately led to lower energy recovery compared to that obtained when fermentation and subsequent AD were applied. The extraction process and separate bioconversion of the extract and the solid fraction led to higher yields of biofuels and consequently to higher energy recovery. It should be mentioned that the most viable overall process scheme will be the result of a technoeconomic study, accounting for the extra cost involved in separating fractions and in adding enzymes. The present study is a valuable prerequisite for such an assessment.

26 Thank you for your attention!!! 5th International Conference on Sustainable Solid Waste Management, June 2017, Athens, Greece