Honors College Theses

Publication Date



Civil Engineering (B.S.)

Document Type and Release Option

Thesis (open access)

Faculty Mentor

Dr. Francisco Cubas


Phosphorus, a finite element, is necessary for all living organisms and directly impacts biota growth as well as productivity in freshwaters. The demand for phosphorus is continually increasing, but the supply of phosphorus is continually decreasing. In response to depleting resources, phosphorus in surface water sediments is being explored as a sustainable solution to the forecasted phosphorus shortage. Phosphorus in sediments is generally bound to oxidized iron (Fe3+) forming iron phosphate complexes. This form of phosphorus is released when iron reduces to Fe2+ in anaerobic environments. Under such conditions, soluble phosphorus (i.e., orthophosphate) may then be recovered using compounds that have a high affinity to resorb phosphorus. Gypsum, CaSO₄·2H₂O, is proposed to recover phosphorus released from sediments. As calcium and sulfate from gypsum interact with released phosphorus and reduced iron respectively, it forms new compounds: Ca(PO4)-3 and FeS. These compounds can then be collected, and the calcium phosphate can presumably be used as fertilizers. An experimental setup has been designed to evaluate the potential to recover phosphorus from sediments. In this setup, the effectiveness of gypsum is evaluated by measuring phosphorus levels in the sediments prior to the anaerobic conditions, during the anaerobic phase, and after forming compounds with Gypsum. This experimental approach provided data at all phases to ensure there were no factors affecting the success of the interaction. It is expected that a significant amount of calcium phosphate will be recovered that can be used in fertilizer applications providing a sustainable alternative for nutrient recovery.