TÍTULO

BACTERIA-MICROALGAE INTERACTIONS DURING NITRIFICATION/DENITRIFICATION PROCESSES IN A PHOTOBIOREACTOR TREATING SWINE WASTEWATER

DOCUMENTO - ARTIGO CIENTÍFICO

AUTORES - MELISSA P. MEZZARI1; MARCIO L.B. DA SILVA; ALINE VIANCELLI; ADRIANA M.G. IBELLI; AIRTON KUNZ; HUGO M. SOARES.

RESUMO/ABSTRACT

The economic feasibility of photobioreactors for the production of valuable microalgae feedstock can be limited to some extent by the nitrogen (N) and phosphorus (P) fertilizers costs. In this regard, N- and P-rich residues from agribusiness have been widely considered for microalgae cultivation. Therefore, the use of photobioreactors not only constitutes a promising engineered technology to generate valuable feedstock for renewable energy but can also serve as an alternative tertiary treatment for swine nutrient-rich wastewaters. The objective of this study was to investigate the interaction between naturally occurring anaerobic biodigestion effluent wastewater bacteria and Chlorella sp. during nitrogen removal by nitrification/ denitrification processes within a photobioreactor. qPCR assays were used to quantify the abundance of total bacteria (16SrDNA) and denitrifiers (nirS). Ammonia removal coincided with the increasing growth of total bacteria (1.2×1010 copies L-1 at 48 h) and accumulation of NO3 and NO2 intermediates. Low oxygen concentrations prevailed (< 0.2 mg/L) in the photobioreactor during dark periods and low microalgae biomass (up to 48 h) thus stimulating the growth of denitrifying bacteria (1.8×106 copies L-1 at 48 h). NO3 accumulation coincided with denitrification inhibition by the increased dissolved oxygen-derived photosynthesis. Overall, the oxidative-reductive environment encountered in a non-sterile photobioreactor can benefit swine wastewater nutrient removal by the simultaneous enhancement of nitrification and denitrification processes. This is particularly important since the application of external oxygen sources to maintain nitrification processes can be costly and/ or insufficient to warrant adequate bacterial metabolism.