Comparison Efficiency of The Flocculants

Microalgal biotechnology is an ever-evolving industrial area for sustainable biomass with a wide range of applications (e. g. , feed, human food, or pharmaceuticals products) (Wells, 2017; Bharathiraja, 2015). However, the microalgae growing process is quite costly in a large-scale production considering the amount of water, nutrients and trace elements needed and this represents more than 20% of total production costs. Nowadays alternative environment sources are becoming increasingly popular as nutrient sources for microalgae cultivation. Since N: P forms the essential nutrient for microalgae, rich nutrient waste products which are like pig manure, biogas digestate, sewage after anaerobic digestion, dairy industry, or domestic wastewater can be used for the growth of algae. Anaerobic digestion (AD) industrial plants produce around 10 million tons of excess products during electricity production from biogas. Digestates are rich in nutrients (e. g. , N, P, K, S, Mg, Ca, Fe, and Na) and trace elements (e. g. , Co, Fe, Se, Mo, and Ni) (Marcato, 2008), therefore it provides the ideal environment for growing algae. Thus, the use of digestion products reduces production costs by providing the required nutrients and water from the environment. This makes digestate a good alternative for fresh culture mediums that are more expensive to use on a large scale. Harvesting is needed to collect the algae for further processing into usable products after the cultivation. Another challenge is the harvesting process of the cultivated algae due to their small size, low concentration, and electrical charge on the cell surface. The coagulation/flocculation technique is becoming very popular in the field since a low energy process. Various organic or inorganic flocculants have been studied in wastewater treatment in the flocculation technique. . Inorganic salts such as Al2(SO4)3, Fe2(SO4)3, and FeCl3 contain salts of polyvalent cations and these salts are neutralized the negative surface charges on microalgal cells, therefore they have been applied effectively in both wastewater treatment and microalgae biomass recovery. However, the selection of flocculants is crucial as it will affect the harvesting efficiency and quality of the products. In this sense, different biological flocculants such as bacteria, yeast, fungi, plant seed or chitosan have been applied to microalgae biomass recovery. The aim of this study is to compare the efficiency of three commonly used inorganic flocculant; iron chloride, aluminum sulfate, aluminum potassium sulfate, and one biological flocculant chitosan to harvest microalgae cultures grown on digestate medium and fresh medium.