United Utilities chemical investigation programme 2 and low
by Wendy Rostron & Dominic Holt
electic suction lift pumps - Courtesy of MMB
Water Framework Directive (WFD) all water environments in the UK
must meet ‘Good Chemical Status’ for a number of chemicals. The
chemicals cover a range of over 70 substances (often referred to
generically as priority substances) including metals,
pharmaceuticals, combustion products and regular sanitary
determinands (including phosphorus). The Environment Agency
instigated a national programme of works to investigate the
impact of wastewater discharges on the concentrations of these
chemicals in the receiving waters and the ability of
technologies to remove these chemicals from such discharges.
Each of the UK’s Water and Sewerage Companies (WaSCs) was
assigned a different set of process technologies to investigate
and as such the scope of the projects was very prescriptive. The
work will enable the water industry to ascertain what is
technically feasible at reasonable cost and allow the EA to set
future permit limits.
The programme is governed
by a national steering group and is managed by Atkins and UKWIR
on behalf of the EA. The information from all the studies will
be shared in order to maximise information and minimise
duplication of effort.
The programme of work
comprised many projects including the Chemical Investigation
Programme 2 (CIP2) which primarily focussed on the more complex
chemicals which are not commonly controlled under current
regulations. In addition, since 45% of the rivers in the UK fail
predicted WFD standards for phosphorus (P), this was given its
own programme known as P1 or low P.
Analysis of data has
shown that many wastewater treatment works will have to meet
very tight final effluent P concentrations and low P permits
will be enforced. Current P consents are generally between
1-2mg/l and the national trials set out to investigate the
belief that current methods of P removal (commonly ferric
dosing) could possibly be optimised to achieve a final effluent
standard of 0.5mg/l P but below this advanced/tertiary P removal
technology will be required.
GreenCAT pilot plant - Courtesy of MMB
United Utilities trials
As part of the national
programme United Utilities (UU) were required to complete the
following 12 month trials:
CIP2 process technology
pilot trial projects
‘BlueCAT’ (since renamed
‘GreenCAT’) priority substances (PS) removal trial.
process (AOP) PS removal trial using ozone and hydrogen
P1/low P pilot trial
Rapid gravity sand
filtration (RGF) dosing trial.
continuously operated upflow filters (COUF) for P removal.
Activated sludge plant
ferric dosing optimisation trial.
Mineral filter works
ferric dosing optimisation trial.
pilot plant - Courtesy of MMB
Scope of work definition
From MMB’s first
involvement it was clear that the approach to how the scheme
would be defined and implemented would be heavily influenced by
the required trial commencement dates, set nationally as part of
the wider programme.
In defining the detailed
scope of works to allow costing and sub-contract tendering, UU
and MMB worked collaboratively to reach an agreed level of scope
detail, with due consideration to the following:
The need to place
sub-contract orders as soon as possible for the three key
subcontract elements of work, due to the impact of long lead
time items on the start on site dates.
These elements represented a combined valve of nearly 50% of the
£6.6m scheme value. In order to do this, the sub-contract
packages had to be sufficiently defined and finalised to allow
the tendered scopes to quickly be converted into final order
packages. This also meant the subcontract competitive tendering
process had to be integrated into the cost definition phase.
An awareness and
appreciation of how the trials would interact with the existing
site operations, how the integration of the plant would be
achieved and also how decommissioning would be approached and
the works returned to their original status.
On some of the sites this included utilising existing chemical
storage facilities, but providing new kiosk housed dosing rigs,
that were then linked to existing storage tanks. On another site
it required designing and installing compact dosing rigs that
followed the current design specifications, but could be
installed into existing cabinets that presented significant
Whilst acknowledged to be
temporary plant, it was also fully appreciated that the plant
solutions would have to provide safe, reliable, maintainable,
operational solutions, for 24/7 operation over the course of
both the optimisation and trial operation periods.
Where operated by UU operations it was also appreciated that
compliance with UU standard design and specifications would
enable the site teams to accept and operate the plant more
confidently than might be the case with purely temporary or
hired plant solutions.
This was particularly the case for the design and specification
of the chemical dosing systems. Framework compliant plant would
also allow ready relocation and reuse of the plant post-trials,
with minimal rework or modification.
considerations also needed to be accounted for, such as bunded
chemical delivery areas and associated safety and washdown
facilities. One site was designed and installed as a permanent
installation, in a high-profile location within a national park
and the works included providing an external covering to the
kiosks, to allow them to blend in with local construction
materials for the existing buildings.
Avoidance of construction
of traditional civils assets, such as wet well pumping stations,
buried pipework and duct routes, on sites where the assets would
be removed post-trial. In particular on two sites, a Selwood
suction lift and centrifugal pumps were used to avoid the need
for new submersible pumping stations. In addition, due to the
cost benefit of bought versus hire purchase, they were bought
outright. As the units are variable speed, electric motor
driven, each with a dedicated control panel, they should be
readily suitable for redeployment on either a permanent or
temporary basis by UU.
Ferric sulphate dosing rig in existing cabinet
Courtesy of MMB
backboard for phosphax analyser
Courtesy of MMB
MMB contract delivery
UU contracted MMB to
design and build the six trial plants, and to operate the two
CIP2 demonstration plants for 12 months following commissioning
and a period of optimisation. On completion of the trials, the
plant was to be decommissioned. As principal designer and
principal contractor, MMB’s approach was to form subcontractor
partnerships with the key suppliers:
Solutions: Sole UK supplier of GreenCAT technology.
Xylem: Ozone equipment.
Verder UK Ltd: Chemical
A collaborative working
approach was taken with MMB, UU and the key suppliers focussing
on design for manufacture and assembly (DfMA) so that projects
could be delivered safely to a tight programme.
Due to the nature of the
trials, there were common aspects of the designs; for example 7
(No.) Hach Phosphax analysers were installed to measure the
orthophosphorus in the sewage.
A bespoke backboard was
designed to hold the analyser equipment, and this was replicated
for all sampling locations. The design of the board was
completed by MMB in consultation with Hach to ensure the correct
siting and levels for each component in the system.
On sites where existing
ferric dosing systems were located, the P control was achieved
by both new crude and mid-process analysers, that allowed
operation of the secondary dosing to optimise the P removal.
The same approach was
taken with the iron analysers, installed to ensure compliance
with the iron permits. As part of the control philosophy, high
concentrations of iron would inhibit the dosing.
The GreenCAT process was
specified by UU following successful trials of Evergreen’s
BluePRO process, which achieved over 95% removal of total
phosphorus when trialled at a constant flow rate. The GreenCAT
includes ozone dosing upstream of the COUF to enable both PS and
TP to be removed within the same plant.
GreenCAT pilot plant - Courtesy of MMB
Due to the ozone dose
levels involved, Evergreen selected a system utilising a
pressure swing absorption (PSA) process to feed a compact
self-contained ozone generator.
The PSA system was fed by
duty/standby blowers, which were co-located within a dedicated
container with the ozone generation and also duty, standby ozone
destructors (which removed excess ozone from the process). The
container also included a separate, dedicated MCC room and
control section, sealed off from the ozone generation section.
Internal oxygen and ozone
detectors ensured the environment within the generation area was
constantly monitored and a traffic light indication was provided
externally to prevent entry in the event of alarm levels being
The system was fed from
an existing wet well structure, into which duty, standby,
guide-rail mounted, variable speed, submersible pumps were
installed to provide up to 24.6l/s of flow taken as a
side-stream from the secondary treated effluent (ASP) channel,
and returned just downstream after treatment through the
GreenCAT. The system was protected by a Bollfilter automatic
The process feed was
dosed with sodium hydroxide, ozone and ferrous chloride prior to
being fed into an arrangement of selectable vertical, ozone
contactors. Selection or bypass of the 4 (No.) available
contactors determined the ozone contact time and the preferred
selection was developed during optimisation. After passing
through the contactors the process then fed into the GreenCAT
filter. Excess ozone was captured at the head of the reactors
and GreenCAT filter and piped back to the ozone destructors in
AOP trial plant
Xylem was the
subcontractor for the large scale AOP trial, (10ML/d plant),
providing the ozone dosing equipment and in turn subcontracting
the hydrogen peroxide dosing to WES.
contactors - Courtesy of MMB
Given the relatively high
ozone dose level needed, the Xylem system presented a well
proven, self-contained, portable dosing system. Whilst used
extensively in clean water applications, the use of this
technology in wastewater applications is less common, but as the
effluent was post-humus tanks and fed via a Bollfilter automatic
backwashing filter, this did not present any significant issues.
The system worked on the
basis of a pumped circuit, fed via Selwood suction lift
centrifugal pumps to provide up to 116l/s of flow, taken as a
side-stream from the humus outlet channel and returned
downstream into the BAFF feed pumping station wet well.
A branch off leg from the
pump main fed a secondary side-stream to the ozone generation
container, where ozone was introduced via a pumped eductor
Prior to injection back
into the pump main, hydrogen peroxide was dosed via a static
mixer. The injection system was housed within the hydrogen
peroxide dosing and storage container. An above ground degassing
chamber was provided at a point sufficiently downstream of the
injection point to ensure adequate ozone contact time. Flow then
gravitated to the BAFF feed wet well.
The degassing chamber was
a sealed chamber and any excess ozone was captured and fed to an
adjacent ozone destructor.
The Xylem system used
liquid oxygen storage (provided by BOC) for the ozone
pilot plant feed pumps - Courtesy of MMB
Ferric, ferrous and
Verder was chosen as the
chemical dosing subcontractor, providing ferric/ferrous dosing
and sodium hydroxide dosing kiosks and modifying existing dosing
plants where required.
Maximum use was made of
the existing dosing rigs on site. For the purposes of the trials
it was agreed that existing duty, standby pumps could be
modified to operate as duty, assist where the maximum expected
dosing rates were only slightly above the existing duty
New dosing packages were
designed as self-contained pumping and dosing units built in to
a bespoke GRP housing. This helped simplify installation and
commissioning, and also meant that following decommissioning, UU
has dosing kiosks which can be readily moved to other sites.
A key element of work
involved developing the control software systems which would
regulate the dosing activities. Although the dosing control
requirements varied across the sites, it was decided to progress
one control philosophy which included different modes of
control. In this way one set of software was developed and
implemented and if a change to the dosing control method was
required, a different operating mode could be chosen on the HMI.
The main control of the
ferric dosing for P removal was based on UU’s dosing rate
algorithm, as previously reported in UK Water Projects 2014 -
Phosphorus Removal AMP5 Programme. Phosphax analysers were
installed to give measured real-time control to the dosing. The
GreenCAT and the COUF removal trial used a set dose rate in
terms of mg/l of iron. Where required, alkalinity dosing was
installed and controlled as a ratio of the ferric/ferrous dose.
plant - Courtesy of MMB
Interaction with main
The two CIP2 trial plants
were side-stream processes with negligible impact on the main
wastewater treatment works, and so could be installed and
commissioned with minimal regard to the works. However, the four
low P trials were full-scale trials, carried out on sites with
existing P, iron and pH permits which could not be put at risk.
Risk to compliance plans were developed and agreed with
Operations for each site prior to commissioning in order to
Detailed site surveys
were carried out to consider elements such as site access
through to the location of the new dosing equipment and dosing
line routes. Storage tank capacities had to be evaluated to
ensure that sufficient quantities of each chemical could be
maintained on-site, combined with assessment of existing storage
facilities and associated delivery areas and blind tank
3D CAD software was used
by Verder for the design and layout of the chemical dosing plant
and MMB developed a 3D model of the AOP plant to aid layout and
integration of the ozone and HP containers in relation to the
pumped main circuit.
also allowed careful considerations of dosing point locations
and assessment of the respective benefits or drawbacks
associated with each.
Given the significant
proportion of factory built and tested package plant, emphasis
and attention was placed on the FAT tests to ensure that the
plant was delivered to site in optimum condition. On site
commissioning was carried out collaboratively between MMB, the
subcontractors and UU.
covering to GRP kiosk - Courtesy of MMB
Operation and performance
The CIP2 sites were
operated by MMB Process Operators, whilst UU Process Operators
managed the four low P sites. Regular meetings were held at each
site to discuss the performance.
Reports were written on
all the trials and submitted to Atkins, who are collating all
the information on behalf of the EA. The results from all the
trials are due for publication in Summer 2017.
and publishers would like to thank Wendy Rostron, Senior
Process Engineer, and Dominic Holt, Project Leader, both
with MMB, for providing the above article for publication.
The authors would like to thank Carolyn Heath, Project
Engineering Manager with United Utilities, for kind
permission to publish this article.