Effect of feeding strategy on the performance of a pilot scale vertical flow wetland for the treatment of landfill leachate

Constructed wetlands combined with microbial fuel cells (CW-MFCs) as a sustainable technology for leachate treatment and power generation

The physical and chemical treatment processes of leachate are not only costly but can also possibly produce harmful by products. Constructed wetlands (CW) has been considered a promising alternative technology for leachate treatment due to less demand for energy, economic, ecological benefits, and simplicity of operations. Various trends and approaches for the application of CW for leachate treatment have been discussed in this review along with offering an informatics peek of the recent innovative developments in CW technology and its perspectives. In addition, coupling CW with microbial fuel cells (MFCs) has proven to produce renewable energy (electricity) while treating contaminants in leachate wastewaters (CW-MFC). The combination of CW-MFC is a promising bio electrochemical that plays symbiotic among plant microorganisms in the rhizosphere of an aquatic plant that convert sun electricity is transformed into bioelectricity with the aid of using the formation of radical secretions, as endogenous substrates, and microbial activity. Several researchers study and try to find out the application of CW-MFC for leachate treatment, along with this system and performance. Several key elements for the advancement of CW-MFC technology such as bioelectricity, reactor configurations, plant species, and electrode materials, has been comprehensively discussed and future research directions were suggested for further improving the performance. Overall, CW-MFC may offer an eco-friendly approach to protecting the aquatic environment and come with built-in advantages for visual appeal and animal habitats using natural materials such as gravel, soil, electroactive bacteria, and plants under controlled condition.

Analysis of ammonia-nitrogen removal kinetics by stage in pilot scale vertical flow wetlands treating landfill leachate in series

This study explored the effect stage number and plant type have on ammonia-nitrogen (NH3-N) removal kinetics in a two-stage pilot-scale vertical flow constructed wetland (VFCW) system treating landfill leachate. Half of the VFCW columns were planted with Typha latifolia and the other half Scirpus californicus, and half of the columns were loaded with municipal solid waste landfill leachate (diluted to 1 part leachate to 2 parts total) with the effluent from these columns was collected in two separate barrels. The remaining columns were loaded with the effluent collected from the first columns, creating a two-stage VFCW system with four unique pairs to be tested. The leachate used here experienced no prior pre-treatment, and average influent concentrations of NH3-N for the first- and second-stage VFCWs were 508 and 321 mg L-1, respectively- much higher than many other VFCW treatment systems. Some reduction in chemical oxygen demand was observed, as well as generation of nitrate and nitrite, evidence of nitrification. No apparent correlation between aboveground biomass and removal of NH3-N was observed. Overall removal efficiency of NH3-N through two stages of VFCWs was 53.7% for columns planted with T. latifolia and 58.3% for those planted with S. Californicus. Average NH3-N removal efficiencies for the first stage VFCWs were 32.7% and 34.3%, while those in the second stage were 31.3% and 36.5%; no significant difference was observed between the first and second stage, suggesting that stage number does not have a significant effect on the removal efficiency of NH3-N in the primary treatment of landfill leachate via VFCWs. However, average mass removal rates of NH3-N in the first stage were 166 and 175 mg L-1 d-1; the second stage was significantly lower at 99.4 and 112 mg L-1 d-1, indicating that the first stage removed more pollutants overall.

Pollutant removal from swine wastewater and kinetics in constructed rapid infiltration system (CRI system)

The purpose of this paper is centred on the kinetics of removal of main pollutants in wastewater and to compared different hydraulic loading conditions of the constructed rapid infiltration system (CRI system) in terms of removal efficiencies, effluent concentrations, mass removal rate (MRR), and the first-order removal rate coefficient (k) of COD, TOC, NH₄⁺-N, TN, and TP. The results showed that the higher the hydraulic loading, the higher the effluent concentration. The results that synthesized hydraulic loading, effluent concentrations, removal efficiencies, and other conditions showed that the best hydraulic loading was 40 cm/d. When the hydraulic load was 40 cm/d, the effluent average concentrations of COD, TOC, NH₄⁺-N, TN, TP, Cu²⁺ and the removal efficiencies were 27.31 ± 16.40 mg/L, 86.11%, 10.55 ± 5.25 mg/L, 84.64%, 0.59 ± 0.87 mg/L, 99.60%, 143.31 ± 14.77 mg/L, 7.04%, 5.64 ± 1.38 mg/L, 79.20%, and 0.13 ± 0.47 mg/L, 97.51%, respectively. According to a kinetic study of the primary pollutants, the MRR increased with an increase in the hydraulic loading, except for ammonia nitrogen. CRI-3, CRI-4 were high significant correlated with ammonia nitrogen (with R²= 93.65% and R²= 95.03%, respectively), while CRI-2, CRI-3, and CRI-4 were high significant correlated with total nitrogen (with R²= 94.56%, R²= 96.70% and R²= 96.56% respectively).

Removal of organochlorine pesticides and metagenomic analysis by multi-stage constructed wetland treating landfill leachate

Constructed wetlands (CWs) can effectively treat landfill leachate (LL). However, there is limited research on the removal of organochlorine pesticides (OCPs) refractory organics during LL treatment in CWs. In this study, multi-stage subsurface flow CWs was used to treat LL, and the removal fate of hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) in CWs was investigated. The structural differences between plant roots and substrate microbial communities were compared and the Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathway of organic matter was analyzed based on metagenomic analysis. The results showed that substrate adsorption (50.55%-72.74%) and microbial degradation (20.38%-27.89%) were the main ways to remove OCPs. The Proteobacteria occupied a dominant position in the CWs system, among which Betaproteobacteria (34.37%-35.90%) were contained in the substrate, and Alphaproteobacteria (21.19%-23.84%) was a more dominant microorganism in plant roots. Formaldehyde assimilation and serine pathway were the main pathways of methane metabolism. This study provides a reference for the removal mechanism of OCPs to promote the application of CWs technology in LL treatment.

Treatment of the actual landfill leachate in different constructed wetlands through intermittent and varied aeration mode

This study focused on the removal of organic matter and nitrogen and explored the feasible operation strategies to achieve short-cut nitrification and denitrification in two constructed wetlands (CWs), which were designed to treat the actual landfill leachate from a small county in parallel. The two CWs were horizontal sub-surface flow constructed wetlands (HFCW) with partial-area aeration and vertical sub-surface flow constructed wetlands (VFCW) with full-area aeration. The experimental results showed that both CWs could achieve an excellent organic matter and nitrogen removal performance under the conditions of intermittent aeration with high frequency and medium intensity (2 h of aeration and 4 h of rest). The removal efficiencies of COD and total nitrogen by HFCW were 89.08% and 73.22%, and the corresponding values of VFCW were 84.51% and 71.44%, respectively. Meanwhile, the inhibition kinetics model indicated that HFCW with partial-area aeration could enhance the free ammonium (FA) tolerance of ammonium-oxidizing bacteria (AOB) and reduce the conversion percentage of ammonia nitrogen. In addition, the intermittent aeration mode with high frequency and medium intensity could keep the DO concentration below under 0.60 mg L-1 in HFCW, which helped to achieve stable short-cut nitrification and ensure the average nitrite accumulation rate (NAR) reach 50.96%. These results suggested that the intermittent aeration in partial-area could achieve successful short-cut nitrification in HFCW, thereby improving the removal efficiency of nitrogen in landfill leachate.

Application of constructed wetlands in treating rural sewage from source separation with high-influent nitrogen load: a review

Constructed wetlands (CWs) are characterized by low construction cost, convenient maintenance and management, and environmentally friendly features. They have emerged as promising technologies for decentralized sewage treatment across rural areas. Source separation of black water and gray water can facilitate sewage recycling and reuse of reclaimed water, reduce the size of treatment facilities, and lower infrastructure investment and operating cost. This is consistent with the concept of sustainable development. However, black water contains high concentrations of ammonia nitrogen, and the denitrification capacity of CWs is not excellent due to insufficient carbon source. Therefore, application of CWs for black water treatment faces challenges. This article provides a review on the progress in CWs for treatment of the sewage with high-influent nitrogen load, with emphasis on the commonly used strengthening means and the role of plants in nitrogen removal via CWs. The current issues of rural sewage treatment with high-influent nitrogen load by CWs are also assessed. Finally, the challenges and perspectives are discussed for the optimization of CWs-enhanced denitrification strategies.

Cr, Ni, and Zn removal from landfill leachate using vertical flow wetlands planted with Typha domingensis and Canna indica

Chromium (Cr), Nickel (Ni), and zinc (Zn) removal from landfill leachate using mesocosm-scale vertical flow wetlands, the effect of recirculation, and the ability of macrophytes to retain metals were evaluated. Wetlands were filled with coarse sand and light expanded clay aggregates and planted with Typha domingensis or Canna indica. Wetlands were operated using intermittent loading, with and without recirculation. Raw leachate was diluted and spiked with metals to reach the following concentrations: 0.2 mg L^-1 Cr , 0.2 mg L^-1 Ni, and0.2 mg L^-1 Zn and 1.0 mg L^-1 Cr, 1.0 mg L^-1 Ni, and 1.0 mg L^-1 Zn. Wetlands planted with T. domingensis presented higher metal removal than those planted with C. indica. Recirculation enhanced metal removal efficiencies significantly, being for T. domingensis/C. indica: 60/54, 49/47, 61/47% for Cr, Ni, and Zn at 0.2 mg L^-1, and 80/71, 76/62, 73/59% for Cr, Ni, and Zn at 1.0 mg L^-1, respectively. Metals were efficiently retained by macrophytes. Plant biomass and metal concentrations in roots were significantly higher than in shoots. Scanning electron microscopy and X-ray microanalysis showed that metals were absorbed by internal root tissues. A hybrid wetland planted with T. domingensis may be implemented to improve not only metal but also chemical oxygen demand and total nitrogen removals.

Effectiveness of two lightweight aggregates for the removal of heavy metals from contaminated urban stormwater

Contaminated runoff stormwater from urban environments carries several contaminants to water bodies, thereby affecting the health of living beings and ecological systems. Among all the contaminants, heavy metals possess high toxicity and impact water quality. The stormwater management through green infrastructures composed by adequate materials can provide an excellent solution, simultaneously ensuring the appropriate hydraulic performance and contaminant removal rate. The proposed research aims at the elimination of heavy metals (i.e. Ni, Cu, Zn, Cd and Pb) through column experiments by selecting four possible and novel treatments for urban stormwaters. Two lightweight aggregates (Arlita and Filtralite) were tested separately and in combination with CaCO₃. The study determines the efficiency and lifetime of each treatment by varying the interaction time between the filter materials and contaminated water and the type of filter. The observed removal mechanisms were closely related to the changes in pH due to the interactions between water and different materials. The reductions in heavy metal concentrations depend on the type of heavy metal, interaction time and type of filter material. Results indicate that the combined use of CaCO₃, Arlita and Filtralite did not improve the removal rates of heavy metals. However, it decreased the efficiency of the decontamination process. The significance of this study lies on the removal efficiency of Arlita and Filtralite as decontamination treatments. Both the tested lightweight aggregates led to a considerable decrease in the heavy metal concentrations in urban runoff stormwater although Filtralite was particularly efficient. After 4 weeks, the treatments were still successfully reducing and stabilising 99% of the heavy metals in the contaminated stormwater. These results confirm that the lifetime of the tested lightweight aggregates is adequate and emphasise, as a novel application of these materials, on their feasibility for the improvement of urban stormwater quality.

Effects of hydraulic loading rate and substrate on ammonium removal in tidal flow constructed wetlands treating black and odorous water bodies

The efficient removal of ammonium nitrogen (NH₄⁺-N) is vital to eliminating black and odorous water bodies. In this work, tidal flow constructed wetlands with gravel (TFCW-G) and with a mixture of zeolite and gravel (TFCW-Z) were set up to treat black and odorous water bodies at different hydraulic loading rates (HLRs). Results showed that zeolite significantly enhanced nitrogen removal, and the maximum NH₄⁺-N removal efficiency of 96.69% was achieved in TFCW-Z at HLR of 3 m·d^-1 with a flooding and drying cycle of 2 h. Zeolite addition changed the microbial community structure and the abundance of nitrification genes. Comammox Nitrospira was the only enriched strain accounting for NH₄⁺-N removal in TFCW-G, while the co-occurrence of comammox Nitrospira and the canonical and potential ammonia-oxidizing bacteria were identified in TFCW-Z. Summarily, high performance, together with low footprint and low maintenance cost, are characteristics that make the TFCW-Z a promising and competitive alternative.

Pollutant removal from landfill leachate employing two-stage constructed wetland mesocosms: co-treatment with municipal sewage

Constructed wetlands are low-cost, natural technologies that are often employed for the treatment of different types of wastewater. In this study, landfill leachate and municipal wastewater were co-treated by the three parallel two-stage Phragmites- or Vetiver-based constructed wetland mesocosms. Two-stage wetland mesocosms included vertical flow (VF) units as the first stage, followed by horizontal flow (HF)/surface flow (SF)/floating treatment (FT) units. VF and HF wetland mesocosms were filled with gravel, steel slag, concrete block, and intermittent carbon-saturated ceramic filters as substrates. Mean input nitrogen, organics, and phosphorus load across first stages were 75 g N/m² day, 283 g COD/m² day, 88 g BOD/m² day, and 10 g P/m² day, respectively. N and P accumulation rate was not substantial (< 10%) with respect to total removal in most wetland mesocosms. Gravel-based VF wetland mesocosm achieved better NH₄-N and BOD removal (55-59%) during landfill leachate treatment phase, when compared with co-treatment periods (12-52%). Slag-concrete- and ceramic filter-based VF wetland mesocosms maintained stable NH₄-N and BOD removals; the former wetland mesocosm was the most efficient VF unit (than other two wetland mesocosms) due to media characteristics. Media-based adsorption accelerated P removal (93%) in slag-concrete-based VF wetland mesocosm. Carbon scarcity limited denitrification in all VF wetland mesocosms; removal of TN was < 32%. Second stage wetland mesocosms achieved higher nitrogen (85-92%), organics (66-90%), and phosphorus (97-100%) removals regardless of operational variations; low input load, long retention time, media, and rhizosphere enhanced removal performances, particularly in HF and FT wetland mesocosms. In general, this study demonstrates potential application of two-stage wetland mesocosms for landfill leachate treatment or co-treatment with municipal sewage.

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.

Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment

Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.

Vertical flow wetlands and hybrid systems for the treatment of landfill leachate

Landfill leachates contain a variety of toxic compounds, which makes them one of the most difficult types of wastewater to be treated. An alternative "green" technology for leachate treatment is the use of constructed wetlands (CWs). The aims of this study were to select macrophytes and substrates to be used in vertical flow wetlands (VFWs) and to evaluate the performance of hybrid systems composed by a VFW and a horizontal subsurface flow (HSSW) or a free water surface flow (FWSW) wetlands for the treatment of a high ammonium concentration landfill leachate. In microcosms scale experiments, Typha domingensis, Scirpus californicus, and Iris pseudacorus were studied to assess their tolerance to raw and diluted leachate. Substrate selection for VFWs was evaluated using different layers of light expanded clay aggregate (LECA), coarse sand, fine sand, and gravel. Contaminant removals were higher in planted than in unplanted wetlands. Plants did not tolerate the raw effluent but showed a positive effect on plant growth when exposed to the diluted leachate. T. domingensis and I. pseudacorus showed higher contaminant removal ability and tolerance to landfill leachate than S. californicus. VFW with LECA + coarse sand showed the best performance in removal efficiencies. Hybrid system composed by VFW-FWSW planted with T. domingensis presented the best performance for the treatment of landfill leachate with high concentrations of ammonium.