April, according to the company behind the venture, Argent Energy.
Biodiesel production through-out the whole of Britain was only around 10,000 tonnes last year, whereas the Motherwell facility will be capable of producing around 45,000 tonnes per annum and will provide nearly 5% of Scotland's diesel needs. Argent Energy is in talks with a number of transport companies that have expressed an interest in using the fuel.
Environmental director Chris Bond said the plant is "the only one in the world that can handle both saturated and unsaturated fats".
Animal fats will be sourced from an adjacent rendering plant, while UCO is being cleaned at a site in Leeds prior to shipment in tankers to Motherwell.
The plant has been built by Mowlem Engineering with Austrian specialist Biodiesel International providing the technology. The project has received development funding from Bank of Scotland Corporate Banking and a £1.2m Regional Selective Assistance grant from the Scottish Executive.