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In search of an efficient technology for phosphorus removal
Ecofiltration presented their Polonite® technology at UK TAG 35 in June 2014. In 2016 an opportunity for testing the effectiveness of the technology for phosphorus (P) removal and disinfection arose at Somerton Sewage Treatment Work in England with a water flow corresponding 21 000 pe.
A collaborative trial, with 6 out of 10 water companies (Anglian Water, Irish Water, Severn Trent Water, United Utilities, Welsh Water, Wessex Water) was organised to validate the Polonite® technology. The trial commenced in June 2016, and the plant was run continuously for 12 weeks as a stress test.
Phosphorus removal without chemical precipitation
Polonite® is formed from a highly porous calcium silicate mineral. P in wastewater reacts with free calcium released from the media to form various calcium phosphates, which are precipitated onto the media. Previous studies on wastewaters with levels of total-P between 5-20 mg/l have shown a reduction to 0.1-0.3 mg/l after treatment with Polonite®. In addition, Polonite® has been shown to achieve a 99% reduction in bacteria. The reactive mineral has a limited life (up to 5 years at low flow rate and low consent limit for P discharge) but once spent can potentially be recycled as a nutrient rich, slow release fertiliser.
Wastewater following treatment by the Polonite® filter has a high pH, starting at pH 12 and successively decreasing to pH 8-9. The rise in pH comes from the initial high content of calcium compounds in Polonite, which decreases during time as the material is used. Previous trials using pine bark demonstrated a good reduction in pH.
A successful trial
The main objectives of the trial were to determine:
- the P removal efficiency of Polonite®;
- the impact of the Polonite® media on pH and the performance of the bark pH control solution.
The main results of the Polonite® collaborative trial indicated the following, based on the success criteria:
- P removal. The Polonite® was considered to be successful as it removed >90% total phosphorus during the first six weeks, treating wastewater at a flow of 2 l/min.
- pH control. The bark was considered to be successful as a pH control strategy following the first 5 weeks, which occurred after the bark retention time was increased.
- Disinfection. While the combined Polonite® and bark treatment did not meet the 99% bacterial inactivation target, the effluent met the EU Bathing Water Directive during the trial except for weeks 5 and 7, and it did meet 90% bacterial inactivation.
The continuation of the collaborative trial is under discussion, which will allow a better understanding on the Polonite® media life. In addition, the potential use of P loaded Polonite® is being investigated at the University of Reading with real samples collected from the Polonite® tank. The objective is to verify nutrient content, P availability and plant uptake of P loaded Polonite® as well as the sorption capacity of heavy metals that might be present in contaminated soils and/or wastewaters.
- Somerton Sewage Treatment Work, England
- A collaborative trial to investigate the efficiency of Polonite on small/medium STW
- Polonite and pine bark for pH control
- >90% total phosphorus removal and 90% bacterial inactivation with pH 8-9
- The saturated media can be used as a slow fertilizer enabling a circular economy
- Ilse Utilities and Anglian Water, Irish Water, Severn Trent Water, United Utilities, Welsh Water, Wessex Water
Read more about the trial on Isle Utilities webpage: http://www.isleutilities.com/news/ecofiltrations-polonite-technology-is-successfully-tested-at-somerton-sewag
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