ABSTRACT
Waste stabilization ponds (WSP) are one of the most common forms of wastewater treatment for smaller communities globally, but have poor phosphorus removal. It is known that WSP algae can accumulate polyphosphate within their cells in excess of that needed for cell function. If polyphosphate accumulation could be triggered at the higher range of WSP cell concentrations, phosphorus removal from domestic wastewater could be significantly improved. However, this phenomenon is sporadic and still not fully understood. With a view of building a fundamental understanding to underpin the engineering of a new phosphorus removal process, this paper examines eight previously untested variables that may influence the cellular phosphorus content of WSP biomass. Although calcium, magnesium, and potassium are key constituents of polyphosphate granules, the concentrations tested were not limiting to polyphosphate accumulation. While literature also pointed to inoculum characteristics as potentially having an impact, no significance was found in this research. Conversely, three important new triggers where identified that significantly (90% confidence) affected the cellular phosphorus content of WSP biomass. An increase in cellular phosphorus content was triggered by decreasing the organic load, or allowing the pH to increase as compared to pH control. By contrast, the presence of mixing decreased the phosphorus content of the WSP biomass.
Subject(s)
Phosphorus/analysis , Scenedesmus/chemistry , Waste Disposal, Fluid/methods , Biomass , Calcium/metabolism , Magnesium/metabolism , New Zealand , Phosphorus/metabolism , Polyphosphates/metabolism , Ponds , Potassium/metabolism , Scenedesmus/metabolism , Wastewater/chemistryABSTRACT
The New Zealand Greenhouse Gas Inventory (the NZ Inventory) uses country-specific data to quantify CH emissions from anaerobic ponds treating dairy farm effluent (315 Gg CO equivalent [CO-e] in 2009). In this study, we used literature data to: (i) evaluate the accuracy of the NZ Inventory's parameters used to quantify these CH emissions; and (ii) determine whether the NZ Inventory's scope is capturing the full spectrum of sources with bio-CH potential entering anaerobic ponds. The research indicated that the current NZ Inventory methodology is underestimating CH emissions from anaerobic ponds across New Zealand by 264 to 603 Gg CO-e annually. Moreover, the NZ Inventory is currently not accounting for (i) manure from supplementary feed pads and stand-off pads (annual CH emissions = 207-330 Gg CO-e); (ii) waste milk (153-280 Gg CO-e); and (iii) supplementary feed waste (90-216 Gg CO-e). Annual CH emissions from anaerobic ponds on dairy farms across New Zealand are thus more likely to be 1029 to 1744 Gg CO-e, indicating that the NZ Inventory is reporting as little as 18% of actual CH emissions produced by this sector. These additional wastes are not accounted for in the methodology prescribed by the Intergovernmental Panel on Climate Change for estimating CH emissions from dairy manure. Consequently, other significant dairying nations will also probably be underestimating their waste CH emissions. Our research highlights that, if governments attempt to include country-specific emission factors in their greenhouse gas inventories, these factors must be based on an assessment of the full spectrum of sources contributing to greenhouse gas emissions within any given sector.
Subject(s)
Climate Change , Greenhouse Effect , Animals , Carbon Dioxide , Dairying , Manure , Methane , Milk/chemistrySubject(s)
Biotechnology , Phosphorus/supply & distribution , Agriculture/methods , Animals , Cells/metabolism , Humans , Phosphorus/metabolism , Survival , Waste ManagementABSTRACT
At present, resource recovery by irrigation of wastewater to plants is usually driven by the value of the water resource rather than phosphorus recovery. Expanded irrigation for increased phosphorus recovery may be expected as the scarcity and price of phosphorus increases, but providing the necessary treatment, storage and conveyance comes at significant expense. An alternative to taking the wastewater to the plants is instead to take the plants to the wastewater. Algal ponds and macrophyte wetlands are already in widespread use for wastewater treatment and if harvested, would require less than one-tenth of the area to recover phosphorus compared to terrestrial crops/pastures. This area could be further decreased if the phosphorus content of the macrophytes and algae biomass was tripled from 1% to 3% via luxury uptake. While this and many other opportunities for plant based recovery of phosphorus exist, e.g. offshore cultivation, much of this technology development is still in its infancy. Research that enhances our understanding of how to maximise phosphorus uptake and harvest yields; and further add value to the biomass for reuse would see the recovery of phosphorus via plants become an important solution in the future.
Subject(s)
Aquatic Organisms/metabolism , Eukaryota/metabolism , Phosphorus/isolation & purification , Phosphorus/metabolism , Plants/chemistry , Plants/metabolism , Wastewater/chemistry , Animal Feed , Animals , Biodegradation, Environmental , Biomass , Fertilizers , Humans , Phosphorus/supply & distribution , Phosphorus, Dietary/isolation & purification , Phosphorus, Dietary/metabolism , Phosphorus, Dietary/supply & distribution , WetlandsABSTRACT
Phosphorus removal in waste stabilization ponds (WSP) is highly variable, but the reasons for this are not well understood. Luxury uptake of phosphorus by microalgae has been studied in natural systems such as lakes but not under the conditions found in WSP. This work reports on the effects of phosphate concentration, light intensity, and temperature on luxury uptake of phosphorus by WSP microalgae in continuous culture bioreactors. Increasing temperature had a statistically significant "positive effect" on intracellular acid-insoluble polyphosphate concentration. It is likely that elevated temperature increased the rate of polyphosphate accumulation, but because the biomass was not starved of phosphate, the stored acid-insoluble polyphosphate was not utilized. Increasing light intensity had no effect on acid-insoluble polyphosphate but had a "negative effect" on the acid-soluble polyphosphate. A possible explanation for this is that the faster growth rate at high light intensity results in this form of polyphosphate being utilized by the cells for synthesis of cellular constituents at a rate that exceeds replenishment. The variability in the phosphorus content of the microalgal biomass shows that with this new understanding ofthe luxury uptake mechanism there is the potential to optimize WSP for biological phosphorus removal.