Abstract
Activated sludge from wastewater treatment plants was seeded into a sequencing batch reactor (SBR) in which synthetic wastewater was used as the influent. The sludge was bulked by decreasing the concentration of dissolved oxygen (DO). By adding a 30 min step of anaerobic stirring after the water inflow, the sludge bulking was rapidly inhibited after 10 running cycles, and the sludge volume index (SVI) decreased from 222 to 74 mL·g−1. The results of high-throughput sequencing showed that the relative abundance of bacteria Thiothrix, bacteria norank_o_Sphingobacteriales and fungi Trichosporon was increased by 6.3, 4.3 and 81.2%, after initial SBR stages, but these bacteria were inhibited by the addition of an anaerobic step, as their relative abundances decreased by 0.7, 0.8 and 14.7%, respectively. The proliferation of Thiothrix, norank_o_Sphingobacteriales and Trichosporon was the primary reason for the observed sludge bulking in the reactor. After the anaerobic step was added, the sludge extracellular polymeric substances (EPS) concentration was increased from 84.4 to 104.0 mg·(gMLSS)−1 (grams of mixed liquor suspended solids). Thus, the addition of an anaerobic step can inhibit the growth of filamentous bacteria, increasing the sludge EPS concentration and promoting the precipitation of activated sludge.
Highlights
Activated sludge processing is the most widely used biological wastewater treatment technique[1]
Research capabilities and technical approaches have improved in recent years, few studies have taken advantage of these advances to explain the inhibition of sludge bulking in the anaerobic step
After sludge was bulked in a sequencing batch reactor (SBR), an anaerobic step was added after the influent step to investigate its effect on the settleability of sludge
Summary
Activated sludge processing is the most widely used biological wastewater treatment technique[1]. Based on the storage selection theory, the organic carbon sources in the influent are largely consumed by various biochemical reactions, such as storage and phosphorus release during the anaerobic step. This will cut the nutritional supplies for the subsequent growth of filamentous bacteria during the aerobic step[17], inhibiting the growth of filamentous bacteria. This study aims to provide a theoretical basis and support for the prevention and resolution of sludge bulking issues in the design and operation of activated sludge processes in wastewater treatment plants
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