Sulfur Autotrophic Denitrification Treatment of Dibasic Acid Wastewater From Adipic Acid Production Coupled With...

Highly toxic dibasic acid (DBA) wastewater, a by-product of oxalic acid production, suppresses microbial activity and causes incomplete organic degradation, necessitating efficient and economical technologies for compliant discharge and resource recovery. Mixed DBA wastewater from adipic acid production was treated by sulfur autotrophic denitrification, with a comprehensive analysis of wastewater toxicity, the effect of sulfur particle size on reactor performance, and reclaim elemental sulfur from the resulting sludge. The results showed that the major organics in the DBA wastewater were valeric acid, cyclopentanecarboxylic acid, cyclohexaneacetic acid, 2,4-dinitrophenol, 1'-(butyn-3-1-yl)-(1S, 2S, 5R)-menthol, and 3,4,5-trimethoxyphenylacetonitrile. The concentrations of Cu²⁺ and 2,4-dinitrophenol in the DBA wastewater were metabolic toxins, and the IC₅₀ were 4.83 and 11.46 mg·L^-1, respectively, and the IC₅₀ of the DBA wastewater was 17.09% (v/v), representing a test medium containing 17.09% undiluted DBA wastewater. Compared with sulfur powder and 1- to 6-mm sulfur particles, 0.25- to 0.35-mm sulfur particles are a more suitable source of sulfur for up-flow reactors, such as fluidized beds and expanded beds. The maximum load of DBA wastewater operated in a sequencing batch reactor was only about 0.22 gNO₃ ^--N·L^-1·d^-1, with a nitrogen removal efficiency of 92.7%, and increasing the load required further sludge domestication or proper pretreatment of the DBA wastewater. The minimum sulfur content of sulfur autotrophic denitrifying sludge was 16.20%. Sulfur autotrophic denitrification sludge was mixed with sulfide solution for sulfur release, and elemental sulfur was precipitated and reclaimed after acid addition. Peak values of 93.58% for S⁰ recovery rate and 95.20% for the purity of recovered S⁰ were achieved. This process achieves waste reduction and resource recovery, aligning with the principles of a circular economy.