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

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


  1. Frankie T.K. LAU, Senior Chemist Drainage Services Department Smart City ∙ Innovative Wastewater Management 5 Dec 2018 DSD R&D Forum 2018

  2.  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) Anaerobic Digestion and Renewable Energy Generation in DSD 2

  3.  Chemical energy in wastewater = 12-15 MJ/kg COD  Energy-nutrient-water nexus Source: WERF (2011) Anaerobic Digestion and Renewable Energy Generation in DSD 3

  4.  Energy-neutral wastewater treatment plant (WWTP)  Renewable Energy (RE) external ◦ Anaerobic sludge digestion organic ◦ Other RE WWTP  Energy efficiency (EE) biogas ◦ Energy-efficient equipment Electr tricity ty ◦ Process selection Other REs Anaerobic Digestion and Renewable Energy Generation in DSD 4

  5.  Biogas is ~65% CH 4  Digester biogas use in China and in India Influent port Effluent port Source: J. Joseph. India Anaerobic Digestion and Renewable Energy Generation in DSD 5

  6.  Anaerobic Digestion ◦ Sludge stabilization ◦ Sludge reduction Sha Tin STW ◦ Biogas production Anaerobic Digestion and Renewable Energy Generation in DSD 6

  7.  Biogas is clean and renewable ◦ Combustion for Heat ◦ Convert to Electricity digestate  Generated equivalent Source: American Biogas Council energy >27 million kWh in 2017-18 ◦ Reduced 18,900 t CO 2 e emission Anaerobic Digestion and Renewable Energy Generation in DSD 7

  8.  Number of generators CHP generator at Sha Tin STW CHP generator at Shek Wu Hui STW Micro-turbine at Sha Tin STW SWHSTW: Sheu Wu Hui STW STSTW: Sha Tin STW YLSTW: Yuen Long STW Micro-turbine at Yuen Long TPSTW: Tai Po STW STW Anaerobic Digestion and Renewable Energy Generation in DSD 8

  9. 5365 kW To be commissioned 4765 kW in 2020 To be commissioned in 2019 330 kW Anaerobic Digestion and Renewable Energy Generation in DSD 9

  10. Commissioned  PV (Photovoltaic Panel) at Siu Ho in Dec 2016 Wan STW ◦ Largest PV system in HK (1,100 kW) ◦ Generate as much as 1.1 million kWh/yr  PV systems in other facilities Solar Farm at Siu Ho Wan STW ◦ Total capacity: 292 kW ◦ Generate as much as 0.27 million kWh/yr Anaerobic Digestion and Renewable Energy Generation in DSD 10

  11. Generate More Renewable Energy 1 2 Sewage sludge Anaerobic Digestion Trial Co-digestion Process PV System (To be commissioned in 2019,2021) 3 Power Grid Food Waste RE contribution:  27M kWh/yr Combined Heat and Power (9% of DSD’s energy use) Generator Air Blower Anaerobic Digestion and Renewable Energy Generation in DSD 11

  12. Operating conditions of food waste : sewage sludge co-digestion Study on Anaerobic Application of digestion of CEPT Bench-scale study Ultrasound sludge and of anaerobic sludge pretreatment for metagenomics digestion anaerobic digestion analysis of digester sludge Pilot study on using Nitrous Acid enhancement of biogas production in YLSTW Source: USGS Anaerobic Digestion and Renewable Energy Generation in DSD 12

  13. ◦ 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 Source: USGS Anaerobic Digestion and Renewable Energy Generation in DSD 13

  14.  Digester Operation ◦ HRT, Organic Loading, Temp, pH, (FeCl 3 dosing)  Volatile Solids Reduction (VSR) = VS IN – VS OUT  Biogas production ◦ Specific biogas production Source: American Biogas Council Anaerobic Digestion and Renewable Energy Generation in DSD 14

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

  16.  Cell lysis is the rate limiting step Cell ◦ Thickened surplus activated sludge (TSAS) / biomass  Sludge Pretreatment ◦ Weaken cell walls or ◦ Break cells (lysis) Anaerobic Digestion and Renewable Energy Generation in DSD 16

  17.  Principles of Ultrasound sludge floc sludge floc sludge floc sludge water sludge water sludge water sludge water ◦ Prof Uwe NEIS, Hamburg Univ. of Tech. ◦ Sonication of sewage sludge: weaken eakens cell wall ◦ 20 kHz bacteria bacteria inert particles inert particles extracellular polymers extracellular polymers Source: Ultrawaves GmbH ◦ Typical: sonicate 1 / 3 of TSAS Anaerobic Digestion and Renewable Energy Generation in DSD 17

  18.  Pilot test ◦ Shek Wu Hui STW, using one 5 kW sonicator (20 kHz) ◦ Sonicate TSAS (12%) Feed = centrifuge TSAS Sonicator: 5 oscillating units Source: Ultrawaves GmbH Anaerobic Digestion and Renewable Energy Generation in DSD 18

  19.  Ultrasound (US) Pilot test results ◦ %VSR (%volatile solids reduction) ◦ Biogas production TEST +Biogas TEST probably too high Anaerobic Digestion and Renewable Energy Generation in DSD 19

  20.  Prof T. ZHANG, HKU  Laboratory sonication (20 kHz) ◦ TSAS of SWHSTW, at 4.5 kWh/m 3 dose  4 Lab digesters ◦ 2 Contro rol ◦ Test1 t1  12% TSAS treated ◦ Test2 t2  18% TSAS treated Source: Prof T. ZHANG, HKU Anaerobic Digestion and Renewable Energy Generation in DSD 20

  21.  Laboratory test results +11% Biogas Cumulative biogas production Anaerobic Digestion and Renewable Energy Generation in DSD 21

  22.  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 Anaerobic Digestion and Renewable Energy Generation in DSD 22

  23.  Principles ◦ Prof Z.G. YUAN, AWMC / Univ Queensland ◦ Slow hydrolysis rate of TSAS ◦ FNA – cell lysis & enhance biodegradability Source: Prof Z.G. YUAN, AWMC  Pilot-trial at Yuen Long STW ◦ One digester as TEST (= receiving most feed) Anaerobic Digestion and Renewable Energy Generation in DSD 23

  24.  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 NaNO 2 and HCl  Add to TSAS  >250 mgNO 2 N/L  pH ~5.5 Source: DSD R&D Study Report – RD2100 Anaerobic Digestion and Renewable Energy Generation in DSD 24

  25. TEST Test Period Control Period Description (1 Apr – 12 Jul 2017) (1 Aug – 31 Oct 17) Feed TPS Volume (m 3 /day) 160 160 Feed TSAS Volume (m 3 /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 (m 3 /day) 1,254 1,479 +12% VS Reduction (%) 48 43 +9% Specific Biogas Production (m 3 /kgVSS destroyed ) 0.94 0.86 Anaerobic Digestion and Renewable Energy Generation in DSD 25

  26.  FNA pretreatment enhanced digestion at YLSTW ◦ %VSR 43%  48% +12% ◦ Sp.biogas production 0.86  0.94 m 3 /kg VS destroyed +9%  Combined improvement +21% 21% ◦ short HRT 12d +21% Biogas Anaerobic Digestion and Renewable Energy Generation in DSD 26

  27.  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 Anaerobic Digestion and Renewable Energy Generation in DSD 27

  28.  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 Anaerobic Digestion and Renewable Energy Generation in DSD 28

  29.  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) Anaerobic Digestion and Renewable Energy Generation in DSD 29

  30.  Upgrade of Shek Wu Hui STW ◦ Small footprint to treat sewage 190,000 m 3 /d  External sludge load from other plants  Probable FW:SS co-digestion ◦ Not enough gh Digester Volume for conventional digestion SWHEPP  Consider Thermal Hydrolysis Process (THP) 30

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