Cr(VI) and COD removal from landfill leachate by polyculture constructed wetland at a pilot scale

Micro- and Macroelements Content of Plants Used for Landfill Leachate Treatment Based on Phragmites australis and Ceratophyllum demersum

One of the key problems associated with the functioning of landfills is the generation of leachate. In order to reduce their negative impact on the environment, various treatment technologies are applied. Among them, solutions based on the use of phytotechnology deserve special attention. The aim of this study was to evaluate the impact of landfill leachate on the content of micro- and macroelements in plant material. The research was carried out in four municipal waste landfills located in Poland. Emergent macrophytes (P. australis) and submergent macrophytes (C. demersum) were used in this research. The migration and distribution of pollutants reaching the roots and shoots of P. australis from water solutions were also studied. The concentrations of heavy metals in the studied plants were low in all analysed cases. Higher metal contents could often be observed in roots rather than in shoots, but these differences were insignificant. The chemical composition of the studied plant samples was primarily related to the source of origin of the treated leachate (landfill), as clearly demonstrated by cluster analysis. In the conducted studies, no important differences were noted in the accumulation of the studied components between submergent plants (C. demersum) and emergent macrophytes (P. australis).

Constructed Wetlands in Latin America and the Caribbean: A Review of Experiences during the Last Decade

The review aims to report the state-of-the-art constructed wetlands (CW) in the Latin America and Caribbean (LAC) region not limited to national and local conditions. The aim is with a broader view, to bring updated and sufficient information, to facilitate the use of the CW technology in the different countries of LAC. Thus, 520 experiences extracted from the 169 reviewed documents in 20 countries were analyzed. According to the data, horizontal subsurface flow wetlands are the most reported CW in the region (62%), the second most common CW technology in the region is free water surface CW (17%), then vertical flow systems (9%), followed by intensified constructed wetlands (8%), and finally French systems (4%). The performance for nutrient removal is analyzed, finding that the mean of Chemical Oxygen Demand (COD), Total Nitrogen (TN), and Total Phosphorous (TP) removal efficiencies varies from 65% to 83%, 55% to 72%, and 30% to 84%, respectively. The results suggest a generally good performance for COD and TN removal, but a low performance for TP removal. Regarding plant species used for CWs, 114 different plant species were reported, being until now the most extensive report about plant species used in CWs in the LAC region.

Characterization of Microbial Communities, Identification of Cr(VI) Reducing Bacteria in Constructed Wetland and Cr(VI) Removal Ability of Bacillus cereus

In this study, the contribution of substrates microorganisms in three different constructed wetlands (CWs) to Cr(VI) purification was discussed. In addition, the microbial communities in the substrate of different CWs were characterized, and rhizosphere Cr(VI) reducing bacteria was also identified. The results showed that microorganisms could improved Cr(VI) removal to 76.5%, and result in that more Cr(VI) was reduced to Cr(III). The dominant strains in the substrates of different CWs were Sphingomonas sp., Cystobacter sp., Acidobacteria bacterium, Sporotrichum and Pellicularia species. The Cr(VI) reducing bacteria from Leersia hexandra Swartz rhizosphere was identified as Bacillus cereus. Furthermore, under suitable conditions, the removal rate of Cr(VI) by Bacillus cereus was close to 100%.

Chromium removal capability and photosynthetic characteristics of Cyperus alternifolius and Coix lacryma-jobi L. in vertical flow constructed wetland treated with hexavalent chromium bearing domestic sewage

In this study, the chromium removal capability and photosynthetic capacity response of plants were investigated in vertical flow wetland microcosms (VFWM) treated with Cr(VI) bearing domestic sewage. Two plants, Cyperus alternifolius (C. alternifolius) and Coix lacryma-jobi L. (C. lacryma-jobi L.) grown in the VFWM enhanced the purification of Cr(VI) enriched domestic sewage. Cr concentration in the effluent fell below detection limit (<0.03 mg L^-1), except for the C. alternifolius wetland treated with 40 mg L^-1 Cr(VI). The biomasses of both plants species were increased at 10 and 20 mg L^-1 Cr(VI) exposure but inhibited at 40 mg L^-1 Cr(VI). The photosynthetic capacities of both plants were not affected at 10-40 mg L^-1 Cr(VI) exposure during the days 20-60. However, they were inhibited significantly (P < 0.05) at 40 mg L^-1 Cr(VI) exposure during days 80-100. These results demonstrated that a VFWM with C. alternifolius and/or C. lacryma-jobi L. was capable of maintaining its efficiency and recovering its vegetation. VFWM with C. alternifolius and/or C. lacryma-jobi L. was promising for purifying wastewater which contains low to medium concentrations of Cr(VI) (<20 mg L^-1).

Occurrence, distribution and bioaccumulation behaviour of hydrophobic organic contaminants in a large-scale constructed wetland in Singapore

This study involved a field-based investigation to assess the occurrence, distribution and bioaccumulation behaviour of hydrophobic organic contaminants in a large-scale constructed wetland. Samples of raw leachate, water and wetland plants, Typha angustifolia, were collected for chemical analysis. Target contaminants included polychlorinated biphenyls (PCBs), organochlorine pesticides (OCP), as well as several halogenated flame retardants (HFRs) and personal care products (triclosan and synthetic musks). In addition to PCBs and OCPs, synthetic musks, triclosan (TCS) and dechlorane plus stereoisomers (syn- and anti-DPs) were frequently detected. Root concentration factors (log RCF L/kg wet weight) of the various contaminants ranged between 3.0 and 7.9. Leaf concentration factors (log LCF L/kg wet weight) ranged between 2.4 and 8.2. syn- and anti-DPs exhibited the greatest RCF and LCF values. A strong linear relationship was observed between log RCF and octanol-water partition coefficient (log K_OW). Translocation factors (log TFs) were negatively correlated with log K_OW. The results demonstrate that more hydrophobic compounds exhibit higher degrees of partitioning into plant roots and are less effectively transported from roots to plant leaves. Methyl triclosan (MTCS) and 2,8-dichlorodibenzo-p-dioxin (DCDD), TCS degradation products, exhibited relatively high concentrations in roots and leaves., highlighting the importance of degradation/biotransformation. The results further suggest that Typha angustifolia in this constructed wetland can aid the removal of hydrophobic organic contaminants present in this landfill leachate. The findings will aid future investigations regarding the fate and bioaccumulation of hydrophobic organic contaminants in constructed wetlands.