of various technologies, recommendations are made on further research on the appropriate low cost technologies, especially using solid waste as low cost materials for biogas purification and upgrading.

A study of cooling crystallisation of a potassium sulphate solution in a batch reactor is described in this paper. The effect of ultrasound on primary nucleation was investigated by measures of induction time and metastable zone width of unseeded solutions. The appearance of crystals is detected by conductivity measurements. The experimental results show that ultrasound has an effect on the primary nucleation of potassium sulphate. Ultrasound allows induction time and metastable zone width to be significantly reduced.

The synthesis of calcium hydroxyapatite (Ca-HA) starting from calcium carbonate and different orthophosphate sources, including orthophosphoric acid, potassium, sodium and ammonium dihydrogen orthophosphates, was investigated under ambient conditions. The reaction started with calcium carbonate dissolution in an acid medium, followed by rapid precipitation of calcium cations with orthophosphate species to form calcium phosphate based particles which were in the size range of 0.4-1 m. These particles then agglomerated into much larger ones, up to 350 m in diameter (aggregates). These aggregates possessed an unstable porous structure which was responsible for the porosity of the final products. The highest specific surface area and pore volume were obtained with potassium dihydrogen orthophosphate. On the other hand, orthophosphoric acid led to the highest dissolution of calcium carbonate and the complete precipitation of orthophosphate species. Under ambient conditions, calcium phosphate based solid products of low crystallinity were formed. Different intermediates were identified and a reaction pathway proposed.

Relevant literature which deals with the presence of metals during the catalytic pyrolysis of biomass is reviewed. Only those conditions where the metal was in intimate contact with the biomass components are included. Cellulose, hemicellulose and lignin all fuse during the early stages of pyrolytic heating and the dehydration and decomposition processes begin during this transition. Hemicelluloses such as xylan are more labile and difficult to isolate, whereas both cellulose and lignin produce mostly bio-oils when demineralised and flash pyrolysed. The dominant primary products from 'pure' cellulose are anhydrosugars as well as smaller oxygenates. Lignin gives aromatics based on the syringol and guiacol molecules. The alkali and alkaline earth metals are found to curtail the yield of bio-oil and modify product distribution, even in the low concentrations naturally found in biomass. All other metals act to catalyse cross-linking reactions, with the nickel and zinc most studied. The electropositivity of the metal tends to correlate with the extent of catalytic activity. The presence of metals causes little change to the production of gases, but more char is formed at the expense of liquids. If the aim of pyrolysis is bio-oil for fuel, prewashing of biomass to remove metals is beneficial.