Addition of thiourea host monomer to polymer flocculants to improve selectivity of phosphate sorption

Authors: GOEBEL, TIMOTHY - Texas Tech University; MCINNES, KEVIN - Texas A&M University; SENSEMAN, SCOTT - University Of Tennessee; Lascano, Robert; CULLEN, ALEX - United States Air Force; FUHRER, TIMOTHY - Radford University; PICKLE, SARAH - Idaho State University; ADEOLOKUN, NETOCHI - Idaho State University; DAVIS, TODD - United States Air Force

Submitted to: Journal of Agricultural Chemistry and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2020
Publication Date: 8/24/2020
Citation: Goebel, T.S., McInnes, K.J., Senseman, S.A., Lascano, R.J., Cullen, A.M., Fuhrer, T.J., Pickle, S., Adeolokun, N.O., Davis, T.A. 2020. Addition of thiourea host monomer to polymer flocculants to improve selectivity of phosphate sorption. Journal of Agricultural Chemistry and Environment. 9:147-158.
DOI: https://doi.org/10.4236/jacen.2020.93013

Interpretive Summary: Fertilizers are chemicals that are applied to crops, such as cotton and corn, and to urban landscapes, such as golf courses and lawns, to promote crop yield and healthy plants. The main chemicals in most fertilizers are nitrogen, potassium and phosphorus. The majority of time the application of fertilizers does not harm the environment; however, when an excessive amount is applied it can be toxic. For example, too much application of phosphorus can lead to the fertilizer washing into ponds and streams and a sudden increase in the concentration is unsafe and may lead to what is called algal blooms as bacteria in the water grow very rapidly. When this happens water in ponds and streams is harmful to fish and other organisms in the water and they may perish. How can we remove the excess phosphorus that ends in streams and ponds? A collaborative project between scientists from different universities and federal agencies conducted experiments to test if the application of an experimental chemical compound (thiourea) could be used to remove the excess phosphorus without removing beneficial compounds from the water. Scientists, used a previously described polymer that along with the thiourea was able to attach to 43% of the phosphorus in the water and remove it by forming flakes or settling, without affecting other compounds in the water. This value compares well with other more expensive treatments and has encouraged us to further investigate its application as a safe compound to remove toxic levels of phosphorus that may contaminate our ponds and streams.

Technical Abstract: Inorganic phosphate is a common nutrient that is applied as a fertilizer to both agricultural fields as well as urban settings such as private yards, public parks and other urban landscaping. While phosphate typically binds tightly to soil, movement of phosphate off of application sites can occur through soil erosion. The soil and its bound phosphate can then end up in surface waters such as rivers and lakes. Phosphate found in surface water bodies exists both as bound to the suspended clay as well as that free in solution. Elevated phosphate concentration in surface waters can lead to algal blooms and eutrophication. While the phosphate bound to clay in suspension in surface water bodies can be removed by commercially available polymer flocculants, the phosphate that is free in solution is more challenging as it is usually found in low concentrations and other anionic salts are generally present in higher concentrations. To remove phosphate from contaminated water systems, where other anions exist at higher concentrations, it is favorable to have a method of removal that is selective for phosphate. As a proof of principle, thiourea derivatized polymer flocculants were examined for the selective removal of phosphate in the presence of competing anions. The polymer flocculants exhibited selectivity for phosphate through hydrogen bonding and were effective at removing up to 43% of phosphate from simulated wastewater. Computational studies and 1H NMR were used to investigate the selectivity of the thiourea monomer for phosphate over competing anions such as chloride and sulfate.