Treatment of high organic content wastewater from food-processing industry with the French vertical flow constructed wetland system

This study aimed at determining the treatment performances of a full-scale vertical flow constructed wetlands designed to treat wastewater from a food-processing industry (cookie factory), and to study the influence of the organic loading rate. The full-scale treatment plant was designed with a first vertical stage of 630 m(2), a second vertical stage of 473 m(2) equipped with a recirculation system and followed by a final horizontal stage of 440 m(2). The plant was commissioned in 2011, and was operated at different loading rates during 16 months for the purpose of this study. Treatment performances were determined by 24 hour composite samples. The mean concentration of the raw effluent was 8,548 mg.L-1 chemical oxygen demand (COD), 4,334 mg.L-1 biochemical oxygen demand (BOD5), and 2,069 mg.L-1 suspended solids (SS). Despite low nutrients content with a BOD5/N/P ratio of 100/1.8/0.5, lower than optimum for biological degradation (known as 100/5/1), mean removal performances were very high with 98% for COD, 99% for BOD5 and SS for the two vertical stages. The increasing of the organic load from 50 g.m(-2).d(-1) COD to 237 g.m(-2).d(-1) COD (on the first stage) did not affect removal performances. The mean quality of effluent reached French standards (COD< 125 mg.L-1, BOD5 < 25 mg.L-1, SS < 35 mg.L'(-1)).