Document Type : Original Article

Authors

• Somayeh Kheiri ¹
• Mohammad Ghasemian ¹
• Mohammad Koushafar ¹
• Seyed Mohammad Mousavi ²
• Nasim Rafiei ³
• Ensiyeh Taheri ⁴
• Ali Fatehizadeh ⁴
• Mohammad Mehdi Amin ⁴

¹ Department of Agriculture Sciences, Islamic Azad University, Ardestan Branch, Ardestan, Iran

² Esfahan province Water and Wastewater Company, Isfahan, Iran

³ Environment Research Center, Research Institute for Primordial Prevention of Noncommunicable Disease; Student Research Committee, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran

⁴ Department of Environmental Health Engineering, School of Health; Environment Research Center, Research Institute for Primordial Prevention of Noncommunicable Disease, Isfahan University of Medical Sciences, Isfahan, Iran

Abstract

Aims: This study was carried out to investigate the effect of predators' growth on biological excess sludge reduction of adsorption/bio-oxidation process (A/B process) as a modification of activated sludge system. Materials and Methods: The real municipal wastewater after screening and gritting was pumped into A/B pilot plant which consists of two aeration and sedimentation tanks in series. The hydraulic residence time for A and B stages was set at 1 and 4 h, respectively, at an average flow rate of 32 L/h. During operation, the mixed liquor suspended solids (MLSS) in A and B stages was gradually increased. In this period, the operational parameters including dissolved oxygen, pH, volatile suspended solids (VSS), MLSS, alkalinity, biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), phosphorus, nitrogen, and sludge volume index were monitored. Results: The results showed that with increasing solid retention time (SRT) from 0.6 to 56.8 days in Stage A, the biomass yield (Y) decreased from 1.29 to 0.23 g VSS/g COD. Similar results were observed in Stage B and correspondence to 67% reduction of Y as SRT increased from 1.6 to 123.8 days. During the A/B operation, overall tBOD₅and tCOD removal was 70% ± 20% and 57% ± 24%, respectively. Conclusion: Based on the results, A/B process operation with high SRT led to predator growth enhancement and lower biological excess sludge production.

Keywords

• Aquatic worm
• predators
• sludge reduction
• solid retention time
• two‑stage activated sludge