Phycoremediation of treated palm oil mill effluent (TPOME) using Nannochloropsis sp. cells immobilized in the biological sodium alginate beads: Effect of POME concentration

Abstract

The use of freely suspended cells of microalgae culture to treat wastewater is of current global interest because of their effective photosynthetic uptake of pollutants, carbon dioxide sequestration, and biomass production for desirable high value-products. Biomass immobilization is a promising option to overcome the harvesting problem that is encountered when using free-cells upon completion of the wastewater treatment process. In this study, Nannochloropsis sp. cells were immobilized in sodium alginate beads to eliminate the harvesting limitation. The microalgal beads were further cultivated in treated palm oil mill effluent (TPOME) for removal of chemical oxygen demand (COD). The effect of POME concentration on COD removal and microalgal cells growth was investigated, respectively. It was found that the maximum biomass concentration of 1.23 g/L and COD removal of 55% from 10% POME were achieved after 9 days. An increment of POME concentration did not cause any improvement to the treatment efficiency due to the inhibitory effect of high initial COD of POME on the biomass concentration and was further responsible for low COD removal. The immobilized cells showed a systematic growth, demonstrating that the beads are biocompatible as immobilization carrier. In conclusion, the immobilized microalgal cells could be a viable alternative technology system for POME treatment as well as biomass production.

Alginate: Wastewater Treatment

“…Solvents are used to dissolve the beads and then oven-dried (where this process is also done in suspended free cells). Also, the immobilized microalgal cells exhibited higher removal efficiency of pollutants from wastewater as compared to the suspended free cells of microalgal culture [18,23].…”

“…The living cells move independently within the treatment bottles. To ensure uniform cell distribution the application of immobilized cells is a good approach [23].…”

“…In comparison to the other immobilization methods, such as adsorption on a surface, encapsulation, entrapment within a matrix,entrapment of microalgal cells in natural(agar, cellulose, alginate, pectin), and synthetic (polyacrylamide, polyurethane, polyvinyl, polypropylene) gel polymers carriers presents advantages of higher nutrients/products diffusion rates, non-toxic, hydrophilic, more environmentally friendly character, greater stability and produce less hazardous waste upon completion of the process [23] and retention time of cells in the reactor is prolonged, metabolic activity of the cells is maintained for long periods, protection of entrapped microorganism from toxic substances in the wastewater by the polymers, increased nutrient removal is achieved because the population of the microorganisms increase within the polymer, competition of the entrapped microorganism with other microorganism in the wastewater is avoided [22], inert aqueous matrix with high porosity that help preserve the physiological properties and functionality of the encapsulated cells [28], reduces the environmental impact. Besides, beads in nutrient-rich wastewater, can be recovered after cultivation, dry, and used as a soil fertilizer [27].…”

“…In a study, immobilization of the microalgal cells of Nannochloropsis sp. using sodium alginate was carried out to enhance the harvesting and efficiency of POME treatment [23]. The microalgal cell culture was mixed with the sodium alginate solution at a ratio of 1:1 (v/v) and extruded using a syringe to form a spherical shape of the beads in CaCl 2 solution.…”

Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment

“…Immobilized cells could present systematic growth and biocompatible activity in the carrier even under environmental stresses or toxicity [ 81 ]. For example, the immobilized cells Chlamydomonas reinhardtii maintained a higher rate of nitrate uptake and viability in a wider range of pH (5.5–8.0) and temperature (25–38 °C) compared with suspended cells [ 82 ].…”