Microplastics in wastewater are actively disrupting biological treatment processes. New research published in Water examines how polyethylene terephthalate (PET) microplastics impact aerobic granular sludge (AGS), a promising technology for wastewater treatment. The findings suggest that even relatively low concentrations of PET microplastics can destabilize sludge structure, alter microbial composition, and potentially reduce treatment efficiency.
For wastewater treatment professionals, this research underscores the growing threat of microplastics to biological treatment systems and highlights an urgent need for mitigation strategies. Let’s dive in.
Why Aerobic Granular Sludge Matters
AGS technology has been gaining traction as a more efficient alternative to conventional activated sludge. It forms dense, self-aggregating microbial granules that offer superior settleability, better resilience to toxic compounds, and enhanced nutrient removal. Because of these advantages, many wastewater treatment plants have been exploring AGS as a way to improve performance while reducing energy and chemical costs.
However, the long-term stability of AGS depends on the integrity of extracellular polymeric substances (EPS), a complex mix of proteins and polysaccharides that help maintain the granule structure. Any disruption to EPS composition can weaken the granules, making the system less effective at treating wastewater.
How PET Microplastics Disrupt AGS Structure
The study examined four granular sequencing batch reactors (GSBRs) exposed to increasing concentrations of PET microplastics. The results showed significant structural changes in the AGS as microplastic levels increased.
Higher concentrations of PET microplastics led to an increase in smaller granules. This suggests that PET microplastics may be physically breaking apart granules or interfering with microbial aggregation. EPS composition also shifted in response to microplastic exposure, with polysaccharide levels generally declining while protein concentrations increased. The PN/PS ratio rose, making the sludge more hydrophobic and potentially affecting its ability to settle properly. These changes indicate that AGS may become more fragile over time when exposed to microplastics, increasing the risk of biomass washout and reducing overall treatment efficiency.
Why This Matters
Microplastics are already entering wastewater treatment plants in significant amounts through household and industrial discharges. Studies show that WWTPs retain a large fraction of incoming microplastics, with much of it accumulating in sludge. This new research raises concerns that prolonged exposure to microplastics could reduce the performance of AGS systems by destabilizing sludge and interfering with microbial function.
In practical terms, this could lead to more frequent system upsets and granule disintegration, reducing overall process stability. Nutrient removal efficiency may decline as microbial communities are disrupted, potentially impacting water quality. Additionally, sludge management could become more challenging if microplastics interfere with dewaterability or alter sludge properties, making disposal and processing more difficult.
How Can Plants Respond?
While microplastics are a systemic issue requiring policy intervention, wastewater treatment plants can take steps to minimize their impact on AGS systems:
1. Pretreatment Upgrades
- Installing advanced filtration systems (e.g., membrane bioreactors or fine screens) can help remove microplastics before they reach biological treatment stages.
2. Optimizing Sludge Management
- Understanding how microplastics interact with sludge can help adjust operational strategies to maintain granule stability.
- Frequent monitoring of EPS composition and granule size distribution can provide early warning signs of microplastic-related disruptions.
3. Collaboration on Microplastic Reduction
- Partnering with regulatory agencies and industries to reduce microplastic pollution at the source can prevent these particles from reaching wastewater treatment plants in the first place.
- Public awareness campaigns encouraging the reduction of plastic waste and microplastic-shedding products (like synthetic fibers) can also contribute.
This study provides clear evidence that microplastics pose a direct threat to biological wastewater treatment systems. PET microplastics, in particular, can alter sludge structure, disrupt microbial communities, and compromise treatment performance in AGS reactors. As the microplastic contamination challenge continues to mount, understanding its effects on AGS and other biological treatment processes will be critical for maintaining stable and efficient wastewater treatment operations for the future.
SOURCES: Water
