Abstract
Constructed wetlands (CWs) can remove a high amount of pollutants from wastewater, and therefore play an important role in water purification. In this study, a pilot system to improve the traditional treatment of industrial wastewater from the tannery industry was tested. The main objective of this research was to remove nitrogen, phosphorus, boron, and chromium from a tannery’s industrial wastewater using a horizontal subsurface flow constructed wetland (HSSFCW) formed from three cells, planted with Phragmites australis and operated in batch mode as an ecofriendly system. P. australis was selected due to its ability to adapt to climatic conditions, its wetland and management characteristics, and its high capacity for pollutant absorption. The concentrations of total Kjeldahl nitrogen (TKN), total phosphorus (TP), boron (B), and chromium (Cr) were analyzed in both wastewater and purified water, and the removal efficiencies were calculated. In addition, both the absorption capacity of P. australis in the aerial and root parts and the adsorption capacity of substrates (gravel and washed sand) were analyzed. Results showed that the concentrations of TP and Cr decreased in the wastewater at both hydraulic retention times (HRTs) tested (3 and 7 days), with 3 days being the most effective, showing removal efficiency values of 78% and 48% for TP and Cr, respectively. However, concentrations of TKN and B were not statistically reduced at either HRTs. Regarding the absorption capacity of P. australis, the highest absorption efficiencies for TKN and TP were reported at 7 days in the aerial part of the plants. In contrast, B was retained in roots at HRT of 3 days. Finally, Cr was more significantly absorbed at 3 days by P. australis. Moreover, the substrates also played important roles in the adsorption of nitrogen and boron. Therefore, CWs planted with P. australis could be used as an ecofriendly technique to the reduce pollution load of the wastewater from tannery industry, especially for P and Cr, although in order to increase the removal efficiency of B and N, the combination with other plant species and different retention times should be tested.
Highlights
The use of water in industrial processes is an operational process that inevitably generates a huge amount of wastewater in many industrial sectors
B was retained in roots at hydraulic retention times (HRTs) of 3 days
The results showed that P. australis has a high capacity to absorb Cr, there is a lack of knowledge about root absorption capacity and the processes involved in translocation to aboveground biomass [21]
Summary
The use of water in industrial processes is an operational process that inevitably generates a huge amount of wastewater in many industrial sectors. Both industrial and municipal sources are increased at a similar pace by the pre-eminent economic growth. Freshwater demand and shortages have both increased, with this situation being aggravated by the lack of or improper treatment of industrial wastewaters, creating risks such as food production reduction, industrial expansion obstruction, and difficulties related to both environmental and human health [5]. Water contamination and scarcity are phenomena that have increased all over the world and are two of the biggest challenges that humankind faces today. Innovative, ecofriendly, inexpensive solutions should be implemented, where the treatment and reuse of wastewater must have a prominent place [6]
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