improving the resilience of the wastewater treatment
infrastructure serving parts of the North Thanet coast
by Jon Yates BSc (Hons)
WwPS is surrounded by a high concentration of Blue Flag
beaches and sits within a popular tourist area - Courtesy of
Southern Water completed significant improvements to the
wastewater treatment infrastructure serving the North Thanet
catchments of Margate and Broadstairs to meet the requirements
of the Urban Waste Water Treatment Directive. The existing
marine head works at Joss Bay, Broadstairs and at North
Foreland, Margate were upgraded to process screened flows and
remove grit, alongside the construction of a new Wastewater
Treatment Works adjacent to Southern Waterís existing site of
Weatherlees Hill, named Weatherlees Hill B WwTW, to serve a
population equivalent of 89,000.
Background to the
Prior to these upgrades,
the sites at Broadstairs and Margate worked independently. The
completion of the 2008 upgrade scheme created the Broadstairs
Wastewater Pumping Station (WwPS), and a wastewater pumping
station with preliminary treatment at Foreness Point, called
Margate WwPS. Both these pumping stations are surrounded by a
high concentration of Blue Flag beaches and sit within a popular
Broadstairs WwPS receives
wastewater flows from the town of Broadstairs and its
surrounding area via a combined sewer system. It has a lift and
transfer pump system which can transfer up to 264l/s to Margate
WwPS via a 2.4km, 450mm diameter pipe.
Margate WwPS receives
wastewater flows from the North Thanet catchment via a combined
sewer system, which mixes with the flows received from
Broadstairs WPS. All receiving flows are screened and grit is
removed before being forwarded by three transfer pumps, pumping
in excess of 809l/s to Weatherlees Hill B WwTW over 11km away.
Wastewater flows received at Weatherlees Hill B proceed through
a step fed activated sludge plant, final settlement and
ultra-violet disinfection before being pumped 11km back to
Margate WPS where it is released via the long sea outfall in to
the North Sea.
In 2012, pumping station
failures during heavy rain resulted in pollution events, the
closure of many of Thanetís beaches for a period of nine days,
and a follow up hand clean costing £400,000.
A fine of £2m was
received in relation to this incident in December 2016. This
followed a fine of £200,000 received in 2013 for breaching an
Environmental Permit during 2011. As a consequence, and in order
to reduce the risk of future incidents occurring, an extensive
resilience scheme was initiated.
Significant improvements have been made to the
wastewater treatment infrastructure at Margate and
Broadstairs - Courtesy of Southern Water
The initial approach to
the scheme was to first fix and rectify the results of the 2012
failures. Since those incidents, Margate WPS has been manned
24-hours a day to ensure that the process remains constant and
any issues are spotted instantly and can be acted upon.
Heavy localised rainfall
and plant failures over the Jubilee Bank Holiday weekend of 2012
resulted in the main treatment area of Margate WPS being under
two foot of flood water. The resulting clean-up and remedial
works to stabilise the process was the starting point to
highlight which areas needing improved resilience.
Inlet penstock control:
As part of the resilience works a review into the inlet penstock
control was carried out.
Greater control over the
operation of the penstock was added to ensure that the maximum
flows are sent to site at all times. In addition, an isolation
is to be installed to allow greater control and isolation of the
inlet screws to maintain maximum flows to site, run on a
► Inlet screw auger:
A review of the inlet screw auger was also undertaken. The screw
augers were installed during the overhaul of the marine works in
1984, and a bearing replacement was undertaken after multiple
failures of the pumps. It was found that the lubrication system
was the failure point for the bearings.
The way in which the oil
lines had been installed needed modifying to prevent rag from
catching and resting on the oil line, causing the pipe to buckle
and preventing oil from getting to the lower bearing. The
bearing lubrication was upgraded to a larger tank with the
delivery and return hoses upgraded to a heavy duty armoured
A critical spares
assessment was carried out - a spare set of bearings are now
housed on site at Margate WPS as well as changes being made to
the monitoring of the oil lines and planned proactive
maintenance. The frequency of the inlet sump clean has been
increased to reduce the risk of blockages.
► Screw pumps:
As part of the asset life cycle process, further investigations
are being carried out on the existing screw pumps to assess the
remaining life span of the current units.
► Inlet screens:
The inlet screens, duty/standby in dry weather and duty/duty in
high flows, have been in operation since 2011. These have been
reviewed with modifications and amendments being made to ensure
maximum removal rate. This has included modifications and storm
upgrades to the screen panels, the addition of teeth to the
panels and the manufacture of a panel to ensure maximum cleaning
of the panels during routine maintenance. Each screen now
processes flows up to 1,000l/s.
► Inlet macerators:
The inlet macerators also received upgrades between 2011 and
2015. The method in which the macerators process the screenings
has altered from cutting to ribbons, to cutting the screening
into confetti. The liseptors (liquid separator) and lipactors
(liquid compactor) which receive the macerated flow have been
subject to increased planned maintenance with a greater number
of critical spares being held on site.
This element of the inlet
process has historically been the area that results in the
highest number of reactive callouts. In 2015, the inlet
screening handling was diverted to two Kuhn Washpactors
operating duty/standby. These units dramatically reduced the
number of repairs and improved the overall screening removal
rate. The macerated flow system filled a screening skip over a
10 day period; the washpactors fill a skip within 7 days.
Since the trial of the
new washpactors in 2015, Southern Water has taken the strategic
step to process all screenings at Margate using these.
► Transfer pumps:
The transfer pumps had previously had a high number of reactive
call outs alongside planned maintenance due to excessive
vibrations when running at high flows. As a trial, a temporary
replacement pump was installed in 2011. The pumping
characteristics and the reliability of the temporary pump lead
to a replacement of the three remaining transfer pumps, albeit
with a modified speed of 60Hz.
This replacement also
lead to a replacement of ducks foot and guide rails, as well as
sump modifications. Manual valves were added between the balance
pipework to allow isolation for proactive cleaning and
maintenance whilst allowing for the treatment process to
continue. The site now runs on four new transfer pumps operating
a duty/assist/assist/standby regime. The site also has a box
spare transfer pump to minimise the amount of down time from
four operational pumps.
► Washwater system:
After the issues in 2012, the washwater system has been modified
and strengthened by the addition of a surge vessel to maintain
the correct pressure and flow within the system.
The washwater on site at
Margate WwPS is final effluent and is taken from a point on the
return rising main from Weatherlees Hill B WwTW. To maintain the
constant supply of washwater the site has duty/assist/standby
pumps. The delivery valve has also been upgraded to allow for
maintenance and reliability purposes.
► Air valves:
A review and replacement of the air valves on the rising main
from Broadstairs WwPS to Margate WwPS and from Margate WwPS to
Weatherlees Hill B was undertaken in view of the transfer pump
replacement at Margate WwPS.
Flows in excess of 809l/s, and once the 8,000m3 of upstream
storage has been filled, are processed via the storm pumping
station on site at Margate WwPS.
full site wide review of the control and automation of
the process is now underway - Courtesy of Southern Water
The Margate WwPS storm
process has been improved as part of the resilience review; the
storm screens have received the same upgrades and modifications
as the inlet screens. Both inlet and storm screens are the same
model albeit with different size specifications. Both remove
screenings to 6mm 2D. The storm macerators have also received
the same upgrades and modifications as the inlet. Both process
areas, inlet and storm, share the common liseptor and lipactor
equipment. To ensure these continue to operate during storm
conditions, manning of the site has been increased to allow for
a quick manual interception to bring any blocked pumps back into
service in the shortest time possible.
As part of the current
resilience scheme the storm macerated flows and receiving liceps
and lipactors are to be replaced by the new Washpactors.
Once storm flows have
been screened they pass to 5 (No.) canister storm pumps. These
pumps operate duty/assist/assist/assist/standby and will
transfer flows from the storm sump to the storm return tank at a
rate of 6,400l/s. To ensure that the maximum flows are delivered
by these pumps we will be fitting flowmeters to the vertical
rising mains. Due to the size of these pumps and the turnaround
time when the pumps need to be overhauled, a box spare is stored
on site at Margate WwPS to minimise down time.
The storm return tank is
a 30m deep, 12m diameter storage tank constructed within the
boundary of the site. This tank will store approximately 4,000m3
of stormwater. Once this storage has been used, flows will then
be released via the long sea outfall pumps. These pumps will
forward flows to the long sea outfall where the screened storm
flows will mix with the treated final effluent from Weatherlees
Hill B WwTW. As part of the resilience project a full overhaul
of the pumps has been carried out along with a review of the PLC
and control system.
Margate WPS receives wastewater flows from the North
Thanet catchment via a combined sewer system - Courtesy
of Southern Water
A full site wide review
of the control and automation of the process is now underway;
this review is a comprehensive review of the code. To ensure the
system if fully auditable a new server has been installed and
there are now individual access codes to access the control
Currently, Margate WwPS
is in the final stages of installing the new screening handling
equipment. All screenings are being processed by new Washpactors
from 1 May 2017.
The completion of this
extensive resilience scheme at Margate WwPS is scheduled to be
completed by 2020.
The inlet pumps and storm
pumps at Broadstairs WwPS are also being captured as part of the
scheme. Works are to be carried out on the inlet lift pumps and
the storm lift pumps. This configuration works in a duty/assist,
duty/standby arrangement. The inlet lift pumps will lift flows
up to 600l/s; if the flows are higher the storm lift pumps will
lift flows up to 1,125l/s. An overhaul of the inlet lift pumps
is still to be carried out. The storm pumps are to be replaced
with larger pumps which have increased headroom.
Due to all three sites
communicating with one another, a review of the control and
automation at Broadstairs WwPS will now be carried out. This
comprehensive review will look at the way in which the site
currently runs and consider any changes that could be made to
further increase the resilience of the process. Work at
Broadstairs WwPS is due to be completed by 2020.
Margate WPS is located at Foreness Point and combines
flows from the Margate catchment and Broadstairs WPS -
Courtesy of Southern Water
Educating the local
Alongside the investment
on site, an extensive education campaign has been conducted with
local residents and stakeholders. Issues are often encountered
on site due to the levels of screenings received via the
combined drainage network.
Through educational talks
to schools as well as community and business groups, a number of
open days at Margate WwPS, action days and face to face contact,
Southern Water has helped to engage with customers and explain
what should and should not be flushed down the toilet or washed
down the sink, and to highlight the impact on our infrastructure
caused by the incorrect disposal of fats, oils, grease and
unflushable items, such as wet wipes and sanitary items.
In 2014, a Bathing Water
Steering Group was established which includes representatives
from Thanet District Council, the Environment Agency and local
business and community groups to progress joint activities aimed
at further improving bathing water quality across Thanet through
and publishers would like to thank Jon Yates, Project
Manager with Southern Water, for providing the above article