DIGESTER CAPACITY UPGRADE AT MUNICIPAL WASTEWATER PLANTS

Transcription

1 DIGESTER CAPACITY UPGRADE AT MUNICIPAL WASTEWATER PLANTS BANZ Biogas Conference, Auckland Jurgen H Thiele 14 August 2014 A Downer A Downer Company Company

2 The Approach Waste Value Recovery Project Commissioning (mechanical, electrical, biological) Operation Support Options Review Project Analysis Concept Design Economic Feasibility Study Construction management and supervision support Downer/HCC PNCC LanzaTech Trustpower Project construction by client -appointed contractor Prelim design Confirmation of Construction Costs by Client Detailed design by Client Surveying, Process Design, Civil Design, Structural Design

3 Why Capacity Upgrades? Typical drivers for digester capacity upgrades in municipal wastewater treatment plants (WWTP s) are: Increased sludge production / urban population growth Growth in primary/food processing industries New discharge compliance requirements Extreme weather events, increased flow Example: Upgrade at Pukete, Hamilton (2013/14) Additional: Co-digestion of trade waste in municipal WWTPs: Added revenue from gate fees for trade waste reception Reduced WWTP operating costs from on-site power production Example: Upgrade at Totara Road, Palmerston North (2009/11)

4 The Options 1. Quantity Growth by New Construction Increased space requirements/footprint Increased operating costs High CAPEX $ (1,200 1,800 $/m 3 new digester volume) Inflexible response to rapid sludge load changes Risks of process instability 2. Performance Growth of Existing Digester Capacity Increased capacity by Modernisation/Tune-up/Upgrade Booster to double digester throughput Footprint practically unchanged Improved digester mixing, performance and efficiency Lower operating costs Lower CAPEX $ ( $/ m 3 new digester volume) Option for stepwise upgrade to fit to council budgets Variable load capability (booster: on/off on demand) Immediate availability ( plug and play )

5 Performance Growth: Improved Mixing + Booster Pukete plant, Hamilton Methane stage digesters ( 2 ) Each 2,200 m 3 volume Mesophilic (35 37 C) HRT: days Totara Road plant, Palmerston North Methane stage digesters ( 2 ) Each 1,350 m 3 volume Mesophilic (35 37 C) HRT: days Daily load: t DS/day t VS/day Daily load: t DS/day t VS/day

6 Upgrade on Operating Digester Plant 1. Digester Performance Check (Determine what needs to be done) 2. Temporary mixing upgrade and temporary booster installation in one digester tank (increased treatment capacity) 3. Transfer full load to the digester tank with temporary installations 4. Empty, clean out and install mixing upgrade in the 2 nd digester tank 5. Permanent installation of Booster (recuperative thickener) 6. Seed upgraded digester tank with sludge from 1 st tank 7. Full load on upgraded digester tank (tank capacity 2 fold increased) 8. Empty, clean out and install permanent mixing upgrade/booster to 1 st digester 9. Seed with sludge from 2 nd tank and apply full load on both digesters 10. Monitor system performance

7 Booster Recuperative Thickening 1. Low power consumption 2. Fully automated 3. Low maintenance 4. Low polymer consumption (4-5 kg polymer/t DS) Digester Feed Polymer Dosing System Anaerobic Digester Drum Thickener Thickener Filtrate Thickened Sludge Sludge dewatering

8 Process Advantages Cleaner Effluent Production of thickened sludge and clean filtrate

9 Booster Technology Installation Booster technology doubles treatment capacity in well mixed digesters Booster technology adds process robustness to digesters - solids residence time (SRT) is typically 2 x hydraulic residence time (HRT)

10 Digester Capacity Check - Mixing Upgrade Lithium tracer test

11 System Upgrade, Hamilton Thickening Building Ring Main Pumps Shunt Pump

12 Process Advantages Sludge Health COD Removal Activity in the Digesters (kg CH 4 COD/kg VSS/day) Digester Upgrade Pukete plant, Hamilton Totara Road plant, Palmerston North Operation w/o Thickener (prior to upgrade) COD: Chemical Oxygen Demand Operation with Thickener (6 months after upgrade) Operation with Thickener (12 months after upgrade)

13 Process Advantages Doubled Throughput Full load on 2 digester tanks prior to Quality upgrade - 12 days HRT 1 tank 6 days HRT

14 Summary of Key Features: Lower construction costs ( $/m 3 new digester capacity) Production of cleaner effluent (filtrate) Production of pre-thickened sludge as feed to the dewatering stage Fast response capability to hydraulic and solids load changes Good digestion process stability at short residence times Immediate response to organic loading rate changes Improved activity and health of the anaerobic digester sludge More stable digester process

15 Process Advantages Application to Trade Waste Co-digestion

16 Examples of Typical Feedstocks Feedstock Material Dissolved Air Floatation (DAF) (dairy factory, meat processing) % Dry Solids (DS) Range % (high fat content) Cheese whey 5 % (high sugar content) Grease trap waste (municipal, commercial collection) Municipal biosolids (primary sludge) 5 10 % (high fat content) 3-4 % (medium fat content)

17 Economic Benefits Digester Capacity & Health Check (Spiire) PNCC: 4 fold biogas production increase needed for PNCC genset target Screening Grit Removal Primary treatment Secondary treatment Targeted trade waste collection (PNCC, TTS) 1,000 kg/d BOD, (selected liquid trade waste): 180 $ gate fee (@ 30 $/m 3 ) : 2-3 x /week Primary Sludge Municipal sludge DIGESTER Added biogas : 5,200 kwh biogas /t BOD (105 $/t BOD) Increased sludge costs: 0.25 t wet/t BOD (- 12 $/t BOD) Gross Earnings (@ 30 $/m 3 ): 275 $/t BOD, $/m 3 trade waste (with biogas use) 27 $/m 3 trade waste (w/o biogas use ) A Downer A Downer Company Company

18 It s a Game Changer Lower construction costs Enhanced co-digestion capacity of existing plant (about 4-6 fold) Improved economy of scale / profit margins for digester operation Attractive gate fees can be offered (30 $/m 3 trade waste) Attractive gate fee improves access to feedstock Higher treatment performance / lower sludge production Cleaner effluent with low solids contents

19 Business Case Example - (50 m 3 /d trade waste) Digester Upgrade Stage Costs ($NZ) 1a: Initial investigations $ 30,000 1b: Process design, concept design, detailed design $ 170,000 2a: Digester mixing system upgrade (2 tanks) $ 370,000 2 b: Liquid trade waste reception $ 440,000 3 a: Digester booster installation (1 tank) $ 390,000 3 b: Connection of booster to 2 nd digester $ 100,000 (nominal sum) Total costs $ 1,500,000 Co-digestion upgrade 3a: Installation costs: 1.4 M$ 4,000 kg BOD/day liquid trade waste capacity (D2) Simple payback period: Less than 3.8 years Co-digestion upgrade 3b: 7,500 kg BOD/day liquid trade waste capacity (D1+ D2) Installation costs: 1.5 M$ Simple payback period: Less than 2.2 years

20 Summary and Conclusion The Digester Capacity Upgrade approach with improved mixing and recuperative thickening is proven technology ( 2 sites in New Zealand, 4 sites overseas). It is applicable to council or industry operated WWTP sludge digesters and co-digestion schemes. The upgrade capital costs are less than 50 % of new digester construction costs for the same capacity. Good economy of scale exists for applications at medium size to large municipal WWTP treatment plants. This enables more profitable co-digestion of trade waste in municipal digesters

21 Summary and Conclusion.. ctd New potential opportunities exist for trade waste co-digestion service businesses. Some commercial challenges remain for trade waste codigestion schemes, planning and waste procurement. Expansion of scale for individual co-digestion plants is likely to be limited by transport distance/ transport costs for the trade waste materials.

22 Acknowledgements Spiire would like to thank Hamilton City Council and Palmerston North City Council for providing digester sludge samples, plant photographs and digester operation data from the capacity upgrade at their municipal treatment plant digesters.