Abstract: Implementation of PHA bio-plastic to improve stream and runoff water quality

Last year, I began working in Dr. Randy Chambers’ lab with polyhydroxyalkanoates (PHAs), organic material produced by certain kinds of bacteria under conditions of high carbon availability and low nutrient presence. Bacteria sequester this carbon polymer product and can use it as an energy source for growth. When removed from the bacteria that produced it, polyhydroxyalkanoates are readily combined with other materials to produce PHA polymer-blends as a kind of ‘bioplastic.’ There are many potential applications of PHA-based products, and therefore research on the material is gaining popularity. For example, this biodegradable material could be invaluable to reducing petroleum-based plastic waste. As another example, when placed in stream water, the naturally occurring bacteria could use the PHA polymer as a carbon source and eliminate excess nutrients via processes like denitrification. This summer, I hope to assess the potential for PHA use by bacteria in water quality improvement efforts and answer the question of the material’s effectiveness and the significance of its impact. 

Because Dr. Chambers introduced me to this research last year, I have a good idea of how the methodology would work. We began testing the product in microcosm experiments in the lab by placing PHA polymer blends into buckets and filling them with water from local streams. We took timed samples of input and output buckers and as water ran through the system, and then performed nitrate and phosphate analyses on the water as a way of determining bacterial usage and nutrient elimination. Later in the process, we placed 5-10 meter pieces of PHA blends directly into the streams themselves and continued with the same sampling processes. For this summer, the plan is to scale up these experiments by rolling out 50-100 meters of PHA woven fibrous matting in a drainage ditch adjacent to an agricultural field.  The runoff from the field should be high in phosphorus and nitrogen; I anticipate that both nutrients will be removed from the water, thereby improving water quality prior to discharge farther downstream. I think that performing this study during the summer has the potential to yield more significant results than we have seen previously, as nutrient concentrations are likely to be higher and dissolved oxygen is likely to be lower. These conditions could encourage the bacteria to rely on PHA as a carbon source and thus reduce the nutrients in the water via anaerobic respiration and denitrification.

I hope that this project yields promising knew knowledge about the potential of PHA-based materials in restoration efforts. Significant results from this study could certainly clear a path for further research and understanding of the capacity for PHA use in a variety of settings. Ideally, results from this study could even inform decision making about direct implementation of the product on a commercial scale. For example, the woven PHA matting could be a potential substitute for the polyethylene plastic netting commonly used at construction sites to reduce soil erosion.  The PHA matting reduces erosion AND reduces nutrient concentrations, thereby providing a water quality benefit. VIMS faculty have been in discussion with Virginia Department of Transportation personnel who are interested in using PHA matting at VDOT road sites, as the matting would help them meet nutrient reduction requirements as part of the Chesapeake Bay TMDL program. I envision that the product of this study will be a clear and concise data set with appropriate analyses along with written explanation of the outcomes. This deliverable could serve as a resource for people looking into PHA projects in the future, so I believe this field-based study deserves to be explored to its full capacity. 

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