Critical review of phytoremediation for the removal of antibiotics and antibiotic resistance genes in wastewater.

Antibiotics in wastewater are a growing environmental concern. Increased prescription and consumption rates have resulted in higher antibiotic wastewater concentration. Conventional wastewater treatment methods are often ineffective at antibiotic removal. Given the environmental risk of antibiotics and associated antibiotic resistant genes (ARGs), finding methods of improving antibiotic removal from wastewater is of great importance. Phytoremediation of antibiotics in wastewater, facilitated through constructed wetlands, has been explored in a growing number of studies. To assess the removal efficiency and treatment mechanisms of plants and microorganisms within constructed wetlands for specific antibiotics of major antibiotic classes, the present review paper considered and evaluated data from the most recent published research on the topics of bench scale hydroponic, lab and pilot scale constructed wetland, and full scale constructed wetland antibiotic remediation. Additionally, microbial and enzymatic antibiotic degradation, antibiotic-ARG correlation, and plant effect on ARGs were considered. It is concluded from the present review that plants readily uptake sulfonamide, macrolide, tetracycline, and fluoroquinolone antibiotics and that constructed wetlands are an effective applied phytoremediation strategy for the removal of antibiotics from wastewater through the mechanisms of microbial biodegradation, root sorption, plant uptake, translocation, and metabolization. More research is needed to better understand the effect of plants on microbial community and ARGs. This paper serves as a synthesis of information that will help guide future research and applied use of constructed wetlands in the field antibiotic phytoremediation and wastewater treatment.

Zebra mussel shells as an alternative mineral resource for lime production as a phosphorus precipitant.

Zebra mussels are an invasive species to North America and are presently found in many rivers and lakes in prolific numbers. Along with many other issues, zebra mussels present a problem when their shells are deposited on shore, carpeting beaches and reducing beach usability. A possible solution presented in this study is to use the zebra mussel shells as an alternative mineral resource to mined calcium carbonate for the production of lime to remove phosphorus in wastewater. Heat-treated coarse (500-1000 µm) and fine (<75 µm) zebra mussel shell dosed to 10 mg L-1 phosphate solution at 0.50 g L-1 and 0.25 g L-1, removed over 99% phosphorus while maintaining pH levels significantly lower than pure calcium hydroxide dosed under the same conditions. It was found that ground zebra mussel shells (<75 µm) heated for 1 h at temperatures of 600°C, 700°C, 800°C, 900°C, and 1000°C were capable of removing varying levels of phosphorus in water. Shells heated at 800°C and dosed at 1.00 g L-1 reduced phosphorus in collected real wastewater effluent by 99.48%. It was also shown that shells heat treated at 1000°C achieved 98.7% phosphorus removal when dosed at 0.25 g L-1, while maintaining a final effluent pH of 9.13, demonstrating the lowest overall energy costs of any of the effective shell treatments. The results indicate that zebra mussel shells show promise as an alternative resource for phosphorus precipitation in wastewater.