Ecological Engineering Maleny Effluent Irrigated
Rainforest and Wetland
Irrigation Australia
Conference
2-6 June 2014
Ecological Engineering
Defined as:
 The design of sustainable ecosystems that integrate
human society with its natural environment for the
benefit of both.
Ecological Engineering involves:
 The development of new sustainable ecosystems that
have both human and ecological value.
Spawned by:
 Realisation that not all pollution problems can be
solved through technological means; and
 Realization that with technological means, pollutants
are just being moved from one form to another.
Key principles of Ecological Engineering
1.
2.
3.
4.
5.
6.
7.
It is based on the self-designing capacity of
ecosystems;
It can be the acid test of ecological theories;
It relies on system approaches;
It conserves non-renewable energy sources; and
It supports biological conservation;
It involves the design of the natural environment
through quantitative approaches that rely on basic
science;
Primary tool is the self-designing ecosystem.
The challenge
 Pre-existing Maleny STP (designed for 2000 EP) was





operating beyond its hydraulic and biological capacity.
Infrastructure was at the end of its serviceable life.
Maleny is located in the headwaters of Obi Obi Creek,
approximately 10 km upstream of Baroon pocket Dam (i.e.
within the water supply catchment).
Maleny population forecast to grow to 5000 EP (185 L/EP/d
average dry weather flow) by 2026.
With no change to treatment systems, nutrient loads to
surface waters will more than double.
The marginal cost of an engineered system to remove
residual nutrients from the Maleny STP is high (diminishing
returns).
Licence considerations
Expected
Target max mass
Implemented
Release from
discharge
load based on
licence limits to
STP to forest &
Nutrient
concentrations
old licence
Obi Obi Creek
wetland (mg/l)
from wetland
(kg/yr)
(mg/l)*
(mg/l)**
N
1095
5
3
0.9
P
219
1
0.8
0.07
* At 925 Kl/day = 5000 EP
** For an average rainfall year, (expected concentration higher in wet years)
Indicative marginal cost of treatment
Indicative cost ($/Ml)
Engineered Treatment System
Cost increases
significantly below
residual N of 3 to 5 mg/l)
Cost relatively insensitive
above residual N of
3 to 5 mg/l
Target residual N
= 3 to 5 mg/l
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Residual N concentration (mg/l)
Engineered Treatment System
Allowable Concentration (mg/l)
Implications of load-based licencing
9
8
7
6
5
4
3
2
1
0
2,000
4,000
6,000
8,000
10,000 12,000 14,000 16,000 18,000 20,000
Population (EP)
Allowable N concentration (mg/l)
Allowable P concentration (mg/l)
Proximity to water supply dam
Baroon Pocket Dam
Effluent irrigation site
8
Objectives
 To provide a safe, environmentally and financially
sustainable method of releasing treated water back to
the environment.
 Water discharged to the environment should have no
negative impact on the water quality of Obi Obi Creek.
 Zero harm, both during construction and ongoing
operation.
 Whole of life project cost is minimised.
The solution
 Construction of a MBR treatment plant producing






“Class A” effluent
Irrigation of a constructed rainforest and wetland system.
“Treatment” via the forest and wetland system to remove 70%
of residual N and P and achieve residual nutrient loads of:
 0.9 mg/l N (in an average rainfall year at the design horizon);
 0.07 mg/l P (in an average rainfall year at the design horizon);
Irrigation to forest to remove N, reduce P and utlise water.
Lateral seepage though the soil profile to remove P.
Passage through a wetland system to further remove N,
equilibrate the water with natural aquatic ecosystem conditions,
and manage high flows.
Final discharge to Obi Obi Creek.
Key design approaches
 Forest water use and deep drainage – Tchobanoglous
& HYRDRUS 1D modelling
 Soil phosphorous absorption - Langmuir isotherm
 Wetland N and P removal – MUSIC modelling, Kadlec
and Wallace Model
 Seepage and ET correction - Muskingum-Cunge
Treatment process flow
Forest
N = Uptake
P = Uptake
E = Transpiration
Soil
N = Transmission
P = Sorption
E = Evap/Drainage
0-1 ADWF
STP
N = 5-10 mg/l
P = 1-2 mg/l
E = 925 Kl/day
1-3 ADWF
Flow rate
3-5 ADWF
Baroon Pocket
Dam
Obi Obi Creek
N = 0.9 – 2.2 mg/l
P = 0.07-0.43 mg/l
E = <365 Kl/day
Wetland
N = Metabolism
P = Sediment
E = Transp/Evap
Overview of irrigated forest & wetland
system
 Designed to treat 925kL of effluent per day
 Established within the Maleny Community Precinct on
ex grazing pasture land.
 Irrigated forest area of 13.7 hectares with 6 ha of
unirrigated buffer.
 Palette of over 100 canopy and understory rainforest
species established at a stocking of up to
2500 stems/ha.
 Wetland system of 3 ha to manage high flows.
System features
 A 45 kW 3 phase pump and control system.
 Over 25,100 metres of mainline, sub-mains and lateral








irrigation pipe (225mm to 16mm).
Over 2,500 pop up sprinklers.
Irrigation of up to 925kL/day over 10 hours.
Autonomous operation 8:00pm to 6:00 am.
Feedback control from weather and soil moisture sensors.
2,500 mixed rainforest seedlings per irrigated hectare and
associated dry buffer plantings.
Extension of the existing walking track system.
Land slip restoration, stabilisation and construction of gully
check dams.
Practical completion March 2014.
Pump and control systems
Irrigation and wetland layout
Forest and wetland “treatment system”
co-benefits
 Community recreational facility;
 Enhance biodiversity by providing habitat linking remnant







vegetation;
Provide floodwater attenuation, energy dissipation and
erosion control;
Improve visual amenity;
Sequester carbon;
Landslip remediation;
Improve water quality (reduced sediment)
Low operating and maintenance costs;
Appreciating community asset with economic,
environmental and community benefits.
Tree Crop Technologies
Level 14, 97 Creek Street
Brisbane QLD 4000
Tel: 07 3221 1102
www.treecroptech.com.au
Topic Summary
Topic: Ecological Engineering - Maleny Effluent Irrigated Rainforest and Wetland
Abstract: The marginal cost of removing nutrients from sewage effluent
increases significantly as the required nutrient concentration falls, but even at
low concentrations, total discharged nutrient loads may be
significant. Unitywater’s Maleny Irrigated Forest and Wetland presents an
innovative solution. This “ecological engineering” based approach is designed to
remove 70% of residual nitrogen from treated sewage effluent to achieve total
nitrogen values <1mg/l.
The forest will double as a community recreational facility, enhance biodiversity
by providing habitat linking remnant vegetation, provide floodwater attenuation,
energy dissipation and erosion control and improve visual amenity, with low
operating and maintenance costs. Significantly, the forest and wetland
“treatment system” represents an appreciating community asset with economic,
environmental and community benefits.
Presenter:
Dr Glenn Dale, Managing Director, Tree Crop Technologies Pty Ltd