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; andRealization that with technological means, pollutants are

just being moved from one form to another.

Key principles of Ecological Engineering

1. It is based on the self-designing capacity of ecosystems;

2. It can be the acid test of ecological theories; 3. It relies on system approaches; 4. It conserves non-renewable energy sources; and5. It supports biological conservation;6. It involves the design of the natural environment

through quantitative approaches that rely on basic science;

7. Primary tool is the self-designing ecosystem.

The challengePre-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

NutrientTarget max mass

load based on old licence

(kg/yr)

Release from STP to forest & wetland (mg/l)

Implemented licence limits to Obi Obi Creek

(mg/l)*

Expected discharge

concentrations from wetland

(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

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

Engineered Treatment System

Engineered Treatment System

Residual N concentration (mg/l)

Indi

cativ

e co

st ($

/Ml)

Cost relatively insensit-ive above residual N of 3 to 5 mg/l

Cost increases signific-antly below residual N of 3 to 5 mg/l)

Target residual N = 3 to 5 mg/l

Implications of load-based licencing

2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,0000

1

2

3

4

5

6

7

8

9

Allowable N concentration (mg/l)Allowable P concentration (mg/l)

Population (EP)

Allo

wab

le C

once

ntra

tion

(mg/

l)

Proximity to water supply dam

8

Baroon Pocket Dam

Effluent irrigation site

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 isothermWetland N and P removal – MUSIC modelling, Kadlec

and Wallace ModelSeepage and ET correction - Muskingum-Cunge

Treatment process flow

STPN = 5-10 mg/lP = 1-2 mg/l

E = 925 Kl/day

ForestN = UptakeP = Uptake

E = Transpiration

Flow rate

WetlandN = MetabolismP = Sediment

E = Transp/Evap

SoilN = Transmission

P = SorptionE = Evap/Drainage

Baroon Pocket Dam

Obi Obi CreekN = 0.9 – 2.2 mg/lP = 0.07-0.43 mg/lE = <365 Kl/day

0-1 ADWF

1-3 ADWF

3-5 ADWF

Overview of irrigated forest & wetland system

Designed to treat 925kL of effluent per dayEstablished 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 featuresA 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 StreetBrisbane QLD 4000Tel: 07 3221 1102www.treecroptech.com.au

Topic SummaryTopic: 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