This liquid requires further treatment as it is high in nitrogen and phosphorus, particularly if the sludge has been anaerobically digested. The treatment can take place in the sewage treatment plant itself (by recycling the liquid to the start of the treatment process) or as a separate process.
verb (used with object), abrogated, abrogating. 1. to abolish by formal or official means; annul by an authoritative act; repeal: to abrogate a law. 2. to put aside; put an end to. Origin of abrogate. Latin.
You repeal it, of course, so abrogate means to officially revoke, cancel or abolish. The meaning of this word has expanded a bit since its earliest usage, but it still appears most often in a legal or political context, or when serious rights and responsibilities are being discussed.