Water Engineering Australia July 2009 Cover Story.pdf - Hastings ...

COVER
Improving
water quality
on NSW’s mid
north coast
A $25 million investment by Port Macquarie-Hastings Council to improve the
quality of its drinking water has been recognised by Engineers Australia’s Newcastle
Division for its engineering excellence.
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WATER TREATMENT
The Wauchope Water Treatment Plant
(WTP) Project has been recognised with
two prestigious awards at the Engineers
Australia Newcastle Division’s 2009 Engineering
Excellence Awards.
Commissioned in 2008, the project won an
overall award for Excellence, placing it in the
running for the national Excellence Awards at
the end of the year. It also received the Award for
Innovation in Sustainable Engineering Excellence.
The plant, which is near Port Macquarie on the
NSW mid north coast, is a $25 million investment
by Port Macquarie-Hastings Council to
improve the drinking water quality for all consumers
and to better achieve the quality standards
set by the Australian Drinking Water Guidelines.
The plant fi lters the drinking water for the
Wauchope water supply scheme, west of Port
Macquarie, which includes the Wauchope,
Beechwood, King Creek and Sancrox areas. Water
conditioning facilities within the plant also help
to increase the alkalinity and stabilise the pH
of all water pumped from the Hastings River at Koree Island,
before it is stored in the Port Macquarie and Cowarra off-creek
storage dams.
The site at Quarry Road includes a treatment plant building,
a 5ML clear water reservoir, a clear water pumping station and
educational facilities to further enhance Council’s WaterWise
education and community awareness programmes.
The filtration plant has a daily water treatment capacity of
6ML, with the ability for future upgrade to 18ML/d. The water
conditioning facilities are able to treat 120ML/d.
The main players
The project’s construction was managed by the NSW Department
of Commerce; the NSW Government Architect’s Office designed
the building and educational facilities; Reed Constructions
Australia was the constructor; Veolia Water Systems installed
the ultra-filtration membrane process, electrical and mechanical
equipment; Water Treatment Australia installed the lime and
carbon dioxide dosing equipment; and the NSW Department
of Water & Energy was a funding partner under the Country
Towns Water Supply and Sewerage Subsidy Scheme.
As for subcontractors, Coffey Geotechnics was the geotechnical
engineer; Jung Constructions Pty Ltd provided concrete construction
works; Brian Mansfield Plumbing were consulted for building
hydraulic services; Oxley Air Conditioning Services provided
ventilation and air conditioning services; Eire Contractors were
consulted for the water pipeline construction; Mid Coast Telemetry
performed electrical installation works; HERC Equipment
did metal fabrication and installation works; and Gean Custom
Marine worked on the lime silo steel protective shell.
The council’s water supply, electrical, mechanical and telemetry
staff were also involved in investigation, design and construction.
Origins of the project
The project was prompted by the release of the draft National
Health and Medical Research Council’s (NHMRC) Australia
Drinking Water Guidelines in 1994. In the council’s subsequent
review of its drinking water quality compliance and water
The membrane modules for the treatment plant.
treatment processes, two major drinking water quality issues
were identified.
Firstly, the level of water treatment provided at existing river
water sources needed to be improved. In particular, local communities
at Wauchope and three rural villages had no effective
protection from parasite contamination such as giardia and
cryptosporidium.
Secondly, there was the need to provide water conditioning
to overcome the natural “softness” or low alkalinity and calcium
levels, of the river water obtained from the Hastings River at
Koree Island. This soft water was found to be potentially corrosive
to water supply infrastructure including; pumps, pipes,
concrete reservoirs and plumbing fi xtures. Evidence of this
long-term corrosion of water supply infrastructure had previously
been identified through asset performance monitoring and asset
management investigations.
The effectiveness of the existing chlorination disinfection
process would be improved due to the increased “buffering”
capacity or the ability to resist changes in pH value, of the
conditioned water. Less sodium hypochlorite would need to be
dosed to achieve “breakpoint” chlorination and disinfection of
the drinking water. This would also reduce consumer complaints
regarding chlorine smell and tastes in the drinking water due to
the improved chemistry of the drinking water.
In addition it was highlighted that the conditioned water would
provide more favourable and stable water quality parameters in
the council’s off-creek storage dams.
In locating the water conditioning facilities at the Wauchope
WTP, it would be possible to condition all the water pumped
from the Hastings River prior to it being transferred and stored
in the off-creek storage dams.
With further consideration of the adopted NHMRC Australian
Drinking Water Guidelines in 1996, it was determined that
additional water treatment processes were needed.
Membrane filtration preferred
The council conducted site visits to existing water treatment
plants in New South Wales, Queensland and Victoria were
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WATER TREATMENT
Submerged membrane filtration became the preferred treatment option for the water treatment plant, shown here, as it did not
require the addition of further chemicals to achieve the drinking water quality targets.
undertaken with the assistance of the NSW Department of
Commerce and Hunter Water Australia to investigate currently
available and merging water treatment technologies. This included
water conditioning plants, as low alkalinity water is a
common feature of many river water supplies sources in NSW
and Victoria.
Submerged membrane filtration was selected as the preferred
treatment option, as it did not require the addition of further
chemicals to achieve the drinking water quality targets. This
treatment option also provided significantly lower energy requirements
and future operating costs.
The membranes are tiny hollow fibres with miniscule holes
(0.04 micron), which allow water molecules to pass through,
but do not allow any sediment or contaminants through the
membrane fibres. Nearly 10,000 of these fibres are bundled
together to form a module unit and each module provides 34m 2
of filtration surface area.
“It is pleasing to note that this ultra-fi ltration membrane
technology has been developed and manufactured by Memcor
Australia at the company’s factory and research facilities based
in Windsor just west of Sydney,” said Port Macquarie-Hastings
Council’s water supply manager Murray Thompson.
The membrane module racks are located inside a membrane
tank and submerged in the raw water which is fed into the tank
during the filtration process, which involves a suction pressure
being applied to the inside of the hollow fibres. Clear water is
then drawn through the fibres with contaminants remaining on
the outside of the fibres and inside the tank.
The water conditioning included the addition of hydrated
lime to the raw water pumped from the river to raise calcium
and alkalinity levels and then post pH correction dosing with
carbon dioxide gas to stabilise the pH in the water.
Operation of the plant
The operation of the Wauchope WTP involves the conditioning
of all water pumped from the Hastings River and then the
subsequent filtration of drinking water supplied to consumers
in the Wauchope area.
Council operates three pumping stations on the Hastings
River at Koree Island. The three rising mains from these pumping
stations pass through the WTP site allowing for the water
“conditioning” process to be competed via the injection of lime
slurry and CO 2
gas into each rising main. The conditioned water
is then stored in the Rosewood Reservoirs, before being transferred
to the council’s two off-creek storage dams.
A portion of this conditioned water is returned to the Wauchope
WTP via a separate pipeline from the Rosewood Reservoirs
for filtration before it is supplied to consumers in the Wauchope
area.The operation of the membrane filtration plant involves the
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WATER TREATMENT
WTP clear water reservoir “calling” for water; the “conditioned”
water is then delivered by gravity flow from the Rosewood raw
water reservoir into the membrane tank via an automatic self fl
ushing Thompson Filter Screen which removes any debris, which
may damage the membranes.
This conditioned water has been dosed with sodium hypochlorite
solution (known as hypo), which provides disinfection for the
water. This hypo dosing process also precipitates dissolved iron
and manganese in the raw river water and helps to discourage
algal growth on the membranes.
The water then enters the membrane tank and is drawn through
the membranes by suction pressure applied using the filtrate/
backwash pump units. The membrane tank contains 192 membrane
modules. Impurities and contaminants in the water are
trapped on the outside of the membrane fibres, while the filtered
or “clear water” is drawn through the hollow membrane fibres
and into a clear water reservoir ready for transfer to the Rosewood
clear water reservoir and onto consumers in the Wauchope area.
Monitoring and control
The water treatment plant is automatically monitored and controlled
by an intelligent Programmable Logic Control (PLC)
programme. This PLC system provides a user friendly and cost
effective control system, which includes an Operator Machine
Interface (OMI) screen to allow plant operations to be visually
displayed and monitored easily by water staff.
The information monitored by the PLC system including
reservoir levels, plant flow rate and water quality, river water
quality parameters together with warning and shutdown alarms
are sent via Council’s Telemetry network to the Council’s offi ces
and other operational sites to allow remote monitoring.
A standby SCADA Control Centre has been established at
The tank farm for the plant. The far tank is the backwash
pumping station.
Aboriginal artworks at the site recognise the Hastings
River as the source of the water supply for the area. They
depict animals and fish found within the local aquatic
environment.
the Wauchope WTP to act as an alternative emergency site if
problems occur with Council’s main
Water Supply SCADA and Operations Control Centre, which
is located in Port Macquarie. A standby generator and UPS system
installed at the Wauchope WTP ensure that this control centre
can continue to function during emergency situations.
A local optic fibre network is currently being established to
provide secure data transfer between all water supply sites in
this area including the Koree Island River Pumping Stations,
Koree Island High Voltage Substation, Hastings River CCTV
Monitoring System, Koree Island River Flow and Water Quality
Monitoring Station, Rosewood Reservoirs, Rosewood Fluoridation
Plant and Rosewood Telemetry Repeater Station.
A high speed microwave link between the Wauchope WTP
and Transit Hill Reservoir Communications Tower in Port Macquarie,
will allow all of this operational data to be monitored and
controlled from Council’s Water Supply SCADA and Operations
Centre. Due to the effectiveness of the monitoring and control
system, problems can be easily identified, diagnosed and rectified
remotely, with operator attendance only required during normal
working hours.
Cleaning the filters
From an operational point of view, as the submerged membranes
are a physical barrier to contaminants, the quality of water
produced is constant regardless of feed water quality. However,
raw water quality parameters such as turbidity, pH, temperature
and nutrient levels are continually assessed to ensure compliance
with the treatment plant and dam filling operating rules.
When turbidity and/or nutrient levels in the river are above
acceptable limits, the treatment plant automatically enters a
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WATER TREATMENT
River Dirty mode. During this mode the filling of the council’s
off-creek storage dams is suspended to prevent dirty and high
nutrient water from contaminating the dams, which could promote
excessive and undesirable algal growth within the dams.
In the River Dirty mode, the river pumping stations continue
to operate in a reduced manner to only feed water into the
treatment plant for filtration in order to supply water to the
Wauchope area. Should river water quality deteriorate further
due to in extremely high turbidity levels or other water quality
problems such as eg toxic algae outbreaks, it is then possible to
backfeed water from the Port Macquarie off-creek storage dam
to maintain an adequate water supply to the Wauchope area.
The membranes are able to treat very high turbidity water
however this will shorten their lifespan and increases the required
frequency of cleaning. The membranes have two methods for
cleaning – backwashing (every 30-40 minutes) and clean in place
(CIP) chemical cleaning (typically every 600 hours of operating)
using citric acid and concentrated sodium hypochlorite.
Backwashing aims to remove sediment particles that have been
drawn onto the membranes during the filtration process. These
sediments gradually clog the pores in the membranes and reduce
the efficiency of the filtration process, which is continuously
monitored using a trans-membrane pressure differential system.
During a backwash cycle, filtration is ceased and a series of
pneumatically operated valves close to ensure no backwash water
enters the clearwater tank.
Low pressure air is delivered at the base of the membrane
modules to agitate the membrane fi bres. Clearwater is also
pumped back into the membranes in the reverse direction to
normal filtration. These processes dislodge and free solids that
have attached themselves to the membrane fibres.
Backwashing of the membranes is undertaken automatically
every 30-40 minutes of plant run time. Large amount of sediment
particles are collected on the membranes even in a short
time period.
The backwash water is then directed by automatic valve operation
into the backwash pumping station; the backwash water is
then pumped into a clarifier and dosed with a small amount of
coagulant to ensure the settlement of solids in the clarifier unit.
The clear water outflow from the clarifier is collected in the
supernatant pumping station and returned to the membrane tank
during normal filtration operation. This backwash water recovery
system is able to achieve a 98% recovery rate. The small amount
of backwash solids collected in the clarifier are discharged into
the sewerage pumping station and transferred to the Wauchope
Sewerage Treatment Plant (STP).
These backwash solids, which include a small amount of
residual coagulant, have seen an improvement in the settling
characteristics of the activated sludge treatment process at the
Wauchope STP. So this additional waste stream has actually
improved the overall performance of the STP.
The clean in place (CIP) chemical cleaning process principally
removes inorganics including metals that have attach themselves
to the membranes and are not removed by the regular backwashes.
This CIP process is completed after every 600 hours of operation.
The continuously monitored Trans-membrane Pressure
(TMP) can also determine the need for a CIP. The TMP is the
differential pressure between the inside and outside of the membrane
fibres during normal filtration. The TMP increases as the
pores in the membranes become progressively more clogged.
CIP cleans are completed using citric acid and concentrated
sodium hypochlorite on an alternating basis as organics are more
susceptible to sodium hypochlorite while the citric acid is more
effective in removing in-organics and metal deposits.
The CIP process is completed using warm water supplied from
an on-site water heater, as this is more conductive to the cleaning
process and concentration levels of the cleaning solution are
more easily maintained.
The CIP process consists of four soak and four recirculation
periods, each 15 minutes long. The sodium hypochlorite or citric
acid is dosed into the warm water via a dedicated automatic dosing
system controlled by the PLC programme. The membranes
soak in the solution for 15 minutes to allow penetration into
hard-to remove build-ups. The solution is then recirculated
through the membranes to allow the internals of the membranes
to be cleaned. This process is repeated with air blower agitation
of the membranes during recirculation for additional cleaning
power.
The membrane tank has been specifically designed to minimise
the wet volume of the tank to reduce regular backwash water
volume and also the CIP wastewater stream. As such only 8
kilolitres of CIP wastewater is produced from each cleaning cycle.
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These are the filtrate suction/backwash pumps for the plant’s membrane tank.
Wastewater from both the citric acid and concentrated sodium
hypochlorite CIP processes is directed into the Chemical Neutralisation
Tank where it is neutralised and pH corrected before
discharge into the Sewerage Pumping Station.
Initially it had been planned to use sulphuric acid as the acid
for CIP cleans but due to the raw water chemistry is was found
that citric acid would produce better cleaning results and is a far
less dangerous and a relatively harmless product to work with
for both operational staff and the environment.
The operation of the water “conditioning” plant involves
the dosing of lime slurry and CO 2
gas into each of the three
rising mains from the Koree Island Pumping Stations as water
is pumped passed the Wauchope WTP from the river into the
Rosewood Reservoirs.
A 80t lime silo and 60t CO 2
storage vessel provide approximately
three months supply of lime and CO 2
when the “water
conditioning” plant is operating at full capacity of 120ML/day.
The hydrated lime is added to water in a batch feed arrangement
to produce a lime slurry, which is then injected into the
three individual rising mains pumping water from the river to
the Rosewood reservoirs.
A separate above ground lime dosing building has been installed
to provide safe access for staff to operate and maintain the
lime dosing and rising main injection systems. Staff are now able
to easily gain access to this equipment utilising a platform and
overhead gantry crane installed above the rising mains, which
pass through the lime dosing building.
A problem identified during the early stages of the plant’s design
was that operators at other existing plants were required to
often enter deep and confined pits in order to gain access to this
equipment and the dosing lines which require regular removal,
cleaning and maintenance. It was therefore decided to reduce
the workplace risks associated with this regular work activity by
providing an appropriately designed lime dosing building.
In addition the lime dosing building was utilised to house both
static and mechanical mixers which were installed in the rising
mains to ensure the adequate mixing of the lime slurry prior to
pH stabilisation with CO 2
gas injection further downstream in
the each rising main. ●
This article is an edited version of a submission by Port Macquarie-Hastings
Council for the Engineers Australia Newcastle Division's Excellence Awards.
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