Water, Sewage & Effluent March April 2019 | Page 24

The decentralised choice
The decentralised model collects,
treats, and then discharges to the
subsurface at, or very close to, the
point of origin, restoring the original
water resource to the local aquifer at
a much lower energy cost. With rapid
aquifer depletion and dropping water
tables, minimising the controllable
impacts to the water cycle is critical for
sustainability. Where no wastewater
treatment exists or the systems
are outdated and under capacity,
traditional and advanced decentralised
treatment system possibilities can
protect local waterways and water
supplies, upgrade outdated systems to
reduce nitrogen loading, and improve
overall wastewater management for
the community.
Many communities are turning
to a combination of approaches to
solve their wastewater treatment
challenges. These systems often
provide decentralised collection that
moves to a centralised treatment
facility, then to a large disposal
field. Most are centrally managed,
including publicly and privately owned
community systems, and staffed with
trained personnel like centralised
systems.
Ageing, ineffective cesspools, cost
concerns, and a need to prevent effluent
nitrogen from damaging the sensitive
lagoon and open ocean surrounding the
Kwajalein atoll, spurred local officials
and residents, led by Senator Mike
Kabua, to seek a new approach.
The project, designed by International
Wastewater Technologies (IWT), was
challenging due to the remote atoll
location and the shallow six-foot water
table. The first-phase solution was to
contain wastewater from each individual
dwelling that could later be pumped and
transported to a centralised treatment
facility on neighbouring Ebeye Island.
IWT arranged the delivery of four
5 678-litre Infiltrator IM-1530 tanks
4 130 kilometres by boat from Honolulu to
Ebeye Island and finally to the Kwajalein
atoll. A subsequent delivery of three
3 785-litre Infiltrator IM-1040 tanks and
alarm panels was completed, with each
delivery taking two weeks to a month.
The plastic two-piece tanks offered the
ideal solution as they ship nested to be
assembled on site upon arrival.
Assuming there would be no
equipment or tools to complete the
tank and tank alarm assembly and
installation, IWT packaged and shipped
the tanks, control panel conduit, alarm
float switches, and all materials for
future O&M to the atoll.
The tanks travelled first to the west
coast of the United States, then by
Case study 1: Kwajalein Atoll,
Micronesia
IWT staff trained Senator Kabua and his
staff and local townspeople to assemble
the Infiltrator IM-Series plastic tanks on
Ebeye Island.
vehicles (specialised service trucks),
and specialised equipment.
Advanced wastewater treatment
products such as fixed-film bioreactors,
modular products such as chambers
and geosynthetic aggregate bundles,
and lightweight, high-strength plastic
septic tanks offer individuals and
communities effective and efficient
options. In these cases, there is also
no concrete used in the system, which
benefits the environment along with
providing ease of installation.
Ebeye Island townspeople carry a
5 678-litre lightweight, plastic Infiltrator
IM-Series Tank.
boat to Hawaii and on to Ebeye Island,
part of the Kwajalein atoll. They were
trucked via causeway to Lojjairok
Island. Assembly instruction was
provided by IWT to the senator, his
assistant, and the townspeople. Future
systems under consideration include
wastewater packaged plants and
expanded aerobic technology.
Decentralised treatment enables a community to focus on
specific and most critical treatment needs and allows for
smaller design flows and disposal areas.
Applications and products
Designing a small-scale, advanced
treatment train prior to dispersal of
the effluent into the native soil can
decrease both the absorption area and
depth to limiting layers that are required
for adequate treatment and increase
the volume of groundwater recharge.
Decentralised systems as large as four
million litres can now be developed
for
commercial
and
industrial
sites, decreasing the hydraulic and
nutrient stress placed on centralised
wastewater treatment plants.
The new generation of on-site
wastewater
treatment
products
enhance design options and system
22
Case study 2: Nova Scotia,
Canada
Forest Lakes Country Club is a four-
season resort community outside
Halifax with 2 700 residential units,
a championship golf course, and a
Village Centre. No centralised municipal
sewer or wastewater treatment
infrastructure was available, and a key
design consideration was that it works
reliably 24/7, 365 days a year in the
northern, maritime climate typical of
Water Sewage & Effluent March/April 2019
Nova Scotia. Each neighbourhood uses
a decentralised wastewater collection,
treatment, and disposal system. One
neighbourhood system serves 50 homes
and has a peak flow design of 51 200
litres per day. The watertight septic
tank effluent pump (STEP) pressurised
effluent sewer collection system delivers
primary effluent via small-diameter
mainlines to a secondary wastewater
treatment plant, followed by dosing
tanks, and an Infiltrator Quick4 Plus
Standard Chamber soil dispersal system.
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