Accumulation and Distribution of Lead and Chromium in Laboratory-Scale Constructed Wetlands Inoculated with Metal-Tolerant Bacteria

Phytosphere purification of urban domestic wastewater

Industrialization and overpopulation have polluted aquatic environments with significant impacts on human health and wildlife. The main pollutants in urban sewage are nitrogen, phosphorus, heavy metals and organic pollutants, which need to be treated with sewage, and the use of aquatic plants to purify wastewater has high efficiency and low cost. However, the effectiveness and efficiency of phytoremediation are also affected by temperature, pH, microorganisms and other factors. The use of biochar can reduce the cost of wastewater purification, and the combination of biochar and nanotechnology can improve the efficiency of wastewater purification. Some aquatic plants can enrich pollutants in wastewater, so it can be considered to plant these aquatic plants in constructed wetlands to achieve the effect of purifying wastewater. Biochar treatment technology can purify wastewater with high efficiency and low cost, and can be further applied to constructed wetlands. In this paper, the latest research progress of various pollutants in wastewater purification by aquatic plants is reviewed, and the efficient treatment technology of wastewater by biochar is discussed. It provides theoretical basis for phytoremediation of urban sewage pollution in the future.

Enhanced removal of heavy metals and metalloids by constructed wetlands: A review of approaches and mechanisms

Constructed wetlands (CWs) are increasingly employed to remediate heavy metal and metalloid (HMM)-polluted water. However, the disadvantages of HMM removal by conventional CWs (without enhancement), such as an unstable and unpredictable removal efficiency, hinder the reliability of this technology. The objective of this study was to review research on enhanced CWs for HMM removal. In particular, we performed a bibliometric analysis to evaluate research trends, critical literature, and keyword evolution in recent years. Subsequently, we reviewed various enhanced approaches for the application of CWs for the removal of HMMs, including the use of improved substrates, aquatic macrophytes, microorganisms, bioelectrochemical coupling systems, hybrid CW, external additives, and operation parameters. Furthermore, the main mechanisms underlying HMM removal by these approaches are summarized. Our review clearly reveals that research on the remediation of HMM-polluted water via CW technology is receiving increased attention, with no apparent trends in topics. The selection of appropriate enhanced approaches or operation parameters as well as methodological improvements should be based on the dominant environmental conditions of the CW column and removal mechanisms for the targeted HMMs. Based on the established literature, several suggestions are proposed to guide the optimization of the design and operation of efficient CWs for the treatment of HMM-polluted water.

Efficient Malathion Removal in Constructed Wetlands Coupled to UV/H2O2 Pretreatment

Intensive agriculture has led to the increasing application of pesticides, such as malathion, thus generating large volumes of untreated cropland wastewater (CropWW). In this work, a hybrid system constructed wetlands (CW) coupled in continuous with an optimized UV/H2O2 pretreatment was evaluated for the efficient removal of malathion contained in CropWW. In the first stage, 90 min UV irradiation time (UV IR) and 65 mM hydrogen peroxide (H2O2) were identified as optimal operation parameters through a central composite design. The second stage consisted of CW planted with Phragmites australis collected from the agricultural discharge area and operated as a piston flow reactor. Furthermore, CW hydraulic residence times (HRT) of 1, 2 and 3 days, including hydraulic coupling, were evaluated. The removal efficiencies obtained in the first stage (UV/H2O2) were 94 ± 2.5% of malathion and 45 ± 2.5% of total organic carbon (TOC). In stage two (CW) 65 ± 9.6% TOC removal was achieved during the first 17 days, from which around 24% was associated to the biosorption of malathion byproducts. Subsequently, and until the operation ends, CW removed about 80% of TOC for 2 and 3 days HRT, with no significant differences (p > 0.2), which is higher than those reported in several studies involving only advanced oxidation processes (AOP) with UV IR times above 240 min and even for systems using catalysts. The results obtained indicate that the system UV/H2O2-CW is a technically suitable option for the treatment of CropWW with a high content of malathion mainly found in developing countries. Moreover, the hybrid system proposed also represent significant reduction in the size of the treatment plant.

Evaluation of the ultrasound effect on treated municipal wastewater

In this research, ultrasound (US; 26 kHz) application was evaluated as tertiary treatment of treated municipal wastewater coming from conventional activated sludge (AS) and constructed wetland (CW) systems. The degree of disinfection was evaluated through the total (TC) and faecal (FC) coliforms and by somatic coliphages (SCs) determinations. The experiments were carried out without temperature control at times of 200, 400 and 600 s and with temperature control (298.1 K) at 600, 1200 and 1800 s. Changes in the concentrations of C, N and P were also studied. The results shown that treatment without temperature control allowed 100% inactivation for TC, FC and SC at 600 s, while maximum with temperature was achieved at 1800 s. Temperature was an important factor influencing pathogens inactivation. In both cases, microorganism concentrations complied with different international guidelines for the reuse of treated wastewater. At 1800 s sonication concentrations of biochemical oxygen demand, chemical oxygen demand and total phosphorus were reduced 39.5, 39.4, 50.0 and 37.3% TN in the AS-treated water and 24.0, 49.8, 20.2 and 7.7% in the CW-treated water, respectively. In both cases, the formation of H⋅ and OH⋅ radicals is most likely related to the observed pollutants removal. While energy consumption of ultrasound was higher than other advanced treatments such as electrocoagulation, its implementation allows the simultaneous removal of pathogens and organic pollutants without the generation of toxic by-products. In conclusion, ultrasound can be implemented as tertiary treatment of municipal wastewater for the removal of biological and organic pollution, according to reuse guidelines in terms of pathogens presence.

Fate of mercury in a terrestial biological lab process using Polypogon monspeliensis and Cyperus odoratus

Mercury has been extracted in Queretaro, Mexico since the 1960s. The mining wastes were open-air disposal and these mercury wastes have polluted the zone. The aim of this research was to evaluate mercury's fate in lab scale terrestrial reactors considering the following mercury species: soluble, interchangeable, strongly bound, organic, and residual ones. Soils were sampled in two former mines of Pinal de Amoles, Queretaro, Mexico (N 20° 58' to 21° 21' and West 99° 26' to 99° 43') with initial mercury concentrations were 424 ± 29 and 433 ± 12 mg kg^-1 for "La Lorena" and "San Jose" former mines, respectively. Two vegetal species Polypogon monspeliensis and Cyperus odoratus were used and 20 reactors were constructed for the lab process. Total mercury was removed to 49-79% from both soils. Mercury elemental, exchangeable, and organic species had the most removal or exchange in the process. Metal uptake, by the plants, was of 5-6% for P. monspeliensis and 5-15% for C. odoratus. Also, mercury fate was estimated to the atmosphere to be 3.3-4.5 mg m^-2 h^-1 for both soils.

Emulating natural wetlands oxygen conditions for the removal of N and P in agricultural wastewaters

The aim of this research was to evaluate a constructed wetland system (CW) operated under aerobic-anoxic-aerobic conditions to remove C, N and P from water with high concentrations of the last two nutrients. A series of three CW were operated continuously for 190 days. An aerobic vertical CW was used in the first and third stages and an anoxic horizontal CW was used in the second stage. The total nitrogen (TN) removal efficiency was 70 ± 1.5%. Similar removal efficiency behavior was observed in others nitrogen compounds, where a removal of 85 ± 1.5% for NO₃^--N and 97 ± 2.2% for NH₃⁺N were achieved. The combination of different oxygen conditions enhanced oxidation of nitrates and the assimilation of ammonium by vegetation. On the other hand, 54 ± 6.5% total phosphorus (TP) was removed in the entire system, which is higher than the reported in several investigations, including mechanized and controlled systems such as activated sludge. The phosphorous removal efficiency was attributed to the adequate design and configuration of CW, which facilitated dissolved oxygen (DO) conditions required for phosphorus capture. Despite in this investigation the CW was not designed for an optimal removal of organic matter the removal efficiency of this parameter was 64 ± 7.5%. The successful results suggest that the combination of aerobic-anoxic-aerobic stages is a technically suitable option for the treatment of agricultural wastewater with high content of N and P.

Review of Constructed Wetlands for Acid Mine Drainage Treatment

The mining industry is the major producer of acid mine drainage (AMD). The problem of AMD concerns at active and abandoned mine sites. Acid mine drainage needs to be treated since it can contaminate surface water. Constructed wetlands (CW), a passive treatment technology, combines naturally-occurring biogeochemical, geochemical, and physical processes. This technology can be used for the long-term remediation of AMD. The challenge is to overcome some factors, for instance, chemical characteristics of AMD such a high acidity and toxic metals concentrations, to achieve efficient CW systems. Design criteria, conformational arrangements, and careful selection of each component must be considered to achieve the treatment. The main objective of this review is to summarize the current advances, applications, and the prevalent difficulties and opportunities to apply the CW technology for AMD treatment. According to the cited literature, sub-surface CW (SS-CW) systems are suggested for an efficient AMD treatment. The synergistic interactions between CW components determine heavy metal removal from water solution. The microorganism-plant interaction is considered the most important since it implies symbiosis mechanisms for heavy metal removal and tolerance. In addition, formation of litter and biofilm layers contributes to heavy metal removal by adsorption mechanisms. The addition of organic amendments to the substrate material and AMD bacterial consortium inoculation are some of the strategies to improve heavy metal removal. Adequate experimental design from laboratory to full scale systems need to be used to optimize equilibria between CW components selection and construction and operational costs. The principal limitations for CW treating AMD is the toxicity effect that heavy metals produce on CW plants and microorganisms. However, these aspects can be solved partially by choosing carefully constructed wetlands components suitable for the AMD characteristics. From the economic point of view, a variety of factors affects the cost of constructed wetlands, such as: detention time, treatment goals, media type, pretreatment type, number of cells, source, and availability of gravel media, and land requirements, among others.

Remediation of mercury-polluted soils using artificial wetlands

Mexico's mercury mining industry is important for economic development, but has unfortunately contaminated soils due to open-air disposal. This case was seen at two sites in the municipality of Pinal de Amoles, State of Queretaro, Mexico. This paper presents an evaluation of mercury dynamics and biogeochemistry in two soils (mining waste soil) using ex-situ wetlands over 36 weeks. In soils sampled in two former mines of Pinal de Amoles, initial mercury concentrations were 424 ± 29 and 433 ± 12 mg kg^-1 in La Lorena and San Jose, former mines, respectively. Typha latifolia and Phragmites australis were used and 20 reactors were constructed (with and without plants). The reactors were weekly amended with a nutrient solution (NPK), for each plant, at a pH of 5.0. For remediation using soils from San Jose 70-78% of mercury was removed in T. latifolia reactors and 76-82% in P. australis reactors, and for remediation of soils from La Lorena, mercury content was reduced by 55-71% using T. latifolia and 58-66% in P. australis reactors. Mercury emissions into the atmosphere were estimated to be 2-4 mg m^-2 h^-1 for both soils.