The　fabrication　of　a　green,　high　activity　and　low-cost　carbon-based　catalyst　capable　of　activating　new　oxidant　(peroxymonosulfate,　PMS)　for　contaminants　abatement　is　needed.　In　this　research,　we　prepared　novel　N-doped　biochars　via　one-step　pyrolysis　of　algal　sludge　without　external　nitrogen　sources.　The　obtained　ASBC800　possessed　the　largest　specific　surface　area　(SBET　=　145.596　m2　g−1)　and　thus　it　displayed　the　best　catalytic　performance,　as　revealed　by　the　effective　elimination　of　sulfadiazine　(SDZ,　＞95%　within　70　min)　with　0.2　g　L−1　ASBC800　and　0.5　mM　PMS.　Both　radical　species　(e.g.,　SO4•−,　and　•OH),　and　nonradical　regime　(1O2　and　electron-transfer)　contributed　to　SDZ　oxidation,　in　which　ASBC800　played　essential　roles　in　activating　PMS,　accumulating　SDZ,　and　regulating　electron　shuttle　from　SDZ　to　ASBC800-PMS*.　Overall,　this　work　not　only　provides　a　novel　strategy　for　the　synthesis　of　N-rich　and　cost-effective　biochar　but　also　promotes　the　development　and　application　of　carbon-based　functional　materials　in　environmental　remediation.　©　2023　by　the　authors.