Sludge treatment in the Huddersfield area was previously provided by incineration at Calder Valley Incinerator, located at Yorkshire Water Upper Brighouse Site. This incinerator has been inoperable since a weather event in 2015. Following a strategic review, Yorkshire Water Services (YWS) decided to progress with conventional mesophilic anaerobic digestion (MAD) plant supported by lime sanitisation of the digested product to secure the long-term treatment of sludge for the area. The change in treatment direction brings the benefit of renewable generation from biogas production and increased reliability and performance.
The Huddersfield Energy & Recycling Facility project involved the construction and commissioning of a new mesophilic anaerobic digestion facility that will produce renewable electricity from sewage sludge while also producing a high-quality lime stablised sludge, suitable for sustainable reuse as an agricultural fertiliser.
The project entailed the demolition of the old sludge incineration and site clearance prior to construction and commissioning of a new facility which includes:
New import acceptance facility for both liquid sludge and sludge cake.
New sludge thickening plant (drum thickeners) to thicken combined import and SAS to circa 6% dry solids.
New holding tanks (2 no.) for mixing and holding re-watered sludge cake and thickened sludge prior to pumped feed to digesters.
2 no. anaerobic digesters each with 7,306m3
Biogas storage and handling system comprising biogas treatment (carbon scrubber for siloxane removal), gas holder and flare stack
2 no. 1.2MW CHPs to generate electricity so as to reduce the site reliance on imported power with the waste heat from the CHPs used to heat the digesters.
High voltage infrastructure to allow energy generated from the CHP to be fed to the external grid.
1 no. dual fuel boiler (biogas or natural gas) to supplement CHP heat output when required.
47m high exhaust stack for dispersion of exhaust gases from the boiler and CHP.
Heat exchangers to transfer heat from CHP to sludge so the digesters are operated in the range 36-39°C.
New holding tanks (2 no.) for storage of digested sludge prior to dewatering.
Lime dosing facility to allow powdered quick lime to be dosed into the digested sludge so that conventional product status is achieved.
2 no. dewatering centrifuges to produce sludge cake at circa 25% dry solids.
Cake barn providing storage for 844m3of sludge cake.
Liquor treatment plant to reduce liquor ammonia levels by 85% prior to return to Lower Brighouse STW.
Odour control
Welfare and laboratory facilities.
Key Challenges:
The site was located in an air quality monitoring zone. Dispersion modelling was used in the design of the exhaust stack for the CHPs and boiler, as well in the sizing and location of odour control units, to ensure that the completed plant meets stringent quality standards and nuisance odours from the site are avoided.
Although the Covid pandemic hit at a critical period in the project delivery, site works never stopped and Yorkshire Water, Murphy, suppliers and subcontractors adapted to new ways of working. This allowed the delivery of project to remain on programme.
Project Delivery & Innovation:
The project was designed to mitigate against the inherent flood risk at the site with key assets raised above maximum flood water levels to achieve the required resilience.
3D modelling was used across the project to coordinate design, manufacturing and installation activities, avert clashes and verify installation confirms to design.
The new thickening and sludge dewatering facility were brought online in December 2020. This was followed by the import sludge (Liquid and Cake Streams) in March 2021. Seeding of the Digesters commenced in May 2021 and they are now fully operational, including the boiler and CHP. Lime addition to digested sludge commenced in June 2021 and a sanitized sludge is being achieved.
The new sludge imports facility is fully operational and accepting liquid and sludge cake imports daily. Scope of works includes
Imported sludge tanker points for cake and liquid sludge: The imported liquid sludge is discharged to the Sludge Screen Feed Tank before screening. Sludge Cake is received at the cake reception plant where it is re-watered to 6 % DS.
Imported sludge screening: Liquid Sludge gravitates from the storage tank through the screens and it is then pumped to the thickener feed tanks upstream of the sludge thickening facility.
Sludge Thickening: Progress December 2020
A new project milestone was introduced to the scheme to provide YW with beneficial use of the thickening and dewatering facility. These processes were brought on stream for indigenous SAS in December 2020. Thickening of imported sludge commenced with acceptance of imports in March 2021
The new sludge thickening facility includes combined Import and SAS thickening
Liquid polyelectrolyte addition
3 (No.) dual drum thickeners (duty/duty/standby). thickening to >6%
Pre and post thickening sludge storage
Sludge Digestion: Progress August 2021
The sludge digestion process was commissioned successfully in May 2021, using seed sludge from Knostrop WWTW. The digestion plant is currently accepting loads of 38.5 tDS and producing 15,000 Nm3/d of biogas, with a methane content of 63-66 %. The boiler and CHPs are also operational, with in excess of 28,000 kWh produced daily.
Digestion mixing is provided using Landia mixing pumps. Lithium tracer tests have been completed and confirm the required mixing performance has been achieved.
The Digestion plant comprises
Digester feeding system: Re-watered sludge cake and thickened sludge are fed to the digester feed tanks from where it is pumped to the digesters.
Digesters: 2 (No.) each 7,306m3 capacity. Peak sludge load to the digesters is 65.753tDS.
Gas holder and handling system: This comprises pipework from the digesters to the new gas holder (2,000m3)) and from the gas holder to the CHP/boiler. A flare stack has been provided, where excess gas that cannot be used within the process is burnt off.
Biogas Treatment: A carbon scrubber has been provided for the removal of siloxanes from the biogas. It is operational and scrubs biogas prior to use in the CHPs and boiler.
2 (No.) CHPs: These will be the primary users of the biogas from the process. The CHPs generate electricity to reduce the site reliance on imported power and the waste heat from the CHP is used to heat the digesters.
1 (No.) dual fuel boiler: This will operate either on failure of the CHP or to provide supplementary heat when the CHP’s are operating but cannot provide the full heat requirement. The boiler can run on biogas or natural gas.
Exhaust Stack: A 47 m high stack is provided for the dispersion of exhaust gases from the Boiler and CHP
Sludge heat exchangers: The heat exchangers take the heat, from the hot water provided by the CHP/boiler and transfer it into the sludge contained within the digesters.
Sludge Dewatering: Progress August 2021
The sludge decanters were commissioned as part of Key date 2 in December 2020. More recently the lime addition has been brought on stream, to provide a sanitized sludge. Initial testing has demonstrated HACP compliance and sludge cake DS concentrations of 26-30 %.
The RLTP plant is fully operational, treatment liquors from limed dosed dewatering process.
The dewatering plant comprises
2 No. Dewatering feed tanks: Digested sludge is transferred by gravity to these storage tanks
Lime addition. Sludge is pumped from the dewatering feed tanks to the lime mixing tank. Powdered Quick lime is added, to raise the pH of the sludge, increasing biological inactivation to achieve Conventionally Treated Sludge Status
2 No. dewatering centrifuges: The centrifuges dewater the limed digested sludge to >25% DS prior to loading onto HGVs for export.
Final Product Storage: A cake barn provides storage for 844 m3 of sludge cake
Liquor treatment plant: The E&RF has a purpose-built liquor treatment plant (LTP) which is based on the Amtreat® process (supplied by ACWA). The ammonia levels from the LTP will be reduced prior to returning to Lower Brighouse STW such that the liquors do not have a detrimental impact on the existing activated sludge process.
“I am incredibly proud of the entire Project Team achieving this completion milestone as we handover the Facility to our Client, Yorkshire Water.” – Murphy Ireland, Senior Project Manager, Gary Dolan. “Covid-19 has brought unprecedented challenges however this achievement is a testament of the team who have worked tirelessly, taking extraordinary measures to ensure this milestone was safely delivered.”
Key Facts:
Harnessing the power of sewerage, Huddersfield Energy & Recycling Facility is now generating 28MW of power each day by processing 38.5 dry tonnes of sludge through an Anaerobic Digestion Plant and using biogas to fuel CHP’s. Digested sludge is then dosed with lime and dewatered achieving a sanitised cake product.
Electricity generated by the new facility is equivalent to that required to power 5,280 homes.
The plant will treat 24,000 tonnes (dry solids) of sludge each year.
Fully Operational.
Site after demolition of incinerator in 2018.
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