Monthly Archives: April 2015

Cranfield University’s Anaerobic Digestion Research Pilot Plant Facility

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In our first guest blog, Dr Cecilia Fenech from Cranfield University gives an overview their AD Research pilot plant. Dr Fenech was previously a fellow in the Marie Curie ITN ATWARM, which was also coordinated by the QUESTOR Centre at Queen’s University Belfast. 

Cranfield University’s AD research pilot plant facility provides a unique integrated facility for companies to use as a ‘plug-and-play’ opportunity for research and development. The commissioning and opening of the plant is one of the Bio-Thermal RED (Biological and Thermal Renewable Energy Demonstrator) project milestones. The Bio-Thermal RED project is partly (40%) funded by the European Regional Development Fund (ERDF), with match funding (60%) by Cranfield University. Additionally, the AD reactor vessels and part of the commissioning cost were donated by Shanks Waste Management.

The AD pilot plant at Cranfield University will treat food-waste arising from the Cranfield University campus and be available for large-scale R&D projects. Companies can use the demonstration facility as an open access “plug and play” facility. Thus companies can robustly and objectively demonstrate, de-risk and develop their technology as required to commercialise their products with subsequent promotion through the knowledge hub events and services. This will create and develop regional expertise in AD design and deployment ensuring regional businesses and the knowledge base are at the centre of developments within these sectors and thus best positioned to capture the emerging opportunities.


The Cranfield University AD’s units are at the m3 size to ensure initial manufacturing and development costs for company equipment are kept as low as possible. The demonstrator is of a modular construction and mounted on skid-type frame assemblies. This facilitates integration of skid mounted equipment into the AD plant. In addition state of the art laboratories for independent testing of materials are available and qualified staff can help trouble shoot and optimise equipment. In addition to its function as a research facility, the plant will divert more than 10 tonnes of food waste from landfill, save around 5 tonnes of carbon dioxide emissions and produce 8 tonnes of fertiliser each year.

In addition to the creation of the demonstrator facility, the Bio-Thermal RED project was also responsible for setting-up a knowledge and networking hub for SMEs in the East of England region involved in bioenergy.  Over the past  two years the Bio-Thermal RED project has been involved with a number of SMEs based in the East of England that are part of the renewable energy chain, by providing free project-based support and a number of topical workshops relevant to the AD and thermal renewable energy SME sector, combining Cranfield University’s world class expertise in biological and thermal engineering.

Projects carried out to date include work on the utilisation of new feedstocks for AD, engineering optimisation, feasibility studies and technology analyses. The workshops delivered so far have also covered a wide variety of topical subject, including finance and planning for AD, nutrient recovery and digestate management, biogas treatment and upgrading and thermal technologies for energy from waste. In addition to this various technology show case demonstrations, business-to-business networks and on-line support have also been delivered.


The outputs of this project so far resulted in:

  • The creation of 2 new jobs
  • Support to over 25 East of England SMEs involved in renewable energy
  • Delivery of over 65 innovation initiatives
  • Delivery of over 30 environmental initiatives

For more information contact:

Dr Raffaella Villa: or Dr Cecilia Fenech:

Developing an AD plant in Northern Ireland

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The QUB ATBEST fellows were recently lucky enough to visit an AD plant under construction by ATBEST associate partners AgriAD. In this blog, researcher Fabio De Rosa describes the visit and what he learned from it. 

Most of the jokes in my country start with “there were once a German, a French, a British and a guy from Naples…”. Things were slightly different during this trip, not only because of the company, but because when it comes to biogas we are not talking about jokes but about a great business instead.

Rawan (Lebanon), Liang (China), Joanna (Poland), Simon (Ireland) and I (the Italian guy) went to visit a 500 KW AD plant under construction located in Banbridge, County Down, Northern Ireland, owned by the directors of agriAD Ltd Thomas Cromie (Figure 1) (Figure 2).


Figure 1 - QUB fellows with Mr Thomas Cromie

Figure 1 – QUB fellows with Mr Thomas Cromie


Figure 2 - Aerial view and map of the AD plant in Banbridge, County Down, Northern Ireland from AgriAD

Figure 2 – Aerial view and map of the AD plant in Banbridge, County Down, Northern Ireland from AgriAD

Thomas Cromie has 20 years’ experience in small and medium-sized enterprises active in the agricultural and energy industries. He has worked in collaboration with local government like the Department of Enterprise, Trade and Investment of Northern Ireland (DETI NI), for the development of regional policies in these sectors and on matters related to the exploitation and commercialisation of science, technology and R&D.

He is founder and partner in agriAD Ltd, which deals with the development and operation of joint-venture biogas projects, providing funding, technology and expertise in anaerobic systems. Thomas comes from a farming family, and graduated in geology at Queen’s University Belfast and after a working experience for an oil company in Saudi Arabia (back when the oil price was still 25$/barrel) he came back to the Emerald Island in the late 80s, recognizing what was raising in Germany during those years as a possible bargain for his family agricultural business: anaerobic digestion.

It took several years of travelling to the USA, Germany, Italy, France and Netherlands to understand the developing market, build contacts and meet politicians.

AgriAD’s purpose is to develop a network of standalone farm-based AD plants across Northern Ireland. It is proposed that the AD plants will be strategically located on large farms and operate in partnership with the farmer. Under the partnership, the farmer will provide a suitable site with planning permission for the AD facility, guaranteed feedstock (typically grass silage and animal manure) and the manpower to operate the facility. AgriAD will in turn provide the majority of finance, engineer, procure and construct (EPC) contractor, project delivery experience, project development and process management, biological support and plant maintenance.

The advantages from this network and the partnership between farmers and landowners include project experience and credibility, purchasing power, operational economies of scale and operational resilience (e.g. feedstock pooling, mitigating the key supply risk). The plant is currently under construction and will be operational in June 2015.

As Thomas says, “anaerobic digestion is a matter of opportunity”. Anaerobic digestion in Northern Ireland is a well-established technology and a great opportunity thanks to the perfect grassland conditions for AD and the most attractive financial regime in Europe. Indeed, Renewables Obligation Certificates (ROCs) represent the driving force of this economy.

ROCs are green certificates issued in UK to operators of renewable generating stations for the renewable electricity they generate and are basically used by suppliers to demonstrate that they have met their obligation [1]. Every year the RO requires UK electricity suppliers to source a specified proportion of the electricity they provide to customers from renewable sources. ROCs are tradeable commodities that have no fixed price, i.e. the amount an electricity supplier pays for a ROC is a matter for negotiation between the supplier and generator [2] and changes according to the technology priority. Currently AD ( 500kW), Hydro ( 20kW), Onshore wind ( 250kW) and Solar Photovoltaic ( 50kW) technologies have all been assigned the highest values for 2014/2015 [3], which is equal to 4 ROCs. There is significant on the ground interest, with 86 AD project permissions granted in 2014 [4] (Figure 2).

According to Mr. Cromie, AD brings more benefits to the rural communities. For example wind turbines have virtually no operating costs, whereas AD generates 200-300k£/year that can be spent to further develop the renewable energy sector. Moreover electricity generation through biogas has a constant load, whereas wind energy is more fluctuating.

It might seem odd, but also giant oil companies like Shell and its subsidiaries are very interested in renewable energies, photovoltaic and biogas on top [5]. This is what looking ahead means.

The electricity grid in Northern Ireland was constructed to push the electricity from three large fossil fuel generating stations (Maydown, Kilroot and Ballylumford) around the coast into the interior of the country. Reconfiguring the grid to allow generation in other locations requires major investment.

Figure 3 - Projects with planning approval in Northern Ireland

Figure 3 – Projects with planning approval in Northern Ireland

The challenges for AD in NI are the funding scheme, small scale and individual projects as a barrier, the limited experience of project financing within the NI farming sector, the infrastructures and also the number of farmers in the UK that has been decreasing of the 4-5% per year in the last decade.

Nowadays only the 7% of the AD projects in NI is operational, 10% are under construction, 54% have been approved but seeking for funding while 29% is waiting for planning. Only 16% of the total fundings are secured. Regarding the source, 50% are provided by banks, 23% by contracts, 14% by leasing and 9% are unsecured [6].

The total project cost of the plant in Banbridge is around £2.5m and two thirds of the heavy concrete construction is already done. Usually it takes 9 months to build the plant, under and EPC contractor: fixed price and time and penalty in case of late delivery of the plant.

At the beginning the whole feedstock will be grass silage secured within Cromie family landholdings.

Later industrial wastes from a near milk factory will be integrated, representing the 25% of the feedstock. The advantage is that the feedstock composition is known (there is no need for pre-processing) and in any case these wastes have to be pasteurized before disposal, so that using them in an AD plant makes sense.

The biogas yield will be equal to around 2Mm3/year. The combined heat and power system creates the opportunity to transport heat to a number of major heat users nearby (Figure 4). It will work for 8000 h/year in order to produce 4MKWh of electricity with a 91.3% operational efficiency. There are operation responsibilities and should the electricity generation be less than planned a penalty has to be paid. Knowing the outputs is paramount with respect to the funding.

Statistically 55-60% of the problems in an AD plant arise from CHP inefficiencies and only the 10-15% is due to human operators.


Figure 4 - Combined heat and power (CHP) unit

Figure 4 – Combined heat and power (CHP) unit

Figure 5 - CHP engine

Figure 5 – CHP engine 

The CHP engine is basically a modified Diesel engine, factory made and tested, operating with a biogas consisting of 55% of methane (Figure 5).

There are radiators for the excess heat developed in the CHP unit, activated carbon filters and a gas boiler to keep the biological temperature during the start up of the plant and in case of problems with the CHP unit (Figure 6). It takes 4-5 weeks to heat the system up to the biological temperature of the process.

Figure 6 – Gas boiler, radiators for excess heat and activated carbon filter.

Figure 6 – Gas boiler, radiators for excess heat and activated carbon filter.

There is a primary digester, which receives the feedstock by gravity, and a secondary digester (Figure 7). The tanks are factory-made, which means that the concrete wasn’t poured on site, but each slab was shaped singularly elsewhere and put together in loco. This allows for a faster construction.

Figure 7 - Primary and secondary digester and control room (on the left)

Figure 7 – Primary and secondary digester and control room (on the left)

The control building is on the left in Figure 7, with the pumps in the cellar.

Usually the retention time depends on the feedstock and it is around 40 days. It will be around 100 for this plant, because of the grass silage.

The pumps and the pipes going to the second digester from the control room cellar offer a high operational flexibility to this plant (Figure 8).

Figure 8 - Pump room

Figure 8 – Pump room

There are 3 points in the tank at three different heights where the temperature is monitored (Figure 9). The optimal value is around 35-40°C and when the variation between the three points is no more than 0.1°C then it means that there is a good mixing inside the tank.

The sampling point is at 3-4 feet, while the other 2 holes below are the drain points.

In both tanks there is a propeller mixing system. When you have to fix the mixing system in case of faulty, large tanks have to be emptied first. These two tanks have a particular sleeve which allows for fixing the propellers without emptying the tank and venting the gas.


Figure 9 - Inside of the digester

Figure 9 – Inside of the digester

Figure 10 - Primary and secondary digester from the inside

Figure 10 – Primary and secondary digester from the inside

The concrete tank lifetime is equal to 25 years, also because of the black coating in the top part. It protects the concrete from the biogas, which is corrosive (Figure 9 and Figure 10).

Small amount of oxygen can be fed in the overhead in order to oxidize hydrogen sulphide, producing elemental sulphur. This is a way to get a grass fertilizer which is even better than the commercial ones (11% more yield).

The digestate will be first collected in a storage tank and then spread in the surrounding fields after September (Figure 11). This is because NI is a nitrates and phosphorous vulnerable zone and spreading is not allowed through the winter.

Figure 11 – Digestate storage tank

Figure 11 – Digestate storage tank

Operation should start in 2 months, with slurry at the beginning and a little of digestate from another AD as inoculum. Before that the two domes have to be put in place and a pressure test, using just water, has to be carried out.

As a conclusion, this trip was extremely interesting and stimulating. We had the chance to see first-hand how an anaerobic digester plant is constructed and moreover to discuss with a professional in the sector.



1. [Online]

2. [Online]

3. [Online]

4. [Online]

5. [Online]

6. [Online],465992,en.pdf.

7. S. Murray, E. Groom, C. Wolf,. WRAP – feasibility reports. [Online] October 2012.

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