Abstract
The present work evaluated the influence of filling substrate material (crushed PET bottles or fine gravel) on the efficiency of pollutant removal in horizontal subsurface flow constructed wetlands (HSSF-CWs). They were cultivated with a consortium of elephant grass cv. Napier (Pennisetum purpureum Schum) and Tifton 85 (Cynodon spp.) to treat wastewater from a common milk cooling tank (WWMT). For this, six HSSF-CWs were used which had dimensions of 0.6 m tall x 1.0 m wide x 2.5 m long. In order to investigate possible efficiency loss in the removal of pollutants from the system, operation was divided into two periods: Period I (from April to December 2015) and Period II (April to December 2016). Thus, the removal efficiencies of BOD5, solids and total nitrogen (TN), total phosphorus (TP), potassium (K) and sodium (Na) from WWMT were statistically compared. Results indicated that the efficiency of the HSSF-CWs for removing pollutants increased or remained similar after one year and nine months of their operation; and PET bottles were a viable alternative substrate in HSSF-CWs based on the efficient removal of pollutants from WWMT during the one year and nine months of monitoring. Crushed PET bottles constitute a viable substrate for filling HSSF-CWs. Altering the cultivation positions of the plant species did not change pollutant removal efficiencies, but indicates the importance of species arrangement to maximize system performance.
Highlights
There is an increasing demand for alternative technologies to treat polluted waters and wastewater that require minimal economic resources, both to implement and operate the treatment system
The use of constructed wetlands (CWs) has shown to be a sustainable option, which is why they have been used for decades in the treatment of wastewater (Wang et al, 2017)
The units had been in operation since April 2015 for the treatment of wastewater from a common milk tank (WWMT)
Summary
There is an increasing demand for alternative technologies to treat polluted waters and wastewater that require minimal economic resources, both to implement and operate the treatment system. In treatment with HSSF-CWs, the pollutant removal efficiency varies considerably (Zhang et al, 2014) in function of a complex combination of physical, chemical and biological processes for the removal of contaminants. These are further dependent on many variables, including water application rate, type of wastewater, organic application rate, hydraulic retention time, operating mode (intermittent or continuous), variation of environmental conditions such as temperature, presence and types of vegetation, substrate, biofilm formation and others (Brix, 1997; Kadlec and Wallace, 2009; Ávila et al, 2013). With the use of plastic beads, a high porosity medium (0.8 m3 m-3), Sklarz et al (2009) obtained an average efficiency of 95%, while Costa et al (2013) found 69 to 72% when using blast furnace slag as a substrate
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