Food Waste with Sewage Sludge HKU team Chunxiao WANG, Yubo WANG, - - PowerPoint PPT Presentation

Co-digestion of Food Waste with Sewage Sludge

• Prof. Tong Zhang

Environmental Biotechnology Laboratory The University of Hong Kong 5th December, 2018

HKU team： Chunxiao WANG, Yubo WANG, Yulin WANG, Tong ZHANG DSD team: Sussana LAI, KK CHEUNG Drainage Service Department Research & Development Forum Smart City • Innovative Wastewater Management

https://newint.org/features/2008/12/01/food-crisis-facts; https://www.youtube.com/watch?v=ExH6kSwoFBw

民以食為天 《漢書》

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 Introduction  Materials and Method  Results and Discussion  Conclusion

 Nearly about 1.4 billion tonnes food waste (one third of total food production) generated from farmland to meal table annually till 2011 revealed by the United Nations

(FAO, 2014).

 3584 tonnes food waste generated daily accounting 36% of the municipal solid waste landfilled in Hong Kong (EPD, 2017).  Conventionally, food waste was disposed in composting, incineration, landfill and anaerobic digestion (Astals et al., 2014; Wang et al., 2014; Chiu & Lo, 2016; ).  AD of food waste became more attractive due to high moisture and organic content in the FW and higher energy recovery potential (Zhang et al., 2007; Astals et al., 2014; Ingrid et

al., 2014; Chiu& Lo, 2016).

 What is the current situation of food waste around the world?

( Peek , 2014) 3

 Introduction  Materials and Method  Results and Discussion  Conclusion

 Why co-digestion for food waste and sewage sludge? From engineering perspective:

 There are excess capacities in the anaerobic digesters. Food waste could be added and co-digested with sewage sludge to recovery more energy (EPA, 2013; Wang et al., 2015).

From technical perspective:

FW/FSS ratio (basis) Methane yield (mL/g VS) Improvement (%) Reference 10:90 (Volume) 293 18.1

Cabbai et al., 2013

20:80 (Volume) 600 54

Zupancic et al., 2008

50:50 (Volume) 365 47.2

Cabbai et al., 2013

 More energy recovered from the bio-wastes (FSS and FW):

• Increase in methane (biogas) production rate (Zhang et al., 2007; Sonsnowski et al., 2008;

Cabbai et al., 2013).

 Increasing the stability of anaerobic-digesters:

• Nutrition balance (C/N) ratio: 5< C/N <30 is regarded as optimal C/N ratio for a stable
• perated AD system (Dai et al., 2013).

Table 1. Biogas production performance of co-fermentation system

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 Introduction  Materials and Method  Results and Discussion  Conclusion

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Co-digestion at a US wastewater treatment plant

Turning Food Waste into Energy at the East Bay Municipal Utility District (EBMUD) If there is excess capacity in the anaerobic digesters, food waste can be added to generate more energy. In California alone there are almost 140 wastewater treatment facilities that utilize anaerobic digesters, with an estimated excess capacity of 15-30%.

http://www3.epa.gov/region9/waste/features/foodtoenergy/index.html

 Introduction  Materials and Method  Results and Discussion  Conclusion

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To digest food waste in anaerobic digesters, food waste must be 1) pre-treated into a slurry in the slurry tank 2) grinded into small pieces of 2 inches 3) to remove heavy debris. 4) added to the anaerobic digester as pulp after going through the paddle finisher.

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If 50%

• f

the food waste generated each year in the U.S. was anaerobically digested, enough electricity would be generated to power over 2.5 million homes for a year.

EBMUD Process

http://www3.epa.gov/region9/waste/features/foodtoenergy/index.html

 Introduction  Materials and Method  Results and Discussion  Conclusion

Co-digestion at a Germany wastewater treatment plant

Braunschweig wastewater treatment plant

Plant with biological sewage treatment and thermophilic digestion of sludge.

• Capacity (Sewage flow): 52,000 m3/day.
• Co-digestion of sludge with biowaste (grease and oil).
• Recycling of biogas from landfill.
• Recycling of methane from fermentation of green waste nearby.

This plant currently achieves 100% electricity self-supply (energy neutral).

 Introduction  Materials and Method  Results and Discussion  Conclusion

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Sewage Sludge (SS): TP-STW: PS /TSAS = 4.5/1(v/v)  PS and TSAS from TaiPo sewage treatment work

 Anaerobic seed sludge: Digested sludge, sampled from anaerobic digester

 Materials: Feeding Sewage Sludge (FSS)

screening Grit chamber Aeration Primary settling Secondary setting Anaerobic digester Sludge dewatering Raw wastewater Efflunet PS Primary sludge TSAS Thickened secondary activated slduge Screenings Grits Air Disinfection

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 Introduction  Materials and Method  Results and Discussion  Conclusion

 Materials: Food Waste (FW)

Food waste origin Carbohydrates Proteins Lipids References

Household

55 17 13

(la Cour et al.,2004)

Household

61 14 14

(Hansen et al.,2007)

Urban (Households, markets, restaurants)

78 17 5

(Redonals et al., 2012)

University dining hall

64 15 17

(Ferris et al.,1995)

Military facilities

57 18 22

(Ferris et al.,1995)

Institution restaurant

64 21 12

(Yan et al.,2011)

This test

78 16 6

• Table 2 The reported compositions of food waste from different sources on dry weight (%) basis

Table 3 Preparation of synthesized food waste Category Wet Weight (g)

Meat

95

Vegetable (lettuce)

300

Fruit (apple)

140

Steamed Rice

400

Bread

350

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 Introduction  Materials and Method  Results and Discussion  Conclusion

 Higher FW:FSS ratios correspond with higher biodegradation efficiency in term of VSR (from 36% to 57%).

 FW:SS ratios: FW:FSS (TS:TS) ratios

Table 5 Bioconversion efficiency

• f the co-digestion process

Methane yield (mL/g VSR) Methane production rate (mL/L/d) R1 504 279 R2 515 402 R3 526 804

605 mL/g VSR 564 mL/g VSR 526 mL/g VSR

Volatile solid reduction (%) Methane yield (mL/g VSR) Methane production rate (mL/L/d)

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 Introduction  Materials and Method  Results and Discussion  Conclusion

6 12 18 24 30 36 42 48 54 60 66

10 20 30 40 50 60 70 Methane content (%) Digestion day (d)

SRT_5d SRT_10d SRT_15d SRT_25d 6 12 18 24 30 36 42 48 54 60 66 100 200 300 400 500 600 700 800 900

methane yield (mL/gVSR) Digestion day (d)

 Solid Retention Time (SRTs)

 Longer SRT corresponded with higher VSR (from 32% to 47%).  Methane content decreased significantly at short SRT conditions (5 d, 10 d and 15 d) and kept at a stable level during the whole fermentation process at SRT of 25 days.  Methane yield decreased more quickly along with shorter SRT conditions (SRT of 5, 10 and 15 days).  At SRT of 25 days, the methane yield kept stable during the whole digestion process.  The highest methane yield (547 mL/g VSR) was

• btained in R4 with SRT of 25 days.

Theoretical methane yield=571 mL/g VSR

Methane content (%) Methane yield (mL/g VSR) Volatile solid reduction (%)

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 Introduction  Materials and Method  Results and Discussion  Conclusion

6 12 18 24 30 36 42 48 54 60 66 100 200 300 400 500 600 700

Methane production rate (mL/L/d)

Digestion day (d) SRT_5d SRT_10d SRT_15d SRT_25d 6 12 18 24 30 36 42 48 54 60 66 1000 2000 3000 4000 5000 6000 7000 8000

Total organic carbon (mg/L)

Digestion day (d) 6 12 18 24 30 36 42 48 54 60 66 4.5 5.0 5.5 6.0 6.5 7.0 7.5

pH

Digestion day (d)

 Solid Retention Time (SRTs)

 The methane production rate (MPR) kept stable in R4 (289 mL/L/d) with SRT of 25 days and shorter SRT conditions led sharper MPR decrease.  Along with the pH drop, methane production decreased significantly and kept in low level (less than 100 mL/L/d). Methane production rate (mL/L/d) pH Total organic carbon (mg/L)

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 Introduction  Materials and Method  Results and Discussion  Conclusion

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 FW composition

Reactor ID FW description Carbohydrates Proteins Lipids R1 R1_boiled meat 27% 39% 34% R2 R2_herbal Tea 75% 14% 11% R3 R3_cateen leftover 58% 26% 16% R4 R4_fresh meat 3% 73% 24% R5 R5_soup slag 1% 62% 36% R6 R6_Equal TS of all five types of FW 35% 41% 24%

Table 8 Food waste composition in collected real food waste

R2 _ herbal tea R1 _ boiled meat R4 _ fresh meat R3 _ canteen leftover R5 _ soup slag

 Introduction  Materials and Method  Results and Discussion  Conclusion

 The FW composition fed in R2 was similar with the artificial FW synthesized based on food consumption pattern in Hong Kong.

14 0% 20% 40% 60% 80% 100% R1 R2 R3 R4 R5 R6 Carbohydrate protein lipid R2 _ herbal tea R1 _ boiled meat R4 _ fresh meat R3 _ canteen leftover R5 _ soup slag

 The highest protein content were detected in the FW fed to R4 and R5 and the NH4

+-N

after digestion was corresponded with the protein content in the feed (FW).

 Introduction  Materials and Method  Results and Discussion  Conclusion

Ammonium nitrogen concentration (mg/L)

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 Introduction  Materials and Method  Results and Discussion  Conclusion

579 620 561 615 633 589

Volatile solid reduction (%) Methane yield (mL/g VSR) Methane production rate (mL/L/d) Total organic carbon (mg/L)  The VSR is not only related with hydrolyzed microbes, but also the characteristics of the substrates, e.g. whether the substrate is easy to be destroyed and pretreated (R1).  The R2 with the lowest protein content (14%) in the feed realizes the highest methane yield (534 mL/g VSR) and production rate (408 mL/L/d) and less TOC accumulation (2622 mg/L) compared with other digesters.  The low methane yield and production rate are detected in the R4 (315 mL/g VSR and 211 mL/L/d), R5 (309 mL/g VSR and 226 mL/L/d).

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 Introduction  Materials and Method  Results and Discussion  Conclusion

Volatile solid reduction (%) Total organic carbon (mg/L) Methane yield (mL/gVSR) Methane production rate (mL/L/d)  The highest methane yield (581 mL/g VSR) and production rate (1051 mL/L/d) were detected in L2 with mixing condition of 80 rpm.  Along with the increasing mixing intensity, less methane yield and production were

• bserved in L3 and L4.

We may observe the shapes microorganisms under microscope. But it is difficult to know their names and functions.

 Microorganisms in reactors under microscope

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 Introduction  Materials and Method  Results and Discussion  Conclusion

https://en.wikipedia.org/wiki/Whole_genome_sequencing

Moore’s Law Carlson Curve

“in the long view of history, the impact of DNA sequencing will be on a par with that of the microscope.”

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 Introduction  Materials and Method  Results and Discussion  Conclusion

Bioinformatics : translation (from the different combinations of A, T, G and C to some biological terms, such as names of bacteria species and names of genes/enzymes) of big data, based on databases (like “dictionaries”). Bioinformatics : another kind of the “microscope” to study microorganisms in wastewater reactors. It tells us the names and functions of different microbial populations.

Environmental Bioinformatics

A “new frontier” in Environmental Engineering

 Bioinformatics

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 Introduction  Materials and Method  Results and Discussion  Conclusion

 Classification of microorganisms at phylum level

31.9% 21.9% 14.9% 6.7% 5.4% 4.5% 2.3% 1.6% 1.5% 1.5% 7.7% Firmicutes (hydrolyser) Bacteroidetes (hydrolyser) Proteobacteria (fermenter) Chloroflexi Actinobacteria (fermenter) Thermotogae (hydrolyser) Euryarchaeota (methanogen) Spirochaetae Cloacimonetes Planctomycetes Others  Bacteria accounted for 97.4%, Archaea 2.3%, plus a minor part of unknown sequences.  The top six phyla were Firmicutes, Bacteroidetes, Proteobacteria, Chloroflexi, Actinobacteria, and Thermotogae were general hydrolysers and/or fermenters (acidogens).

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 Introduction  Materials and Method  Results and Discussion  Conclusion

 Diversity of methanogens in the co-digestion reactor

Methanocorpusculaceae 64% Methanomicrobiaceae 9% Methanomicrobiales Incertae Sedis 2% Methanoregulaceae 1% Methanospirillaceae 1% Methanosaetaceae 19% Methanosarcinaceae 4%

 The most abundant family was Methanocorpusculaceae. This family was reported to grow on H2/CO2 or formate with the optimal pH of 7 under mesophilic conditions (Zellner et

al., 1989).

 The family of Methanosaetaceae was well-reported to use acetate for the production of methane (Cavalier-Smith.,2002; Zielińska et al., 2013).

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 Introduction  Materials and Method  Results and Discussion  Conclusion

Co-digestion is one of the promising solutions to treat food waste.

Reactor operation and performance :

• Waste stabilization (VSR):
• Higher VSR result was obtained from the reactors with higher FW:FSS ratio & longer SRT conditions.
• Aggressive mixing conditions assisted creating homogenous distribution of substrates, heat and mass transfer,

and facilitate particle size reduction.

• Positive effect was also observed if the FW was pretreated before the co-digestion (e.g. R1_boiled meat).
• Energy recovery (Methane/Biogas production): :
• FW:FSS ratio of 40:60 with SRT

≥17 days were the most appropriate operating parameters for the co- digestion system, considering the volatile solid reduction (57%) and methane yield (0.53 m3CH4/kg-VSR).

• A sufficient SRT is highly need to ensure the complete methanogenic co-digestion process (no less than 17

days).

• Suitable mixing conditions (80 rpm) would ensure the integrity of microbial consortia proximity but not

impeded the mass and heat transfer among the functional groups to guarantee the efficiency of energy recovery (referred as methane/biogas production).

Microbial analysis :  Major hydrolysers : Firmicutes, Bacteroidetes, and Thermotogae  Major fermenters: Proteobacteria and Actinobacteria  Major methanogens: Methanocorpusculaceae

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 Introduction  Materials and Method  Results and Discussion  Conclusion

Thank you

Your comments are welcome !

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