Nitrogen removal in vertical flow constructed wetlands: influence of bed depth and high nitrogen loadings

Efficiency of saturated vertical-flow filters planted with Panicum maximum reeds for passive wastewater treatment

A vertical-flow unit containing four filters filled with shale was used to study the removal of phosphorous, nitrogen and organic matter of an urban residual wastewater during a period of 90 days. The influence of both the shale granulometry and the plant density of Panicum Maximum were studied. The decrease of the shale granulometry led to a significant improvement of all the measured parameters, while the presence of plants did only influence the phosphate retention with a lower extent. By comparing the results to previous studies, we hypothesised that the effect of the root system of Panicum maximum would be different depending on the size and the depth of the reactors. For practical application, adjusting the material granulometry was proposed to be the most important parameter for improving the filtration efficiency. Concomitantly, adjusting the plant density helps to control the clogging percentage of the filters.

Removal Efficiency of Heavy Metals Such as Lead and Cadmium by Different Substrates in Constructed Wetlands

In order to find an efficient and economical wetland substrate to treat mine wastewater containing various heavy metals, and effectively realize the resource utilization of water treatment residuals, in this paper, the treatment efficiency of mine wastewater containing various heavy metals was investigated using unburned ceramsite prepared from water treatment residuals (UCWTR) and clay ceramsite. The continuous dynamic test results showed that the removal rate of Pb, Cd, Cu, Zn, and Fe can reach more than 98.5% after the UCWTR-based CWs runs for 56 days, and its concentration was 30.05%, 24.85%, 20.82%, 14.63%, and 7.91% lower than that of the clay ceramsite-based CWs, respectively. SEM, XPS, and FT-IR showed that the characteristic peaks of two ceramsites were basically similar. The ceramsite undergoes ion exchange, coordination complexation, and chelation reaction with Pb, Cd, Cu, Zn, and Fe under the action of the gel of internal groups -OH, C=O, Al-OH, Si-Fe-O and C-S-H. Compared with clay ceramsite, the ion exchange reaction and chelation reaction of -OH effect and the coordination reaction of C=O effect of carboxyl group in UCWTR were enhanced. In conclusion, using UCWTR as a CWs substrate can effectively enhance the adsorption capacity of heavy metals, providing a scientific basis for the application of UCWTR-based CWs in mine wastewater treatment.

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.

Vertical flow constructed wetland as a green solution for low biodegradable and high nitrogen wastewater: A case study of explosives industry

The removal of nitrogen compounds from a pretreated explosives wastewater in vertical flow constructed wetland planted with Vetiveria zizanioides (0.24 m² × 0.70 m), filled with light expanded clay aggregates (Leca®NR 10/20), was studied. Experiments under constant hydraulic load, 50 ± 4 L m^-2 d^-1 and 83 ± 5 L m^-2 d^-1 without and with flooding level (25%), respectively, were made at different ammonium (3-48 mg NH₄⁺-N L^-1), nitrate (56-160 mg NO₃^--N L^-1) and nitrite (0.3-1.1 mg NO₂^--N L^-1) concentrations. Results indicate that without flooding level (unsaturated) the removal efficiencies obtained were 30 ± 9, 7 ± 1 and 96 ± 2%, respectively to NH₄⁺-N, NO₃^--N and NO₂^--N. When using flooding level and an external carbon source (C/N ratio from 1.3 ± 0.19 to 2.5 ± 0.20), the organic matter (COD) removal efficiencies were above 90%, 75% for NH₄⁺-N and 55% to NO₃^--N. Increasing the C/N ratio from 2.9 ± 0.21 to 4 ± 0.22 did not contributed to upgrade the efficiencies of COD, NH₄⁺-N and NO₃^--N removal. The denitrification process was occurred in aerobic conditions and nitrite production have ben occurred, probably due to the presence of aerobic conditions that inhibited partially denitrification.

Sustainability and performance analysis of constructed wetland for treatment of greywater in batch process

In the current scenario, there is a rising interest in the treatment of greywater to be used for non-potable purposes. However, there is a need to understand the role of plants in the treatment process. In this context, this paper addresses the comparison of the treatment efficiency of planted systems with the unplanted system. Thus, three gravel-based constructed wetlands were made, i.e., one without plants and two with plants (Typha latifolia and Phragmites australis). The wetland system was used in batch mode operation. The results suggested that the efficacy of the planted system was better than the unplanted system. The removal efficiency of different physicochemical parameters (Chemical oxygen demand, Biochemical oxygen demand, Solids and Total kjeldahl nitrogen) were observed to be more in planted system(61, 43,23 and 25% respectively for plant-1(P-1) system and; 51, 29, 23, and 27% respectively for plant-2 (P-2) system) as compared to the unplanted system(38, 15, 18, and 14% respectively). In addition, it was also observed that P. australis cannot sustain for a longer time in the treatment process but it recovers after some time.

The configuration, purification effect and mechanism of intensified constructed wetland for wastewater treatment from the aspect of nitrogen removal: A review

Constructed wetland (CW) for wastewater treatment has attracted increasing attention. In this review, the system configuration optimization, purification effect and general mechanisms of nitrogen removal in CW are systematically summarized and discussed. Ammonia oxidation is a crucial and primary process for total nitrogen (TN) removal in domestic or livestock wastewater treatment. Aeration, waterdrop influent and tidal operation are three main methods to strengthen the oxygen supplement and nitrification process in CW. Aeration significantly increases the ammonia removal rate (almost 100%), followed by the removal of chemical oxygen demand (COD) and TN. Solid carbon source, iron and anode material can be filled as electron donor for the denitrification process. The co-adjustment of oxygen and carbon/electron donor can form different conditions for different nitrogen removal pathways (e.g. the simultaneous nitrification-denitrification, the partial nitrification-denitrification and the anammox process), and achieve the optimal removal of nitrogen.