Microalgae-mediated bioremediation of cattle, swine and poultry digestates using mono- and mixed-cultures coupled with an optimal mixture design

Abstract

Microalgae-based wastewater treatment (MbWT) has been proposed as a promising approach to revalorize anaerobically digested effluents (digestates) from the livestock sector, resulting in the production of high added-value products, while reducing pollutants in the digestates. This study is the first to address MbWT using digestate mixtures of different species (swine, cattle and poultry). A centroid mixture design was used to determine the optimal mixture to promote higher cell concentrations and pollutant removal efficiencies of the microalgae Chlorella vulgaris, Haematococcus pluvialis and Chlamydomonas reinhardtii cultured as mono-, bi-, and tri-cultures. The best results, obtained from the mixture design, were achieved using C. vulgaris as a monoculture in a digestate mixture of 0.125:0.4375:0.4375 (ADSW:ADPW:ADCW), which resulted in a cell growth of 3.61 × 107± 2.81 × 106 cell mL−1, a total nitrogen removal of 85.00±1.58%, a total phosphorus removal of 65.69±3.05% and a chemical oxygen demand removal of 43.95±7.92%. The optimal mixture design, using the global performance index (GPI), suggested that using a mixture of 0.125 ADSW, 0.200 ADPW and 0.675 ADCW will promote higher cell growth and pollutant removal efficiencies using C. vulgaris as a monoculture. Additionally, a redundancy analysis was performed to analyze the correlation between microalgal cultures and the removal efficiencies of the digestate pollutants. The results herein suggest that the specific composition of the effluents plays a key role in microalgal performance due to their respective nitrogen and phosphorus content. Furthermore, this study suggests that a mixture of the three most common digestates generated by livestock farms offers a promising alternative for the treatment and revalorization of LW, by taking advantage of the unique composition that each digestate possesses. Further studies are warranted to gain a deeper understanding of the interspecific microalgal interactions occurring in mixed cultures that may enhance or hinder the performance of MbWT.