Nutrient processing in a novel on-site wastewater treatment system designed for permeable carbonate sand environments

•We developed a low cost, low technology system for treating domestic wastewaters.•The system removed 63% of total phosphorous and 43% of total nitrogen.•Simultaneous nitrification/denitrification occurred in both aerobic and anaerobic zones.•Complete attenuation of NH4+was seen as wastewater passed...

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Bibliographic Details
Published in:	Ecological engineering 2013-08, Vol.57, p.413-421
Main Authors:	Tait, Douglas R., Erler, Dirk V., Dakers, Andrew, Davison, Leigh, Eyre, Bradley D.
Format:	Article
Language:	eng
Subjects:	Animal, plant and microbial ecology Applied ecology Applied sciences Biological and medical sciences Carbonate sand Ecology EcoTrench Effluent Effluents Environment and sustainable development Exact sciences and technology Fundamental and applied biological sciences. Psychology Groundwater Islands Nutrient Nutrients On-site treatment Permeable carbonate sands Pollution Trenches Waste water Wastewater treatment Wastewaters Water treatment and pollution
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Summary:	•We developed a low cost, low technology system for treating domestic wastewaters.•The system removed 63% of total phosphorous and 43% of total nitrogen.•Simultaneous nitrification/denitrification occurred in both aerobic and anaerobic zones.•Complete attenuation of NH4+was seen as wastewater passed through the system. This study was the first to develop, install and examine a secondary treatment system for domestic wastewater specific to permeable carbonate sand systems. The ‘ecoTrench’ (eT), relied on effluent passing through a number of different treatment layers including a coconut husk humus ecology, a saturated trench and unsaturated carbonate sands. An eT was installed on a residential property on the main island of Rarotonga in the Cook Islands and received primary treated effluent from a septic tank over a 21 month period from May 2009 until February 2011. Nutrient removal efficiencies for the eT averaged 63% of total phosphorous and 43% of total nitrogen. The eT was an effective nitrifyer of NH4+ to NO3− with almost complete attenuation of NH4+ as effluent passed through the system. Uptake rates of NH4+ averaged 36.7±4.1mmolm−3h−1 as wastewaters left the saturated trench. The addition of labelled stable isotope (15NH4+), showed that simultaneous nitrification/denitrification was occurring in both aerobic and anaerobic treatment layers. Elevated concentrations of dissolved organic nitrogen (DON) were seen as effluent left the saturated treatment layer before largely being attenuated as effluent moved down through the sediment profile. This may have contributed to a significant build-up of NO3− as effluent moved towards groundwater largely due to inhibited denitrification and the mobilization and remineralisation of previously assimilated DON. The eT represents an efficient and effective way to reduce nutrient loading to groundwater and can work well within the constraints of many island communities based in permeable carbonate sand systems.
ISSN:	0925-8574 1872-6992