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Nutrient recovery from waste is a promising strategy to conserve inputs while reducing nutrient discharge to the natural environment. Multiple waste streams have shown promise with respect to nutrient recovery. Multiple technologies also show promise at a pilot or full scale. These technologies, however, must not exacerbate other environmental issues, with excessive energy use, unsustainable material extraction (e.g., mineral extraction, cement use), or toxin release into the environment. Such technologies must also be feasible from economic and social perspectives. Work, therefore, should focus on both improving our current suite of available technologies for nutrient recovery from waste and framing policies that blend affordability with incentives, thereby fostering an environment conducive to innovation and adoption of sustainable approaches. This review considers the issues associated with nutrient recovery from waste, including technical feasibility and economic, environmental, and social factors, and identifies current knowledge gaps and emerging opportunities for nutrient waste recovery. 

Abstract Bacteria capable of dehalogenation via reductive or hydrolytic pathways are ubiquitous. Little is known, however, about the prevalence of bacterial dechlorination in deep terrestrial environments with a limited carbon supply. In this study we analyzed published genomes from three deep terrestrial subsurface sites: a deep aquifer in Western Siberia, the Sanford Underground Research Facility in South Dakota, USA, and the Soudan Underground Iron Mine (SUIM) in Minnesota, USA to determine if there was evidence to suggest that microbial dehalogenation was possible in these environments. Diverse dehalogenase genes were present in all analyzed metagenomes, with reductive dehalogenase and haloalkane dehalogenase genes the most common. Taxonomic analysis of both hydrolytic and reductive dehalogenase genes was performed to explore their affiliation; this analysis indicated that at the SUIM site, hydrolytic dehalogenase genes were taxonomically affiliated with Marinobacter species. Because of this affiliation, experiments were also performed with Marinobacter subterrani strain JG233 (‘JG233’), an organism containing three predicted hydrolytic dehalogenase genes and isolated from the SUIM site, to determine whether hydrolytic dehalogenation was an active process and involved in growth on a chlorocarboxylic acid. Presence of these genes in genome appears to be functional, as JG233 was capable of chloroacetate dechlorination with simultaneous chloride release. Stable isotope experiments combined with confocal Raman microspectroscopy demonstrated that JG233 incorporated carbon from 13C-chloroacetate into its biomass. These experiments suggest that organisms present in these extreme and often low-carbon environments are capable of reductive and hydrolytic dechlorination and, based on laboratory experiments, may use this capability as a competitive advantage by utilizing chlorinated organic compounds for growth, either directly or after dechlorination.