Remediation of textile bleaching effluent by bacterial augmented horizontal flow and vertical flow constructed wetlands: A comparison at pilot scale

Abstract

Fabric bleaching is one of the most widely used processes of the textile industry that also produces a significant amount of highly polluted wastewater. Previously, expensive and chemically extensive conventional remediation systems were used to treat bleaching effluent. Despite this, the potential of constructed wetlands (CWs) as a treatment system remains un-investigated. Furthermore, most research on the use of CWs for textile effluents are conducted at laboratory scale and therefore further research at field-scale is timely. This study compares the efficacy of bacterial augmented vertical flow constructed wetlands (VFCWs) and horizontal flow constructed wetlands (HFCWs) for the remediation of textile bleaching wastewater at pilot scale. To this end, CWs macrocosms of 1000 L water capacity were planted with Phragmites australis and inoculated with bacterial strains possessing pollutant degradation and plant growth-promoting traits. The results showed that both variants of CWs were effective in attenuating pollutants from the wastewater; however, the performance of HFCWs exceeded that of the VFCWs for almost every pollutant measure undertaken. For HFCWs, a significant reduction in COD (89%), BOD (91%), TOC (96%), and toxicity was achieved in a period of 72 h during the first month of operation. Bacterial inoculation in CWs further improved the system's performance and these bacteria also exhibited persistence in the rhizoplane (43%), root interior (56%) and shoot interior (29%) of P. australis. This study, therefore, suggests that the bacterial augmented HFCWs is a suitable approach for industrial scale textile bleach wastewater treatment.