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Insights into activated sludge/Chlorella consortia under dark condition compared with light condition.
Jie Fan1, Xujie Zhang2, Xingyu Du2
1Department of Water and Wastewater Engineering, Wuhan University of Science and Technology, Wuhan 430065, China E-mail: fanjie@wust.edu.cn; State Environmental Protection Key Laboratory of Mineral Metallurgical Resources Utilization and Pollution Control, Wuhan University of Science and Technology, Wuhan 430065, China.
Bacteria-algae consortia effectively treat wastewater in the dark, achieving nutrient removal comparable to light conditions. This performance relies on bacterial activity and aeration, with specific gene expressions indicating adaptation to dark environments.
Area of Science:
- Environmental Microbiology
- Wastewater Treatment Technologies
- Algal Biotechnology
Background:
- Bacteria-algae consortia offer benefits for wastewater treatment, including oxygen production and carbon dioxide reduction.
- A key limitation for their application is understanding their performance under dark conditions.
Purpose of the Study:
- To investigate the performance of bacteria-algae consortia in wastewater treatment under dark conditions.
- To determine the impact of inoculum ratio and sludge retention time (SRT) on nutrient and chemical oxygen demand (COD) removal.
- To analyze the microbial community structure and gene expression changes in response to dark conditions.
Main Methods:
- Cultivation of bacteria-algae consortia under varying inoculum ratios and SRTs.
- Monitoring of nutrient removal and COD levels.
- Analysis of pigment ratios (Chla/Chlb, Caro/(Chla + Chlb)) to assess algal stress.
- Microbial community analysis using 16S rRNA sequencing.
- Quantitative PCR (qPCR) to analyze the expression of key functional genes.
Main Results:
- Inoculum ratio and SRT significantly influenced nutrient removal but not COD removal.
- Dark conditions, with a sludge/Chlorella ratio of 1:2 and SRT of 15 days, showed comparable performance to light conditions due to bacterial contributions and mechanical aeration.
- Algal pigment ratios indicated a response to oxidative stress in the dark.
- Specific microbial associations were observed: algae with Nitrosomonas and Dechloromonas in the dark, and Flavobacterium with Chlorella in the light.
- Upregulation of nitritation (amo, Hao) and denitrifying (narH) genes, and downregulation of phosphorus metabolism genes (PPX, PPK) were observed in the dark.
Conclusions:
- Bacteria-algae consortia can achieve effective nutrient removal in wastewater treatment under dark conditions.
- Optimizing inoculum ratio and SRT is crucial for nutrient removal efficiency.
- Mechanical aeration and bacterial activity are key factors for dark performance.
- Microbial community and gene expression adapt to dark conditions, suggesting potential for targeted process optimization.
- A strategy involving enrichment of Nitrosomonas at night and denitrifying polyphosphate accumulating organisms (DPAO) during the day is proposed for enhanced nitrification and phosphorus removal.
