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Abstract
A series of experiments was conducted through a full-scale subsurface wastewater infiltration system (SWIS) to investigate the impact of hydraulic loading rate (HLR), organic loading rate (OLR) and underground temperature on nutrient removal and microbial settlement. Taking the hydraulic and treatment performance into consideration, HLR of 0.10 m3/(m2·d) was recommended with average NH3-N, TN, COD and TP removal rates of 82.6%, 81.5%, 80.9% and 90.9%, respectively.Considering treatment performance, OLR of 10.4 g BOD/(m2·d) was recommended with average NH3-N, TN, COD and TP removal rates of 88.1%, 84.8%, 86.3% and 91.3%, respectively. The number of nitrifying bacteria in each layer in the matrix decreased with increasing HLR, and the number of denitrifying bacteria increased with increasing HLR, at 0.8 and 1.0 m depths. When OLR increased, the number of bacteria and denitrifying bacteria at 0.8 and 1.0 m depths increased, and the number of nitrifying bacteria decreased. Average NH3-N, TN and COD removal rates increased with underground temperature increasing. The number of bacteria, nitrifying bacteria at 0.4 and 0.6 m depths and denitrifying bacteria at 0.8 and 1.0 m depths, increased with underground temperature increasing.
Highlights
Wastewater treatment is becoming ever more critical due to diminishing water resources, increasing wastewater disposal costs, and stricter discharge regulations that have lowered permissible contaminant levels in waste streams
Former studies have revealed that hydraulic loading rate (HLR) or organic loading rate (OLR) is one of the major operational factors affecting the performance of a soil treatment system (Kadam et al, 2009; Li et al, 2011b; Fei et al, 2016)
The reason for this decrease was due to there being fewer adsorption sites. These observations indicated that hydraulic loadings affected COD removal in the following ways: Firstly, increasing hydraulic loadings led to scour of more media surfaces
Summary
Wastewater treatment is becoming ever more critical due to diminishing water resources, increasing wastewater disposal costs, and stricter discharge regulations that have lowered permissible contaminant levels in waste streams. The subsurface wastewater infiltration system (SWIS) has proven to be a good alternative for decentralized wastewater treatment, with consideration to pollutant removal, and construction and operating costs (Zhang et al, 2005; Li et al, 2011a). Former studies have revealed that hydraulic loading rate (HLR) or organic loading rate (OLR) is one of the major operational factors affecting the performance of a soil treatment system (Kadam et al, 2009; Li et al, 2011b; Fei et al, 2016). Zou et al (2009) explored the effect of amended soil and hydraulic load on biological nitrogen removal in lab-scale SWIS. Very few studies have been carried out on the effects of HLR, OLR and underground temperature on pollutant removal performance of a full-scale SWIS treating domestic wastewater. The main purpose of this study was to: (i) investigate the effects of HLR, OLR and underground temperature on nutrient removal and microbial settlement in a full-scale SWIS; (ii) to provide a reference point for full-scale SWIS operation
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