Environmental sustainability analysis of UK whole-wheat bioethanol and CHP systems

The UK whole-wheat bioethanol and straw and DDGS-based combined heat and power (CHP) generation systems were assessed for environmental sustainability using a range of impact categories or characterisations (IC): cumulative primary fossil energy (CPE), land use, life cycle global warming potential over 100 years (GWP100), acidification potential (AP), eutrophication potential (EP) and abiotic resources use (ARU). The European Union (EU) Renewable Energy Directive's target of greenhouse gas (GHG) emission saving of 60% in comparison to an equivalent fossil-based system by 2020 seems to be very challenging for stand-alone wheat bioethanol system. However, the whole-wheat integrated system, wherein the CHP from the excess straw grown in the same season and from the same land is utilised in the wheat bioethanol plant, can be demonstrated for potential sustainability improvement, achieving 85% emission reduction and 97% CPE saving compared to reference fossil systems. The net bioenergy from this system and from 172,370 ha of grade 3 land is 12.1 PJ y−1 providing land to energy yield of 70 GJ ha−1 y−1. The use of DDGS as an animal feed replacing soy meal incurs environmental emission credit, whilst its use in heat or CHP generation saves CPE. The hot spots in whole system identified under each impact category are as follows: bioethanol plant and wheat cultivation for CPE (50% and 48%), as well as for ARU (46% and 52%). EP and GWP100 are distributed among wheat cultivation (49% and 37%), CHP plant (26% and 30%) and bioethanol plant (25%, and 33%), respectively. -- Highlights: ► UK whole-wheat energy system can achieve 85% GHG emission reduction. ► UK whole-wheat energy system can achieve 97% primary energy saving. ► The land to energy yield of the UK whole-wheat system is 70 GJ ha−1 y−1. ► Fertiliser production is the hotspot. ► DDGS and straw-based CHP system integration to wheat bioethanol is feasible