Environmental Benefits and Burdens of Phosphorus Recovery from Municipal Wastewater

Abstract

The environmental benefits and burdens of phosphorus recovery in four centralized and two decentralized municipal wastewater systems were compared using life cycle assessment (LCA). In centralized systems, phosphorus recovered as struvite from the solids dewatering liquid resulted in an environmental benefit except for the terrestrial ecotoxicity and freshwater eutrophication impact categories, with power and chemical use offset by operational savings and avoided fertilizer production. Chemical-based phosphorus recovery, however, generally required more resources than were offset by avoided fertilizers, resulting in a net environmental burden. In decentralized systems, phosphorus recovery via urine source separation reduced the global warming and ozone depletion potentials but increased terrestrial ecotoxicity and salinization potentials due to application of untreated urine to land. Overall, mineral depletion and eutrophication are well-documented arguments for phosphorus recovery; however, phosphorus recovery does not necessarily present a net environmental benefit. While avoided fertilizer production does reduce potential impacts, phosphorus recovery does not necessarily offset the resources consumed in the process. LCA results indicate that selection of an appropriate phosphorus recovery method should consider both local conditions and other environmental impacts, including global warming, ozone depletion, toxicity, and salinization, in addition to eutrophication and mineral depletion impacts.

Energy use and carbon footprints differ dramatically for diverse wastewater-derived carbonaceous substrates: An integrated exploration of biokinetics and life-cycle assessment

“…However, further research is still needed to determine how the offsets of embodied energy for varying energy recovery strategies change in relation to both scale and technologies. This is important because the scale of implementation has been observed to affect the energy consumed or recovered in wastewater treatment with integrated resource recovery 22, 23 . The residual biosolids released from the anaerobic digestion (AD) systems still have sufficient energy potential for further capture, ranging from 0.099 to 0.153 kWh/m 3 (Fig.…”

Enhanced phosphorus solubility during anaerobic digestion

“…Some of these precipitants deposit and scale within the digester and in downstream accessories (Doyle, Oldring et al 2002). Moreover, because it is precipitated, the P passes through to the biosolids during solids separation (BradfordHartke, Lane et al 2015). This reduces the availability of P and reduces recovery yield for the P recovery technologies.…”

“…This highly diluted stream is concentrated (in P) through waste activated sludge (WAS), clarification, and post-thickening, making waste activated sludge (WAS) as a final feed for the digester, with a total P concentration of 350-470 mg L -1 achieved, having 60-90% as organic P (Stratful, Scrimshaw et al 2001). Nearly 100% of P is converted to inorganic P at the completion of AD process, with 90% of P in the form of insoluble inorganics (Bradford-Hartke, Lane et al 2015).…”

“…As soluble fraction of P always tries to bind with available cation such as calcium (Ca) and magnesium (Mg), a lesser amount of P remained in the sludge supernatant due to its unwanted precipitation in the reactor and biosolids. It has been widely reported that almost 90% of the total P ends up in sludge biosolids, while rest of it goes to the sludge supernatant (Smil 2000, Bradford-Hartke, Lane et al 2015. About all of the supernatant P is recoverable as struvite, but a minor fraction is recoverable from biosolids due to P binding with iron (Fe) and aluminum (Al).…”

Electrochemical phosphorus removal and recovery

“…Phosphorus (P) is an irreplaceable nutrient, but it is also associated with eutrophication [10,22,46,47]. On the one hand, a large amount of P is discharged to surface waters resulting in eutrophication [47].…”