The application of mine waste for the removal of phosphorus from wastewater

Abstract

The research presented in this thesis aimed to investigate the use of ochre, produced during mine water treatment, for the removal of phosphorus from wastewater. Three methods of ochre application were tested: as part of a filter-based system, dosed directly into wastewater and transformed into a coagulant. Ochre from five sites in North East England were used in the trials; Acomb, Bates, Blenkinsopp, Dawdon and Saltburn.

Prior to the ochre-based filter trials, three binder materials were tested for mixing with Dawdon ochre to produce an adsorbent layer. Based on these trial results, the Dawdon ochre was mixed with sand for the onsite ochre-based filter trials. These trials were completed on two scales: within an IBC and within pond filter units. The filter trial results suggest that ochre-based filters are capable of removing phosphorus as a tertiary treatment, but removal is not consistent. Small-scale growth experiments were completed to determine whether phosphorus-saturated ochre adsorbent from filter systems could be used as a fertiliser. The results from these trials suggested phosphorus-saturated ochre does not improve plant growth.

Phosphorus removal when dosing ochre was investigated at bench-scale. The trial showed that the ochre was capable of removing phosphorus but was not able to equal the removal of ferric sulphate. Phosphorus removal when dosing ochre was found to be affected by ochre dose, source and form as well as flocculation time. All five ochres were trialled.

The coagulant produced from the five ochres (ochre derived ferric; ODF) was trialled as part of bench-scale jar tests which demonstrated the phosphorus removal potential. The results showed that the ODF was not as effective as ferric sulphate and does not have an equivalent iron content. A trial was completed dosing Bates ODF upstream of primary settlement tanks at a sewage treatment works, however, the results were inconclusive.