Microalgal-Bacterial Granular Sludge Process in Non-Aerated Municipal Wastewater Treatment under Natural Day-Night Conditions: Performance and Microbial Community

Shulian Wang,Huan Hou,Lin Zhu,Yingqun Ma,Bin Ji

doi:10.3390/w13111479

Abstract

The microalgal-bacterial granular sludge (MBGS) process is expected to meet the future requirements of municipal wastewater treatment technology for decontamination, energy consumption, carbon emission and resource recovery. However, little research on the performance of the MBGS process in outdoor treatment was reported. This study investigated the performance of the MBGS system in treating municipal wastewater under natural alternate day and night conditions in late autumn. The results showed that the average removal efficiencies of Chemical oxygen demand (COD), NH4+-N and PO43−-P on daytime before cooling (stage I, day 1−4) could reach 59.9% ± 6.8%, 78.1% ± 7.9% and 61.5% ± 4.5%, respectively, while the corresponding average removal efficiencies at night were 47.6% ± 8.0%, 56.5% ± 17.9% and 74.2% ± 7.6%, respectively. Due to the dramatic changes in environmental temperature and light intensity, the microbial biomass and system stability was affected with fluctuation in COD and PO43−-P removal. In addition, the relative abundance of filamentous microorganisms (i.e., Clostridia and Anaerolineae) decreased, while Chlorella maintained a dominant position in the eukaryotic community (i.e., relative abundance > 99%). This study can provide a theoretical basis and technical support for the further engineering application of the MBGS process.

Highlights

Traditional activated sludge (CAS) process had been applied to treat municipal wastewater for more than ten decades
In this study, Chemical oxygen demand (COD), NH4+-N and PO43−-P removal was investigated for the first time by microalgal-bacterial granular sludge (MBGS) process under actual 33 day-outdoor conditions experienced two cooling and lasted continuous rainy days
It was found that COD and NH4+-N removal was better at daytime than at night, while PO43−-P removal was insignificantly different at daytime and night

Summary

Introduction

Traditional activated sludge (CAS) process had been applied to treat municipal wastewater for more than ten decades. The CAS process typically consumes a large amount of energy for electrical aeration to oxidize organic matter and ammonia nitrogen, while it releases greenhouse gases (GHGs) and produces excessive sludge [1,2,3,4,5]. In the MBGS process, microalgae can provide O2 for the oxidation of organic matter, as well as consume CO2 as a carbon source produced from bacterial respiratory [6,7]. Compared with CAS, the MBGS process owns the superb merits of low energy consumption, robust adaptability and resource recovery potential, which has been extensively reported [8,9,10,11]

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Conclusion