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WATER TREATMENT LEVELS
Quality of Water Treatment & Use of Treated Water
- Since Biosphere 2, over 100 WWG systems have been installed worldwide
with purifying results still as effective:
- 90-95% BOD reduction (Biological Oxygen Demand)
- 90-95 % TSS reduction (Total Suspended Solid reduction)
- 45-80% Nitrogen reduction - This ratio varies greatly in regards to local conditions and time of test.
- 30-60% Phosphorus reduction - The same variability of ratio as in Nitrogen can be observed.
- Over 98% Coliform bacteria reduction
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If the effluent coming out of the WWG unit/s
is to be further used for subsurface irrigation, the waters will
know a secondary nutrient uptake process and thus meet even higher
standards at final discharge.
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While the treated water discharged from the Wastewater
Gardens® is highly reduced in
bacteria, it is not up to drinking standards as we normally don't
use a final disinfectant such as chlorine or ultra-violet lights.
This means that you can grow and eat fruits and some types of medicinal
plants for example, or grow fodder for animals, but shouldn't plant
leafy vegetables destined to human or animal consumption.
The discharge water could also be used for flushing toilets but
the cost of pumping it back into houses usually makes this option
uneconomical.
Examples of laboratory water analyses of water froma WWG treatment unit
(Birdwood Downs homestead, Derby, West Australia)
Another example of water laboratory analysis of a WWG treatment unit
(Krempna, Poland)
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| Parameter |
Influent concentration |
Effluent concentration |
Required level by
health authorities |
|
| DBO5 |
55,0 mg O2/l |
11,0 mg O2/l |
40 mg O2/l |
| COD |
88,0 mg O2/l |
32,0 mg O2/l |
150 mg O2/l |
| TSS |
74,5 mg/l |
49,5 mg/l |
50 mg/l |
| Total N |
73,7 mg N/l |
24,6 mg N/l |
30 mg N/l |
| Total P |
7,2 mg P/l |
2,0 mg P/l |
5 mg P/l |
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Comparison of principal parameters removal efficiency of Wastewater
Gardens® subsurface flow systems with
average North American surface and subsurface flow wetlands (based on
data from early prototypes in Mexico) and EPA study.
Summary of Water Quality Tests at Emu Creek (Gulgagulganeng)
Wastewater Garden System, Kununurra, West Australia, August 2002 - May 2004
|
| Parameter |
BOD-5
(Biochemical
Oxygen Demand)
mg/l |
Total
Suspended Solids
(TSS)
mg/l |
Total
Nitrogen
mg/l |
Total
Phosphorus
mg/l |
|
| Average in Septic Tank |
214 |
99 |
228 |
18 |
Average
Wastewater Garden
discharge |
23 |
10 |
66 |
7.8 |
| Percent Reduction |
89% |
90% |
73% |
58% |
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Tests performed at MPL Laboratories, Perth, an accredited testing facility. If evapotranspiration is 20% for above system, then wetland reduction of BOD is 91%, Reduction of TSS is 92%, reduction of nitrogen is 77% and reduction of P is 65%.
Average influent and effluent concentration (mg/l) and removal efficiencies (%) of organics (BOD5) in horizontal, subsurface flow constructed wetlands
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| Country |
Influent concentration |
Effluent concentration |
Efficiency |
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| Czech Republic |
87,2 |
10,5 |
88,0 |
| Denmark and UK |
97,0 |
13,1 |
86,5 |
| North America |
27,5 |
8,6 |
68,5 |
| Germany - L. Saxony |
248 |
42 |
83,0 |
| Germany - Bavaria |
106 |
21,6 |
79,6 |
| Poland |
7,65 |
4,10 |
46,4 |
| Slovenia |
107 |
11,3 |
89,0 |
| Sweden |
80,5 |
5,9 |
92,7 |
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Average influent and effluent concentration (mg/l) and removal efficiencies (%) of suspended solids in horizontal, subsurface flow constructed wetlands
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| Country |
Influent concentration |
Effluent concentration |
Efficiency |
|
| Czech Republic |
64,8 |
10,2 |
84,3 |
| Denmark and UK |
98,6 |
13,6 |
86,2 |
| North America |
48,2 |
10,3 |
78,6 |
| Poland |
140 |
38,6 |
77,4 |
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Recent testing of early systems implemented along the Yucatan coast
in Mexico indicated reduced levels of performance due to a lack of proper
garden maintenance, with shading of understory plants, lack of aeration
and possibly short-circuiting of wastewater. System performance can
be improved through enhanced planting of the systems especially with
robust and deep-rooted wetland species; regular pruning to prevent tall
vegetation out-competing shorter species; and through reuse of the treated
water for further irrigation. Newer systems have been designed with
longer length: width ratios to increase wastewater residence time in
the wetlands and with greater end-use of the water for increasing total
system treatment and water reuse. For applications requiring even higher
initial treatment standards, use of "vertical flow" wetlands with dosing
siphons or pumps to batch load an initial wetland compartment will increase
aeration and thus boost treatment levels.
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