WWT Wastewater conference, Birmingham, January 2020 THE INFLUENCE - PowerPoint PPT Presentation

WWT – Wastewater conference, Birmingham, January 2020 THE INFLUENCE OF INTERMEDIATE THERMAL HYDROLYSIS PROCESS (ITHP) ON THE KINETICS OF MESOPHILIC ANAEROBIC DIGESTION OF SEWAGE SLUDGE By Dr Achame Shana and Paul Fountain Thames Water Operational Excellence

Overview ◼ Introduction - Project objectives ◼ Problem definition ◼ Conventional Mesophilic Anaerobic Digestion (MAD) process – basic principles and limiting factors ◼ Thermal Hydrolysis Process ◼ Intermediate Thermal Hydrolysis Process (ITHP) and Double MAD ◼ Laboratory set up ◼ Results ◼ Conclusions 2

Project scope & objectives To assess whether the use of Thermophilic Hydrolysis process (THP) as an Intermediate technology could enhance sludge digestion process efficiency compared to standard digestion technologies Specific project objectives: • To investigate the Intermediate THP digestion process performance compared to existing technologies • To assess the sludge composition degradation kinetics • To quantify and describe the organic matter conversion rate to biogas as a consequence of the application of ITHP configuration 3

Introduction - problems The cost of sludge treatment and disposal is almost half of the operating cost of Sewage Treatment Works ( Apples et al., 2008;Spinosa et al., 2011). This cost could be offset or savings could be made by ◼ Optimising sludge treatment process ◼ Investing in novel treatment technologies ◼ Changing existing process configuration These steps could lead to more sustainable overall sludge treatment process 4

Introduction - problems ▪ In conventional sludge digestion process: the organic matter degradation efficiency during anaerobic digestion process raged from 35 - 45% ▪ A significant part ( 55 -65%) remain in the digested sludge normally recycled to land or disposed of via number of routes. ▪ About 1.4 million dry tonne of sludge was produced in the UK, of which 77% was recycled to agriculture ( water UK,, 2010). 5

Two legged Bioreactor – the substrate digestion efficiency problem starts with human food metabolism rate! Food in: Waste Out: ◼ High fibre content ◼ Rich in Fibre (carbohydrate) (carbohydrate) ◼ Protein ◼ Protein ◼ Fat ◼ Fat ◼ Minerals ◼ Minerals Waste full of energy sent to Sewage treatment Works 6

Wastewater and treatment process 7

Introduction – sludge cake ( residual solids from wastewater treatment- our feedstock) 8

Single stage conventional Mesophilic Anaerobic Digestion (MAD) Process - Problem Electricity generation Biogas SAS Methane Mixed feed Final product Products Hydrolysis (Digested or Acids Primary Stabilised sludge) Catalys ts Reactants - food Hydrolysis, acid generation and methanogenesis taking place in a single tank (digester), the system is not efficient 9

Simplified mass balance of 100 kg sludge digestion and transformation process Volatile Solids Inert Solids 70 kg 30 kg Biogas Volatile Solids Inert Solids CH 4 +CO 2 30 kg 30 kg 40 kg Digested Sludge Biogas 60 kg CH 4 +CO 2 50% Volatile Solids 40 kg 10

Description of sludge make (substrate)

Thermal Hydrolysis Process (THP) 12

Full scale Plant at Chertsey STWs in Thames Treatment capacity: 8000 Tonnes of dry solids sludge per year 13

Sludge pre-treated at Chertsey STWs in Thames Sludge cake, hydrolysed sludge and digested sludge respectively 14

Introduction Some basic initial points: Thermal Hydrolysis Process Mesophilic Anaerobic Digestion ( THP ) ( MAD ) • improves SAS / combined sludge digestion in • efficient process for primary sludge MAD process • improves ultimate dewatering ability of digested • less efficient process for SAS sludge • limitations on final dewatering ability • does not discriminate between easily digestible of digested sludge sludge and difficult to digest sludge • Often struggles to produce • high consumption of energy, needed to heat bacteriologically compliant product in digester feed to 170 deg C own right 15

Intermediate Thermal Hydrolysis Process (I-THP) – An Improved configuration 16

Introduction Some basic initial points: Intermediate Thermal Hydrolysis Process ( ITHP ) • Stage one softens the hard to digest sludge organic matter, after thermal hydrolysis many of these will digest in stage two • Greater digestion of organic matter to biogas = higher energy production and lower mass to recycle to agriculture • Improves ultimate dewatering ability of digested sludge due to enhanced organic matter breakdown and reduction • Less energy consumption than conventional THP due to mass reduction in stage one digestion • Produces a Class A compliant sludge as conventional THP 17

Laboratory Scale testing Control Conventional MAD I-THP Control Double MAD 18

Experiments In order to assess the performance of ITHP (MAD+THP+MAD), THP (THP+MAD) and MAD configurations, the following Facilities were used: Laboratory scale digestion rig set up Laboratory scale THP reactor 19

Performance Results – Volatile Solid in the feed 20

Performance Results – digested sludge volatile Solid 21

Results – Volatile Solids Destruction (%) Digester volatile solid reduction in all the digestion configurations investigated 75 Digester volatile reduction (%) 70 65 60 55 50 45 40 35 30 25 20 15 Week1 Week2 Week3 Week4 Week5 Week6 Week7 Week8 Week9 Week10 Week11 Week12 Week13 Week14 Week15 Week16 Week17 Week18 Week19 Week20 Week21 Week22 Week23 Week24 Week25 Week26 Week27 Week28 Week29 Week30 Week31 Week32 Week33 Week34 Week35 Week36 Week37 Week38 Week39 Week40 Calendar week CMAD Double MAD ITHP THP 22

Results – Biogas Yield 550 500 Biogas yield (m3/TDS) 450 400 350 300 250 200 Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9 Week 10 Week 11 Week 12 Week 13 Week 14 Week 15 Week 16 Week 17 Week 18 Week 19 Week 20 Week 21 Week 22 Week 23 Week 24 Week 25 Week 26 Week 27 Week 28 Week 29 Week 30 Week 31 Week 32 Week 33 Week 34 Week 35 Week 36 Week 37 Week 38 Week 39 Week 40 Calendar Weeks Con MAD-contrl Gas production (m3/TDS) Double dig contrl MAD Gas production from Double MAD plus full-scale CMAD (m3/TDS) THP Gas production (m3/TDS) ITHP Gas production (m3/TDS) from ITHP plus full-scale CMAD 23

Results – Pathogen count Pathogen count ( log 10/gram dry solid) in all the digestion configuration studed in comparison to digester feed pathogen content E.coli log count (log10/gram dry solid) 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 Week 1 Week 4 Week 8 Week 13 Week 17 Week 21 Week 25 Week 29 Week 33 Week 34 Week 35 Week 36 Week 37 Week 38 Week 39 Week 40 Calendar week Raw Feed E.coli LOG DRY (LOG10/gram dry solid) THP E.coli LOG DRY (LOG10/gram dry solid) ITHP E.coli LOG DRY (LOG10/gram dry solid) Double MAD E.coli LOG DRY (LOG10/gram dry solid) Con MAD E.coli LOG DRY (LOG10/gram dry solid) 24

Results – Sludge cake Dry Solids (%) Piston press simulation of Belt press 25

Results – Polymer dose rate (kg/TDS) 26

Laboratory scale batch digestion testing - extent of sludge constituents degrade – HRT matters THP control I-THP 27

Laboratory scale batch digestion testing 28

Sludge carbohydrate degradation Carbohydrate degradation during Batch digestion 10 day HRT Total Carbohydrate conentration ITHP 1,400.0 Measured 1,200.0 12 day HRT 1,000.0 15 day HRT ITHP (mg/l) 800.0 Modelled 600.0 400.0 THP Measured 200.0 0.0 0 50 100 150 200 250 300 350 400 THP Modelled t (hr) Modelled values calculated from measured value by first calculating the slope and intercept from the regression equation. Then using the slope, intercept and corresponding time span, the modelled substrate concentration was calculated i.e. C t = EXP( slope*t + intercept) 29

Sludge protein degradation Protein degradation during Batch digestion 10 day HRT ITHP Measured Total Protein conentration 1,200.00 12 day HRT 1,000.00 15 day HRT ITHP 800.00 Modelled (mg/l) 600.00 400.00 THP Measured 200.00 0.00 0 50 100 150 200 250 300 350 400 THP Modelled t (hr) 30

Sludge lipid degradation Fat degradation during Batch digestion 10 day HRT ITHP 700 Measured Total Fat conentration (mg/l) 12 day HRT 600 15 day HRT 500 ITHP 400 Modelled 300 200 THP 100 Measured 0 0 50 100 150 200 250 300 350 400 THP Modelled t (hr) 31

Conclusions The use of THP as an intermediate technology enhanced the sludge digestion process efficiency compared with existing digestion technologies 1. The ITHP process showed improved overall organic matter degradation process due to additional, extended digestion process it allows 2. The use of THP as an intermediate thermal hydrolysis process (ITHP) configuration offers significant advantages over existing conventional technologies in terms of overall anaerobic digestion process efficiency. The ITHP configuration enhanced sludge volatile solid reduction and produced correspondingly higher biogas yield and enhanced sludge dewaterability. 3. The ITHP configuration provided compliant sludge that meets Class A sludge recycling to Agricultural land regulation. 32

Thank you for listening! Any questions? 33