Low concentration of zeolite to enhance microalgal growth and ammonium removal efficiency in a membrane photobioreactor

ABSTRACT

The aim of this work was to study the growth and nutrient removal efficiency of a mixed microalgal culture with and without the addition of low concentrations (0.5, 1, and 5 g L^-1 of total liquid volume in the reactor) of natural zeolite. A control test in which only zeolite was added into a similar membrane photobioreactor was also conducted. The addition of 0.5 g L⁻¹ zeolite to a continuously-fed membrane photobioreactor increased the microalgal biomass concentration from 0.50 to 0.90–1.17 g particulate organic carbon per L while the average ammonium removal efficiency increased from 14% to 30%. Upon microscopic inspection, microalgal cells were observed growing on the surface of zeolite particles, which indicates that zeolite can support attached microalgal growth. With higher zeolite doses (1 and 5 g L⁻¹) inside the reactor, however, the breaking apart of added zeolite particles into finer particles dramatically increased solution turbidity, which likely was not beneficial for microalgal growth and ammonium removal due to reduced light penetration. This work shows that low doses of zeolite can be used as microcarriers to enhance microalgal biomass concentration and ammonium removal efficiency, while minimizing zeolite dose would likely reduce the turbidity effects.

GRAPHICAL ABSTRACT

KEYWORDS:

• Microalgal growth
• nutrient removal
• membrane photobioreactor
• wastewater treatment
• turbidity

Acknowledgments

We would like to thank Ahmet Erkan Uman and Manuel Delgado-Navarro for their suggestions about the experimental set-up and their help in the laboratory.

Disclosure statement

No potential conflict of interest was reported by the author(s).

ORCID

Melanie Pickett http://orcid.org/0000-0001-8277-9959

Aino-Maija Lakaniemi http://orcid.org/0000-0001-7189-8741

Jukka A. Rintala http://orcid.org/0000-0002-9667-0134

Additional information

Funding

This work was supported by the Marie Skłodowska-Curie Innovative Training Network European Joint Doctorate (ITN-EJD) in Advanced Biological Waste-To-Energy Technologies (ABWET) funded from Horizon 2020 [grant number 643071], the U.S. Environmental Protection Agency [grant number RD835569], and the U.S. National Science Foundation [award number 1602087].