Abstract
The influences of influent surface organic loading rate (SOLR) and aeration mode on matrix oxygen, organic matter, nitrogen, phosphorus removal, greenhouse gases emission and functional gene abundances in lab-scale wastewater ecological soil infiltration systems (WESISs) were investigated. In WESISs, intermittent or continuous aeration improved oxygen supply at 50 cm depth and hardly changed anaerobic condition below 80 cm depth, which enhanced chemical oxygen demand (COD), NH4+-N, total nitrogen (TN) removal, the abundances of bacterial 16S rRNA, amoA, nxrA, narG, napA, nirK, nirS, qnorB, nosZ genes and reduced CH4, N2O conversion efficiencies with SOLR of 16.9 and 27.6 g BOD/(m2 d) compared with non-aeration. Increased SOLR resulted in high TN removal, low N2O emission in aeration WESIS, which was different from non-aeration WESIS. High average COD removal efficiency of 90.7%, NH4+-N removal efficiency of 87.0%, TN removal efficiency of 84.6%, total phosphorus (TP) removal efficiency of 93.1% and low average N2O emission rate of 12.8 mg/(m2 d) were achieved with SOLR of 16.9 g BOD/(m2 d) in intermittent aeration WESIS. However, continuous aeration WESIS obtained high average removal efficiencies of 90.1% for COD, 87.5% for NH4+-N, 84.1% for TN, 92.9% for TP and low average emission rate of 13.1 mg/(m2 d) for N2O with SOLR of 27.6 g BOD/(m2 d). Aeration could be an optional strategy for WESISs to achieve high pollutants removal and low CH4, N2O emission when treating wastewater with high SOLR.
Highlights
Wastewater ecological soil infiltration system (WESIS) is an optional technology for decentralized wastewater treatment, which has been applied in United States, Russia, Japan, Australia and China (Zhang et al ; Ji et al )
Continuous aeration WESIS was in aerobic condition at 50 cm and in anaerobic condition below 80 cm
In WESIS C, matrix oxygen concentrations at 50 cm depth were higher than 3.3 mg/L during aeration and higher than 1.0 mg/L when aeration closed with surface organic loading rate (SOLR) of 4.4, 8.5, 16.9 and 27.6 g BOD/(m2 d), respectively
Summary
Wastewater ecological soil infiltration system (WESIS) is an optional technology for decentralized wastewater treatment, which has been applied in United States, Russia, Japan, Australia and China (Zhang et al ; Ji et al ). The WESIS has many advantages such as lower cost of construction and operation, lower energy consumption, easier management, better resistance of load shock and better wastewater recovery and reuse compared with conventional biological or chemical wastewater treatment methods (Zheng et al ; Jiang et al ). During wastewater treatment process of WESISs, CO2 emits in aerobic degradation of organic matter by microorganisms; CH4 is produced in the anaerobic decomposition of organic matter by methanogen; N2O emission occurs during nitrogen biological transformation processes by nitrifying and denitrifying bacteria (Kong et al , ). A few studies about greenhouse gases (GHGs) emission have been conducted in WESISs. Kong et al ( ) found that influent C/N affected N2O emission in the WESIS. Field study found that influent loading and drying-wetting ratio affected N2O emission in the WESIS (Li et al ). Few studies have simultaneously investigated three GHGs (CO2, CH4 and N2O) emission of WESISs
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