Evaluation of a hybrid anaerobic reactor–constructed wetland system with fixed biofilm as an ecotechnology for COD reduction in piloncillo wastewater

ABSTRACT Process diagram showing influent piloncillo wastewater entering hydrolytic FBBR, then flowing to horizontal subsurface constructed wetlands with biofilm, achieving overall COD removal above 90 percent. Rural piloncillo mills in Mexico preserve artisanal production methods but generate wastewater with high organic load (COD 38-55 g L−1), acidity (pH 3.9–5.5), and high total solids, exceeding NOM-001-SEMARNAT-2021 limits. Untreated discharge contaminates water bodies and depletes dissolved oxygen, impacting ecosystems and nearby communities. This study evaluated a pilot-scale hybrid system combining a fixed-bed biofilm anaerobic reactor (FBBR, 150 L) with fixed-biofilm constructed wetlands (CW-FBB, three 30 L cells) filled with tezontle and polymer fiber substrate and planted with Canna indica and Cyperus papyrus. Over 120 days, COD removal reached 58.74% in the FBBR and 79.99% in the CW-FBB, achieving an overall efficiency of 91.75%, higher than conventional wetlands or simple anaerobic systems. Additionally, pH was stabilized, and partial removal of nitrogen, phosphorus, and solids was achieved. These findings demonstrate that the FBBR–HC-BF hybrid system is a low-cost, efficient, and nature-based ecotechnology suitable for rural piloncillo wastewater treatment, contributing to SDGs 6 and 7.