A new process for the removal of nitrogen from wastewater is introduced. The process involves three steps: (1) partial nitrification of NH 4 + to NO 2 À ; (2) partial anoxic reduction of NO 2 À to N 2 O; and (3) N 2 O conversion to N 2 with energy recovery by either catalytic decomposition to N 2 and O 2 or use of N 2 O to oxidize biogas CH 4 . Steps 1 and 3 have been previously established at full-scale. Accordingly, bench-scale experiments focused on step 2. Two strategies were evaluated and found to be effective: in the first, Fe(II) was used to abiotically reduce NO 2 À to N 2 O; in the second, COD stored as polyhydroxybutyrate (PHB) was used as the electron donor for partial heterotrophic reduction of NO 2 À to N 2 O. For abiotic reduction with Fe(II), the efficiency of conversion of NO 2 À to N 2 O was over 90% with 98% nitrogen removal from water. For partial heterotrophic denitrification, different selection conditions were imposed on acetate-and nitrite-fed communities initially derived from waste activated sludge. No N 2 O was detected when acetate and nitrite were supplied continuously, but N 2 O was produced when acetate and nitrite were added as pulses. N 2 O conversionefficiency was dependent upon the method of addition of acetate and nitrite. When acetate and nitrite were added together (coupled feeding), the N 2 O conversion efficiency was 9-12%, but when acetate and nitrite additions were decoupled, the N 2 O conversion efficiency was 60-65%. Decoupled substrate addition selected for a microbial community that accumulated polyhydroxybutyrate (PHB) during an anaerobic period after acetate addition then consumed PHB and reduced NO 2 À during the subsequent anoxic period. The biological N removal efficiency from the water was 98% over more than 200 cycles. This indicates that decoupled operation can sustain significant long-term N 2 O production. Compared to conventional nitrogen removal, the three-step process, referred to here as Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO), is expected to decrease oxygen requirements, decrease biomass production, increase organic matter available for recovery as biogas methane, and enable energy recovery from nitrogen, but pilot-scale studies are needed. Broader contextThe release of reactive forms of nitrogen is a major environmental threat causing hypoxia and eutrophic zones in water bodies. Globally, rising energy costs and increasingly stringent discharge regulation are major drivers for efficient wastewater treatment processes that lower costs and increase recoverable energy from waste. While many processes recover energy from carbon waste as CH 4 , none recovers energy from waste nitrogen. This work introduces a new wastewater treatment process that removes and recovers energy from nitrogen waste by exploiting the thermodynamic properties of N 2 O for energy recovery. The proposed process, referred to here as Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO), involves three steps: (1) partial aerobic nitrication of NH 4 + to ...

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A Gram-negative, non-motile, aerobic bacterial strain, designated MJ20 T , was isolated from farm soil near Daejeon (South Korea) and was characterized taxonomically by using a polyphasic approach. Comparative 16S rRNA gene sequence analysis showed that strain MJ20 T belongs to the family Cytophagaceae, class Sphingobacteria, and was related most closely to Dyadobacter fermentans DSM 18053 T (98.9 % sequence similarity), Dyadobacter beijingensis JCM 14200 T (98.0 %) and Dyadobacter ginsengisoli KCTC 12589 T (96.4 %). The G+C content of the genomic DNA of strain MJ20 T was 48.5 mol%. The detection of MK-7 as the predominant menaquinone and a fatty acid profile with summed feature 4 (C 16 : 1 v7c and/or iso-C 15 : 0 2-OH), iso-C 15 : 0 , C 16 : 0 and C 16 : 1 v5c as major components supported the affiliation of strain MJ20 T to the genus Dyadobacter. The new isolate exhibited relatively low levels of DNA-DNA relatedness with respect to D. fermentans DSM 18053 T (mean±SD of three determinations, 47±7 %) and D. beijingensis JCM 14200 T (38±8 %). On the basis of its phenotypic and genotypic properties together with phylogenetic distinctiveness, strain MJ20 T (5KCTC 22481 T 5JCM 16232 T ) should be classified in the genus Dyadobacter as the type strain of a novel species, for which the name Dyadobacter soli sp. nov. is proposed.