Hydrogen generation performance from Taihu algae and food waste

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Biofuels and Biomass

Hydrogen generation performance from Taihu algae and food waste by anaerobic co-digestion Jin Xu, Thomas Upcraft, Qing Tang, Miao Guo, Zhenxing Huang, Mingxing Zhao, and Wenquan Ruan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b04052 • Publication Date (Web): 14 Jan 2019 Downloaded from http://pubs.acs.org on January 19, 2019

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Energy & Fuels

1

Hydrogen generation performance from Taihu algae and food waste

2

by anaerobic co-digestion

3

Jin Xua, Thomas Upcraftb, Qing Tanga, Miao Guob, Zhenxing Huanga, Mingxing

4

Zhaoa,c*, Wenquan Ruana

5

a School

6

b

Department of Chemical Engineering, Imperial College London, London SW72AZ, UK

7

c

Department of Civil and Environmental Engineering, Imperial College London, London SW72AZ,

8

UK

of Environment and Civil Engineering, Jiangnan University, Wuxi 214122,China

9 10

*Corresponding

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85197091.

author: Mingxing Zhao, E-mail address: [email protected], Tel/Fax: +86-510-

12 13

ABSTRACT: The rigid cell wall and low carbohydrate content of Taihu algae

14

inhibit its application for hydrogen generation by anaerobic digestion (AD). In this

15

study, algae was co-digested with food waste (FW) in order to evaluate the influence

16

of dried/wet condition and different mixing ratios on the digestion performance,

17

where the dried algae (DA) showed an advantage over the wet algae (WA) by

18

co-digestion with FW. This was attributed to a suitable C/N ratio, more readily

19

biodegraded organic substances and microbial synergistic effect. The peak cumulative

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hydrogen production (CHP) was 31.42 mL H2/g VS when FW/DA ratio was 40:10,

21

which was 12.13 times higher than that from DA only (2.59 mL/g VS). Meanwhile,

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the co-digestion group of FW:DA (40:10) showed the best performance, contributing

ACS Paragon Plus Environment

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to the highest value of 82.06% for the carbohydrate degradation rate, 95.54% for the

24

protein degradation rate, and 11.60 g/kg for the total soluble metabolites

25

concentration. During the DA co-digestion process, it was found that the readily

26

biodegradable materials in dissolved organic matter (DOM) were utilized more fully

27

and with the least amount of non-biodegradable matter content according to the EEM

28

fluorescence spectra, which could provide a new insight to the bio-utilization process

29

of co-substrates. Furthermore, co-digestion selectively enriched hydrogen production

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bacteria (HPB) and achieved high relative abundances of Clostridium sp. (78.46%)

31

and Bacillus sp. (8.64%) for more efficient AD performance.

32 33

Keywords: Hydrogen production; Taihu algae; Food waste; Co-digestion; Synergistic

34

effect; Microbial community

35 36

1. INTRODUCTION

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Fossil fuels still dominate the total energy consumption (about 86%) and they are

38

the main source of greenhouse gas, resulting in many environmental problems 1.

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However, energy production from biomass provides a renewable alternative to fossil

40

fuels, and hydrogen has recently gained considerable research interest 2. Hydrogen is

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considered to be a clean energy source, having the largest calorific value (142.35

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kJ/kg) amongst other fuels 3. Compared to various hydrogen production technologies,

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anaerobic digestion (AD) is deemed to be a practical and feasible method, due to it

44

being unaffected by weather conditions, non-requirement of large land areas, and its


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greater hydrogen generation rate 4, 5. The choice of substrates is particularly important

46

for the AD process for hydrogen. Recently, studies have proved the possibility of

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coupling hydrogen generation with the complex organic substrates, including the

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organic fraction of municipal solid waste (OFMSW), industrial waste and agricultural

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wastes 2, 6. Hydrogen production from organic wastes could offer both environmental

50

and economic benefits, helping to meet the growing demand for renewable energy

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supply.

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Among the potential biomass feedstock, algae has gained interest as a source of

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energy generation owing to its high productivity, high concentration of organic

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substances, and lower lignin and hemicellulose content, thereby allowing easier

55

degradation and digestion 5. As the third largest freshwater lake in China, Taihu lake

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has suffered from eutrophication and the algae collected from the lake amasses to

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more than 0.2 million tons every year 7. Several algae species, e.g., Chlorella sp.,

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Nannochloropsis oceanica and Dunaliella tertiolecta have been directly used as

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substrates for hydrogen production. The hydrogen yield of Chlorella sp. by dark

60

digestion was 0.37-7.13 mL H2/g VS 8, while the species of Nannochloropsis

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oceanica and Dunaliella tertiolecta reached 2 mL H2/g VS 9 and 12.6 mL H2/g VS 10,

62

respectively. However, algae digestion alone was usually not very efficient because

63

the presence of different nutrient distribution and structural barriers could have a

64

negative impact on their degradation. For the nutrient composition of dry algae

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biomass, protein accounts for 40-60%, which is higher than the amount of

66

carbohydrate (20-30%), however, carbohydrate was preferentially utilized by


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11.

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hydrogen production bacteria (HPB)

Insufficient carbon source can led to the

68

imbalance of C/N ratio for optimal HPB growth 12. The hydrolysis performance could

69

also be limited by the rigidity of its cell wall. In addition, possible toxic compounds

70

such as excessive heavy metals (i.e. cadmium, chromium, copper, etc) could destroy

71

the microorganism, further inhibiting enzyme activity, resulting in low AD efficiency

72

13.

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Nevertheless, algae co-digestion with other substrates can be a choice. Besides, the

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synergistic effect from different substrates can also exist. The co-digestion technology

75

has several advantages including the ability to balance the C/N ratio, dilute toxic

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compounds, improve biodegradability and enhance microbial synergistic effect.

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Food waste (FW) is considered to be an ideal choice for low C/N algae co-digestion

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due to its characteristics of rich organic content, facile hydrolysis and sufficient

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carbon availability. The amount of OFMSW produced in China reached 188.6 million

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tons in 2015, of which FW accounted for 37%-62% 14. With the increasing amount of

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food waste, efficient technology for FW treatment is urgently needed

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research has proved that FW could be an appropriate substrate for co-digestion. The

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bio-conversion of protein and hydrogen production were sufficiently enhanced by

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co-digestion of waste activated sludge and FW

85

shown the synergistic effect when co-digested with FW 19. However, to the best of our

86

knowledge, few studies have investigated algae co-digestion with FW for hydrogen

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production. Besides, there are two types of Taihu algae (dried and wet) after salvage

88

treatment. One is fresh algae with about 85% moisture collected from Taihu lake. The

17, 18.

15, 16.

Previous

In addition, olive husks have


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other is treated by drying process at the algae treatment center, which is dewatered to

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low than 5% moisture, and then is disposed by the further treatment. Therefore, the

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characteristic and moisture of two algae are different, and it is important to study the

92

influence of the dried/wet condition at different mixing ratios by co-digestion.

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In this study, dried algae (DA) and wet algae (WA) were co-digested with FW by

94

high-solid AD respectively, in order to evaluate the AD performance and synergistic

95

effect. Batch anaerobic co-digestion experiments were performed to demonstrate the

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hydrogen generation. The comparison of dried/wet algae at different mixing ratios on

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organics variation, soluble metabolites composition, dissolved organic matter (DOM)

98

and specific microbial community structure were indicated.

99 100

2. MATERIALS AND METHODS

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2.1. Substrates and Inoculum. FW was collected from a canteen in Jiangnan

102

University, which contained rice, vegetables, meat, fish, noodle, etc. First, plastic

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bags, bonds and other non-biodegradable wastes were manually picked out. Then, FW

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after removing the superficial oil by water wash through a 60-mesh sieve was dried at

105

105℃, and finally crushed into small particles. The Taihu algae was collected from

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Taihu Meiliang Wan Separation Station in Wuxi, Jiangsu Province, China, and

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Microcystis wesenbergii, Microcystis aeruginosaare were the main species

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fresh algae collected from Taihu lake with 85% moisture was labelled as “wet algae

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(WA)”. In order to reduce the volume for the further treatment, the fresh algae was

110

treated by air-flotation separation, dried at 105℃ and milled into powder at the algae


20.

The

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treatment center, which was labelled as “dried algae (DA)”. All substrates were stored

112

at 4℃ for further experiments.

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The anaerobic sludge used as inoculum was obtained from a food waste AD

114

treatment plant located in Wuxi, China, and was pretreated at 121℃ for 10 min in an

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autoclave to inhibit the bioactivity of methanogens 21. Inoculum was then cultured in a

116

water bath (37±1℃) under anaerobic condition for 72h .

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The characteristics of FW, DA, WA and inoculum are indicated in Table 1. FW

118

was mainly composed of carbohydrate and protein, leading to the highest VS ratio

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(93.71%) and good anaerobic biodegradability. As for DA, it was rich in organics, in

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which protein content was as high as 125.14 g/kg. However, due to the wrapping of

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the cell wall, the soluble organics content of WA was relatively lower than that of

122

DA. Table 1. Characteristics of Food Waste, Dried Algae, Wet Algae, and Inoculum Parameters

Unit

Food waste

Dried algae

Wet algae

Inoculum

TS

%

97.86

99.48

14.19

12.93

VS

%

93.71

75.72

5.16

11.84

SCOD

g/kg

171.20

332.80

17.60

24.00

Soluble carbohydrate

g/kg

46.35

25.99

1.93

0.56

Soluble protein

g/kg

18.12

125.14

4.38

0.73

-

26.54

8.15

8.05

9.14

C/N 123 124

2.2. Batch Anaerobic Co-digestion. Batch experiments for hydrogen production


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from dried/wet Taihu algae co-digestion with FW were conducted in serum bottles

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with a working volume of 500 mL under mesophilic condition (37±2℃), and the total

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solids content of the AD system was adjusted to 15%. Each bottle was filled with

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50gTS of substrates, and the inoculum/substrates ratio was 1:3 (TS ratio). Then,

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different quality ratios of substrates, inoculum and distilled water were added as

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shown in Table 2, and then they were stirred at 60rpm using a cantilever mixer. The

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head space of the bottles were flushed with nitrogen gas for 5 min and capped tightly

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with polytetrafluoroethylene stoppers. During the co-digestion process, the pH (initial

133

value of 7 ± 0.6) in all bottles was not controlled. Three replicates were conducted for

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each experiment. Table 2. Batch Anaerobic Co-digestion Experiments for Hydrogen Production from Food Waste and Dried/Wet algae Inoculum

Food waste

Dried algae

Wet algae

Water

(g)

(gTS)

(gTS)

(gTS)

(g)

126

50

0

-

257

126

40

10

-

257

126

30

20

-

257

126

20

30

-

257

126

10

40

-

257

126

0

50

-

257

126

50

-

0

257

126

40

-

10

231

substrates

Food waste + Dried algae

Food waste + Wet algae


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126

30

-

20

172

126

20

-

30

113

126

10

-

40

54

126

0

-

50

0

135 136

2.3. Analytical Methods. 2.3.1. Physicochemical Characterization of Substrates

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and Inoculum Sludge. For the analysis of soluble parameters, the samples which were

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diluted 10 times with distilled water, were centrifuged at 4000 rpm for 10 min, and

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then the supernatant was filtered through a 0.45 um filtration membrane. The total

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solids (TS), volatile solids (VS) and soluble chemical oxygen demand (SCOD) were

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determined according to standard methods 22. Carbohydrate and protein concentration

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were measured according to the phenol-sulfuric acid method and Lowry’s method,

143

respectively 23, 24. The concentration of soluble metabolites were determined using gas

144

chromatograph (GC-2010 Plus, SHIMADZU, Japan) equipped with a flame

145

ionization detector (FID) and a capillary column (peg-20m). The temperatures of the

146

column, injector and detector were 70 ℃ , 250 ℃ and 250 ℃ , respectively, and

147

nitrogen (99.999%) was used as carrier gas.

148

2.3.2. Hydrogen Analysis. The hydrogen content was determined using a gas

149

chromatograph (GC-2014, SHIMADZU, Japan) system equipped with a thermal

150

conductivity detector (TCD) and a stainless column (TDX-1). The temperatures of the

151

column, detector and injector were set at 100℃, 180℃and 180℃, respectively. High

152

purity nitrogen gas (99.999%) was used as the carrier gas.


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2.3.3. EEM Fluorescence Spectroscopy and FRI Analysis. Three-dimensional

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fluorescence excitation-emission matrix (EEM) spectroscopy analysis was conducted

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by a fluorescence spectrometer (F-7000, HITACHI, Japan). Scanning emission (em)

156

spectra from 220 to 600 nm were obtained at 5 nm increments by varying the

157

excitation (ex) wavelength from 220 to 450 nm at 5 nm increments. The scan speed

158

was 2400 nm/min, and the slit for both excitation and emission were set to 5 nm.

159

Raleigh scattering was subtracted with the DI water as the blank.

160

Due to the complexity of spectral response and environmental samples,

161

fluorescence regional integration (FRI), a quantitative technique was used to

162

quantitatively analyze EEM spectra of DOM

163

regions, consisting of tyrosine-like (Region Ⅰ), tryptophan-like (Region Ⅱ), fulvic

164

acid-like (Region Ⅲ), soluble microbial by-product (Region Ⅳ) and humic acid-like

165

(Region Ⅴ) 26. The volume beneath region “i” of the EEM is “Φi”. The normalized

166

ex/em area volumes (Φi,n, ΦT,n) and percent fluorescence response (Pi,n, %) were

167

calculated with Eqs.(1)-(3) 25:

168

φi ,n  MFφ i i  MFi  I (ex em ) ex em

(1)

169

T ,n   i ,n

(2)

170

Pi ,n 

171

In which Δλex is the excitation wavelength interval (taken as 5 nm), Δλem is the

172

emission wavelength interval (taken as 5 nm), and I (Δλex, Δλem) is the fluorescence

173

intensity at each excitation-emission wavelength pair. MFi is the multiplication factor

174

which equals the inverse of the fractional projected excitation-emission area.

ex

25.

The spectra was divided into five

em

i ,n 100% T ,n

(3)


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2.3.4. Sequencing Analysis. The samples for microbial sequencing analysis were

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collected at the end of the digestion experiments and conserved at -80 ℃. Microbial

177

DNA was then extracted in parallel triplicates using a PowerSoil Kit (Qiagen,

178

Shanghai, China). After extraction, DNA concentration and DNA quality were

179

evaluated by NanoDrop 2000 UV-vis spectrophotometer (Thermo Scientific,

180

Wilmington, USA) and 1% agarose gel electrophoresis, respectively. For each DNA

181

sample, the universal primers of 338F (5-ACT CCT ACG GGA GGC AGC AG-3)

182

and 806R (5-GGA CTA CHV GGG TWT CTA AT-3) were used for the

183

amplification of the V3-V4 hypervariable region of the bacterial 16S rDNA by

184

thermocycler PCR system (GeneAmp 9700, ABI, USA). PCR reactions were

185

performed in triplicate 20μL mixture containing 10 ng of template, 4 μL of 5 ×

186

FastPfu Polymerase, 2 μL of 2.5 mM dNTPs, 0.8 μL of each primer (5μM). The PCR

187

reactions were conducted using the following program: 95℃ for 3 min, 95℃ for 30

188

s repeated 27 cycles, 55℃ for 30 s, 72℃ for 45 s and a final extension at 72℃ for

189

10 min. The resulted PCR products were extracted from a 2% agarose gel and further

190

purified by the AxyPrep DNA Gel Extraction Kit (Axygen Biosciences, Union City,

191

CA, USA) and quantified by QuantiFluor™-ST (Promega, USA) according to the

192

manufacturer’s protocol.

193

Purified amplicons were pooled in equimolar and paired-end sequenced (2 × 300)

194

using an Illumina MiSeq platform (Shanghai Majorbio Bio-Pharm Technology Co.

195

Ltd., China). Raw fastq files were processed by QIIME (version 1.17). Operational

196

taxonomic units (OTUs) were clustered with a 97% identity threshold using UPARSE


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(version 7.1) with a novel algorithm that performs chimera filtering and OTU

198

clustering simultaneously. The analysis of taxonomy of each 16S rRNA gene

199

sequence was analyzed by RDP Classifier algorithm against the Silva (SSU123) 16S

200

rRNA data base with a confidence threshold of 70%. Besides, the Venn diagram,

201

Chao and Simpson indices were calculated to compare the bacterial richness,

202

community diversity and similarity for each digestion sample.

203 204

2.4. Kinetic Studies. Cumulative hydrogen production curves were analyzed using

205

the modified Gompertz equation 27:

206

H  P exp{ exp[

207

Where H represents the cumulative hydrogen production (mL) at the reaction time

208

t(h); P represents the hydrogen production potential (mL); Rm represents the

209

maximum hydrogen production rate (mL H2/h); e is 2.71828; λ is the lag phase time.

210

The standard deviation was found to below 10%.The obtained values for each batch

211

were estimated using Origin 8.0.

Rm  e (  t )  1]} P

(4)

212 213

3. RESULTS AND DISCUSSIONR

214

3.1. Effects of Dried/Wet Algae at Different Mixing Ratios on Hydrogen

215

Production. Fig. 1 shows the hydrogen production rate from FW/DA and FW/WA at

216

different mixing ratios via AD process. A rapid increase of the hydrogen production

217

rate can be seen in Fig. 1a. In the initial period of digestion, the peak time occurred at

218

18h for most experimental groups and three co-digestion groups outstripped the FW


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only. The optimal co-digestion group of FW:DA (40:10) reached the highest

220

hydrogen production rate at a value of 15.10 mL/g VS/h. With the digestion time, the

221

hydrogen production rate gradually decreased and became stable. This may be due to

222

the utilization of the available substrates in the first 18h.

223

Cumulative hydrogen production (CHP) with different mixing ratios of FW and

224

DA are illustrated in Fig. 2-a. The low biomass concentration in DA resulted in the

225

lowest CHP of 2.59 mL H2/g VS for DA only, which was similar to the previous

226

research (2 mL H2/g VS) 9. However, significantly increase in CHP was noticed with

227

increase of FW proportion. CHP achieved 22.40, 22.12 and 12.62 mL H2/g VS at

228

FW/DA ratios of 30:20, 20:30 and 10:40, respectively. The maximum CHP of 31.42

229

mL H2/g VS occurred at co-digestion of FW:DA (40:10) (Fig. 2a), which was 12.13

230

and 1.11 times than that of DA only (2.59 mL/g VS) and FW only (28.35 mL/g VS),

231

respectively. The reason for the increase in CHP might be the more balanced C/N

232

ratios for the activity and growth of HPB by FW addition as co-substrate 28. The ratio

233

of C/N in the algae was relatively low (about 8) and could prove to be an issue for AD.

234

While C/N ratio of FW reached 26.54, which could provide suitable carbon source for

235

the algae based hydrogen production. As a result, the FW/DA co-digestion under

236

different mixing ratios of 40:10, 30:20, 20:30 and 10:40 showed a better C/N ratio

237

(22.65, 19.04, 16.29, 15.04), which were in the optimal value for AD (15-30) and was

238

corresponded to higher hydrogen

239

from algae biomass was also significantly increased due to an suitable C/N ratio

240

According to above results, co-digestion of FW and DA was feasible and hydrogen

28.

In the study by Xia et al., hydrogen production


29.

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241

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production could be enhanced.

242 243

Fig 1. Effects of different mixing ratios on hydrogen production rate: (a) DA co-digestion with

244

FW and (b) WA co-digestion with FW.

245 246

Fig 2. Changes in cumulative hydrogen production at different mixing ratios: (a) DA co-digestion

247

with FW and (b) WA co-digestion with FW.

248

A similar trend was found for the hydrogen production rate and CHP from FW/WA

249

by AD process (Fig. 1-2). As shown in Fig. 1b, the hydrogen production rate from

250

co-digestion of FW:WA (40:10) was slightly higher than that of FW only at 18h,


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whereas the other four groups obtained low values. As for CHP, there was no

252

significant improvement in all co-digestion groups (Fig. 2b). The C/N ratios and CHP

253

values at different FW/WA ratios of 40:10, 30:20, 20:30, 10:40 were 21.56, 19.11,

254

17.42, 13.04 and 21.72, 15.60, 1.54, 1.18 mL/g VS, respectively. Although adding

255

FW with high carbon source to WA, the CHP still showed poor results and all lower

256

than that of FW only (28.35 mL/g VS). This was probably because of the rich

257

carbohydrate content in FW, which was more easily degraded than the

258

polysaccharides surrounded by the rigid cell wall in WA 29, 30. The hydrolysis of WA

259

was a rate-limiting step and the cell wall of untreated WA was still not easily broken

260

during the digestion process. Even intact algae cells could be found in the

261

fermentation liquid, thereby hindering the contact between intracellular nutrient and

262

HPB. The explanation was confirmed by the lowest CHP from WA only (0.25 mL/g

263

VS). In order to enhance the hydrogen production of the algae AD process, the drying

264

step was required to damage the algae cell wall to release the organic substrates,

265

making them readily degradable. Moreover, toxic compounds such as excessive heavy

266

metals (i.e. cadmium, chromium, copper, etc) in WA that could inhibit bacteria and

267

inactivate hydrogenase were not neglected 20.

268

In order to understand the synergistic effect from the co-digestion on the hydrogen

269

production performance, the data of hydrogen generation is indicated in Table 3.

270

When the substrate concentration (TS basis) was the same, taking the observed unit

271

hydrogen generation from FW only (26.57 mL/gTS), DA only (1.96 mL/gTS) and

272

WA only (0.09 mL/gTS) as standard, the predicted hydrogen generation values from


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co-digestion groups were calculated in accordance with the mixing ratios of two

274

substrates

275

significantly higher than those predicted for the co-digestion of FW:DA (40:10, 30:20,

276

20:30, 10:40) by a value of 30.79%, 15.85%, 55.38% and 45.48%, respectively, and

277

the FW:DA (20:30) group had the best performance. The above results meant that

278

based on the same amount of DA and FW, more hydrogen could be generated by

279

co-digestion process. In other words, the co-digestion of FW and DA was not simply

280

a superposition but was mutually reinforcing, exhibiting a certain synergistic effect.

281

This could be attributed to that algae biomass not only balanced nitrogen source in the

282

co-digestion system, but also provided nutrients to the HPB 2. In addition, the initial

283

DA concentration was diluted, which may avoid or decrease the toxic compounds 32.

284

Our former research also found a similar synergistic effect on biogas by the

285

co-digestion of rice straw and municipal sewage sludge

286

hydrogen generation in the FW/WA co-digestion groups was all lower than the

287

predicted values, and when the ratio of WA in the mixture rose to 40%, an

288

antagonistic effect was obviously noticed. This may be due to the characteristics of

289

strong and thick cell wall structure. Previous study reported that the cell wall of algae

290

contained about 31% of hemicellulose, 15% of α-cellulose and 5% of ash, and the

291

cellulose was not easily consumed by HPB

292

co-digestion group, it still had no obvious effect on the hydrolysis of algae cells.

31.

As shown in Table 3, the observed values of hydrogen were all

33.

31.

However, the observed

Although FW was added to the

Table 3. Parameters of Predicted Hydrogen Generation, Observed Hydrogen Generation and


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 42

Modified Gompertz Equation Gompertz kinetics a

Pred.H2

b Obs.H

2

Batches

P (mL)

a

Rmax

ʎ

(mL)

R2 (mL)

(mL/h)

(h)

Food waste : Dried algae (50:0)

1328.54

1328.54

1332.19

62.43

10.76

0.9991


1082.43

1415.67

1382.16

103.00

10.30

0.9957


836.32

968.85

947.54

70.97

9.29

0.9963


590.20

917.05

893.55

67.18

9.54

0.9896


344.09

500.60

491.25

33.18

9.89

0.9974


97.97

97.97

114.50

2.54

11.71

0.9909

Food waste : Wet algae (50:0)

1328.54

1328.54

1332.19

62.43

10.76

0.9991


1063.75

892.96

885.61

48.22

11.50

0.9924


798.97

551.99

550.11

26.96

11.19

0.9917


534.19

45.70

44.89

2.72

9.93

0.9884


269.40

28.30

27.15

1.36

11.34

0.9798


4.62

4.62

4.75

0.17

8.22

0.9829

Pred.H2: Predicted hydrogen generation. b Obs.H2: Observed hydrogen generation .

293

The kinetic parameters during AD are shown in Table 3. The fit parameter of R2

294

was higher than 97%, which showed that the modified Gompertz equation could fit

295

the hydrogen production for all groups. As for hydrogen production potential (P), the

296

largest value of 1382.162 mL was found for DA co-digestion with FW at a mixing

297

ratio of 40:10, which was about 91.71% higher than that of DA only (114.502 mL).


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Energy & Fuels

298

This increase might be due to that in the systems with high biomass concentration, the

299

movement of mixed substrates and inoculum, as a result of the presence of liquid

300

water and agitation, allowed higher mass transfer. In addition, the lag time (ʎ) and

301

maximum hydrogen production rate (Rmax) were visibly affected by the mixing ratios.

302

Compared with the FW only, the co-digestion of FW:DA (40:10) resulted in a

303

decrease in ʎ from 10.76 to 10.30 h and led to an increase in Rmax from 62.43 to

304

103.00 mL/h. In addition, the results demonstrated that the other three groups of DA

305

co-digestion with FW all showed a reduced lag time, indicating that HPB could be

306

quickly adapted to the anaerobic environment. A similar improvement on both of P

307

and Rmax values from sewage co-digestion with FW was also observed by Liu et al. 18.

308

On the contrary, the groups of WA co-digestion with FW showed poor results on P,

309

Rmax and extended the lag time by approximately 3 hours. The longer lag time may be

310

due to the need for HPB to modify their physiological state for the new condition.

311 312

3.2. Comparison of Carbohydrate and Protein Variation. Carbohydrate and

313

protein are the main organic components of food waste and Taihu algae. Besides,

314

carbohydrate rather than protein has been reported as the main substrate which could

315

be most easily utilized by microbes, resulting in a greater potential for hydrogen

316

production 34. The effects of adding FW at various ratios on carbohydrate and protein

317

degradation via AD for hydrogen production were studied, and the results are shown

318

in Fig. 3-4.

319

The initial concentration of carbohydrate was increased with the FW proportion,


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

320

while protein had a different trend. The initial concentration of carbohydrate was 8.20,

321

8.06, 6.02, 3.56, 3.38, 2.07 g/kg, and protein was 2.01, 5.38, 6.16, 7.17, 9.70, 9.72

322

g/kg in co-digestion groups at FW/DA ratio of 50:0, 40:10, 30:20, 20:30, 10:40, 0:50,

323

respectively. The initial concentration of carbohydrate and protein was only 0.44 g/kg

324

and 3.16 g/kg for WA only, respectively, while it was 0.54-5.85 g/kg and 2.62-3.02

325

g/kg for mixing groups. The data suggested that compared to WA co-digestion, DA

326

co-digestion with FW could increase the availability of nutrients and improve the

327

condition of the substrates for microorganism utilization, thus increasing hydrogen

328

production.

329 330

Fig 3. The carbohydrate concentration and degradation rate at different mixing ratios: (a) DA

331

co-digestion with FW and (b) WA co-digestion with FW.

332

At the end of digestion, carbohydrate and protein degradation rates for individual

333

substrates were relatively low with 72.04% and 81.64% for FW only, 69.33% and

334

75.21% for DA only, 15.72% and 68.99% for WA only, respectively. However, they

335

were increased from DA co-digestion with FW. The carbohydrate degradation rate


Page 18 of 42

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Energy & Fuels

336

reached 82.06%, 79.41%, 75.23%, 73.56% at FW/DA ratio of 40:10, 30:20, 20:30,

337

10:40, 0:50, respectively (Fig. 3a), and the protein degradation rate exhibited the

338

similar trend (Fig. 3b). The difference in organics degradation rates could account for

339

the various in hydrogen production. The data indicated that compared to DA only,

340

improving C/N ratios could enhance the conversion efficiency of protein, and higher

341

utilization efficiency of carbohydrate could contribute to higher hydrogen yield.

342

Similar findings were reported by Yang et al. who found that maximum total

343

carbohydrate and protein degradation rates of 59.4% and 26.9% were achieved with

344

mixture of sewage sludge and ryegrass, respectively

345

illustrated that the concentration of soluble carbohydrate relevantly decreased to the

346

ratios of 86.0-96.7% at different mixing ratios of sludge and FW 36.

35.

Besides, Liu et al. also

347 348

Fig 4. The protein concentration and degradation rate at different mixing ratios: (a) DA

349

co-digestion with FW and (b) WA co-digestion with FW.

350

Compared to WA only, the carbohydrate and protein degradation rates of WA

351

co-digestion were enhanced, but was not increased compared with FW only. It might


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

352

because that the carbohydrate in FW was more easily utilized than the WA. The

353

addition of FW seemed to improve the issue of WA only digestion, but a certain

354

amount of non-biodegradable organic matter was found in WA only and WA

355

co-digestion groups, resulting in organics degradation rates of WA co-digestion were

356

lower than that of FW only. When FW/WA ratio was 40:10, 30:20, 20:30, 10:40, the

357

values decreased to 70.10%, 35.53%, 34.80%, 23.54% for carbohydrate degradation

358

rate and 80.92%, 80.57%, 70.17%, 69.54% for protein degradation rate, respectively

359

(Fig. 4). The poor degradation performance of the tightly packed carbohydrate and

360

protein in WA, therefore nutrient utilization of WA co-digestion was low. In other

361

words, the higher carbohydrate and protein degradation rates achieved with DA over

362

WA may be a consequence of a higher fragility of the DA cell wall. After the drying

363

process and a step of comminution, the smaller particles of DA resulted in releasing

364

more readily biodegradable organic substances from the algae cells, thus increasing

365

the accessibility of raw materials.

366 367

3.3. The Change of Soluble Metabolites Components. Generally, the organic

368

fraction was converted to soluble metabolites components such as VFAs and ethanol

369

by the metabolism of anaerobic bacteria, which had a certain relationship with

370

hydrogen production 37. Therefore, soluble metabolites components were an important

371

indicator for assessing the performance of AD for hydrogen and identifying the

372

digestion type. The components of main soluble metabolites (acetate, propionate,

373

butyric acid, valerate and ethanol) after the digestion were affected by the different


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Energy & Fuels

374

substrates at various mixing ratios and the results are shown in Fig. 5 (a-b). The

375

concentration of formic acid and lactic acid was very low, and the data was not shown.

376

The digestion of FW, DA and WA only generated 3.50, 1.87, 1.65 g/kg for acetate,

377

0.97, 0.99, 1.00 g/kg for propionate, 4.16, 1.39, 1.22 g/kg for butyric acid and 0.85,

378

0.87, 0.87 for valerate, respectively. Only a small proportion of ethanol was detected

379

in three sole digestion groups, which accounted for 0.29-0.37 g/kg. The yield of total

380

soluble metabolites usually depended on the composition of the substrates, with

381

similar values for the DA and WA only, while relatively high value was obtained

382

from FW only.

383

In comparison with DA only, main soluble metabolites concentration was

384

significantly increased at the rising percentage of FW in DA co-digestion (Fig. 5a),

385

contributing to 4.80, 3.81, 3.79, 3.53 g/kg for acetate and 4.50, 3.83, 3.74, 3.55 g/kg

386

for butyric acid when the ratios of FW to DA were 40:10, 30:20, 20:30, 10:40,

387

respectively. Acetate and butyric acid, which usually showed a positive relationship

388

for hydrogen production, were dominant for all four co-digestion groups, accounting

389

for 80.19%, 77.27%, 76.88% and 76.92% of total soluble metabolites at FW/DA

390

ratios of 40:10, 30:20, 20:30 and 10:40, respectively, followed by propionate, valerate

391

and ethanol. These values were in agreement with the characteristics of butyric acid

392

type digestion. Similar findings were reported by Angenriz-Campoy et al. who found

393

that butyric acid type digestion was dominant in AD for hydrogen 37. The total soluble

394

metabolites concentration had the highest value of 11.60 g/kg in accordance with the

395

maximum CHP of 31.42 mL H2/g VS at FW:DA ratio of 40:10, which was nearly


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

396

11.76% and 111.29% higher than that of FW only (9.85 g/kg) and DA only (5.49

397

g/kg). It was indicated that a suitable co-digestion mixing ratio was beneficial to the

398

hydrogen production and soluble metabolites. Elsamadony et al., also found that the

399

highest value of butyric acid (6.76 g/L), acetate (8.31 g/L), propionate (1.04 g/L ) and

400

hydrogen yield (157.5 mL/gCODremoved) was achieved at co-digestion of 70%

401

OFMSW + 20% GSW + 10% PMS 2.

402

Similarly, co-digestion of FW and WA promoted a higher production of soluble

403

metabolites in the mixture compared to WA only in Fig. 5b, by a value of 3.27, 3.14,

404

2.18, 2.25, 1.65 g/kg for acetate, and 3.69, 3.75, 2.35,1.53, 1.22 g/kg for butyric acid

405

at FW/WA ratio of 40:10, 30:20, 20:30, 10:40, 0:50, respectively. The other soluble

406

metabolites including propionate, valerate and ethanol were not found to be

407

significantly different between each group. Meanwhile, the acetate and butyric acid

408

concentration amounted to 61.77-74.06% of total soluble metabolites, which showed

409

that the change of substrate conditions by co-digestion with FW did not shift the

410

dominant butyric acid digestion type. The total soluble metabolites concentration of

411

the mixture was 9.406 and 9.407 g/kg at FW/WA ratio of 40:10 and 30:20,

412

respectively, but was lower than that of FW/DA (40:10) co-digestion (11.60 g/kg),

413

which indicated that drying treatment of algae led to improvement of the soluble

414

metabolites yields. However, the concentration of 6.87 and 6.12 g/kg significantly

415

decreased at higher WA proportion (FW/WA ratio of 20:30 and 10:40), respectively.

416

This was probably because accessibility of WA intracellular content to HPB was

417

limited by the resistance of its cell wall to hydrolysis and acidification.


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Energy & Fuels

418 419

Fig 5. Composition of soluble metabolites components at different mixing ratios after AD process:

420

(a) DA co-digestion with FW and (b) WA co-digestion with FW.

421 422

3.4. Metabolic Analysis by EEM and FRI. DOM is the most important

423

components of organic matter in the digestion process, accounting for more than 80%

424

of total organic carbon (TOC), and includes volatile fatty acids (VFAs), amino acids,

425

sugars, protein, humus etc. DOM is a direct source of nutrients for microorganisms,

426

whose composition and structural characteristics are significantly important for

427

studying the biodegradability of substrates. Meanwhile, EEM fluorescence spectra

428

can expound the complete fluorescence information of the compound by varying the

429

excitation wavelength and emission wavelength

430

various fluorescent substances at different ratios in the co-digestion. In addition, it is

431

useful to quantitatively assess detailed distribution information of readily

432

biodegradable

433

non-biodegradable (tryptophan-like, fulvic acid-like, humic acid-like) materials in

(tyrosine-like

and

soluble

25.

It can indicate the change of

microbial


by-product)

and

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

434

DOM with FRI analysis methods.

435

To further analyze the synergistic effect of FW addition to Taihu algae via AD

436

process for hydrogen, EEM fluorescence spectra in three single-substrate digestion

437

groups (i.e. the group with FW, DA and WA only) and two co-digestion groups (i.e. a

438

group with a FW/DA ratio of 40:10 and a group with a FW/WA ratio of 40:10) were

439

indicated in Fig. 6. The percent fluorescence response (Pi,n) indirectly indicated the

440

relative content of organic matter represented by each region, and the Pi,n of different

441

types of fluorescent substances in different substrates varied greatly (Fig. 7).

442

443


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Energy & Fuels

444

445

446 447

Fig 6. The fluorescence EEM of the DOM fractions from FW only, DA only, WA only and


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448 449

Page 26 of 42

co-digestion groups.

In the initial state of FW only digestion group, Region Ⅴ presented the lowest Pi,n

450

of 12.97%, along with Region Ⅰ

(22.73%) and Ⅳ

451

tyrosine-like and soluble microbial by-products were the main components with

452

relatively high biodegradability in FW. However, in the initial supernatant of DA only,

453

the highest contribution proportion of Pi,n was 38.11% and 24.55% presented in the

454

Region Ⅴ (humic acid-like) and Region Ⅲ (fulvic acid-like), followed by the

455

Region Ⅱ (tryptophan-like) of 17.48%, the Region Ⅰ (tyrosine-like) of 10.24%,

456

and finally by the Region Ⅳ (soluble microbial by-product) of 9.63% (Fig. 7).

457

Among them, Region Ⅴ and Region Ⅲ were correlated to the least biodegradable

458

and bio-accessible compounds, which indicated a certain amount of recalcitrant

459

compounds presented in DA. Besides, WA only group contributed to 15.39%, 38.74%,

460

22.83%, 12.18% and 10.86% for the Region Ⅰ - Ⅴ at the beginning, respectively.

461

However, tryptophan-like rather than humic/fulvic acid-like fluorescence dominated

462

in EEM fluorescence spectra for WA only, which was common for fresh algae

463

without any treatment and has previously been observed. For instance, Determann et

464

al. detected the tryptophan-like dominated in all EEMs from the diatom Nitzschia 38.

465

Then, the initial Pi,n of Region Ⅰ and Ⅳ presented similar results in both DA and

466

WA only, and they amounted to low proportions. The above results showed that the

467

metabolites production primarily was consisted of more non-biodegradable materials

468

and lower readily biodegradable materials in dried/wet condition, which explained the

469

difficult biodegradable and hydrolyzed characteristics of algae. It was interesting to


(28.88%), implying that

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Energy & Fuels

470

observe that compared to DA only, the initial Pi,n of Region Ⅰ(14.08%) and Region

471

Ⅳ (13.41%) from DA co-digestion were both increased, while Region Ⅴ (28.68%)

472

achieved the smaller percentage (Fig. 7). These results showed that FW addition in

473

co-digestion increased the substrate availability, stimulating the growth of HPB and

474

improving the biodegradability of DA. However, the initial Pi,n from WA co-digestion

475

still maintained a very high value of 39.72% and 22.46% for Region Ⅱ and Ⅲ ,

476

followed by 15.12% and 11.08% for Region Ⅰ

477

indicated that the biodegradability of FW and WA mixtures was not obviously

478

improved compared to WA only.

and Ⅳ , respectively, which

479

As biodegradable substances were consumed, the Pi,n from FW only slightly

480

decreased to 9.93% for Region Ⅰ and 11.10% for Region Ⅳ in the end, besides

481

Region Ⅲ (30.23%) and Region Ⅴ (33.09%) accounted for the main parts, which

482

indicated that the remaining substrates were difficult for HPB to be utilized. These

483

results showed that the biodegradability of FW was more completely than others, and

484

the easily biodegradable compounds were utilized rapidly and effectively for

485

conversion to hydrogen. The Pi,n values of Region Ⅰ (15.05% and 15.93%) and

486

Region Ⅳ (12.85% and 12.33%) from DA and WA only were slightly better than the

487

previous. Although more soluble substances such as carbohydrate, protein, and SCOD

488

could be released after substrates hydrolysis, the Region Ⅴ (27.04%) from DA only

489

and Region Ⅱ (39.83%) from WA only still held on a high level. The accumulation

490

of non-biodegradable humic acid and tryptophan-like was disadvantageous for further

491

utilization of substrates for hydrogen production.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

492 493

Fig 7. Distribution of FRI in DOM from FW only, DA only, WA only and co-digestion groups.

494

Abbreviations: co-dig., co-digestion.

495

However, it was shown in Fig. 7 that the Pi,n obviously increased to 25.14% for

496

RegionⅠ, followed by a higher Pi,n of 18.08% for Region Ⅳ from DA co-digestion,

497

respectively. Meanwhile, the Pi,n of Region Ⅴ in this study with addition of FW was

498

lower than DA only, in agreement with the relatively low concentration of

499

non-biodegraded humic acid. It was illustrated that the substrate metabolism produced

500

more bio-degradable protein-like materials and lower non-degradable materials,

501

which then improved the potential for hydrogen production by AD process. In

502

addition, the co-digestion of FW:DA (40:10) group also attained the best hydrogen

503

production performance, and Pi,n of Region Ⅰ and Ⅳ were enhanced at a value of

504

78.55% and 34.82%, respectively. The Pi,n of Region Ⅱ (30.58%) was obtained from


Page 28 of 42

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Energy & Fuels

505

the WA co-digestion and that of Region Ⅰ and Ⅳ increased to 16.60% and 20.51%,

506

respectively, but the effect of hydrogen production and substrate metabolism was not

507

been greatly improved. This may be due to the fact that microorganism activity was

508

inhibited, which led to incomplete substrate metabolism. Another possibility was that

509

large molecular weight compounds were in the WA and FW mixtures, and this part of

510

the organic matter was less available for bacteria.

511

In general, it seemed that FW addition to DA not only enhanced the utilization

512

efficiency of readily biodegradable compounds, but also improved the breakdown of

513

non-biodegradable substances, resulting in the direct conversion of the soluble

514

substrates to hydrogen by HPB.

515 516

3.5. Microbial Analysis after the Co-digestion. It is well known that for hydrogen

517

generation, microbial communities have a substantial impact on AD performance, and

518

its composition is significantly influenced by the type of substrates and its conditions.

519

Thus, the analysis of microbial communities for the single-substrate digestion groups

520

and two co-digestion groups (i.e. a group with FW/DA ratio of 40:10 and a group

521

with FW/WA ratio of 40:10) by high-throughput pyrosequencing was indicated to be

522

a better understanding on the metabolism.

523

Biodiversity indices, including the total read numbers, OTUs, Coverage, Chao

524

index and Simpson index for samples from the five digestion groups mentioned above

525

are presented in Table 4. The high coverage (>0.998) of all samples suggested the

526

reliability of the above results (Table 4). The Chao and Simpson indexes can reflect


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Page 30 of 42

39.

527

the microbial community diversity in a sample

According to the decreased Chao

528

index and increased Simpson index, the DA co-digestion sample had the lowest

529

microbial diversity, followed by FW only, DA only, WA co-digestion and finally by

530

WA only. This phenomenon indicated that the microbial community diversity was

531

significantly decreased with the mixed substrates and FW addition selectively

532

enriched some bacteria in co-digestion. This was in agreement with Yang et al., who

533

also found that the co-digestion led to the decrease in microbial diversity 39.

Table 4. Diversity Indices for Samples from FW Only, DA Only, WA Only, DA Co-digestion and WA Co-digestion Samples

Reads

OTUs

Coverage

Chao1

Simpson

FW only

56040

233

0.998925

292.913

0.331

DA only

67141

309

0.999115

360.000

0.058

WA only

54980

565

0.998117

611.019

0.035

DA co-digestion

55418

228

0.998998

273.120

0.391

WA co-digestion

58910

524

0.9977

604.275

0.048

534

As shown by the Venn diagram in Fig. 8, only 6.93% of the total OTUs were

535

shared among five samples. In addition, the shared OTUs between the DA

536

co-digestion and FW only was the highest at 42.08%, followed by a value of 38.56%

537

between DA only and FW only, while the lowest value of 22.18% was between WA

538

only and FW only. It can be seen in Fig. 8 that there existed a significant variation

539

among these five digestion groups, which clearly illustrated that a huge change in the

540

microbial community structure was caused by the co-digestion as compared with their


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Energy & Fuels

541

sole digestion. This could be related to the complex substrates composition in the

542

co-digestion groups.

543

544 545

Fig 8. Venn diagram for the samples of FW only, DA only, WA only, DA co-digestion and WA

546

co-digestion.

547

To further reveal the synergistic effect of co-digestion on the microbial community,

548

microbial compositions on genus level of five samples are compared in Fig. 9. As can

549

be seen, there are 14 genera with relative abundance of higher than 6% in at least one

550

sample, and other genera were grouped as “others”. The genus Clostridium, a strict

551

anaerobic bacteria that is known to utilize various kinds of organic matter for

552

hydrogen production during AD, played a major role in FW only and DA co-digestion

553

40.

554

co-digestion (78.46%) compared with FW only (75.71%), DA only (59.89%), WA

555

co-digestion (14.30%) and WA only (11.89%). This was probably because the

The genus Clostridium accounted for the highest relative abundance in the DA


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 42

556

complex composition of FW and DA could significantly stimulate the growth of

557

genus Clostridium, and it became dominant in DA co-digestion. Similarly, the genus

558

Clostridium was considered to be the main bacteria in all the reactors by Gabriel et al.

559

40.

560

obtained from DA co-digestion since many species in Clostridium had a strong

561

hydrolytic ability

562

abundance of 70.57% was observed from DA co-digestion, followed by FW only

563

(65.08%), DA only (7.35%), WA co-digestion (1.78%) and WA only (0.75%),

564

respectively. Interestingly, the rank of relevant abundance of Clostridium sensu stricto

565

1 was almost consistence with the rank of hydrogen generation, organics degradation

566

rates and soluble metabolites production. Thus, compared to WA co-digestion, more

567

Clostridium sensu stricto 1 was observed in DA co-digestion and was committed to

568

efficient AD for hydrogen production and better metabolic performance. Other

569

researchers also showed that hydrogen production has a certain relationship with the

570

Clostridium genus in mixed culture 39, 41. Bacillus which is activated in the hydrolysis,

571

appeared in five digestion samples and was another major HPB

572

co-digestion obtained the highest relative abundance of 8.64%, rather than in FW only

573

(3.74%), DA only (3.62%), WA co-digestion (4.89%) and WA only (3.13%). The

574

genus Bacillus affiliated to class Bacilli is facultative anaerobic bacteria and capable

575

of hydrolyzing complex substrates to simple sugars

576

the genus Bacillus was propitious to degrade lignocellulosic biomass and could

577

produce hydrogen in AD

It was also indicated that higher carbohydrate and protein degradation might be

25.

Regarding Clostridium sensu stricto 1, the highest relative

44.

43.

42.

The DA

Song et al. also reported that

The relative abundances of Lactobacillus were 0.82%,


Page 33 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

578

2.1%, 0.66%, 6.03% and 0.69% for FW only, DA only, WA only, DA co-digestion,

579

and WA co-digestion, respectively. The genus Lactobacillus is often found in

580

vegetables and fruit juices. It can use glucose, fructose, etc. as a carbon source to

581

produce organic acids, which can then be used by other HPB to generate hydrogen 45.

582

It has been reported that the presence of Clostridium sp. and Lactobacillus sp.

583

together in hydrogen-producing reactors could significantly improve hydrogen

584

production 45, 46. In addition, Clostridium sp., Bacillus sp. and Lactobacillus sp. jointly

585

occupied a position of absolute advantage in DA co-digestion, resulting in lower

586

relative abundance of other microorganisms. This may be an important reason

587

explaining the better hydrogen production performance for DA co-digestion

588

compared to other sole digestions. Besides, a small proportion of the genus Georgenia

589

appeared in DA only (0.84%), WA only (8.89%) and WA co-digestion (10.63%),

590

respectively, while the functions of this genus in AD for hydrogen production were

591

unclear.

592

As shown in Fig. 9, the genus Enterococcus was observed in all sole digestion

593

groups and WA co-digestion group, with corresponding relevant abundances of 1.13%

594

in FW only, 0.71% in DA only, 6.45% in WA only and 10.70% in WA co-digestion,

595

respectively. It has been reported that the genus Enterococcus could compete with

596

HPB for available substrates, which would then be harmful for the digestion process

597

for hydrogen

598

could be largely enriched to synchronously metabolize multifarious organics, then

599

achieving high-efficiency hydrogen production. The genus Macellibacteroides was

47.

Therefore, by DA co-digestion, more beneficial microorganisms


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

600

only observed in WA only and WA co-digestion, with a corresponding relevant

601

abundance of 6.69% and 1.9%. Macellibacteroides sp., a hydrogen-consuming

602

microorganism, can simultaneously utilize available readily biodegradable materials

603

with HPB

604

metabolism of WA only and WA co-digestion may be due to the lower relative

605

abundances of Clostridium sp. and Bacillus sp. that were benefit for hydrogen

606

production, along with higher values of Enterococcus sp. and Macellibacteroides sp.

607

in the system. Besides, an imbalance between carbon and nitrogen requirements for

608

the bacterial community led to nitrogen release in the form of ammonia during AD

609

when the C/N ratio was low in WA, and this could lead to HPB inhibition 49.

48.

As a result, the poor digestion performance and insufficient substrate

610 611

Fig 9. Abundance of microbial community for FW only, DA only, WA only, DA co-digestion and

612

WA co-digestion samples at the genus level. Abbreviations: co-dig., co-digestion.

613 614


Page 34 of 42

Page 35 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

615

Energy & Fuels

4. CONCLUSIONS

616

This study showed that dried Taihu algae, after undergoing a drying process

617

compared to wet algae, had a higher synergistic effect on the AD performance for

618

hydrogen when co-digested with FW. The optimal mixing ratio of FW to DA was

619

40:10, where the CHP amounted to the highest value of 31.42 mL H2/g VS and was

620

9.77%, 91.75% higher than that of FW only (28.35 mL/g VS) and DA only (2.59

621

mL/g VS), respectively. In addition, the organics degradation rates and total soluble

622

metabolites concentration also significantly increased with FW addition. The butyric

623

acid type digestion dominated all of the mixing ratios. Different substrates caused big

624

variations on microbial activity and microbial community composition. Clostridium

625

genus (78.46%) and Bacillus genus (8.64%) made the main contribution to efficient

626

co-digestion for hydrogen production.

627 628

ACKNOWLEDGEMENTS

629

This work was supported by the National Natural Science Foundation of China

630

(51508230, 21506076), Major Science and Technology Program for Water Pollution

631

Control and Treatment(2017ZX07203-001), National Scientific and Technological

632

Support of China (2013BAB11B02), Henan Science and Technology Cooperation

633

Project(172106000030), Jiangsu Overseas Visiting Scholar Program for University

634

Prominent Young & Middle-aged Teachers and Presidents, and The Jiangsu Key

635

Laboratory of Anaerobic Biotechnology (JKLAB201601).

636

637


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

638

REFERENCES

639

1.

640

whey and liquid cow manure in a two-stage CSTR system: Effect of hydraulic retention time.

641

Bioresource Technology 2015, 175, 553-562.

642

2.

643

waste with paperboard mill sludge and gelatin solid waste for enhancement of hydrogen

644

production. Bioresource Technology 2015, 191, 157-165.

645

3.

646

hydrogen production from industrial municipal solid waste. Fuel 2016, 180, 343-347.

647

4.

648

Algal Biomass – Advances, Challenges and Prospects. Bioresource Technology 2018, 257,

649

290-300.

650

5.

651

from microalgal biomass (Chlorella vulgaris) in a two-stage combined process. Applied Energy

652

2014, 132, (11), 108-117.

653

6.

654

agricultural waste by dark fermentation: A review. International Journal of Hydrogen Energy

655

2010, 35, (19), 10660-10673.

656

7.

657

and resources utilizations of Taihu Lake blue algae. Journal of Natural Resources 2009, 24, (3),

658

431-438.

Dareioti, M. A.; Kornaros, M. Anaerobic mesophilic co-digestion of ensiled sorghum, cheese

Elsamadony, M.; Tawfik, A. Dry anaerobic co-digestion of organic fraction of municipal

Zahedi, S.; Solera, R.; García-Morales, J. L.; Sales, D. Effect of the addition of glycerol on

Show, K. Y.; Yan, Y. G.; Ling, M.; Ye, G. X.; Li, T.; Lee, D. J. Hydrogen Production from

Wieczorek, N.; Kucuker, M. A.; Kuchta, K. Fermentative hydrogen and methane production

Guo, X. M.; Trably, E.; Latrille, E.; Carrère, H.; Steyer, J. P. Hydrogen production from

Han, S. Q.; Yan, S. H.; Wang, Z. Y.; Song, W.; Liu, H. Q.; Zhang, J. Q. Harmless disposal


Page 36 of 42

Page 37 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

659

8.

Sun, J. X.; Yuan, X. Z.; Shi, X. S.; Chu, C. F.; Guo, R. B; Kong, H. N. Fermentation of

660

Chlorella sp. for anaerobic bio-hydrogen production: Influences of inoculum–substrate ratio,

661

volatile fatty acids and NADH. Bioresource Technology 2011, 102, (22), 10480-10485.

662

9.

663

fermentation followed by photo hydrogen fermentation and methanogenesis between protein and

664

carbohydrate compositions in Nannochloropsis oceanica biomass. Bioresource Technology 2013,

665

138, (6), 204-213.

666

10. Lakaniemi, A. M.; Hulatt, C. J.; Thomas, D. N.; Tuovinen, O. H.; Puhakka, J. A., Biogenic

667

hydrogen and methane production from Chlorella vulgaris and Dunaliella tertiolecta biomass.

668

Biotechnology for Biofuels 2011, 4, (1), 1-12.

669

11. Wang, J. L.; Yin, Y. N. Fermentative hydrogen production using pretreated microalgal

670

biomass as feedstock. Microb Cell Fact 2018, 17, (1), 22-38.

671

12. Borowski, S. Co-digestion of the hydromechanically separated organic fraction of municipal

672

solid waste with sewage sludge. Journal of Environmental Management 2015, 147, 87-94.

673

13. Sambusiti, C.; Bellucci, M.; Zabaniotou, A.; Beneduce, L.; Monlau, F. Algae as promising

674

feedstocks for fermentative biohydrogen production according to a biorefinery approach: A

675

comprehensive review. Renewable and Sustainable Energy Reviews 2015, 44, 20-36.

676

14. Clercq, D. D.; Wen, Z. G.; Fei, F. Performance evaluation of restaurant food waste and

677

biowaste to biogas pilot projects in China and implications for national policy. Journal of

678

Environmental Management 2017, 189, 115-124.

Xia, A.; Cheng, J.; Lin, R. C.; Lu, H. X.; Zhou, J. H.; Cen, K. Comparison in dark hydrogen


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

679

15. Qian, M. Y.; Zhang, Y. X.; Li, R. H.; Nelles, M.; Stinner, W.; Li, Y. Q. Effects of Percolate

680

Recirculation on Dry Anaerobic Co-digestion of Organic Fraction of Municipal Solid Waste and

681

Corn Straw. Energy & Fuels 2017, 31, (11), 12183-12191.

682

16. Han, W.; Wan, C. L.; Melikoglu, M.; Man, T. W.; Leung, H. T.; Chi, L. N.; Yan, P.; Yeung,

683

S. Y.; Lin, C. S. K. Kinetic analysis of a crude enzyme extract produced via solid state

684

fermentation of bakery waste. Acs Sustainable Chemistry & Engineering 2015, 3, (9), 2043-2048.

685

17. Kim, M. J.; Yang, Y. N.; Morikawa-Sakura, M. S.; Wang, Q. H.; Lee, M. V.; Lee, D. Y.;

686

Feng, C. P.; Zhou, Y. L.; Zhang, Z. Y. Hydrogen production by anaerobic co-digestion of rice

687

straw and sewage sludge. International Journal of Hydrogen Energy 2012, 37, (4), 3142-3149.

688

18. Liu, X.Y.; Li, R. Y.; Ji, M.; Han, L. Hydrogen and methane production by co-digestion of

689

waste activated sludge and food waste in the two-stage fermentation process: substrate conversion

690

and energy yield. Bioresource Technology 2013, 146, (10), 317-323.

691

19. Ghimire, A.; Frunzo, L.; Pontoni, L.; D'Antonio, G.; Lens, P. N. L.; Esposito, G.; Pirozzi, F.

692

Dark fermentation of complex waste biomass for biohydrogen production by pretreated

693

thermophilic anaerobic digestate. Journal of Environmental Management 2015, 152, 43-48.

694

20. Cheng, J.; Liu, Y. Q.; Lin, R. C.; Xia, A.; Zhou, J. H.; Cen, K. Cogeneration of hydrogen and

695

methane from the pretreated biomass of algae bloom in Taihu Lake. International Journal of

696

Hydrogen Energy 2014, 39, (33), 18793-18802.

697

21. Hu, B.; Chen, S. L. Pretreatment of methanogenic granules for immobilized hydrogen

698

fermentation. International Journal of Hydrogen Energy 2007, 32, (15), 3266-3273.

699

22. Association, C.; Washington, D. APHA, A. P. H. A. : Standard Methods for the Examination

700

of water and Wastewater. American Physical Education Review 1995, 24, (9), 481-486.


Page 38 of 42

Page 39 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

701

23. Dubois, M.; Gilles, K.A.; Hamilton, J.K.; Rebers, P.A.; Smith F. Colorimetric Method for

702

Determination of Sugars and Related Substances. Analytical Chemistry 1956, 28, 350-356.

703

24. Lowry, O. H.; Rosebrough, N. J.; Farr, A. L.; Randall, R. J. Protein measurement with the

704

Folin phenol reagent. Journal of Biological Chemistry 1951, 193, (1), 265-275.

705

25. Wu, Q. L.; Guo, W. Q.; Zheng, H. S.; Luo, H. C.; Feng, X. C.; Yin, R. L.; Ren, N. Q.

706

Enhancement of volatile fatty acid production by co-fermentation of food waste and excess sludge

707

without pH control: The mechanism and microbial community analyses. Bioresource Technology

708

2016, 216, 653-660.

709

26. Chen, W.; Westerhoff, P.; Leenheer, J. A.; Booksh, K. Fluorescence excitation - Emission

710

matrix regional integration to quantify spectra for dissolved organic matter. Environmental

711

Science & Technology 2003, 37, (24), 5701-5710.

712

27. Lay, J. J.; Lee, Y. J.; Noike, T. Feasibility of biological hydrogen production from organic

713

fraction of municipal solid waste. Water Research 1999, 33, (11), 2579-2586.

714

28. Abudi, Z. N.; Hu, Z. Q.; Sun, N.; Xiao, B.; Rajaa, N.; Liu, C. X.; Guo, D. Batch anaerobic

715

co-digestion of OFMSW (organic fraction of municipal solid waste), TWAS (thickened waste

716

activated sludge) and RS (rice straw): Influence of TWAS and RS pretreatment and mixing ratio.

717

Energy 2016, 107, 131-140.

718

29. Xia, A.; Cheng, J.; Ding, L. K.; Lin, R. C.; Song, W. L.; Zhou, J. H.; Cen, K. Enhancement

719

of energy production efficiency from mixed biomass of Chlorella pyrenoidosa and cassava starch

720

through combined hydrogen fermentation and methanogenesis. Applied Energy 2014, 120, 23-30.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

721

30. Liu, C. H.; Chang, C. Y.; Cheng, C. L.; Lee, D. J.; Chang, J. S. Fermentative hydrogen

722

production by Clostridium butyricum CGS5 using carbohydrate-rich microalgal biomass as

723

feedstock. International Journal of Hydrogen Energy 2012, 37, (20), 15458-15464.

724

31. Zhao, M. X.; Wang, Y. H.; Zhang, C. M.; Li, S. Z.; Huang, Z. X.; Ruan, W. Q. Synergistic

725

and pretreatment effect on anaerobic co-digestion from rice straw and municipal sewage sludge.

726

Bioresources 2014, 9, (4), 5871-5882.

727

32. Cheng, J.; Lin, R. C.; Song, W. L.; Xia, A.; Zhou, J. H.; Cen, K. Enhancement of

728

fermentative hydrogen production from hydrolyzed water hyacinth with activated carbon

729

detoxification and bacteria domestication. International Journal of Hydrogen Energy 2015, 40,

730

(6), 2545-2551.

731

33. Wang, M.; Sahu, A. K.; Rusten, B.; Park, C. Anaerobic co-digestion of microalgae Chlorella

732

sp. and waste activated sludge. Bioresource Technology 2013, 142, (8), 585-590.

733

34. Xiao, B. Y.; Han, Y. P.; Liu, J. X. Evaluation of biohydrogen production from glucose and

734

protein at neutral initial pH. International Journal of Hydrogen Energy 2010, 35, (12), 6152-6160.

735

35. Yang, G.; Wang, J. L. Enhanced Hydrogen Production from Sewage Sludge by

736

Co-fermentation with Forestry Wastes. Energy & Fuels 2017, 31, (9), 9633-9641.

737

36. Yang, G.; Wang, J. L. Co-fermentation of sewage sludge with ryegrass for enhancing

738

hydrogen production: Performance evaluation and kinetic analysis. Bioresource Technology 2017,

739

243, (1), 1027-1036.

740

37. Rubén, A. C.; Álvarez-Gallego, C. J.; Romero-García, L. I. Thermophilic anaerobic

741

co-digestion of organic fraction of municipal solid waste (OFMSW) with food waste (FW):

742

Enhancement of bio-hydrogen production. Bioresource Technology 2015, 194, (1), 291-296.


Page 40 of 42

Page 41 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

743

38. Determann, S.; Lobbes, J. M.; Reuter, R.; Rullkötter, J. Ultraviolet fluorescence excitation

744

and emission spectroscopy of marine algae and bacteria. Marine Chemistry 1998, 62, (1),

745

137-156.

746

39. Yang, G.; Wang, J. L. Synergistic Biohydrogen Production from Flower Wastes and Sewage

747

Sludge. Energy & Fuels 2018, 32, (6), 6879-6886.

748

40. Capson-Tojo, G.; Trably, E.; Rouez, M.; Crest, M.; Bernet, N.; Steyer, J. P.; Delgenes, J. P.;

749

Escudie, R. Cardboard proportions and total solids contents as driving factors in dry

750

co-fermentation of food waste. Bioresource Technology 2018, 248, (Pt A), 229-237.

751

41. Loudet, J. C.; Poulin, P. Application of an electric field to colloidal particles suspended in a

752

liquid-crystal solvent. Physical Review Letters 2001, 87, (16), 165503.

753

42. Palatsi, J.; Vinas, M.; Guivernau, M. Anaerobic digestion of slaughterhouse waste: main

754

process limitations and microbial community interactions. Bioresource Technology 2011, 102, (3),

755

2219-2227.

756

43. Wang, J. L.; Yin, Y. N. Principle and application of different pretreatment methods for

757

enriching hydrogen-producing bacteria from mixed cultures. International Journal of Hydrogen

758

Energy 2017, 42, (8), 4804-4823.

759

44. Song, Z. X.; Li, W. W.; Li, X. H.; Dai, Y.; Peng, X. X.; Fan, Y. T.; Hou, H. W. Isolation and

760

characterization of a new hydrogen-producing strain Bacillus sp. FS2011. International Journal of

761

Hydrogen Energy 2013, 38, (8), 3206-3212.

762

45. Yanga, P. L.; Zhang, R. H.; Mcgarveyc, J. A.; Benemannd, J. R. Biohydrogen production

763

from cheese processing wastewater by anaerobic fermentation using mixed microbial

764

communities. International Journal of Hydrogen Energy 2007, 32, (18), 4761-4771.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

765

46. Perna, V.; Castello, E.; Wenzel, J.; Zampol, C.; Fontes Lima, D. M.; Borzacconi, L.

766

Hydrogen production in an upflow anaerobic packed bed reactor used to;treat cheese whey.

767

International Journal of Hydrogen Energy 2013, 38, (1), 54-62.

768

47. Yang, G.; Wang, J. L. Kinetics and microbial community analysis for hydrogen production

769

using raw grass inoculated with different pretreated mixed culture. Bioresource Technology 2018,

770

247, 954-962.

771

48. Kim, J.; Lee, S. Y.; Lee, C. S. Comparative study of changes in reaction profile and microbial

772

community structure in two anaerobic repeated-batch reactors started up with different seed

773

sludges. Bioresource Technology 2013, 129, 495-505.

774

49. Carver, S. M.; Hulatt, C. J.; Thomas, D. N.; Tuovinen, O. H. Thermophilic, anaerobic co-

775

digestion of microalgal biomass and cellulose for H2 production. Biodegradation 2011, 22, (4),

776

805-814.

777


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Hydrogen generation performance from Taihu algae and food waste

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