Mechanisms of manganese removal from wastewaters in constructed wetlands comprising water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutrient conditions

Remediation of potentially toxic elements -containing wastewaters using water hyacinth - a review

For a long time, water hyacinth has been considered a very stubborn and troublesome weed. However, research has shown that it can be used to remove many pollutants from water. Among the different pollutants, potentially toxic elements (PTE) or their ions have been found to be very toxic for humans, animals, and plants. Among the many conventional methods for removing PTE from wastewaters, phytoremediation has several advantages. This method is highly eco-friendly, cost-effective, and can remove a wide range of metal pollutants and organic pollutants. Both, living and non-living water hyacinth plants, can be used for remediation - either entirely or their parts. Study on mechanisms and different factors involved in the process would help to effectively use water hyacinth for remediation. This review presents different studies conducted in the past thirty years for the removal of PTEs. Detailed analysis of the work done in this field showed that in spite of the main advantages provided by the plant, not much has been done to increase the efficiency of the remediation process and for reusing the water hyacinth biomass for other applications after desorption of the PTE. Hence, the section on scope for future work highlights these prospective ideas. Novelty statement: Water hyacinth, which is a very stubborn weed and has a negative impact on the environment, can be constructively used to remove potentially toxic elements (PTEs) along with other pollutants from wastewaters. Different parts of the water hyacinth plant like roots, leaves, and stems or the entire plant can be used. Further, either the live plant or its other forms, such as dried powder, biochar, or activated carbon can be used. This review focuses on different forms of water hyacinth plant used, the advantages and limitations associated with these methods and the scope for future work.

Are mangrove forests reliable sinks of heavy metals due to phytoremediation and other mechanisms? A Sri Lankan perspective

We present a viewpoint regarding the prospects in Sri Lanka (a tropical island nation) to depend on mangroves in the remediation of heavy metal laden coastal environments. Sri Lanka has a rich array of lagoons and estuaries (total extent of 1580.17 km²) with ideal brackish water habitats to allow mangrove proliferation and for more restoration works. Furthermore, our estimates of Total Potential Ecological Risk (PER < 150) indicate that ecological risk from metallic contamination of coastal sediments is low, which means mangrove ecosystems would be ideal natural treatment systems for such low polluting environments (but as final cum tertiary treatment systems only). Mangroves are neither metal hyperaccumulators nor good phytoremediators (no ability to take up more than 5000 mg/kg dry weight of a given metal or exhibit a bioconcentration factor ≥ 1000), which means not very effective for high polluting environments.

Fractional removal of manganese and ammonia nitrogen from electrolytic metal manganese residue leachate using carbonate and struvite precipitation

A comparative investigation of hydroxide precipitation, sulfide precipitation, carbonate precipitation and the struvite formation process for removing manganese and ammonia nitrogen from electrolytic metal manganese residue leachate (EMMRL) was investigated. Chemical equilibrium model-Visual MINTEQ was applied to simulate the chemical reactions and optimize chemical dosages in manganese and ammonia nitrogen removal. Phase transition, morphology, and valence state of the precipitates were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS). Results indicated that carbonate precipitation prior to the other two methods for removal of manganese and ammonia nitrogen. The removal efficiency of manganese was 99.9%, when molar ratio of C to Mn was 1.1:1 at pH 9.5, and manganese was removed in the form of MnCO₃. When molar ratio of P to N was 1.1:1 at pH 9.5, the removal efficiency of ammonia nitrogen was 97.4%, and ammonia nitrogen was removed in the form of struvite. Economic evaluation reveals that the treatment cost was 9.316 $ m^-3 when carbonate and phosphate was used to remove manganese and ammonia nitrogen from EMMRL.

The efficiency of Eichhornia crassipes in the removal of organic and inorganic pollutants from wastewater: a review

Water is a basic necessity of life, but due to overextraction and heavy input of nutrients from domestic and industrial sources, the contamination level of water bodies increase. In the last few decades, a potential interest has been aroused to treat wastewater by biological methodologies before discharge into the natural water bodies. Phytoremediation using water hyacinth is found to be an effective biological wastewater treatment method. Water hyacinth (Eichhornia crassipes), a notorious weed, being the most promising plant for removal of contaminants from wastewater is studied extensively in this regard. It has been successfully used to accumulate heavy metals, dyes, radionuclides, and other organic and inorganic contaminants from water at laboratory, pilot, and large scale. The plant materials are also being used as sorbent to separate the contaminant from water. Other than phytoremediation, the plant has been explored for various other purposes like ethanol production and generation of biogases and green manures. Such applications of this have been good support for the technocrats in controlling the growth of the plant. The present paper reviews the phytoremedial application of water hyacinth and its capability to remove contaminants in produced water and wastewater from domestic and isndustrial sources either used as a whole live plant grown in water or use of plant body parts as sorbent has been discussed.

Iron and lead ion adsorption by microbial flocculants in synthetic wastewater and their related carbonate formation

Although microbial treatments of heavy metal ions in wastewater have been studied, the removal of these metals through incorporation into carbonate minerals has rarely been reported. To investigate the removal of Fe3+ and Pb2+, two representative metals in wastewater, through the precipitation of carbonate minerals by a microbial flocculant (MBF) produced by Bacillus mucilaginosus. MBF was added to synthetic wastewater containing different Fe3+ and Pb2+ concentrations, and the extent of flocculation was analyzed. CO2 was bubbled into the mixture of MBF and Fe3+/Pb2+ to initiate the reaction. The solid substrates were analyzed via X-ray diffraction, transmission electron microscopy and energy dispersive spectroscopy. The results showed that the removal efficiency decreased and the MBF adsorption capacity for metals increased with increasing heavy metal concentration. In the system containing MBF, metals (Fe3+ and Pb2+), and CO2, the concentrated metals adsorbed onto the MBF combined with the dissolved CO2, resulting in oversaturation of metal carbonate minerals to form iron carbonate and lead carbonates. These results may be used in designing a method in which microbes can be utilized to combine CO2 with wastewater heavy metals to form carbonates, with the aim of mitigating environmental problems.

Spatial distribution of metals in the constructed wetlands

Investigation of the spatial distribution of metals was conducted for two constructed wetlands used as tertiary treatment in Chia Nan University of Pharmacy and Science (CNU) and Metal Processing Industries (MPI) located in Tainan, Taiwan. These two distinguished sites were selected to compare the distribution of metals for constructed wetlands treating different types of wastewater. Along the distance, samples of water, sediment, and macrophytes were analyzed for metals including Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. Additionally, measurements of water quality including temperature, pH, EC, ORP, DO, TSS, BOD, COD, and turbidity were performed. Results show that, at CNU, wastewater contained higher organic consititute (BOD 29.3 +/- 11.7 mg/, COD 46.7 +/- 33.6 mg/L) with low metals content. Wastewater at MPI contained low level of organic consititute (BOD 7.1 +/- 3.3 mg/L, and COD 66.0 +/- 56.5 mg/L) and higher metals content. Metals distribution of both sites showed similar results where metals in the sediments in the inlet zone have greater concentrations than other areas. The constructed wetlands can remove Cd, Cu, Ni, Pb, and Zn. However, there was no removal of Al, Cr, Fe, and Mn. A distance along the constructed wetlands had no effect on metal concentrations in macrophyte and water.