The feed generally tested in these particular set of trials was wood pellets (Section 2). In order to increase the sulphur content of the pellets, they were treated/doped with a sulphuric acid solution. Starting with the target sulphur content of the pellets, the volume and concentration of the acid solution was calculated taking account of the pellets’ natural sulphur content. The acid solution was prepared by diluting concentrated H2SO4 (98% w/w, 1.84 specific gravity) with deionised water. In order to avoid material deterioration, 10% moisture content was also targeted. Care was taken when mixing the wood and acid being mindful of the absorptive capacity and potential friability of the pellets (an important factor when handling both manually and mechanically), as well as health and safety considerations. Once mixed, the wood/acid batches were left to stand overnight to allow the acid solution to be absorbed thoroughly and evenly.