Rotherwas WwTW

Sewage from Hereford and the immediate environs is treated by two wastewater treatment works: Eign WwTW and Rotherwas WwTW. The population served is 156,000 (2019), with a predicted population of 177,000 by 2040. Both sites are located in Hereford, England and fall under the responsibility of Welsh Water, with final effluent being discharged to the River Wye. All incoming flows are screened and de-gritted at Eign.

Subsequently the flows are split at 60% to 40% ratio between Rotherwas and Eign, respectively, to undergo further treatment. This case study is focused on the modification works undertaken at Rotherwas. It should be noted that the chemical dosing plants at Eign have also been refurbished/upgraded to optimise phosphorus removal performance on that site.

Existing works & project need
Flows received at Rotherwas are split between four primary settlement tanks (PSTs). A portion of the effluent from the PSTs is pretreated by a high-rate filter (HRF) to lower biological load and then mixed with the rest of settled flow before passing to 18 biological filter beds. The effluent from the biological filters is dosed with poly aluminium chloride and flows into four humus tanks.

Effluent from the humus tanks flows to the works outfall for discharge into the River Wye. Due to the requirement for a new tighter discharge limit for phosphorus, reducing the total standard from 1 mg/l to 0.4 mg/l, Welsh Water were required to undertake modifications to both sites.

Tertiary Solids Removal (TSR)

Several options were considered for the tertiary treatment stage; all of which achieved the necessary solids removal and P performance.

They were assessed against a number of criteria and the FilterClear process from Bluewater Bio Ltd was selected. It should be noted that a major constraint was space on site, and the Bluewater Bio plant’s low footprint meant that it could be located within the existing site boundary, avoiding use of the neighbouring field which is prone to flooding.