Optimising the manufacture of Organo-Mineral Fertiliser

Martin, N. and Le, M.S., United Utilities Group PLC, UK



With an ever increasing population, sewage sludge management has become a critical issue. The European FP7 project END-O-SLUDG aims to address these challenges by focusing on efficient and innovative processes. One of the processes under consideration is the manufacture of Organo-Mineral Fertiliser (OMF), which is a nutrient balance fertilizer specifically formulated to suit UK farming practices. It is a pasteurized, granular and virtually dust-free product obtained from a series of mixing and dehydration processes.  Under END-O-SLUDG, a pilot OMF manufacturing facility is to be installed at Ellesmere Port Wastewater Treatment Works to test the technology. The plant will provide sufficient product for scientific investigations and trials.

In order to optimise the process from an energy perspective, dehydration technologies and available energy sources were investigated. Each potential energy source was matched to a suitable technology, which ultimately provides warm air for dehydration. It was found that a heat pump would be able to utilise energy in the environment and provide air at the required temperature for dehydration.

By analysing the available quantities and properties of the sludge at each stage of the process, a heat and mass balance of the system was created to determine optimal mass and energy flows. While vital in the design stage, it also illustrated potential energy savings utilising waste heat.

Finally, it is shown that effective experimental design, if analysed correctly, can provide invaluable information for optimising a new process. Each variables effect on a measured output can be accurately estimated, thus allowing for optimal adjustment of the process variables. This work brings the OMF process a step closer to becoming a viable option for sustainable sludge management.

Key words

Biosolids; OMF manufacture; dehydration; granulation; heat efficiency; optimisation


The objectives of this paper are as follows:

  • To provide an overview of the Organo-Mineral Fertiliser (OMF) production process.
  • To analyse the suitability of several dehydration processes for use in the production of OMF.
  • To match dehydration technology to the available energy sources.
  • Through the use of a heat and mass balance of the process, establish an appropriate setup.
  • To put forward a method for determining optimal settings for the variables associated with the dehydration process.

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