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Abstract
Excessive proliferation of filamentous bacteria within activated sludge leads to structural instability and diminished settling properties, a prevalent issue in tannery wastewater treatment. There is a lack of research on the impact of particle addition on filamentous bacteria in activated sludge, specifically regarding sludge bulking reduction. Polyethylene terephthalate (PET) was selected to elucidate the effect of particles on sludge bulking. Results show that 0.1 mm diameter particles significantly influence the quantity and morphology of filamentous bacteria. In an anaerobic-aoxic-oxic (AAO) reactor, using 4000 particles/L reduced the sludge volume index (SVI) from 358 mg/L to 198 mg/L. These findings provide insights for resolving sludge bulking problems in tannery wastewaters and serve as a reference for future investigations on incorporating diverse particulate materials to mitigate activated sludge bulking issues.
Introduction
The activated sludge process is widely used in wastewater treatment plants, covering over 90% of municipal wastewater treatment and approximately 50% of industrial wastewater treatment. However, activated sludge bulking remains a significant challenge due to the excessive proliferation of filamentous bacteria, which accounts for more than 90% of bulking occurrences.
Filamentous bacterial expansion increases sludge volume and decreases settling performance. Environmental conditions such as temperature shifts can exacerbate this issue. Filamentous bacteria adapt better to these changes than bacterial flocs, leading to sludge bulking.
Research has shown that a volume fraction of filamentous bacteria between 1-20% can induce sludge bulking. Even low concentrations of filamentous bacteria can cause significant issues in wastewater treatment plants.
Sustainable Development Goals (SDGs)
- SDG 6: Clean Water and Sanitation – Improving wastewater treatment processes directly contributes to achieving clean water and sanitation.
- SDG 9: Industry, Innovation, and Infrastructure – Innovating wastewater treatment methods supports sustainable industrial practices.
- SDG 11: Sustainable Cities and Communities – Effective wastewater management is crucial for sustainable urban development.
- SDG 12: Responsible Consumption and Production – Enhancing sludge treatment processes promotes responsible production practices.
Material and Methods
Materials
Polyethylene terephthalate (PET) was chosen as the experimental particle due to its prevalence in wastewater effluent. Three different particle sizes were used: 0.075–0.15 mm (PET-1), 0.3–0.6 mm (PET-2), and 0.6–1.18 mm (PET-3). Activated sludge was collected from a wastewater treatment plant in Hangzhou, screened to remove other particles, and tested for biological activity and sedimentation.
Batch (Shaking Flask) Experiment
The effect of PET particles on filamentous bacteria-bulked sludge was investigated using shaking bed experiments. Different sizes of PET particles were added to conical flasks containing bulked activated sludge, and the sedimentation rate was measured over several days.
AAO Continuous-Flow Experiment
Two AAO experimental reactors were used to study the effect of PET particle addition on sludge bulking. One reactor was supplemented with PET particles, while the other served as a control. Various parameters, including PET particle concentration in effluent, water quality, SV, and SVI, were measured over 20 days.
Analytical Methods
- Sedimentation Rate: Measured using a glass cylinder and stopwatch.
- Quantity of PET Particles: Analyzed using filtration and stereomicroscope observation.
- Identification of Filamentous Bacteria: Conducted using morphological observations and microbiological staining techniques.
- Other Methods: Included measuring sludge settling velocity (SV), mixed liquid suspended solid (MLSS), and other water quality indices according to standard methods.
Results and Discussion
Extended Filament Control in the Batch Experiment
The sedimentation rate of activated sludge improved significantly with the addition of PET particles. Larger particles resulted in a higher sedimentation rate, with PET-2 and PET-3 showing the most significant improvements.
The presence of PET particles reduced the density and length of filamentous bacteria, with larger particles having a more pronounced effect. The addition of PET-1 particles facilitated the growth of filamentous bacteria, while PET-2 and PET-3 reduced their abundance.
AAO Experiment
The AAO reactor with PET particle addition showed stable removal rates for COD, ammonia nitrogen, and total phosphorus. However, there was a slight inhibition of nitrification initially observed. The SV and SVI of the sludge decreased significantly, indicating improved settling performance.
Conclusions
The addition of PET particles to filamentous bacteria-bulked sludge significantly impacted the quantity and growth morphology of filamentous bacteria, reducing SVI and enhancing settling performance. Larger particle sizes were more effective in reducing filamentous bacterial mycelia within activated sludge flocs. The findings suggest that incorporating particulate materials can effectively mitigate activated sludge bulking issues without compromising overall treatment efficiency.
Data Availability
Data are available on request from the corresponding author.
Acknowledgements
We thank Dr. Hongwei Luo for assistance with micro-Raman spectroscopic analysis and the graduate students who contributed to sample processing.
Funding
This work was supported by the Grant for National Science and Technology Major Projects for Water Pollution Control and Treatment [grant number 2017ZX07201003] and the Basic Public Welfare Research Project of Zhejiang Natural Science Foundation [grant number LGF21E080009].
Author Information
Authors and Affiliations
- College of Civil Engineering, Zhejiang University of Technology, Hangzhou, China: Su Wei, Ziyang Huang, Yongjiong Ni
- College of Environment,
Analysis of Sustainable Development Goals (SDGs) in the Article
1. Which SDGs are addressed or connected to the issues highlighted in the article?
- SDG 6: Clean Water and Sanitation
- SDG 12: Responsible Consumption and Production
- SDG 14: Life Below Water
2. What specific targets under those SDGs can be identified based on the article’s content?
- SDG 6: Clean Water and Sanitation
- Target 6.3: Improve water quality by reducing pollution, eliminating dumping, and minimizing the release of hazardous chemicals and materials, halving the proportion of untreated wastewater, and substantially increasing recycling and safe reuse globally.
- SDG 12: Responsible Consumption and Production
- Target 12.4: By 2020, achieve the environmentally sound management of chemicals and all wastes throughout their life cycle, in accordance with agreed international frameworks, and significantly reduce their release to air, water, and soil in order to minimize their adverse impacts on human health and the environment.
- SDG 14: Life Below Water
- Target 14.1: By 2025, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution.
3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?
- Indicator for Target 6.3: Proportion of wastewater safely treated (e.g., reduction in sludge volume index (SVI) from 358 mg/L to 198 mg/L).
- Indicator for Target 12.4: Number of studies and implementations of environmentally sound management practices for chemicals and waste (e.g., the use of PET particles to reduce sludge bulking).
- Indicator for Target 14.1: Reduction in marine debris and nutrient pollution (e.g., reduced effluent suspended solids (SS) and improved effluent quality).
4. Findings from Analyzing the Article
SDGs Targets Indicators SDG 6: Clean Water and Sanitation Target 6.3: Improve water quality by reducing pollution, eliminating dumping, and minimizing the release of hazardous chemicals and materials. Reduction in sludge volume index (SVI) from 358 mg/L to 198 mg/L. SDG 12: Responsible Consumption and Production Target 12.4: Achieve environmentally sound management of chemicals and all wastes throughout their life cycle. Studies on the use of PET particles to manage sludge bulking. SDG 14: Life Below Water Target 14.1: Prevent and significantly reduce marine pollution of all kinds. Improved effluent quality and reduced suspended solids (SS) content. The article discusses the impact of PET particles on filamentous bacteria in activated sludge, which is relevant to multiple SDGs. The research provides insights into improving wastewater treatment processes, thereby contributing to cleaner water (SDG 6), responsible waste management (SDG 12), and reduced marine pollution (SDG 14).
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Fuente: nature.com
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