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

WWT – Wastewater conference, Birmingham, January 2020

Thames Water Operational Excellence

By Dr Achame Shana and Paul Fountain THE INFLUENCE OF INTERMEDIATE THERMAL HYDROLYSIS PROCESS (ITHP) ON THE KINETICS OF MESOPHILIC ANAEROBIC DIGESTION OF SEWAGE SLUDGE

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Overview

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Introduction

• Project objectives

◼

Problem definition

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Conventional Mesophilic Anaerobic Digestion (MAD) process – basic principles and limiting factors

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Thermal Hydrolysis Process

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Intermediate Thermal Hydrolysis Process (ITHP) and Double MAD

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Laboratory set up

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Results

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Conclusions

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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

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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

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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).

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Two legged Bioreactor – the substrate digestion efficiency problem starts with human food metabolism rate!

Food in:

◼High fibre content

(carbohydrate)

◼Protein ◼Fat ◼Minerals

Waste Out:

◼Rich in Fibre

(carbohydrate)

◼Protein ◼Fat ◼Minerals

Waste full of energy sent to Sewage treatment Works

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Wastewater and treatment process

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Introduction – sludge cake (residual solids

from wastewater treatment- our feedstock)

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Single stage conventional Mesophilic Anaerobic Digestion (MAD) Process - Problem

Biogas

Hydrolysis

Acids Methane

Primary SAS Electricity generation

Mixed feed

Hydrolysis, acid generation and methanogenesis taking place in a single tank (digester), the system is not efficient Final product (Digested or Stabilised sludge)

Reactants - food Catalysts

Products

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Simplified mass balance of 100 kg sludge digestion and transformation process

Inert Solids 30 kg Volatile Solids 70 kg Volatile Solids 30 kg Inert Solids 30 kg Digested Sludge 60 kg 50% Volatile Solids Biogas CH4+CO2 40 kg Biogas CH4+CO2 40 kg

Description of sludge make (substrate)

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Thermal Hydrolysis Process (THP)

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Full scale Plant at Chertsey STWs in Thames

Treatment capacity: 8000 Tonnes of dry solids sludge per year

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Sludge pre-treated at Chertsey STWs in Thames

Sludge cake, hydrolysed sludge and digested sludge respectively

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Introduction

Mesophilic Anaerobic Digestion ( MAD )

• efficient process for primary sludge
• less efficient process for SAS
• limitations on final dewatering ability
• f digested sludge
• Often struggles to produce

bacteriologically compliant product in

• wn right

Thermal Hydrolysis Process ( THP )

• improves SAS / combined sludge digestion in

MAD process

• improves ultimate dewatering ability of digested

sludge

• does not discriminate between easily digestible

sludge and difficult to digest sludge

• high consumption of energy, needed to heat

digester feed to 170 deg C

Some basic initial points:

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

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Introduction

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
• rganic 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

Some basic initial points:

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Laboratory Scale testing

I-THP Control Double MAD Control Conventional MAD

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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 THP reactor Laboratory scale digestion rig set up

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Performance Results – Volatile Solid in the feed

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Performance Results – digested sludge volatile Solid

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Results – Volatile Solids Destruction (%)

15 20 25 30 35 40 45 50 55 60 65 70 75 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 CMAD Double MAD ITHP THP

Calendar week Digester volatile reduction (%)

Digester volatile solid reduction in all the digestion configurations investigated

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Results – Biogas Yield

200 250 300 350 400 450 500 550

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

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

Biogas yield (m3/TDS)

Calendar Weeks

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Results – Pathogen count

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 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 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) E.coli log count (log10/gram dry solid)

Pathogen count ( log 10/gram dry solid) in all the digestion configuration studed in comparison to digester feed pathogen content

Calendar week

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

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Results – Polymer dose rate (kg/TDS)

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Laboratory scale batch digestion testing - extent of sludge constituents degrade – HRT matters

I-THP THP control

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Laboratory scale batch digestion testing

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Sludge carbohydrate degradation

Carbohydrate degradation during Batch digestion 0.0 200.0 400.0 600.0 800.0 1,000.0 1,200.0 1,400.0 50 100 150 200 250 300 350 400 t (hr) Total Carbohydrate conentration (mg/l) ITHP Measured ITHP Modelled THP Measured THP Modelled

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. Ct = EXP( slope*t + intercept) 10 day HRT 12 day HRT 15 day HRT

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Sludge protein degradation

Protein degradation during Batch digestion 0.00 200.00 400.00 600.00 800.00 1,000.00 1,200.00 50 100 150 200 250 300 350 400 t (hr) Total Protein conentration (mg/l) ITHP Measured ITHP Modelled THP Measured THP Modelled

10 day HRT 12 day HRT 15 day HRT

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Sludge lipid degradation

Fat degradation during Batch digestion 100 200 300 400 500 600 700 50 100 150 200 250 300 350 400 t (hr) Total Fat conentration (mg/l) ITHP Measured ITHP Modelled THP Measured THP Modelled

10 day HRT 12 day HRT 15 day HRT

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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

• ffers

significant advantages

• ver

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.

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Thank you for listening!

Any questions?