Phosphorus and Algae Removal via Adsorption

A Master of Science thesis in Civil Engineering by Ahmad A. Ghadban entitled, "Phosphorus and Algae Removal via Adsorption," submitted in January 2012. Thesis advisor is Dr. Maruf Mortula. Available are both soft and hard copies of the thesis.

Abstract

Algal bloom, commonly known as Red Tide in coastal areas, has become one of the major problems facing desalination plants due to the high biomass concentration of microalgae associated with it. It causes operational problems (i.e. membrane fouling) in addition to health risk associated with deadly species of algae. Phosphorus pollution is considered to be the primary cause of red tide since most of microalgae species grow rapidly in the presence of high phosphorus concentrations. Many recent studies showed the efficiency of using adsorption for phosphorus removal from wastewater; however, none addressed its removal from seawater or the removal of algae via adsorption. The objective of this dissertation was to investigate the efficiency of using adsorption as a treatment process to remove microalgae and phosphorus. A variety of phosphorus adsorbents were tested and compared with each other in order to determine the most efficient material for the treatment system. Batch and fixed bed column tests were conducted to assess the performance of the treatment system for algae and phosphorus removal. The effects of different parameters were investigated to maximize phosphorus and algae removal. Chlorophyll-a concentration was measured as an indicator for algae concentration. Preliminary results showed that activated alumina was the most suitable adsorbent (out of the ones tested in this research) for phosphorus removal from synthetic water. Further results obtained from batch experiments revealed that acidic conditions (pH = 5) and an adsorbent particle size of 0.6 mm were the most feasible experimental conditions for treating both phosphorus and microalgae from actual seawater. The removal percentages were more than 84% for phosphorus and more than 40% for chlorophyll-a using only 4 g/L of activated alumina. Column tests showed more than 50% phosphorus and chlorophyll-a removals even after processing 5000 pore volumes. The pattern of the results suggested that, most probably, adsorption was not the main mechanism of microalgae removal. Phosphorus recovery proved to be reasonably applicable under extreme alkaline conditions (pH = 13.1).