Nanoplastics Detection Method in Wastewater

By Vidhatri Iyer, a freshman

Increased levels of plastics production worldwide have created new challenges to manage waste generation and has become one of the threats to our terrestrial and aquatic environments. Use of single-use plastic bottles and containers has led to accumulation of plastic wastes which undergo fragmentation into microplastics (less than 5 mm size) and nanoplastics (less than 1 micrometer size). Lack of universal and validation analytical methods to measure nanoplastics pollution in our water streams and aquatic environments has created a major gap to implement countermeasures by the local government organizations. Thus, rapid and field-friendly methods to identify hotspots of nanoplastics pollution are needed to implement for routine screening of our watersheds.

Hand-held instruments are routinely used for monitoring various water quality parameters in urban surface streams. These parameters can be obtained directly from grab samples without a need for additional sample processing. I have developed a Nile Red based nanoplastics detection method which is suitable for routine field-testing. Water samples are filtered using a 0.45 micrometer syringe filter to remove any particulate debris. A four to one ratio is used for water samples and plastic binding dye, Nile Red and incubated for 10 minutes. A custom-built fluorometer is used to read fluorescence at 620 nm. A standard curve is generated by mixing increasing concentrations of 50 mm polystyrene beads with Nile Red dye. Thus, the fluorescence values obtained from field-samples are directly quantified and expressed as micrograms per milliliter. Nile Red binds to a wide-variety plastic types such as polystyrene, polyethylene, polypropylene, and polyvinyl chloride This rapid technique would enable detection of hotspots of plastics contamination and allow agencies to take further action to reduce pollution.

Trico Regional Sewer Utility in Zionsville, Indiana provides efficient sanitary service to the local neighborhoods and business by treating millions of gallons of wastewater per day.

Trico Regional Sewer Utility operates a wastewater treatment facility consisting of an influent flow meter, three mechanical bar screens, a new grit removal system, eight vertical loop reactors, six secondary clarifiers, phosphorus removal via chemical addition, ultraviolet light disinfection, post aeration with fine bubble diffusers, and effluent flow metering. Sludge management includes five aerobic digesters and a belt filter press. The plant processes are described below:

1. Pretreatment (Plant Influent): The state-of-the-art pretreatment building accepts all of the sanitary waste via 24 lift stations. It consists of a screening process to remove unwanted and untreatable materials such as plastics and metals. The screenings are conveyed through a screw press to remove the excess water. At the end of the screw press the screenings are dropped into a hopper then hauled to a landfill.

2. Pretreatment is where the incoming wastewater stream is measured for flow and sampled to identify the quantity of organic wastes. An odor control system is used to remove harmful gases such as hydrogen sulfide and methane from our incoming wastewater stream piping making a safe working environment in the pretreatment building. After pretreatment the organic material enters into one of two biological treatment methods or activated sludge process. The current method in use is a Vertical Loop Reactor (VLR). The VLR contains a microbial mass in order to metabolize harmful organic contaminants. Ammonia is the most important contaminant to remove by treatment.

3. Secondary Treatment: Secondary treatment consists of 6 clarifiers. The clarifiers accept the flow from the VLR. The purpose is to separate the solids and the water. A clarifier is a circular basin in which effluent from the activated sludge process is held for a period of time during which the heavier biomass (microorganisms) settles to the bottom as “activated sludge.” This sludge, teaming with hungry microorganisms, can be returned to the first aeration basin to begin the activated sludge treatment process all over again. The solids containing live biological organisms settle to the bottom of the clarifier. The settled solids will then be returned back to biological treatment or permanently removed from our treatment system via pumps. The clear water exits the clarifiers by gravity to the next step of treatment.

4. Once the clear water has exited the clarifiers the water travels to disinfection treatment. The method of treatment is ultraviolet light, which destroys the reproductive cells of disease-causing bacteria which inhibits further growth. E. coli is the indicator organism that is tested to determine the effectiveness of disinfection.

Plant Effluent: The plant effluent is monitored for flow volume, provided with mechanical air to sustain biological life in the receiving stream and sampled for removal of organic materials.

Nanoplastics levels in wastewater samples were monitored by collecting influent and effluent water samples on five independent days each month for a period of six consecutive months. Nanoplastics levels were measured using the one-step fluorometric technique. Nanoplastics load was consistently higher in the influent wastewater samples compared to effluent water. This correlated with the increased levels of total suspended solids in influent wastewater in comparison to effluent water.

Finally, nanoplastics in influent wastewater samples were effectively removed to below detection levels when water is held in the clarifiers prior to exit as effluent water into the waterstreams.

This hand-held fluorometer is simple to use for routine field-based testing and water quality labs that help to monitor the efficiency of wastewater treatment. Routine implementation of this method can lead to the development of next generation of hand-held readers to measure several other water quality parameters in addition to nanoplastics.

About the Author

Vidhatri Iyer is a freshman at University High School of Indiana, in Carmel. Vidhatri cares deeply about the water quality of the Indiana water streams. She recently developed a novel and rapid method to detect nanoplastics contamination in the wastewater generated by our local neighborhoods. Her method has received wide attention from water experts and the local media. Her work has been featured in the Current in

Carmel and Hamilton Reporter newspapers. She was recently interviewed by the Local TV channel, Wish TV. Vidhatri has presented her nanoplastics detection method at area water conferences namely, the Indiana Water Summit and Indiana Rural Water Fall meetings. She also presented at the Indiana Section AWWA’s 115th Annual Conference in April, for which she received the IN AWWA Besozzi Youth Grant Award.