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

Drainage Service Department Research & Development Forum Smart City • Innovative Wastewater Management Co-digestion of Food Waste with Sewage Sludge HKU team ： Chunxiao WANG, Yubo WANG, Yulin WANG, Tong ZHANG DSD team: Sussana LAI, KK CHEUNG Prof. Tong Zhang Environmental Biotechnology Laboratory The University of Hong Kong 5 th December, 2018

 Introduction  Materials and Method  Results and Discussion  Conclusion 民以食為天 《漢書》 2 https://newint.org/features/2008/12/01/food-crisis-facts; https://www.youtube.com/watch?v=ExH6kSwoFBw

 Introduction  Materials and Method  Results and Discussion  Conclusion  What is the current situation of food waste around the world? ( Peek , 2014 )  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) . 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: Table 1. Biogas production performance of co-fermentation system 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., 201 3 ).  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 operated AD system (Dai et al., 2013). 4

 Introduction  Materials and Method  Results and Discussion  Conclusion Co-digestion at a US wastewater treatment plant 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% . Turning Food Waste into Energy at the East Bay Municipal Utility District (EBMUD) http://www3.epa.gov/region9/waste/features/foodtoenergy/index.html 5

 Introduction  Materials and Method  Results and Discussion  Conclusion EBMUD Process 6 If 50% of 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. 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. 6 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 This plant currently achieves 100% electricity self-supply (energy neutral). Plant with biological sewage treatment and thermophilic digestion of sludge. • Capacity (Sewage flow): 52,000 m 3 /day. • Co-digestion of sludge with biowaste (grease and oil). • Recycling of biogas from landfill. • Recycling of methane from fermentation of green waste nearby. 7

 Introduction  Materials and Method  Results and Discussion  Conclusion  Materials: Feeding Sewage Sludge (FSS)  PS and TSAS from TaiPo sewage treatment work Air Disinfection Raw Grit Primary Secondary screening Aeration Efflunet wastewater chamber settling setting Screenings Grits PS Primary sludge TSAS Thickened secondary activated slduge Anaerobic Sludge digester dewatering Sewage Sludge (SS): TP-STW: PS /TSAS = 4.5/1(v/v )  Anaerobic seed sludge: Digested sludge , sampled from anaerobic digester 8

 Introduction  Materials and Method  Results and Discussion  Conclusion  Materials: Food Waste (FW) Table 2 The reported compositions of food waste from different sources on dry weight (%) basis Food waste origin Carbohydrates Proteins Lipids References 55 17 13 Household (la Cour et al.,2004) 61 14 14 Household (Hansen et al.,2007) Urban (Households, markets, 78 17 5 (Redonals et al., 2012) restaurants) 64 15 17 University dining hall (Ferris et al.,1995) Military facilities 57 18 22 (Ferris et al.,1995) 64 21 12 Institution restaurant (Yan et al.,2011) This test 78 16 6 - Table 3 Preparation of synthesized food waste Category Wet Weight (g) 95 Meat 300 Vegetable (lettuce) 140 Fruit (apple) 400 Steamed Rice 350 Bread 9

 Introduction  Materials and Method  Results and Discussion  Conclusion  FW:SS ratios: FW:FSS (TS:TS) ratios Volatile solid reduction (%)  Higher FW:FSS ratios correspond with higher biodegradation efficiency in term of VSR (from 36% to 57%). Methane yield (mL/g VSR) Methane production rate (mL/L/d) Table 5 Bioconversion efficiency of the co-digestion process Methane Methane 605 mL/g VSR yield production 564 mL/g VSR (mL/g VSR) rate (mL/L/d) 526 mL/g VSR R1 504 279 R2 515 402 R3 526 804 10

 Introduction  Materials and Method  Results and Discussion  Conclusion  Solid Retention Time (SRTs) Volatile solid reduction (%) Methane content (%) 70 60 Methane content (%) 50 SRT_5d SRT_10d 40 SRT_15d SRT_25d 30 20 10 0 6 12 18 24 30 36 42 48 54 60 66 Digestion day (d) Methane yield (mL/g VSR)  Longer SRT corresponded with higher VSR 900 (from 32% to 47%). 800  methane yield (mL/gVSR) Methane content decreased significantly at short 700 SRT conditions (5 d, 10 d and 15 d) and kept at Theoretical methane yield=571 mL/g VSR a stable level during the whole fermentation 600 process at SRT of 25 days. 500  Methane yield decreased more quickly along 400 with shorter SRT conditions (SRT of 5, 10 and 15 days). 300  At SRT of 25 days, the methane yield kept 200 stable during the whole digestion process.  The highest methane yield (547 mL/g VSR) was 100 obtained in R4 with SRT of 25 days. 0 6 12 18 24 30 36 42 48 54 60 66 11 Digestion day (d)

 Introduction  Materials and Method  Results and Discussion  Conclusion  Solid Retention Time (SRTs) pH Methane production rate (mL/L/d) Methane production rate (mL/L/d) 7.5 700 600 SRT_5d 7.0 SRT_10d 500 SRT_15d 6.5 SRT_25d 400 6.0 pH 300 5.5 200 5.0 100 4.5 0 6 12 18 24 30 36 42 48 54 60 66 6 12 18 24 30 36 42 48 54 60 66 Digestion day (d) Digestion day (d) Total organic carbon (mg/L) 8000 Total organic carbon (mg/L)  The methane production rate (MPR) kept stable in 7000 R4 (289 mL/L/d) with SRT of 25 days and shorter 6000 SRT conditions led sharper MPR decrease. 5000  Along with the pH drop, methane production 4000 decreased significantly and kept in low level (less 3000 than 100 mL/L/d). 2000 1000 6 12 18 24 30 36 42 48 54 60 66 12 Digestion day (d)

 Introduction  Materials and Method  Results and Discussion  Conclusion  FW composition R1 _ boiled meat R5 _ soup slag R4 _ fresh meat R2 _ herbal tea R3 _ canteen leftover Table 8 Food waste composition in collected real food waste 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%  The FW composition fed in R2 was similar with the artificial FW synthesized based on food consumption pattern in Hong Kong. 13

 Introduction  Materials and Method  Results and Discussion  Conclusion R1 _ boiled meat Carbohydrate protein lipid R5 _ soup slag 100% 80% R2 _ herbal tea R4 _ fresh meat 60% 40% 20% 0% R3 _ canteen leftover R1 R2 R3 R4 R5 R6 Ammonium nitrogen concentration (mg/L)  The highest protein content were detected in the FW fed to R4 and R5 and the NH 4 + -N after digestion was corresponded with the protein content in the feed (FW). 14