Relationships between the composition of sludge and performance of anaerobic digesters Patrick Lee, PhD Assistant Professor School of Energy and Environment City University of Hong Kong 11 November 2015 DSD R&D Forum 2015, Session 1: Wastewater Management 1
An importance source of renewable energy Bioenergy generation and projection by region International Energy Agency (2013) 2
A growing trend worldwide to utilize biogas An important source of renewable energy Production http://newenergynews.blogspot.hk/2012/06/quick-news-june-26-first-solar-plant-ok.html 3 http://www.scielo.br/img/revistas/ambiagua/v9n2/a02fig01.jpg
Feedstocks: Wastewater and sludge China: In 2012, generated >68.5 billion metric tons of wastewater; by 2015 expected to rise to 78.4 billion metric tons The amount of sewage sludge would increase accordingly, from 30 million metric tons (at a moisture content of 80%) in 2012 to 34 million metric tons in 2015 4 Ref: Feng et al, ES&T, 2015
Feedstocks: Wastewater and sludge USA: In 2014, 14,780 municipal WWTP, treating an average wastewater flow of 3,785m 3 /day About 6.5 million metric tons (dry weight) of sewage sludge are generated annually Municipal wastewater treatment accounts ~3 to 4% of USA’s electrical demand, adding 21 million metric tons of GHG emission 5 Ref: Shen et al, Renew Sust Energ Rev, 2015
Energy content in wastewater and sludge 1MGD wastewater equates 26 kW of electric capacity Sludge energy content = 8000 Btu/dry lb Enough to support ~0.5% of USA total energy consumption per year Going from net consumer to producer 6 Ref: Shen et al, Renew Sust Energ Rev, 2015
AD operation in WWTPs in USA Operating temperature Biogas utilization CHP technologies 92% mesophilic 70% utilized ~23% applied 7 Ref: Shen et al, Renew Sust Energ Rev, 2015
Utilization consideration: Wastewater and sludge Feedstocks Usage for AD Primary & secondary sludge from WWTP Organic waste (e.g. agriculture waste, manure, food waste) High-strength industrial wastewater Low-strength ? municipal wastewater 8
AD of municipal wastewater Challenges: Low organic concentrations (500 mg COD/L) Low temperature Retaining biomass May not yield effluent that meets discharge standard (require extra polishing) Demonstration: Anaerobic fluidized membrane reactor with GAC as support Achieved 99% removal of COD < 1 mg/L of suspended solids It’s possible but not conventional aerobic systems 9 Ref: McCarty et al, ES&T, 2015
AD of municipal wastewater: Benefits Methane yield: Enhanced Sludge yield: Reduced Energy yield: Enhanced 10 Ref: McCarty et al, ES&T, 2015
Going forward Research need: In order to increase efficiency , reliability and robustness of AD, need to understand the microorganisms (or the engines) that drive the process in conjunction with engineering process design 11
Anaerobic digestion: A black box ? CH 4 Waste Biological, physical, chemical complexity Engineering 12
Process and microbiology are coupled Substrate A CH 4 Anaerobic digestion Dilemma Microorganisms affect the process The process affects the microorganisms Metabolic interactions 13 Ref: Sales and Lee, Curr. Opin. Biotechnol., 2015
Process and microbiology are coupled A dynamic system Substrate A CH 4 Anaerobic digestion Dilemma Microorganisms affect the process The process affects the microorganisms Metabolic interactions 14 Ref: Sales and Lee, Curr. Opin. Biotechnol., 2015
Process and microbiology are coupled Conc #1 Fluctuate A dynamic system High/Low #2 Occasionally high Performance? Substrate A #3 CH 4 #4 Stable Anaerobic Time digestion Dilemma Microorganisms affect the process The process affects the microorganisms Metabolic interactions 15 Ref: Sales and Lee, Curr. Opin. Biotechnol., 2015
Practical question #1 Same Influent Seed #1 Seed #2 Seed #3 Performance: the same, better or crash? 16
Practical question #2 At a later time Initially Influent “B” Influent “A” Seed #1 Seed #2 Seed #3 If suddenly switch to Influent “B”, performance the same, better or crash? 17
Question? All roads lead to Rome? That is, will the microbes find a way? 18 Ref: http://angieaway.com/wp-content/uploads/2013/03/532968_10102270976272161_2033021876_n.jpg
Practical question #1 19
Practical question #1 Same Influent Seed #1 Seed #2 Seed #3 Performance: The same or different 20
Practical question #1 Substrate Cellulose, cellulose (55 o C), xylan, xylose, foodwaste tested: Outcome: Function (i.e. methane yield), microbial community composition ??? 21
Methane yield Similar methane yield between the two seeds with the five tested substrates Ref: Wilkins and Lee et al, Front Microbiol, 2015 22
Clustering Archaea No strong clustering of the microorganisms based on substrate That is, each seed used a different population to digest the same substrate Bacteria Ref: Wilkins and Lee et al, Front Microbiol, 2015 23
Relative abundance of phyla (a) Archaeal orders (b) Bacterial phyla Wilkins and Lee et al, Front. Microbiol., 2015 24
Practical question #1 Same Influent Seed #1 Seed #2 Seed #3 Summary: Different seeds, different populations, similar functions. “Does seem more than one road leads to Rome” 25
Practical question #2 26
Practical question #2 At a later time Initially Influent “B” Influent “A” Seed #1 Seed #2 Seed #3 If suddenly switch to Influent “B”, Performance the same, better or crash? 27
Practical question #2 Seed samples collected from two AD systems Day-to-day not treating cellulose and xylan Fed with cellulose and xylan X 28 Lee et al, Unpublished data
Performance 40 A B 8.0 CH 4 SWH-C-55 35 GZ-C-35 7.5 produced 30 SWH-C-35 GZ-X-35 7.0 25 SWH-X-35 CH 4 (mL) 6.5 20 pH 15 6.0 10 Except 55 o C 5.5 5 5.0 0 4.5 -5 0 5 10 15 20 25 0 5 10 15 20 25 Duration (days) Duration (days) 6 35 D C Conc. of cellulose or xylan (g/L) Capable to digest 30 5 Conc. of acetic acid (mM) cellulose and xylan 25 4 Cellulose 20 3 15 2 10 1 5 Xylan 0 0 0 5 10 15 20 25 0 5 10 15 20 25 Duration (days) Duration (days) No significant differences in performance regardless of the origin of the seeds 29 Lee et al, Unpublished data
Seed vs. Seed The two seeds are different 30 Lee et al, Unpublished data
Seed vs. Enrichment Before Before Cellulose Xylan SWH After After Before Before Xylan Cellulose GZ After After The selected microorganisms are different from the seed 31 Lee et al, Unpublished data
The correct microbes are present The selected microorganisms have the correct functions 32 Lee et al, Unpublished data
Practical question #2 At a later time Initially Influent “B” Influent “A” Seed #1 Seed #2 Seed #3 Summary: Can select if small quantity of the right microorganisms are in the seed, but absent in the first place (e.g. 55 o C) then nothing will happen 33
Global trend 34
Many plants worldwide Operating AD in Poland http://biogazownierolnicze.pl/mapa-biogazowni Operating AD in the UK http://www.biogas-info.co.uk/resources/biogas-map/ Operating AD in the USA https://www.americanbiogascouncil.org/biogas_maps.asp 35
Many plants worldwide Operating AD in Poland Realistically, the microorganisms in all these systems CANNOT be IDENTICAL, due to differences in the influent, operating conditions (temperature, retention time, etc). At the same time, http://biogazownierolnicze.pl/mapa-biogazowni they CANNOT be all DIFFERENT, otherwise AD is not AD. Operating AD in the UK http://www.biogas-info.co.uk/resources/biogas-map/ Operating AD in the USA 36 https://www.americanbiogascouncil.org/biogas_maps.asp
Many plants worldwide Operating AD in Poland Unique Unique Shared Shared Shared Core http://biogazownierolnicze.pl/mapa-biogazowni Shared Shared Shared Shared Shared Unique Unique Operating AD in the UK http://www.biogas-info.co.uk/resources/biogas-map/ Operating AD in the USA 37 https://www.americanbiogascouncil.org/biogas_maps.asp
Analyzed 4 full-scale anaerobic digesters Focused on the methane-generating organisms Wastewater China Sludge HK 38 Ref: Wilkins and Lee et al, AEM, 2015
There are differences between the digesters mcrA 16S The freshwater sludge digesters were closely clustered and separated from the saline sludge and wastewater digesters 39 Ref: Wilkins and Lee et al, AEM, 2015
There are similarities between the digesters mcrA Hydrogenotrophic Hydrogenotrophic Acetoclastic Acetoclastic Hydrogenotrophic 16S “Methanogen” “Methanogen” The major methane-generating organisms are present; methane are produced in all systems 40 Ref: Wilkins and Lee et al, AEM, 2015
Conclusions 41
Implications: 1.) AD is vital to urbanized cities, an important source of renewable energy and for waste treatment 2.) Reliability and robustness of the process should increase as we look deeper inside the black box 42
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