Seasonal Variation of Nutrient Removal in a Full-Scale Artificial Aerated Hybrid Constructed Wetland

Jun Zhai,Yasinta John,Md Rahaman,Jun Xiao,Jingsong Xiao

doi:10.3390/w8120551

Abstract

To improve nutrient removal, a full-scale hybrid constructed wetland (CW) consisting of pre-treatment units, vertical-baffled flow wetlands (VBFWs), and horizontal subsurface flow wetlands (HSFWs) was installed in August 2014 to treat sewage wastewater. Artificial aeration (AA) was applied continuously in the VBFW stage to improve the aerobic condition in the hybrid CW. Water samples were collected and analyzed twice a month between the period of August 2015 and July 2016. The results suggest that this new hybrid CW can achieve a satisfactory reduction of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) with average removal rates of 85% ± 10% (35% ± 19 g/m2 per day), 76% ± 18% (7% ± 2 g/m2 per day), 65% ± 13% (8% ± 2 g/m2 per day), and 65% ± 21% (1 g/m2 per day), respectively. AA significantly improved the aerobic condition throughout the experimental period, and the positive influence of AA on nitrogen removal was found to be higher during summer that during winter. A significant positive correlation between water temperature and nutrient removal (p < 0.01) was observed in the system. Overall, this study demonstrates the application of AA in a full-scale hybrid CW with satisfactory nutrient removal rates. The hybrid CW system with artificial aeration can serve as a reference for future applications areas where land availability is limited.

Highlights

Constructed wetland (CW) is an engineered ecosystem which is considered an alternative cost-effective wastewater treatment technology [1,2]
The pre-treatment stages of the hybrid constructed wetland (CW) contributed an average of 75%, 72%, 45%, and 52% in the total removal efficiency of chemical oxygen demand (COD), NH4 + -N, total nitrogen (TN), and total phosphorus (TP), respectively
During CW treatment stages, the MA-vertical-baffled flow wetlands (VBFWs) showed better carbon and nitrogen removals, whereas TP removal was maximum in horizontal subsurface flow wetlands (HSFWs)

Summary

Introduction

Constructed wetland (CW) is an engineered ecosystem which is considered an alternative cost-effective wastewater treatment technology [1,2]. This system possesses complex physical, chemical, and biological processes similar to natural wetlands and is widely used to treat different types of wastewater [3,4,5]. CWs performances are frequently reported to be satisfactory (over 80%) for suspended solids (SS) and organic matter [6]; for nutrient removal, high variations in removal rates are often observed. Ammonification (dissolved organic nitrogen (DON)→NH4 + -N) followed by coupled nitrification (NH4 + -N→NO2 − -N→NO3 − -N), and canonical denitrification (NO3 − -N→NO2 − -N→NO→N2 O→N2 ) are the major nitrogen removal pathways in CWs [1,5], which are reported to be approximately 47%–62% of total nitrogen removal [9]

Methods

Results

Conclusion