Reduction of chemical oxygen demand of nejayote and production of potentially bioactive polysaccharides after fermentation with alkaline microalgae-cyanobacteria consortium

Abstract

Alkaline wastewater from maize lime-cooking, commonly known in Mexico as nejayote, contains a significant amount of soluble solids and a chemical oxygen demand (COD) higher than 11,400 ± 141 mg O2 L-1. After a sedimentation process, supernatants of this effluent were fermented for 15 days with an alkaliphilic microalgae-cyanobacteria consortium (AMC). The project was divided in two parts: a laboratory scale and pilot scale. At laboratory scale, flasks of 1000 mL were used to growth AMC in mineral salt medium (MSM) used as control (M) and inoculum. Nejayote was obtained from a local tortilla bakery and sterilized (NE and N) to compare the effect of endogenous microorganisms besides AMC in the production of byproducts after their fermentation. In addition, nejayote was used as a blank without AMC (NB). For pilot scale a 100 L High-Rate Algal Pond (HRAP) photobioreactor was used where AMC was grown with MSM (MSM-HRAP), nejayote was used to grow AMC (N-HRAP) and nejayote was used as a blank (NB-HRAP). At laboratory scale M produced higher AMC biomass, reaching 228%, than N, NE, or NB, which reached 35%, 26% and 28%, respectively. After 15 days, a pH reduction was observed in N fermentation going from 9.5 to 8.76 in contrast to the increase from 9 to 10 in M. NE showed the best COD removal, reaching more than 50% efficiency after 12 days of fermentation. For pilot scale NB-HRAP produced the highest biomass concentration reaching 300% after 7 days. None of the fermentations showed a significant COD removal since organic matter such as carbohydrates increased. Significant differences were observed in the polysaccharides and protein content of the biomass recovered from control (M) compared with the fermentation process using nejayote as a culture media. Particularly, NB had the highest intracellular protein (ICP) content with a 24% ± 2% DW, followed by NE with 19% ± 0.4% and N with 16% ± 1%. Moreover, an increase of extracellular polysaccharides (EPS) and proteins was observed during the fermentations reaching a maximum concentration of 16217 土 1910 μg mL-1 and 7475 土 2152 μg mL-1 at day 6. Further analysis of the amino acid profile, functionality, and stability of this potential single cell protein (SCP) production process should be considered to promote the use of this strategy to reduce COD and generate added value products.