Evaluation of greenhouse gas emissions from municipal UASB wastewater treatment plants

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1 Evaluation of greenhouse gas emissions from municipal UASB wastewater treatment plants Original authors: B. Heffernan, J. Blanc, H. Spanjers Jan Pereboom Biothane Systems International Tel: +31.(0)

2 Contents 1. Introduction 2. Methods 3. Carbon footprint 4. OPEX 5. Conclusions 2

3 1 Introduction

4 Municipal UASB reactor Influent distribution box Gashood Effluent collection Gas Deflector Sludge blanket Sludge withdrawal pipe Influent distribution pipes 4

Final settler Treated water Sludge disposal Sludge thickener Anaerobic

5 Typical UASB process diagram Raw wastewater Influent pumping Coarse and fine screens Aerated grit chamber UASB reactor Activated sludge Final settler Treated water Sludge disposal Sludge thickener Anaerobic digester Centrifuge Biogas holder Biogas scrubber Biogas flare Electricity 5

COD Conversion Anaerobic vs Aerobic Heat loss Biogas 50-60 kg COD Aerobic BOD Air (O 2 ) 100 kg COD Carbon Dioxide

6 COD Conversion Anaerobic vs Aerobic Heat loss Biogas kg COD Aerobic BOD Air (O 2 ) 100 kg COD Carbon Dioxide Biomass 2-10 kg COD BOD Anaerobic (25 O C 35 O C) 100 kg COD kg COD Sludge, kg COD Sludge kg COD

7 Advantages of municipal UASB Capable of removing between 60 80% of COD, BOD and TSS Very low operational costs Low energy demand Energy production in the form of biogas Low sludge production Low or no chemical consumption Example Top view of UASB reactor Onca, Brazil 7

8 The municipal UASB market Countries with municipal UASB treatment plants North Asia North America North America Europe Middle East Central Asia South Asia East Asia South America Africa Southeast Asia Oceania Largest plant constructed to date 340 MLD (2009 India) 8

9 The municipal UASB market Countries with municipal UASB treatment plants 17% 74% 1% 1% 1% 1% 3% 2% India Brazil Mexico Columbia UAE Pakistan Honduras Indonesia Egypt Largest plant constructed to date 340 MLD (2009 India) 9

10 Dissolved methane concentration (mg/l) Dissolved methane in effluent of municipal UASBs Methane has a low solubility Dissolved Methane estimations by Henry s Law Methane conc. (70 80%); Atmospheric 1 Bar; Ambient Temperature Dissolved methane concentration as a function of temperature Temperature

11 Dissolved Methane in UASB effluents COD determines Methane in effluent Parameter Sewage Brewery Units Flow 50,000 6,000 m 3 /d COD 500 3,000 mg/l Temperature C Dissolved CH mg/l Digested COD 55% 80% mg COD/l Effluent COD 20% 15% mg COD/l Sludge COD 25% 5% mg COD/l 11

12 Dissolved Methane in UASB effluents COD determines Methane in effluent Sewage Brewery 3% 29% 71% 97% CH4 effluent CH4 gas phase CH4 effluent CH4 gas phase 12

13 Dissolved Methane in municipal UASB effluents Up to 25 40% of the produced Methane in effluent CH 4 is a potent green house gas Valuable Energy is lost 13

14 2 Methods

15 Basis for carbon footprint analysis Municipal plant for 1.0 mln population equivalents Influent characteristics Parameter Value Flow (m 3 /d) 130,000 COD (mg/l) 600 BOD 5 (mg/l) 300 TSS (mg/l) 315 NH 4 -N (mg/l) 35 Effluent requirements Parameter Value Flow (m 3 /d) - COD (mg/l) 125 BOD 5 (mg/l) 10 TSS (mg/l) 10 NH 4 -N (mg/l) 2 Design sewage temperature was 25 C 15

16 Treatment options UASB is pre-treatment Aerobic post-treatment needed to meet effluent limits 1. Primary clarification Primary clarification + activated sludge + digester 2. UASB with methane recovery UASB + activated sludge + digester 3. UASB without methane recovery UASB + activated sludge + digester 16

17 Treatment options 1. Primary clarification Primary and secondary sludge are digested anaerobic Biogas is used for energy production Screened and degritted sewage Primary clarifier Aerobic reactor Settler Biogas engine Sludge digester Dewatering unit 17

18 Treatment options 2. UASB with methane recovery UASB surplus sludge digested Methane in effluent recovered and utilised Screened and degritted sewage UASB Pre-aeration reactor Aerobic reactor Settler Biogas engine Sludge digester Combustion gas Dewatering unit 18

19 Treatment options 3. UASB without methane recovery UASB surplus sludge digested Screened and degritted sewage UASB Aerobic reactor Settler Biogas engine Sludge digester Combustion gas Dewatering unit 19

20 Emissions considered in carbon footprint Upstream activities: The electricity emissions factor is country specific The emission factor for the UAE is 0.82 kg CO 2 eq/kwh Electricity is used on site excess is sent to grid Chemical consumption (polymer) Onsite activities: Distributed CH 4 loss estimated at 1% for all three configurations Downstream Sludge disposed to landfill with no CH4 recovery 20

21 Emissions not considered in carbon footprint Upstream activities : Plant construction ; usually > 5% of emissions over lifetime CO 2 produced in the treatment process (short cycle) N 2 O emissions (Ahn et al., 2010) 21

22 Direct and avoided emissions Direct emissions are all green house gas emissions from STP: Electricity generation Chemical consumption Avoided emissions by sold by-products Excess electricity that is sold to the grid Fertilizer based on removed N+P Direct emissions are a positive number avoided are negative 22

23 3 Results

Tons CO2 eq/y GHG emissions 30,000 25,000 20,000 GHG emissions for the three configurations 15,000 10,000 22,400 25,500 5,000 0-5,000-10,000

24 Tons CO2 eq/y GHG emissions 30,000 25,000 20,000 GHG emissions for the three configurations 15,000 10,000 22,400 25,500 5, ,000-10,000 6, , Primary clarification UASB with CH4 recovery UASB without CH4 recovery UASB with CH 4 recovery has the lowest carbon footprint

25 Tons CO2 eq/y Influence of electrical emission factor 30,000 India - High carbon power (0.994 kg CO2 eq/kwh) 25,000 20,000 15,000 10,000 5, ,000-10,000 Primary clarification UASB with CH4 recovery UASB without CH4 recovery Energy Process Reagents Sludge Avoided Emissions 25

26 Tons CO2 eq/y Influence of electrical emission factor 30,000 Brazil - low carbon power (0.081 kg CO2 eq/kwh) 25,000 20,000 15,000 10,000 5, ,000 Primary clarification UASB with CH4 recovery UASB without CH4 recovery Energy Process Reagents Sludge Avoided Emissions 26

27 4 OPEX cost estimation

28 Basis for cost comparison Cost price of electricity Sales price of electricity Sludge disposal cost Polymer dosing rate Polymer cost 0.12 $/kwh 0.06 $/kwh 120 $/ton dry solids 10 kg PE/ton dry solids 4500 $/ton PE Technology Development

29 Electricity production/comsumption (kw) Energy production/consumption 3,000 2,500 2,000 1,500 1, Primary clarification UASB with CH4 recovery UASB without CH4 recovery Electricity produced Electricity consumed 29

30 OPEX (US$/yr) OPEX $3,000,000 $2,500,000 $2,390,385 $2,000,000 $1,500,000 $1,000,000 $500,000 $0 -$500,000 -$92,528 $222,833 Primary clarification UASB with CH4 recovery UASB without CH4 recovery Total Electricity cost Sludge disposal cost Polymer cost 30

31 4 Conclusions

32 Conclusions The carbon footprint of a municipal UASB is worse than a conventional aerobic treatment plant Methane recovery can make municipal UASB systems better than conventional aerobic treatment plants Sludge disposal is an important consideration for the carbon footprint of a treatment plant Methane recovery is also cost effective 32

33 Conclusions Thank you for your attention Questions 33

34 Limitations of municipal UASB COD/SO 4 ratio below 3 Organic COD is converted to inorganic COD (H 2 S) in the UASB. Strict nitrogen limits Temperature Below 15 C, the rate of anaerobic digestion is very low Methane dissolved in effluent North America UASB non-applicable UASB applicable South America Example Top view of UASB reactor Onca, Brazil 34

35 Carbon constraint Resource depletion: As fossil fuels becomes scarcer the cost of energy is likely to increase Carbon taxes/carbon credits: As temperatures rise governments are/will take action to reduce GHGs emissions 35

36 Tons CO2 eq/y Detailed GHG emissions Detailed breakdown of sources of CO 2 emissions 30,000 Primary clarification 25,000 22,370 20,000 15,000 10,000 43% 53% 5, ,000 2% 2% Energy Process Reagents Sludge Avoided Emissions 0 Total

37 Tons CO2 eq/y Detailed GHG emissions Detailed breakdown of sources of CO 2 emissions 30,000 UASB with CH4 recovery 25,000 20,000 15,000 10,000 5, % 20.5% 2% 77.5% 6,850-5,000-4,200 Energy Process Reagents Sludge Avoided Emissions Total

38 Tons CO2 eq/y Detailed GHG emissions Detailed breakdown of sources of CO 2 emissions 30,000 25,000 20,000 UASB without CH4 recovery 79% 25,450 15,000 10,000 5, % % ,000 Energy Process Reagents Sludge Avoided Emissions Total

39 kg CO2 eq/kg COD Comparison with literature results PC+AS UASBre+AS UASBno+AS Present study Keller and Hartely 39

40 Influence of electrical emission factor Countries where municipal UASBs plants are in operation North America South America Country Emission factor (kg CO 2 /kwh) Carbon power Mexico Medium Brazil Low India High Egypt Medium UAE High 40

41 Influence of electrical emission factor Electrical emission factor Varies depending on how electricity is produced Country fuel mix determines the electrical emission factor Three Electrical emission factor categories: High carbon power Medium carbon power Low carbon power 41

42 Tons CO2 eq/y Influence of electrical emission factor 30,000 Egypt - medium carbon power (0.447 kg CO2 eq/kwh) 25,000 20,000 15,000 10,000 5, ,000 Primary clarification UASB with CH4 recovery UASB without CH4 recovery Energy Process Reagents Sludge Avoided Emissions 42

43 Excess sludg production (kg TSS/d) Excess sludge production 18,000 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0 Primary clarification UASB with CH4 recovery UASB without CH4 recovery Excess sludge production 43

44 Polymer dosing (Ton/y) Polymer dosing Primary clarification UASB with CH4 recovery UASB without CH4 recovery Polymer use 44

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