Upcycling alkaline maize cooking wastewater (nejayote) for sustainable lettuce (Lactuca sativa) cultivation: Biotechnological innovations for waste-to-food systems

Abstract

The maize processing industry produces large volumes of alkaline maize cooking wastewater (nejayote), presenting both an environmental challenge and a valorization opportunity. This study examines microbial dynamics, metabolomic shifts, and agronomic potential of nejayote fermented for six days in a high-rate algal pond (HRAP) inoculated with an alkaliphilic microorganism consortium (AMC). Untreated fermentation led to a 65.3% increase in total suspended solids (TSS), while AMC inoculation prevented chemical oxygen demand (COD) increase. Metagenomic analysis revealed a shift from Enterobacteriaceae (45-47%) and Xanthomonadaceae (29-34%) to Cyclobacteriaceae (39%) and Dermocarpellaceae (>50%) in AMC-treated systems. By day six of fermentation process, pathogenic bacteria dropped below 2%, supporting ecosystem functionality and bioremediation. Cyclobacteriaceae, a non-pathogenic family, is relevant for wastewater treatment and bioactive compound production. Untargeted metabolomics identified pentose and glucuronate interconversions, starch/sucrose metabolism, and key monomers (xylose, arabinose), along with amino acids, phenolics, terpenoids, carotenoids, and pesticide-associated signals indicative of partial degradation or transformation. Furthermore, to evaluate nejayote’s upcycle potential in fresh food production, fermented AMC-inoculated nejayote treatments (M1: 0-1 days, M3: 2-3 days, M5: 4-5 days) were used to replace one-third of irrigation water for lettuce (Lactuca sativa) cultivation over eight weeks. Compared to water controls, M3 increased lettuce fresh weight by 109.9% and total phenolic content (TPC) by 313.2%, while M5 enhanced TPC by 173.8%. In contrast, untreated nejayote reduced fresh weight by 33.7%. AMC fermentation promoted the potential accumulation of phenolic and polyphenolic compounds, along with stress-associated fatty acids that act as plant elicitors. The carotenoid pathway was biologically and statistically significant in treatment-irrigated lettuces. Irrigation frequency, applied once or twice per week, influenced the macroscopical features of lettuce; however, twice-weekly irrigation did not result in greater fresh leaf weight or length. Additionally, soil water holding capacity of the treatments was comparable to water and M3 did not affect pH over the 8-week period. Demonstrating the potential of this system for agro-industrial wastewater upcycling, contributing to sustainable agriculture, freshwater conservation, and circular bioeconomy strategies.