Nutrient Removal Using Algal-Bacterial Mixed Culture

Abstract

Simultaneous nitrate (N), phosphate (P), and COD removal was investigated in photobioreactors containing both algae and bacteria. The reactors were operated in the semi-batch mode with a hydraulic retention time of 2 days. Reactors were operated in two phases, (1) with 33 % biomass recycle and (2) with no biomass recycle. In both phases, more than 90 % of N and P and 80 % of COD present in synthetic wastewaters with initial N and P concentrations of up to 110 and 25 mg/L, respectively, and initial COD of 45 mg/L could be removed. Biomass growth in reactors did not increase with the increase in initial N and P concentration in either phase. However, biomass growth was slightly more in reactors operated with no biomass recycle. In both phases, N and P uptake was greater in reactors with greater initial N and P concentrations. Also in all cases, N and P uptake in the reactors was far in excess of the stoichiometric requirements for the observed biomass growth. This "luxury uptake" of nitrogen and phosphorus by biomass was responsible for excellent nitrogen and phosphorus removal as observed. However, based on the results of this study, no advantage of biomass recycling could be demonstrated.

Chlamydomonas reinhardtii, a Reference Organism to Study Algal–Microbial Interactions: Why Can’t They Be Friends?

“…Importantly, bacteria naturally present in wastewater effluents promote the growth of microalgal species including Chlamydomonas, which in turn enhances the water treatment process [ 142 ]. In consortium with bacteria, Chlamydomonas can highly reduce the amount of N and phosphorous contaminant, and at the same time it can decrease most of the chemical oxygen demand in photobioreactors containing synthetic wastewater [ 127 , 143 , 144 ]. In addition to contaminant removal, the generated biomass can be used for lipid extraction used in biofuel production, while the remaining biomass may be applied in the generation of fertilizer or animal feed [ 145 ] ( Figure 2 ).…”

<em>Chlamydomonas Reinhardtii, </em>a Reference Organism to Study Algal-Microbial Interactions. <em>Why Can’t They Be Friends</em>

“…Importantly, bacteria naturally present in wastewater effluents promote the growth of microalgal species including Chlamydomonas, which in turn enhances the water treatment process [139]. In consortium with bacteria, Chlamydomonas can highly reduce the amount of N and phosphorous contaminant, and at the same time it can decrease most of the chemical oxygen demand in photobioreactors containing synthetic wastewater [124,140,141]. In addition to contaminant removal, the generated biomass can be used for lipid extraction used in biofuel production, while the remaining biomass may be applied in the generation of fertilizer or animal feed [142] (Fig.…”

A half-century of research on microalgae-bacteria for wastewater treatment

“…Nonetheless, some authors have observed an optimal N/P ratio between 5 and 12 for nutrient removal, using municipal wastewater [76,142]. The range of N/P can vary since the optimal N/P ratio in microalgae biomass is flexible, according to the cell stoichiometry and strongly depends both on the species of microalgae and their capacity of performing luxury phosphorus uptake [63,143,144]. When the N/P ratio is lower than the optimal maximum for biomass production, phosphorus removal decreases due to nitrogen limitation [79,145,146].…”