Treatment of farmer household tourism wastewater using iron-carbon micro-electrolysis and horizontal subsurface flow constructed wetlands: A full-scale study

A full-scale hybrid system utilizing horizontal subsurface flow constructed wetlands (HFCWs) with iron-carbon micro-electrolysis (ICME) pre-treatment was developed for farmer household tourism wastewater (FHTWW) treatment in Wuhan, Hubei Province, China. Results of the 12 months study revealed that the optimal iron-toactive carbon mass ratio (Fe/C), initial pH value and iron with active carbon-to-water volume ratio (Fe-C/water) of ICME were 1: 1, 4.0 and 1: 4 respectively. Meanwhile, the BOD5-to-COD concentration ratio (B/C) of FHTWW was increased from an average value of 0.16-0.39, which indicated the effluent of ICME not only met the national standard for subsequent HFCWs, but also was appropriate to further biological treatment. Generally, the COD removal efficiency of the hybrid system could increase by more than 30% compared with HFCWs only. Although the concentration of ammonia nitrogen (NH4+-N) and total nitrogen (TN) in raw FHTWW varied greatly between seasons, their average removal rate reached 96.8 +/- 1.2% and 95.9 +/- 1.4% respectively depending on appropriate COD-to-TN ratio (C/N) of 3.08-6.19 and limited dissolved oxygen (DO) of 0.5-0.7 mg/L. The hybrid system has withstood the unusually rainy season in July 2016. Results showed that the average COD, BOD5 and NH4+-N concentration in the final effluent were 28.3 mg/L, 5.8 mg/L and 1.3 mg/L respectively, which satisfied the environmental quality standards for surface water in China (COD <= 30 mg/L, BOD5 <= 6 mg/L, NH4+-N <= 1.5 mg/L).