Photosynthetic treatment of piggery wastewater in sequential purple phototrophic bacteria and microalgae-bacteria photobioreactors

Nowadays, piggery wastewater (PWW) management still represents an unsolved global environmental problem. Photosynthetic processes have emerged as an innovative biological platform capable of performing a cost-effective treatment of wastewater with a concomitant assimilation of nutrients into biomass. In this work, the performance of a purple phototrophic bacteria photobioreactor (PPB-PBR) coupled with a microalgae-bacteria photobioreactor (MB-PBR) was assessed during the treatment of PWW at an hydraulic retention time (HRT) of 12.2 (stage I) and 6.2 days (stages II-VI) and intensities of near-infrared radiation in the PPB-PBR of 30 W m(-2) (stages I-II) and 114 W m(-2) (stages III-IV). Maximum removal efficiencies of total dissolved organic carbon (TOC-RE) and total dissolved nitrogen (TN-RE) of 91% and 82%, respectively, were recorded at an HRT of 12.2 days. The decrease in HRT to 6.2 days reduced the TOC-RE and TN-RE in both photobioreactors, but the increase in near-infrared radiation enhanced TOC-RE in the PPB-PBR, contributing to a global carbon recovery of 67% via assimilation in the form of PPB biomass. PPB-PBR was highly efficient in carbon assimilation, while MB-PBR enhanced nitrogen and total suspended solids removals, with a contribution to TN-RE of 63% and a global decrease in TSS of 76%. The culture broth of PPB-PBR was dominated by Rhodopseudomonas sp. up to 54%, supported by the high HRT and the increase in near-infrared radiation, while the sequential MB-PBR favoured the dominance of Mychonastes homosphaera. This work demonstrated, for the first time, the high efficiency of sequentially coupling PPB and microalgae for the treatment of PWW.

Automated summary

Photosynthetic processes can be used to treat wastewater and convert nutrients into biomass. In this study, a combination of purple phototrophic bacteria photobioreactor and microalgae-bacteria photobioreactor was used to treat piggery wastewater, achieving efficient removal of carbon and nitrogen contaminants.