Isle Utilities is excited to announce that the Polonite® collaborative trial at Somerton Sewage Treatment Works (STW) has been completed.
Isle Utilities is excited to announce that the Polonite® collaborative trial at Somerton Sewage Treatment Works (STW) has been completed.
Ecofiltration (formerly Bioptech) 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 when applied to small/medium STW arose at Somerton STW.
A collaborative trial, with 6 water companies (Anglian Water, Irish Water, Severn Trent Water, United Utilities, Welsh Water, Wessex Water) was subsequently organised in order to validate the Polonite® technology. The trial recommenced on the 17th of June, 2016, and the plant was run continuously for 12 weeks (the plant had a few days of down time during the 12 weeks due to maintenance issues).
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
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.
For information, please contact Dr Blanca Antizar ([email protected])