successfully delivering an £18m project in a compressed
timescale by innovative and collaborative techniques to achieve
significant process improvements
by Gary Booth, John Clayton, Nicola Henderson, Sam Carroll &
WwTW aerial - Courtesy of Morgan Sindall Sweco JV/Suave
Water’s Saltend WwTW had a history of environmental
under-performance which resulted in a significant number of
customer complaints due to odour. Between September 2015 and May
2016, £18m of refurbishment and upgrade work was carried out on
a fast track basis to improve this performance. Commercial
arrangements were adjusted from normal framework conditions to
suit the collaborative approach required to deliver the changes
to the works that were necessary in the condensed timescales.
Following this investment, the plant has experienced its best
ever environmental performance during the peak season of the
2016 summer period, with only a single verified odour complaint
(non-process related) received. Yorkshire Water also received
complimentary feedback from both the local council and customer
groups. Subsequent to the works, the plant has seen a 20%
reduction in total power consumption and associated carbon
footprint. The collaborative delivery model was also viewed as
great success and Yorkshire Water are reviewing opportunities
and criteria for using a similar delivery model is they move
Saltend WwTW was built in
2001 and serves a population (Hull) equivalent of over one
million, with more than 50% of the incoming load from trade
discharges. The works receives flows of up to 22,000l/s to its
inlet pumping station via an 8.8km long 3.6m diameter tunnel.
The works treats a flow
to full treatment of up to 2000l/s utilising small footprint
technology, including lamella primary settlers and sequencing
batch reactors (SBRs).
The final effluent
consent requirements are 25mg/l BOD (or 70% removal) and 125mg/l
COD (or 75% removal). Final effluent is discharged to the River
Humber. The primary and secondary sludges are thickened,
digested and dewatered. The resulting sludge cake has lime added
before being removed off site for use on the land. There are 4
(No.) lamella settling tanks which utilise inclined plates to
increase the settling area. The plant has 8 (No.) SBRs (each 42m
diameter with 10m water depth) as the secondary treatment
process to biologically remove the contaminants remaining in the
wastewater from the lamellas.
lamella schematic - Courtesy of Aquability OPS Ltd
Prior to the upgrade, the
SBRs were aerated using jet aeration. Each SBR was provided with
3 (No.) jet aeration headers and 3 (No.) mixing pumps. 5 (No.)
600kW HV Turbo blowers deliver air into a common manifold
(duty/duty/duty/duty/standby). The required air flow was
delivered to each SBRs jet aeration header from the common
manifold, controlled by an air control valve.
The SBRs operate in a
cycle which is continually repeated. Each basin is in a
different time in the cycle and there is only one basin filling
at any one time. The cycle at Hull was circa four hours and
comprised five stages;
(i) fill (static and
aerated) (ii) react (iii) settle (iv) decant (v) idle.
The approach to this
project was different to the conventional approach (ordinarily
the award of an investigation contract followed by a risk based
Whilst the investigation
(and delivery) approach was retained, Yorkshire Water adapted it
to include three key phases:
clarification: The scheme was initiated by Yorkshire
Water in August 2015 with a 3-day workshop to understand the
problems to be solved using all available data. The workshop
drew on Yorkshire Water’s AMP6 Framework partners who provided
‘subject matter experts’ to assimilate knowledge and identify a
prioritised list of remediation measures.
a specially formed collaborative multi-party team (the scoping
team) consisting of Yorkshire Water, specialist engineering
consultants Arup, Aquability OPS Ltd, MWH, Turner & Townsend,
and Yorkshire Water’s T1CPs (Tier 1 Contract Partners) was
established to allow detailed design to progress in advance of a
delivery contract. This approach greatly accelerated the speed
of construction delivery.
Conventional delivery scheme by MS2JV (Morgan Sindall Sweco
The team was located at
the Saltend site to ensure close collaboration, ownership of the
problems and to establish a commitment that the team would ‘fix’
Saltend together by 31 May 2016. Key to driving the tight
timescale was the acceptance of process risk by Yorkshire Water
thus removing the requirement for MS2JV to undertake extensive
investigation works. There were two contract formats employed:
NEC3 Option E (emergency
works) for the workshop and scoping phases.
An amended version of
NEC3 Option C for the delivery phase batch.
The Option E contract was
used to work with multiple organisations in the initial scoping
In the delivery phase,
the NEC3 Option C contract was amended and a mechanism was
incorporated to allow the contract value to be increased in
phases from an initial £2.5m up to its final value as new work
scope was identified and approved. The amended contract and
change mechanism enabled Morgan Sindall Sweco JV to accept the
initial target cost and allowed for early contract signature.
The scoping phase focused
on developing the list of interventions identified at the
initial design workshop into packages of work to be delivered by
the Morgan Sindall Sweco JV. The main packages were:
Inlet pumping station new
odour control unit (OCU) by ATS.
New assets to enable
chemical assisted precipitation in lamellas; new desludge pumps;
refurbished and modified lamellas (NPS).
Secondary Treatment (SBRs)
modifications; conversion of jet aeration system to fine bubble
Enhanced dissolved oxygen
(DO) and redox instrumentation; a change of air control valves
to plug valves; replacement air flow meters; decanter isolation
plug valves; refurbish decanters and modulating valves (Staptina).
Improve control and
availability of air blowers (TCS).
monitoring on each SBR (Hach Lange).
Pre-treatment at source
Pre-treatment at a large
The collaborative model
was taken into the delivery phase of the contract with the
client, the scoping team, the supply chain partners and MS2JV
staff all remaining co-located at Saltend. The MS2JV design team
also moved to site such that they could coordinate and develop
the design with the supply chain partners and scoping team.
In order to fast-track
the design and avoid any duplication of effort MS2JV worked
closely with the supply chain partners to clearly define the
scope and limits of their design. Several of the supply chain
partners were given early works contracts ahead of their main
orders, this to allow them to progress the design in line with
the tight timescales. At one stage or another, representatives
from MS2JV, Circle Controls, NPS, ATS, Nomenca, Suprafilt, CEMA,
TCS, Staptina, Ward & Burke, Waitings and EMS were all based in
the co-located office developing their elements of the design.
allowed the teams to develop the design with continued reference
back to the decisions made by the scoping team. YWS’s
operational team were also based in the co-located office,
providing continuous input to the design both informally and
through the design reviews and the HazOp and HazComm meetings.
Extensive use of CLIP (Construction Lean Improvement
Programming) was made to build, refine, improve and communicate
the planning of the works.
CLIP on action
Courtesy of Morgan Sindall Sweco JV
Mindsafety stand down event
Courtesy of Morgan Sindall Sweco JV
Key factors for success
Frequent (often daily)
programme review sessions were held to ensure any programme
movement was understood and mitigated.
Weekly cross-party ‘Hub’
review of performance dashboard was undertaken.
The appointment of a full
time dedicated Yorkshire Water team to support partner activity,
ensures rapid decision making and engenders overall team spirit
An independent third
party undertook periodic peer reviews.
The team was based at
Saltend in a large site set up. This created adequate space and
facilitated a high level of collaborative working from all
Continuity of key staff
was retained throughout the lifecycle of the project.
Supply chain involvement
As with all large
projects supply chain collaboration was key to the successful
delivery. The supply chain was involved throughout the project
and was given early visibility as to the scope and nature of the
works at a ‘whole team’ initiation workshop. The workshop
allowed the supply chain to engage in understanding the issues,
significance of the project and timescales. During the workshop
a clear project charter was developed that all supply chain
partners were invited to sign up to.
approach was continued throughout the delivery phase with
partners given access to the site office which allowed for team
working, engagement and support.
Treatment at Saltend
Prior to the initial
workshop, an odour survey was carried out by MWH, identifying
that 54% of the odour generated was from the SBRs and 42% from
the inlet pumping station. Further review of the lamella’s and
SBRs identified that the main issues causing the odour
generation and poor performance were:
SBRs were overloaded due
to poor BOD and solids removal in the lamellas.
Major issues with SBR
control (resulting in inadequate aeration and solids carryover
in the final effluent).
Inefficient SBR aeration
(jet tech system), unable to satisfy the biological oxygen
demand of the wastewater (resulting in septic conditions).
Reducing the odour
at the inlet pumping station: To reduce the odour, a
carbon filter OCU (odour control unit) was installed by ATS to
treat 20,000m3/hr of air. Hydrogen sulphide concentrations were
monitored in the vent stack. When levels reached a pre-set
limit, the 30kW duty/standby OCU vent fans started to treat the
odorous air through the carbon filter before it was discharged
This approach meant the
life of the carbon was maximised and prevented unnecessary
operation of the fans with their associated power consumption.
Lamella plant - Courtesy of Morgan Sindall Sweco JV
performance: In order to improve lamella performance as
quickly as possible, and allow the optimum chemical dose rate to
be determined a temporary modular plant was also adopted at the
Saltend WwTW where MS2JV utilised a modular chemical dosing
plant (supplied by NPS) and chemical storage tanks (BakerCorp).
The use of temporary modular plant allowed for the provision of
ferric and polymer dosing ahead of the permanent works
The lamellas had enclosed
inlet flumes with small orifices that fed the wastewater into
the lamella plates. These orifices were prone to blocking up.
The blockages were causing poor flow distribution and high
velocities between the plates which caused solids to carry over
with the effluent.
The solution was to cut
large ports in the bottom of the enclosed inlet flumes (from
Staptina Engineering Services) so that any screenings/large
solids would fall straight in to the bottom of the tank and be
removed with the sludge. The wastewater could then flow evenly
between the plates, unhindered.
modification, removals increased more than two-fold and
approximately 60% solids and 40% COD removal was achieved with a
dose rate of 5-10mgFe/l.
To facilitate the removal
of the increased quantities of sludge from the lamellas, each
lamella was fitted with a new RAM pump (EMS) and dry solids
monitor. Revised desludging control maximised solids removal
whilst maintaining sludge concentrations at around 1-2%DS. This
allowed the downstream sludge thickening process to be optimised
and resulted in a 7% increase in gas production from the
reliable and healthy SBRs: The existing SBR control system had
various defects that included:
Poor dissolved oxygen
(DO) and blower control resulting in low DO (leading to odour
generation and effluent failure).
Excessive stop/start and
failure of the blowers.
Poor decanter control
leading to solids carryover and effluent failure.
Insufficient cycle time
to treat high loads.
A revised SBR control
philosophy was developed by Aquability Ops and Cougar, utilising
three cycles (6, 5.3 and 4 hours respectively) to treat the
wastewater, with a unique method of switching between cycles.
This approach maximised the time available to treat the high
loads. The dissolved oxygen, blower and decant modulating valve
control was also modified to overcome the identified issues.
aeration - Courtesy of Morgan Sindall Sweco JV
Under high load
conditions, there was insufficient blower capacity to satisfy
the oxygen demand with the jet aeration system. The jet aeration
system was susceptible to nozzle blockages, and also caused floc
shear and poor sludge settleability. In order to increase the
aeration efficiency and reduce the air flow requirements, the
jet aeration systems (headers and mixing pumps) were replaced
with a robust stainless steel fine bubble diffused air (FBDA)
system from Suprafilt.
Each SBR was equipped
with 886 tube diffusers. These modifications have had a
significant effect on the SBRs performance and power
consumption. The increased efficiency of the FBDA has reduced
air flow requirements by more than 50%. Aeration power
requirements have reduced by 625kW with a 20% reduction in
overall site power consumption.
The plant has been in
compliance for over eighteen months. Since completion of the
upgrade, the plant has achieved an average COD of 82 mg/l and
85% removal. Settleability has improved with SSVIs reducing to <
70ml/g. The process is now very robust, maintaining compliance
even when operating on only six of the eight basins.
performance - Click to enlarge
Aquability OPS Ltd
SBR Jet Tech
Aquability OPS Ltd
source/network type solution
As part of the solution
the team adopted a ‘treatment at source’ network solution. This
involved the installation of a temporary treatment works within
the catchment to deal with peak flows.
MS2JV worked with Arup
and Siltbuster to design a temporary modular treatment works
that was utilised to treat high loads at source and provide
resilience to the Saltend works. The modular temporary treatment
works, designed to treat an average flow of 208m3/hr, comprised:
Flow control tank.
2 (No.) DAF units.
Sludge dewatering unit
Sludge storage tank.
Chemical storage tanks.
The team designed the
plant to include a number of Siltbuster’s ‘standard product’
treatment units as well as the flow control and balance tanks
that were designed and manufactured specifically for the Saltend
project. The sludge dewatering unit was supplied by MSE Hiller
and the chemical storage tanks by BakerCorp. The installation
works involved extensive site preparation that included drainage
and concrete hardstanding. The narrow elongated nature of the
site required extensive logistics management to ensure the units
arrived on site in the correct order and that they could be
safely lifted into position.
The modular nature of the
plant allowed MS2JV and Siltbuster to adopt factory-type
principles in sequencing the build and con-current MEICA
activities. Commissioning of the plant started within one week
of the first modular unit being delivered to site. In addition,
MS2JV operated the temporary treatment plant.
Morgan Sindall Sweco JV
Morgan Sindall Sweco JV
Interface with Saltend
The project team was very
well supported by the existing Yorkshire Water Saltend
operational team; they were very much brought into the
collaborative approach. A section of the operational team was
permanently seconded to the project team and co-located within
the collaborative office. This approach greatly benefitted the
project. Notable areas included:
Granting of permits.
Coordination of other
works on site, direct for Yorkshire Water.
Daily operational status
of the site.
Assisting with fact
finding on the existing site.
The continued support of
the Saltend operations team was key success factor.
Collaborative approach to
The approach to the safe
delivery of the works with a challenging timescale was managed
with a consistent and shared approach by all involved, and
helped develop good safety culture and behaviours.
Safety was paramount in
the delivery of the works in the short timescales. MS2JV
organised a daily safety coordination briefing that was attended
by all on site. The focus of the briefing being to ensure that
everyone knew what activities were taking place, that
permits/safe systems of work were in place and approved and to
ensure the coordination of site activities/logistics etc.
As well as the day-to-day
management of safety the MS2JV management team implemented a
number of safety measures that included:
Safety leadership tours.
Feedback as regard
‘You Said, We Did’ boards
- indicating how MS2JV had responded to feedback.
Mind safety coaching
session (a half-day stand down session for all site based
personnel was held half way through the scheme).
Implementation of high
Morgan Sindall Sweco JV
Inlet PS OCU
Morgan Sindall Sweco JV
A successful outcome
decision to do things differently using an innovative
collaborative approach, brought together a diverse team of
expertise resulting in the successful outcome of a technically
challenging scheme, on programme, exceeding all expectations:
£18m of investment
delivered in 9 months.
There have been no odour
complaints associated with the process.
Robust plant operation
and performance with continued effluent compliance.
A 20% reduction in
overall site power consumption.
This way of working is
undergoing a thorough post project review, the outcome of which
will inform ways of working for the remainder of AMP6 and into
and publishers would like to thank Gary Booth (Yorkshire
Water), John Clayton (Turner & Townsend), Nicola Henderson (Aquability
OPS Ltd), and Sam Carroll and Stewart Evans (both with
Morgan Sindall Sweco JV) for providing the above article for