(ShareCast News) - Transformer recovery company G&S Technologies Group bought a further stake in Hydrodec's US operation, which provides waste oil and workshop waste services, for $1.7m.G&S is to pay $1.37m of feedstock in raw material and $330,000 in cash for an additional 12.45% stake in Hydrodec of North America leaving Hydrodec with a 62.5% interest in the business.Chief executive Chris Ellis said: "With G&S we continue to focus on creating the best quality transformer oil in the US market and positioning ourselves to take advantage of significant forecast growth in demand in the United States. We will now evaluate the most appropriate timing and location for the expansion programme."According to a 2013 agreement, US-based G&S will be able to buy a final $1.7m interest in Hydrodec of North America to bring its overall interest to 49.9%, when two operating trains are established; this would increase capacity to 15 litres which would be financed equally between the owners.AIM-listed Hydrodec's oil re-refining and chemical process technology for the transformer oil market is used by the electricity industry and the global transformer oil market is expected to grow to $2.79bn by 2020 at a compound annual growth rate of 7.14%.The spent oil process at its two commercial plants eliminates polychlorinated biphenyl, a toxic additive banned under international regulations.Shares in Hydrodec were up 5.38% to 2.45p at 1110 BST.