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.
Filtration is a simple ecological process for the treatment of effluents. This research examined the physicochemical properties of micronutrients, macronutrients, and heavy metals (HM) removed after the slow filtration of pig slurry (PS) through multiple media: sands, silt loam soils, fly ash, and zeolite. The objective was to find a new layer that can be added to our constructed wetland (CW) to improve its efficiency and study how the slurry reacts to these natural materials. The filtration achieved an approximate removal rate of 99.99% for total suspended solids (TSS) and nitrogen and 61, 94, 72, and 97%, respectively, for electrical conductivity (EC), turbidity, chemical oxygen demand (COD), and five-day biological oxygen demand (BOD5). The two sands, soil 1, and zeolite, had a macronutrient reduction median of 60%, whereas soil 2, 3, 4, and fly ash released macronutrients such as Na, Ca, and Mg. All the media achieved nearly 99.99% micronutrient removal for Fe and Zn. The Cu removal rate was over 86% except for sand 1 and 2 and soil 1, which reduced it to only 46%; the overall Mn removal rate was more than 80% except for soil 3 and soil 4, where it was only 9%. Zeolite had a 99.99% removal capacity for HM as opposed to sand 2, soil 4, and fly ash, which released some HMs (Ni, Cu). This inexpensive and abundant media filtration process is sound technically and financially sound and seems to be an ideal cost-efficient treatment for pig slurry.
Resumen: La regeneración de aguas en áreas de escasez y déficit hídrico es una práctica extendida que complementa los procesos físicos y químicos propios de las plantas de tratamiento con otras tecnologías que permiten su reutilización. En este estudio, fue utilizado un sistema de fitorremediación para mejorar el tratamiento de aguas residuales industriales. Se trata de un humedal artificial horizontal de flujo subsuperficial. Phragmites australis, el carrizo común, fue la especie vegetal seleccionada por su habilidad para adaptarse al clima y por su capacidad de absorber contaminantes. Las concentraciones de nitrógeno Kjeldahl (NK), fósforo (P), boro (B) y cromo (Cr) en agua fueron analizadas y se calcularon las eficiencias. Además, la capacidad de absorción de las plantas fue analizada en las partes aérea y radicular. Los resultados del estudio mostraron que los niveles de contaminantes en agua fueron reducidos para ambos tiempos de retención hidráulicos (TRHs), siendo más efectivo para TRH = 3 días con eficiencias de remoción de 9,8, 78, 13 y 36 % para NK, P, B y Cr, respectivamente. Sin embargo, las eficiencias de absorción por P.australis en la parte aérea para NK, P y B fueron mayores a los 7 días. Por el contrario, el Cr fue retenido mayormente a los 3 días. Por lo tanto, P.australis es una especie fitoextractora ideal, que combinada con humedales artificiales reduce considerablemente los contaminantes en aguas residuales.
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