Delivering a Resilient Approach to Tertiary Phosphorus Removal from Wastewater

Lead Research Organisation: Cranfield University
Department Name: School of Water, Energy and Environment

Abstract

The environmental risk associated with the discharge of phosphorus (P) from wastewater treatment plants effluent in freshwaters has been a cause for concern. In that regard,
with the Water Framework Directive coming into place, stricter discharge consents below 1 mgP/L and as low as 0.1 mgP/L are being implemented. In this context, current
approaches for phosphorus removal from wastewater effluents and, in particular, their ability to meet the very low consents are being reviewed so that it can be achieved in a
sustainable and economical way. The dosing of metal salts, coagulation, remains the most efficient commercially available process to remove phosphorus to these very low
levels. However, recent events have also highlighted the limited availability of coagulants and associated to the current political situation, the increased amounts of chemical to
be required to meet new and stricter consents may lead to shortages as well as a significant increase in costs. It is then critical to optimise the coagulation-flocculation process
in order to remove P from wastewater to very low levels sustainably. The efficiency of the overall process is directly affected by floc formation and their subsequent separation
from the water. Recent research work demonstrated the significant impact water characteristics (i.e. solids, alkalinity) have on the process and emphasised the impact chemical
choice, mixing conditions and type of floc separators have on treatment performance but also highlighted the general lack of knowledge available on coagulation in wastewater
to fully understand the mechanisms and optimise the process for all types of conditions. Two aspects are particularly highlighted: (1) the need to understand how the speciation
of phosphorous impact coagulation efficacy as to meet low P standard removal of condensed and poly phosphates will be required. (2) Optimisation of the flocculation
processes is best address with dynamic measurement of floc distributions and is impacted by sampling and transportation. It is expected that to meet effluent P concentrations
as low as 0.1 mgP/L the separation step will have to achieve suspended solids removal down to below 5 mg/L. It then becomes essential to understand these mechanisms to
ensure the right size precipitated aggregates are formed for each type of separator and hence minimise total costs. Consequently, the aim of the proposed project is to develop
a best practice guide of coagulation for tertiary phosphorus removal. To meet this aim, the project will address the following objectives:
- Determine the impact of wastewater characteristics (phosphorus fractions, hardness, alkalinity, competing compounds, suspended solids) on chemical dose, mixing
and separation requirements
- Study and optimise mechanical and hydraulic mixing configurations for optimum floc formation including consideration for retrofit operations
- Determine the connection between floc size development and separation for different solid-liquid separation processes to enable flocculation requirements to be
tailored to the separation processes used.
- Propose a best practice guide for combined coagulation and TSR technologies for P removal to low levels

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023666/1 01/04/2019 30/09/2027
2276616 Studentship EP/S023666/1 03/10/2019 02/10/2023 Rowan Thomas Pearce