Water & Wastewater

Xylem UV Disinfection Facility

Protects New Zealand Coastal Waters

As part of an upgrade to a wastewater treatment plant

near Auckland, New Zealand, an Ultraviolet (UV) dis-

infection facility from Xylem unit will be installed. The

UV disinfection is part of a plan to improve efﬂuent to

an extent that will allow the local coastal waters to be

open to the public for the ﬁrst time in 40 years.

Watercare, Services Ltd (WSL), the New Zealand-based

publicly owned water supply and wastewater treat-

ment company, commissioned the construction of a

UV Disinfection facility as a key process in the NZ $450

million (US $225 M) upgrade of the Mangere WTP,

near Auckland, New Zealand. The plant upgrade in-

cluded both construction of a new ‘state-of-the-art’

plant and full coastal restoration. Two of the four exist-

ing Oxidation Ponds, have already been demolished.

They will eventually be replaced by a natural harbour

foreshore. The improvement in water quality will allow

swimming and shellﬁsh gathering, in an area that has

been off limits to the public for over 40 years.

The overall project delivery is being carried out by

Manukau Wastewater Services Ltd (MWS), under a

design/build contract. MWS is a consortium of both

local and international businesses; CH2M Beca, Bovis

Lend Lease, Fletcher Construction and New Zealand

Water Services.

The construction of new plant includes an upgraded

screening facility, nine new combined reactor/clariﬁers

and a new tertiary treatment system using sand ﬁltra-

tion in combination with UV Disinfection.

Basics of UV Disinfection

The UV disinfection facility is designed to reduce

Enterococci and Fecal Coliform levels of ﬁltered and bi-

ologically treated inﬂuent, to within speciﬁed microbio-

logical requirements. This is achieved by using the phys-

ical effect of ultraviolet light. Within seconds of a water

borne organism coming into contact with the UV radia-

tion emitted from a UV Lamp, a photochemical reaction

is triggered in the organism’s DNA, preventing it from

multiplying, therefore rendering it biologically inactive.

Equipment Selection

The UV disinfection process is the ﬁnal treatment before

efﬂuent discharge. As the sole source of disinfection, it is

critical to the effectiveness of the entire treatment plant.

Therefore, in selecting a suitable supplier WSL complet-

ed extensive pilot plant trails, involving three separate

proprietary systems. In June 1999, Xylem’s WEDECO

unit was awarded the contract to supply their TAK 55

series UV disinfection equipment. The completed UV

Disinfection facility, with a maximum discharge rate of

16,000 l/s (365 MGD) and a total number of lamps close

to 8,000, is now the largest and most sophisticated

wastewater UV disinfection system in the world.

Case Story

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Treatment

•

Wastewater

The 12 channels in the UV gallery contain a total of 7776 300-watt UV

lamps. They achieve a 10,000 reduction in pathogens discharged into

the harbor. It is one of the largest UV treatment installations in the world.

“The UV disinfection process is

the ﬁnal treatment before ef-

ﬂuent discharge.”

Xylem Water Solutions Herford GmbH

Boschstr. 4 – 14

32051 Herford, Germany

Phone: +49 5221 930-0

xyleminc.com

System Speciﬁcs

The Xylem UV disinfection facility is composed of 12

open channels, 17m (56ft) in length. Xylem installed

three banks of UV lamps within each channel. Both the

number of UV lamps in operation and the output power

of each UV lamp is automatically varied, according to

the inﬂuent ﬂow conditions. Thus, the applied level of

disinfection is constant regardless of inﬂuent ﬂow rate or

water quality. At the heart of Xylem’s TAK series is the

unique Spektrotherm® UV lamp. This lamp was speciﬁ-

cally designed by Xylem to generate 3 - 4 times more

UV energy than standard low-pressure lamps. This en-

abled the entire UV facility to be installed with a total

footprint of under 800m2 (8,500sqft).

Advanced Control System

To ensure that the advanced properties of Xylem’s

Spektrotherm® UV lamp were fully exploited, the de-

velopment of a comprehensive system control philos-

ophy was essential. Although Xylem could draw upon

experiences gained in many previous installations, spe-

ciﬁc plant requirements were taken into consideration.

Each UV Channel operates as a ‘stand-alone’ system,

controlled by a dedicated Siemens PLC.

Supervisory control of each ‘stand-alone’ channel is

achieved through a Distributed Control System (DCS).

The use of the DCS allows the UV facility to be fully in-

tegrated into WSL’s existing plantwide control system.

Xylem’s Electrical Engineering Manager, Jens Brede,

states, “This form of control architecture ensures a high

degree of operational ﬂexibility and redundancy.” He

continues, “It also allows the plant operators to view

the UV facility as part of the entire treatment process

and not only as an isolated unit”.

“Zero-Defect” Construction Philosophy

With the core design and manufacturing groups of

Xylem’s WECECO unit based in Herford, Germany, it

was essential that there was an effective ﬂow of infor-

mation between Xylem, MWS and local contractors. As

a means of assisting this, Xylem developed manage-

ment plans in conjunction with MWS, covering all as-

pects of the design, fabrication, construction and test-

ing. MWS Project Engineer, David Rose explains, “The

Management Plans were used to deﬁne key tasks and al-

lowed us to monitor and control those tasks within the

overall construction program. Each phase was complet-

ed and checked on the basis of a ‘zerodefect philosophy’

that ensured issues were resolved as they occurred.”

This ‘zero-defect philosophy’ was applied across all

disciplines; civil, mechanical, electrical and software.

For example, each key task in the civil construction was

inspected and signed off in accordance with agreed

criteria. This further assisted the installation of the vari-

ous pre-fabricated mechanical components. Another

example can be seen in the development of the con-

trol software. Full software simulations of the process

operation were carried out prior to installation, ensur-

ing that all normal and abnormal operating conditions

were known and accounted for.

During a recent meeting evaluating the completion

of construction, Watercare Services Ltd described the

Ultraviolet (UV) Disinfection facility, at the Mangere as

“a world-class installation”.

Coastal Waters Opened Again

The technology developed by Xylem has enabled

them to provide a UV disinfection facility that offers a

safe, reliable and economic solution to the safe dis-

charge of efﬂuent to coastal waters. The treated water

that is discharged into the harbour is very clean by in-

ternational standards. Fecal coliforms in the outﬂows

from the plant have been cut by 99.8 per cent. Other

pollutants, like nitrogen and ammonia, have been re-

duced heavily. There is a 10,000-fold reduction in virus-

es in water discharged from the plant.

The foreshore around the plant – for a distance of

about 13 kilometres – has been restored to conditions

comparable to those prevailing when the ﬁrst waste-

water treatment plant was opened in 1960. About

300,000 native trees and plants have been planted on

the foreshore, and seven new beaches have been built.

Bird roosts have been established and, in the summer

of 2002-03, thousands of migratory seabirds returned

to the restored foreshore around Mangere. Work is be-

ginning on reopening Oruarangi Creek, which has spe-

cial signiﬁcance for local Maori, to the sea. The creek,

which is just to the south of the plant, has been closed

to the sea for almost a generation.

For more information: www.wedeco.com