A continuous self-circulating granular sludge treatment process for real municipal wastewater: Regulation strategy, exploring granularity and stabilization, and processing performance

Abstract

Existing continuous flow reactors (CFR) utilized for the investigation of aerobic granular sludge (AGS) exhibit structural complexity and suboptimal energy efficiency. An innovative aeration self-circulating CFR (Zier rector) was employed in this study for the cultivation of AGS. The experiment was performed 202 days using real municipal wastewater under varying operating conditions. A hydraulic retention time of 10 h and adequate influent organic matter resulted in a chemical oxygen demand removal efficiency of 85%, an ammonia nitrogen removal efficiency exceeding 92%, and a total nitrogen removal efficiency ranging from 60% to 70%. The particle size increased when the up-flow velocity was maintained between 9.8 and 18 m/h, the self-circulating multiple times ratio was sustained within 12 to 30 times, and the food-to-microorganism was set within 0.2 to 0.6 g COD/(g MLSS·d). Ultimately, the mass proportion of sludge with a particle size larger than 0.2 mm was 75%, with 42% exceeding 0.5 mm. The stability of AGS and the treatment efficacy of the Zier process were influenced by the temperature and volume ratio of the nonaerated to the aerated zones. The Zier process demonstrates enhanced advantages and application potential, rendering it a more appealing option for a broader spectrum of water treatment facilities.