In-situ enhancement of autotrophic nitrogen removal in coking wastewater using staged diatomite and pyrite strategy.

Abstract

Due to toxicity inhibition and high external carbon costs, anaerobic/anoxic/oxic technologies for coking wastewater require efficient, low-carbon alternatives. Here we develop a strategy to effectively enhance the autotrophic nitrogen removal process in coking wastewater through a phased addition of diatomite porous material and an inorganic electron donor. Under long-term operation, diatomite increased biomass by 86% and induced micro-granular sludge with an average size of 196 μm. Nitrogen removal pathway analysis showed a shift from heterotrophic to autotrophic mode. Ultimately, SCN^-- and FeS₂-driven autotrophic denitrification contributed 25.6% and 27.9%, respectively. Enrichment of autotrophic sulfur-oxidizing nitrate-reducing bacteria, such as Sulfuritalea and Sulfurisoma, provided strong evidence. Additional pyrite supplementation ultimately increased total nitrogen removal from 77.7% to over 94.0% without external carbon. This study enhanced the in-situ autotrophic process of conventional systems for coking wastewater, offering a cost-effective pathway for energy-saving and carbon-reduction goals.