Two research papers have been published on the extraction of phosphorus from digestate and use in agriculture. Phosphate rock is included in the EU list of ‘critical raw materials’ and is ranked 20th in an index of commodity price volatility, so is an important food security as well as environmental issue.
The University of Surrey worked with Thames Water to assess, across Thames' waste water treatment works, the options for phosphorus recovery and use. The research focussed specifically on the Slough WWTP and the operation of a newly installed Ostara system for recovery of P as struvite from dewatering liquors.
The results are positive:
“Significant operational and maintenance savings totalling to £113K can be made in the first year of operation of the P recovery system in Slough WWTP. Sale of P rich struvite fertiliser produces annual revenue of £20K. “
For further information on this project see here.
The second project was undertaken by Dr Ruben Sakrabati et al of Cranfield University. They say that:
“The nutrient uptake of Phosphorous, (how much of the applied nutrient is used by plants), is generally considered to be lower than for other major nutrients such as Nitrogen. Uptake efficiency is, however, very variable; estimates range from over 90% where soil P is limiting but other nutrients are not (Johnston & Syers 2009) to very close to zero in soils with a high soil P-index.”
They have developed a phosphorus map to “identify areas where an application of biosolids would be economically and agronomically beneficial subject to the perceived constraints of different stakeholder categories”. This tool, which Sakrabati will talk about at our R&I Forum in April, could help the AD industry and the farmers using digestate reap the full benefits of the value contained in this resource. Phosphates must be used effectively for environmental protection and food security purposes. No doubt there will be a lively discussion on this subject at the Forum. The full programme for the Forum can be found here.