Continuous removals of phenol, organics, thiocyanate and nitrogen in horizontal subsurface flow constructed wetland

Abstract

The objective of the present study was to achieve treatment of phenol, thiocyanate and ammonia containing wastewater in a horizontal subsurface flow constructed wetland. Influent wastewater contained acetate of 850 mg/L, phenol of 92 mg/L, thiocyanate of 45 mg/L, ammonium nitrogen of 88 mg/L with chemical oxygen demand of 624 mg/L. The system was operated under aerial organic loading of 24.5 g COD/m2 d and volumetric organic loading of 65.4 g COD/m3 d. The CW was divided into four zones (zones I to IV) and operated in continuous flow mode at hydraulic retention time (HRT) of 3 days. Typha angustifolia was planted in zone I, II and IV. Increase in ambient temperature improved pollutant removal in CW. Intermittent aeration and feed sodium acetate (carbon source) had a negligible effect on the performance of the CW. Phenol and COD removals were 99 % and 93 %, respectively and zone 1 was highly efficient for removal of organics. Feed alkalinity addition improved thiocyanate removal to 91 % and sulphate concentration increased in the effluent. Thiocyanate biodegradation followed both aerobic and anaerobic pathways. Ammonia nitrogen and total nitrogen removal efficiencies varied between 17–30 % and 7–28 %, respectively, and the removal might be mainly due to plant uptake. Typha angustifolia grew well in the wetland without showing any toxicity effects.