Performance of horizontal sub-surface flow constructed wetlands with different flow patterns using dual media for low-strength municipal wastewater: a case of pilot scale experiment in a tropical climate region

Physicochemical and Biological Contribution of Native Macrophytes in the Constructed Wetlands to Treat Municipal Wastewater: A Pilot-Scale Experiment in a Sub-Tropical Climate Region

In this study, the physicochemical and biological contributions of different macrophytes in horizontal sub-surface flow constructed wetlands (HSSF-CWs) to treat low-strength municipal wastewater operated at high hydraulic loads under a sub-tropical climatic region is investigated. Out of the four identical beds, three were planted with locally available macrophytes (P. australis, Sagittaria, and Iris), whereas one bed was kept as a control. The beds were filled with media and operated in parallel continuously for eight months, with increasing the surface loading rate (SLR) from 0.19 to 2.78 m day−1. The results indicate that the planted beds performed significantly (p < 0.01) better to remove TSS (70% to 78%), BOD5 (66% to 77%), COD (59% to 75%), NO3-N (56% to 64%), NH4-N (41% to 69%), TN (36% to 41%), and TP (44% to 61%) as compared to the unplanted bed for the same parameters (48%, 39%, 40%, 33%, 18%, 20%, and 29%, respectively). The presence of macrophytes in HSSF-CWs was found to be highly significant. The average relative growth rate (RGR) was observed in the order of P. australis (0.0086 day−1) > Sagittaria (0.0061 day−1) > Iris (0.0059 day−1). When compared to the performances of the species used, Sagittaria and P. australis produced better results than Iris. The investigations on biomass showed that Sagittaria yielded higher production, followed by P. australis and Iris. The proportions of uptake by the macrophytes were found to be 9.3%, 6.3%, and 3.9% of mass N removal, and 7.6%, 5.1%, and 4.4% of mass p removal in Sagittaria, P. australis, and Iris, respectively. This study contributes to the effective response to the environment, which validates a major role of macrophytes and their disparate response to pollutant removal processes by different species from municipal wastewater through HSSF-CWs.

A review on treatment of petroleum refinery and petrochemical plant wastewater: A special emphasis on constructed wetlands

Petroleum refinery and petrochemical plants (PRPP) are one of the major contributors to toxic and recalcitrant organic polluted water, which has become a significant concern in the field of environmental engineering. Several contaminants of PRPP wastewater are genotoxic, phytotoxic, and carcinogenic, thereby imposing detrimental effects on the environment. Many biological processes were able to achieve chemical oxygen demand (COD) removal ranging from 60% to 90%, and their retention time usually ranged from 10 to 100 days. These methods were not efficient in removing the petroleum hydrocarbons present in PRPP wastewater and produced a significant amount of oily sludge. Advanced oxidation processes achieved the same COD removal efficiency in a few hours and were able to break down recalcitrant organic compounds. However, the associated high cost is a significant drawback concerning PRPP wastewater treatment. In this context, constructed wetlands (CWs) could effectively remove the recalcitrant organic fraction of the wastewater because of the various inherent mechanisms involved, such as phytodegradation, rhizofiltration, microbial degradation, sorption, etc. In this review, we found that CWs were efficient in handling large quantities of high strength PRPP wastewater exhibiting average COD removal of around 80%. Horizontal subsurface flow CWs exhibited better performance than the free surface and floating CWs. These systems could also effectively remove heavy oil and recalcitrant organic compounds, with an average removal efficiency exceeding 80% and 90%, respectively. Furthermore, modifications by varying the aeration system, purposeful hybridization, and identifying the suitable substrate led to the enhanced performance of the systems.

Unveiling the Potential of Novel Macrophytes for the Treatment of Tannery Effluent in Vertical Flow Pilot Constructed Wetlands

The phytoremediation potential of macrophytic species has made them an inevitable component of constructed wetlands (CWs) for the treatment of industrial effluents. The macrophytes must have tolerance for the harsh conditions imposed by effluents for an effective establishment of the CW system. In this context, the basic purpose of this work was to investigate the efficacy of five indigenous emergent macrophytes (Brachiaria mutica, Canna indica, Cyperus laevigatus, Leptochloa fusca, and Typha domingensis) for the remediation of tannery effluent in vertical subsurface flow CWs. The ability of each macrophytic species to tolerate pollution load and to remove pollutants from the effluent was assessed. The effect of tannery effluent on the survival and growth of macrophytes was also studied. The treated tannery effluent samples were analyzed for electrical conductivity (EC), pH, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), chlorides (Cl−), sulphates (SO42−), oil and grease, and Cr levels. All of the studied macrophytes significantly decreased the pollution load of tannery effluent, and the higher nutrient content of effluent stimulated their growth without any signs of negative health effects. Leptochloa fusca and T. domingensis performed better in removing pollutants and showed higher growth rates and biomass than other tested macrophytes and can be considered preferred species for use in CWs treating tannery effluent. Brachiaria mutica showed morphologically better results than C. indica and C. laevigatus.

Nitrogen Removal from Domestic Wastewater and the Development of Tropical Ornamental Plants in Partially Saturated Mesocosm-Scale Constructed Wetlands

Vertical partially saturated (VPS) constructed wetlands (CWs) are a novel wastewater treatment system for which little information is known about its design parameters and performance under tropical climates. The objective of this study is to evaluate the nitrogen removal process from domestic wastewater and the production of tropical ornamental plants (Canna hybrids and Zantedeschia aethiopica) in VPS CWs at a mesocosms scale. Nine VPS CWs, with a free-flow zone of 16 cm and a saturated zone of 16 cm, were used as experimental units. Three units were planted with Canna hybrids., and three, with Zantedeschia aethiopica (one plant per unit); the remaining three units were established as controls without vegetation. They were fed with domestic wastewater intermittently and evaluated for the elimination of COD, N-NH₄, N-NO₃, Norg, NT, and PT. The results showed an increase in the removal for some pollutants in the vegetated systems, i.e., N-NH₄ (35%), Norg (16%), TN (25%), and TP (47%) in comparison to the unvegetated systems. While N-NO₃ removal showed better removal in 10% of the systems without vegetation, no significant differences were found (p > 0.05) for COD removal. The aerobic and anaerobic conditions in the VPS CWs favor the elimination of pollutants in the systems, and also the development of the tropical species evaluated in this study; good development was exhibited by a high growth rate and biomass production.