Organomineral fertilisers (OMFs) were produced by coating biosolids granules with urea and potash. Two OMF formulations with N : P2O5 : K2O compositions: 10 : 4 : 4 (OMF10) and 15 : 4 : 4 (OMF15) were developed for application in grassland and arable crops. Routine fertiliser analyses were conducted on four batches of OMF and biosolids granules and compared with a sample of urea to determine key physical and chemical properties of the materials which affect handling and spreading, soil behaviour, and fertiliser value. Bulk and particle densities were in the range of 608 to 618 kg m−3, and 1297 to 1357 kg m−3, respectively. Compression tests showed that OMF particles undergo deformation followed by multiple failures without disintegration of the granules when vertical load was applied. Static particle strength was between 1.18 and 4.33 N mm−2depending on the particle diameter. The use of a model for fertiliser particle distribution studies showed that OMF granules should be between 1.10 and 5.50 mm in diameter with about 80% of the particles in the range of 2.25 to 4.40 mm to enable application at 18 m tramline spacing. This research utilises novel technology to improve the fertiliser value of biosolids, reduce disposal costs, and deliver a range of environmental benefits associated with recycling.

Sewage sludge, a waste material commonly known as biosolids, has good potential as a valuable agricultural resource, providing that its nutrient imbalances could be overcome. Sewage sludge is rich in phosphorus but low in nitrogen and potassium. Technology exists to supplement sewage sludge with mineral fertilizers, such as urea and muriate of potash as sources of nitrogen and potassium, respectively, to produce an organo-mineral fertilizer with balanced crop nutrient requirements. Here, an experimental plot trial set up in 2008 was established at Broxton, Cheshire, UK, to compare crop yield response for typical crop varieties. Crops included wheat, oilseed rape, barley, beans and forage maize, treated with conventional fertilizer and organo-mineral fertilizer. The organomineral fertilizer is a nutrient-balanced sludge-based product produced by drying digested sewage sludge cake at 80°C in a tumbling evaporator, which produces sludge granules of 3-6 mm in diameter. Analysis was carried out on soil NPK and crop yield. N use efficiency was measured to assess N uptake. Results show that there is no significant difference in crop yield between treatments over the three trial years, with the exception of one crop. This finding demonstrates that the new organo-fertilizer is as efficient as conventional fertilizers. Moreover, levels of heavy metal in soil did not exceed permissible levels. The novelty of this research lies in the fact that it is the first field scale trial of a modified sewage sludge product that has the potential to transform a hitherto waste product into a practical fertilizer product. We conclude that the organo-mineral fertilizer is a promising alternative product for sustainable agriculture.

We report measurements of the energies and angular distributions of positive ions in an inductively coupled argon plasma in a Gaseous Electronics Conference Reference Cell. Use of two separate ion detectors allowed measurement of ion energies and fluxes as a function of position as well as ion angular distributions on the discharge centerline. The inductive drive on our system produced high plasma densities (up to 1012/cm3 electron densities) and relatively stable plasma potentials. As a result, ion energy distributions typically consisted of a single feature well separated from zero energy. Mean ion energy was independent of rf power and varied inversely with pressure, decreasing from 29 to 12 eV as pressure increased from 2.4 to 50 mTorr. The half-widths of the ion angular distributions in these experiments varied from 5° to 9°, or equivalently, the transverse temperatures varied from 0.18 to 0.29 eV with the distributions broadening as either pressure or rf power was increased.

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