Investigation of the Biodegradation of Diazinon by Aerobic Granules in Sequencing Batch Reactor

Diazinon is an organophosphate insecticide widely used in agriculture. Its persistence and toxicity in aquatic environments pose significant risks to both ecosystems and public health. Recently, biodegradation has emerged as an effective and sustainable method for pollutant removal. In this study, the potential for aerobic granule formation from diazinon-adapted activated sludge was evaluated in a sequencing batch reactor. During the adaptation phase, a reactor with a working volume of 1200 mL was inoculated with activated sludge. Initially, glucose was used as the carbon source, which was gradually replaced with diazinon. After 11 weeks, diazinon with a COD concentration of 300 mg/L was used as the sole carbon source. The entire adaptation period, considering the removal of carbon, nitrogen, and phosphorus, lasted 14 weeks. Subsequently, aerobic granule formation was carried out in an SBR with a working volume of 0.8 L, operated in 6-hour cycles for 60 days at ambient temperature and pH= 7 ± 0.2 (adjusted using sulfuric acid and sodium hydroxide). Aeration and mixing were provided by an air pump at a velocity of 5 cm/s. During the adaptation phase, a removal efficiency of 72.33% was achieved at an influent concentration of 300 mg COD/L. After granule formation, the removal efficiency increased to 94.33% under the same conditions. Brown-colored aerobic granules up to 3 mm in diameter formed, with an SVI₃₀/SVI₅ ratio of 0.96. The protein-to-polysaccharide (PN/PS) ratio reached 1.64, indicating good structural cohesion. The results of this study indicate that aerobic granules derived from activated sludge, adapted to diazinon, have a high potential for the biological removal of this pollutant. These findings can serve as an effective and sustainable solution for treating diazinon-contaminated wastewater on an industrial scale and for reducing the environmental impacts of this toxin in water resources.