Client: Manawatu District Council
Commissioning Date: September 2013
Population Equivalent: 1400
Flow Rate: 350m3/day (average dry weather flow)
A design and build Floating Treatment Wetland to manage the demands of a fluctuating population
Himatangi Beach is a popular North Island summer retreat — so much so that its population doubles during the summer months. The challenge was to design a wastewater treatment plant that could cope with this population spike without being too oversized during the rest of the year.
Description
The pond was built with a large buffer capacity that enabled an increase in depth from 1.2m to 2.4m during the peak flow periods. The primary facultative zone, assisted by a mechanical diffused aerator during summer, is separated from the biological floating treatment media (FTM) by a series of impermeable baffles. The hydraulic control and maximizing of retention time within the floating treatment media is of all importance — especially during the peak flow. Flow control baffles were fitted to each section of FTM modules to ensure that short circuiting was eliminated. The final effluent is irrigated to a tree plantation.
Benefits
This wastewater treatment system has the ability to treat short concentrated periods of summer flow and run at a very low operational cost for the remainder of the year.
| Parameter | Avg (mg/L) | Max (mg/L) |
|---|---|---|
| BOD | 163 | 342 |
| TSS | 208 | 428 |
| TKN | 44 | 80 |
| NH4N | 32 | 57 |
| TP | 6.2 | 10.9 |
| pH | 7.5 | 8.6 |
| Tmin | 11°C | 11°C |
| Tmax | 22°C | 22°C |
| Flow Data | ||
| ADWF – 2014 | 540m3/d |
| Parameter | Avg (mg/L) | Consent |
|---|---|---|
| BOD | 20 | Land Based Discharge Consent |
| TSS | 37 | |
| TKN | 17 | |
| NH4N | 16 | |
| TP | 3.8 |
