Frankie T.K. LAU, Senior Chemist Drainage Services Department Smart - - PowerPoint PPT Presentation

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Frankie T.K. LAU, Senior Chemist Drainage Services Department Smart - - PowerPoint PPT Presentation

Nov 23, 2022 151 likes •522 views

Frankie T.K. LAU, Senior Chemist Drainage Services Department Smart City Innovative Wastewater Management 5 Dec 2018 DSD R&D Forum 2018 Current anaerobic digestion & biogas use in DSD Other renewable energy in DSD DSD

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Frankie T.K. LAU, Senior Chemist Drainage Services Department

Smart City ∙ Innovative Wastewater Management DSD R&D Forum 2018

5 Dec 2018

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 Current anaerobic digestion & biogas use in DSD  Other renewable energy in DSD  DSD R&D – pretreatment for anaerobic digestion

(2 studies)

 DSD R&D on other Renewable Energy (RE)  Future – Shek Wu Hui Effluent Polishing Plant

(SWHEPP) & Tai Po Sewage Treatment Works (TPSTW)

2 Anaerobic Digestion and Renewable Energy Generation in DSD

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 Chemical energy in wastewater = 12-15 MJ/kg COD  Energy-nutrient-water nexus

3 Anaerobic Digestion and Renewable Energy Generation in DSD

Source: WERF (2011)

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 Energy-neutral wastewater treatment plant (WWTP)  Renewable Energy (RE)

  • Anaerobic sludge digestion
  • Other RE

 Energy efficiency (EE)

  • Energy-efficient equipment
  • Process selection

4 Anaerobic Digestion and Renewable Energy Generation in DSD

biogas WWTP Other REs Electr tricity ty external

  • rganic
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SLIDE 5

 Biogas is ~65% CH4  Digester biogas use in China and in India

5 Anaerobic Digestion and Renewable Energy Generation in DSD

Effluent port Influent port

Source: J. Joseph. India

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 Anaerobic Digestion

  • Sludge stabilization
  • Sludge reduction
  • Biogas production

6 Anaerobic Digestion and Renewable Energy Generation in DSD

Sha Tin STW

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 Biogas is clean and renewable

  • Combustion for Heat
  • Convert to Electricity

7 Anaerobic Digestion and Renewable Energy Generation in DSD

digestate

Source: American Biogas Council

 Generated equivalent

energy >27 million kWh in 2017-18

  • Reduced 18,900 t CO2e emission
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SLIDE 8

 Number of generators

8 Anaerobic Digestion and Renewable Energy Generation in DSD SWHSTW: Sheu Wu Hui STW STSTW: Sha Tin STW YLSTW: Yuen Long STW TPSTW: Tai Po STW

CHP generator at Shek Wu Hui STW Micro-turbine at Sha Tin STW Micro-turbine at Yuen Long STW CHP generator at Sha Tin STW

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9 Anaerobic Digestion and Renewable Energy Generation in DSD

5365 kW 4765 kW 330 kW

To be commissioned in 2020 To be commissioned in 2019

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 PV (Photovoltaic Panel) at Siu Ho

Wan STW

  • Largest PV system in HK (1,100 kW)
  • Generate as much as 1.1 million

kWh/yr

10 Anaerobic Digestion and Renewable Energy Generation in DSD

Solar Farm at Siu Ho Wan STW

 PV systems in other facilities

  • Total capacity: 292 kW
  • Generate as much as 0.27 million kWh/yr

Commissioned in Dec 2016

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SLIDE 11

Trial Co-digestion Process

(To be commissioned in 2019,2021)

Food Waste Sewage sludge Anaerobic Digestion

Combined Heat and Power Generator

RE contribution: 27M kWh/yr

(9% of DSD’s energy use)

Power Grid

Air Blower

PV System

Generate More Renewable Energy

Anaerobic Digestion and Renewable Energy Generation in DSD 11

1 2 3

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12 Anaerobic Digestion and Renewable Energy Generation in DSD

Bench-scale study

  • f anaerobic sludge

digestion Study on Anaerobic digestion of CEPT sludge and metagenomics analysis of digester sludge Operating conditions

  • f food waste :

sewage sludge co-digestion Application of Ultrasound pretreatment for anaerobic digestion Pilot study on using Nitrous Acid enhancement of biogas production in YLSTW

Source: USGS

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  • Lab anaerobic digestion experiments

 Lab Digestion in-house  CEPT sludge digestion Prof T. ZHANG, HKU

  • Sludge Pre-treatment technologies

 Ultrasound Ultrawaves, Germany  Free nitrous acid (FNA) Kingsford/ Univ. Queensland, Australia

  • Food-waste: sewage sludge co-digestion

 Lab digestion of co-dig Prof T. ZHANG, HKU

13 Anaerobic Digestion and Renewable Energy Generation in DSD

Source: USGS

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 Digester Operation

  • HRT, Organic Loading, Temp, pH,

(FeCl3 dosing)

 Volatile Solids Reduction (VSR)

= VSIN – VSOUT

 Biogas production

  • Specific biogas production

14 Anaerobic Digestion and Renewable Energy Generation in DSD

Source: American Biogas Council

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Study 1 Ultrasound pretreatment Study 2 Free Nitrous Acid (FNA) pretreatment Other studies DSD R&D on Use of Biogas & Generation of other RE

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 Cell lysis is the rate limiting step

  • Thickened surplus activated sludge (TSAS)

/ biomass

 Sludge Pretreatment

  • Weaken cell walls
  • r
  • Break cells (lysis)

16 Anaerobic Digestion and Renewable Energy Generation in DSD

Cell

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 Principles of Ultrasound

  • Prof Uwe NEIS,

Hamburg Univ. of Tech.

  • Sonication of sewage sludge:

weaken eakens cell wall

  • 20 kHz
  • Typical: sonicate 1/3 of TSAS

17 Anaerobic Digestion and Renewable Energy Generation in DSD

bacteria inert particles extracellular polymers sludge floc sludge water bacteria inert particles extracellular polymers sludge floc sludge floc sludge water sludge water sludge water

Source: Ultrawaves GmbH

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 Pilot test

  • Shek Wu Hui STW, using one 5 kW sonicator (20 kHz)
  • Sonicate TSAS (12%)

18 Anaerobic Digestion and Renewable Energy Generation in DSD

Feed = centrifuge TSAS

Sonicator: 5 oscillating units

Source: Ultrawaves GmbH

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 Ultrasound (US) Pilot test results

  • %VSR (%volatile solids reduction)
  • Biogas production

19 Anaerobic Digestion and Renewable Energy Generation in DSD

+Biogas probably too high TEST

TEST

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 Prof T. ZHANG, HKU  Laboratory sonication (20 kHz)

  • TSAS of SWHSTW, at 4.5 kWh/m3 dose

 4 Lab digesters

  • 2 Contro

rol

  • Test1

t1

 12% TSAS treated

  • Test2

t2

 18% TSAS treated

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Source: Prof T. ZHANG, HKU

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 Laboratory test results

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Cumulative biogas production

+11% Biogas

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 Pilot test showed improvement in biogas production  Lab test (at same ultrasound power) co

confirme firmed

 Cost-effectiveness

  • 1 unit; Based on 10%

0% improvement of biogas production

  • Net saving $134,000/yr

($328 biogas to elec - $194K O&M)

 Relatively low-cost & easy installation

  • Useful for a small improvement in digestion

22 Anaerobic Digestion and Renewable Energy Generation in DSD

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 Principles

  • Prof Z.G. YUAN, AWMC / Univ Queensland
  • Slow hydrolysis rate of TSAS
  • FNA – cell lysis & enhance biodegradability

 Pilot-trial at Yuen Long STW

  • One digester as TEST (= receiving most feed)

23 Anaerobic Digestion and Renewable Energy Generation in DSD

Source: Prof Z.G. YUAN, AWMC

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 Pilot test

  • Yuen Long STW

 Add 2 dosing systems for nitrite & for acid  Modify consolidation tank

  • Digester HRT at 12d

2d (one digester)

  • Dosing of NaNO2 and HCl

 Add to TSAS  >250 mgNO2N/L  pH ~5.5

24 Anaerobic Digestion and Renewable Energy Generation in DSD

Source: DSD R&D Study Report – RD2100

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25 Anaerobic Digestion and Renewable Energy Generation in DSD

Description Test Period (1 Apr – 12 Jul 2017) Control Period (1 Aug – 31 Oct 17) Feed TPS Volume (m3/day) 160 160 Feed TSAS Volume (m3/day) 80 80 HRT (days) 12 12 SCOD Loading (kg/day) 190 84 Hydrolysis Rate (kgSCOD/kgVS) 0.12 0.07 TSAS TKN Loading (kg/day) 2,396 2,678 VFA of Digested Sludge (mg/L) 256 269 Total VSS Loading (kgVSS/day) 2,793 3,992 Total VSS Destroyed (kgVSS/day) 1,329 1,709 Biogas Production (m3/day) 1,254 1,479 VS Reduction (%) 48 43 Specific Biogas Production (m3/kgVSSdestroyed) 0.94 0.86

+12% +9%

TEST

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 FNA pretreatment enhanced digestion at YLSTW

  • %VSR

43%  48%

  • Sp.biogas production

0.86  0.94 m3/kg VSdestroyed

 Combined improvement +21%

21%

  • short HRT 12d

26 Anaerobic Digestion and Renewable Energy Generation in DSD

+21% Biogas

+12% +9%

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 Cost effectiveness @YLSTW – 12d HRT operation

  • Saving ~HK$62,000/yr

(= $249K electricity - $187K chemical)

 if digesting TSAS only  in other STWs with higher biogas production (baseline)  Prof YUAN proposed biological nitrite production

  • High Ammonia (reject liquor)  nitrite

 ~90% nitritation in SBR (at short SRT)

  • Incentives:

 Reduced chemical cost  Reduced ammonia loading to sewage treatment process

27 Anaerobic Digestion and Renewable Energy Generation in DSD

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 Biogas-fueled Fuel Cell

  • Prof T.S.ZHAO, HKUST
  • Using Lab-scale Solid Oxide Fuel Cell, at high temperature

 Calculated elec.efficiency > CHP  Tri-generation

  • Prof H.X.YANG, PolyU
  • Combined cooling

ng, heat and power system

  • Adsorption chiller installed at Sha Tin STW
  • For cooling of biogas entering CHP

28 Anaerobic Digestion and Renewable Energy Generation in DSD

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 Thin-film solar panel in STWs

  • Installed at two STWs
  • 3 technologies (CdTe, a-Si, CIGS)
  • 3 manufactories
  • 3 angles (0 deg, 22

22 deg, 90 deg)

29 Anaerobic Digestion and Renewable Energy Generation in DSD

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 Upgrade of Shek Wu Hui STW

  • Small footprint to treat sewage 190,000 m3/d

 External sludge load from other plants  Probable FW:SS co-digestion

  • Not enough

gh Digester Volume for conventional digestion

 Consider Thermal Hydrolysis Process (THP)

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SWHEPP

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SLIDE 31
  • Characteristics of Thermal hydrolysis process (THP)

 Pressure-cook at 165oC for 20-30 min  Thick cken SAS+PS up to 1 16% (before THP)

  • Various drivers to adopt THP

 Footprint nt /  digester volume  Class A Biosolids; fertilizer  More Biogas  Better sludge reduction  Sludge dewaterability

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Reactor 165oC

20-30min

steam Highly Thickened sludge Digester

Thermal energy

Hydrolyzed sludge

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 Tai Po STW

50t trial scheme in 2019

 Sha Tin STW

50t pilot trial in 2021

 Tai Po STW

more FW:SS co-dig?

 Yuen Long EPP

new co-dig?

 Shek Wu Hui EPP

new co-dig?

Anaerobic Digestion and Renewable Energy Generation in DSD

Tai Po STW trial Sha Tin STW trial

Proposed FW pretreatment

Primary settling tanks

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 Tai Po STW – pilot scale FW:SS co-digestion in 2019

  • 50t FW
  • Modify 2 digesters for pilot trial

 More FW to Tai Po STW

  • What if more FW for co-dig?

 Sha Tin STW to Cavern project

  • No digester

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digester

Sha Tin Cavern sewage sludge TPSTW sewage sludge Food-waste

CHP

(or other uses)

Digestate

  • dewatering (sludge quantity)
  • N loading (impact on sewage treatment)

Tai Po STW

FW:SS ratio !!

Food-waste

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 In WWTP, improve biogas production & anaerobic

digestion

 Sludge pretreatment to enhance digestion  Improve primary settling (primary sludge)  Consider food waste co-digestion  Export sewage sludge if local digestion is

impossible

 Better use of Biogas generated  Explore other Renewable Energy sources

34 Anaerobic Digestion and Renewable Energy Generation in DSD

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Anaerobic Digestion and Renewable Energy Generation in DSD

Thank You

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