Wastewater　treatment　plants　(WWTPs)　are　being　challenged　to　operate　as　carbon-neutral　and　energy-efficient　systems.　The　structural　extracellular　polymeric　substances　(St-EPS)　in　waste-activated　sludge　(WAS),　such　as　alginate,　were　revealed　to　form　an　architectural　gel　matrix,　hindering　the　psychrophilic　hydrolysis　and　acidogenesis　and　its　application　in　nitrate　removal.　Consequently,　volatile　fatty　acid　(VFAs)　production　for　nitrate　removal　at　15　degree　celsius　is　demonstrated　by　a　novel,　enriched　psychrophilic　consortium　for　alginate-degrading　and　nitrate-removing.　Both　alginate　lyase　(EC　4.2.2.3)　and　oligo-alginate　lyase　(EC　4.2.2.26)　are　identified　for　alginate　utilization　by　the　metaproteomics　analysis.　A　high　nitrate　removal　rate　of　7.6　(WAS　as　the　substrate)　to　13.0　(alginate　as　the　substrate)　mgN/(gVSS　h)　was　achieved.　By　combining　high-throughput　and　PacBio　sequencing　and　metagenomics　analysis,　two　genera　of　Bacteroides　(69.4%)　and　Dysgonomons　(12.8%)　are　revealed　to　enhance　psychrophilic　WAS　fermentation.　The　VFAs　can　be　utilized　by　denitrifiers　for　nitrate　removal　in　an　indirect　pathway.　Moreover,　other　genera　of　denitrifiers　(Pseudomonas,　0.11%;　and　Massilla,　0.003%)　can　excrete　alginate　lyase,　indicating　the　dual　merits　of　St-EPS　degradation　and　nitrate　removal　in　the　direct　pathway.　This　work　extends　the　application　of　WAS　for　denitrifiers,　providing　a　new　carbon-neutral　and　energy-efficient　system　in　WWTPs,　especially　under　psychrophilic　conditions.