SeaGas : Production of bio-methane from seaweed by Anaerobic Digestion (AD)

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AD currently uses land biomass such as cereals, grass silages or food crops to supplement varying levels of waste streams causing a negative impact on land for food vs fuel and concerns over GHG emissions. While AD has the potential to meet 10% of UK energy demand by 2020 (ADBA 2014), alternative sustainable feedstocks are essential. Seaweed does not compete with food for land or require fresh water. It is fast growing, captures CO2 more efficiently than land plants and is a bio-remediator. It has carbohydrate (CHO) /gross calorific value (GCV) 11-15MJ/kg comparable with cereals (13-19/MJ/kg). Seaweed can replace grass silage in AD combined with food waste to produce the same gas yield 10.4m3 CH4/t.

Utilising all waste streams, the UK AD industry could generate 40.4TWh of biogas, or >10% of demand and be worth £2-3Bn by 2020. AD process knowledge and economics will inform plant design to maximise returns from FIT and RHI. TCE and the steering panel will identify early adopters by M18, in East Anglia and Scotland to build pilot AD plants in the 20ml coastal strip, near waste streams, within 6M of project completion. This will minimise transport costs and GHG emissions and benefit from closed loop energy integration. AD plants can be funded by loans from eg Green Investment Bank, (~£3Bn), Enterprise Finance Scheme(~£2Bn). Small AD plants generating <500kWe, with seaweed at £300/t dwt can return £700k-£1Mpa with build costs of £2M-£3M and ROI <4 yrs, including £5/t for digestate as fertiliser but excluding savings in waste disposal. Larger AD plants generating 2MWe, with seaweed at £150/tdwt can return £2Mpa with build costs of £3M to provide ROI in < 2yrs. Operation of 50 such plants using 2.5Mt seaweed by 2025, with growth of 20% pa to 2030 is feasible. This will require a multi-harvest, high yield, (200t/ha) seaweed farming system (Benchmark Holdings). TCE manage min ~6.6Mha coastal seabed, equivalent to the UK area of arable land, and will licence this to generate Treasury revenue, promote economic growth, job creation and further exploitation of seaweed based on the supply chain economics and the storage system. 2% (132,000ha, 1,320km2) of the coastal seabed producing 200t/ha seaweed would supply up to 26Mt seaweed value ~£390M for AD. To generate the same energy in AD with maize, instead of seaweed (at 22m3 CH4/t), would use 12% UK arable land. TCE will support supply chain development by leasing land for storage, NSMC and Norfolk Council will promote seaweed for biofuel production, CEFAS will lead on marine management. Further exploitation of seaweed in fermentation and energy generation by gasification will be economically enabled and the partners will apply the expertise and knowledge in other IB processes.