Landfill leachate usually contains high concentrations of pollutions that are seriously harmful to the environment and human health. The main purpose of this study was removing organic pollution, ammonia, nitrate and total nitrogen in Isfahan composting facility leachate by horizontal constructed wetland systems. A pilot-scale study was conducted on subsurface flow constructed wetland systems operated in horizontal mode (HFCWs). Two horizontal systems with different plants were constructed, one planted with Vetiver and the other one without plant as a control. They were operated identically at a flow rate of 27 L/day with a 5 day hydraulic retention time. The average removal efficiencies for control and experiment were BOD5, 9% and 30%; COD, 19 and 34%; TN, 37 and 50%; Ammonium, 8 and 26%; nitrate 33 and 40% respectively. Due to high concentration of pollutants (the mean leachate concentrations of COD, BOD5, TSS, NH4+ -N, NO3- -N, TN were 104514.9, 69200.0, 8478.3, 317.5, 4633.2 and 1500 mg/L, respectively) the subsurface flow constructed wetland systems with Vetiver plant is a suitable solution for leachate treatment.

Constructed wetlands are natural systems that have the ability to purify the chemical, physical and biological and can remove variety pollutants from wastewater. The purpose of this study was investigation of the performance of horizontal subsurface flow constructed wetland for lead removal in wastewater treatment. This research was conducted in 2014 at Birjand University and evaluated efficiency of Carex for heavy metal removal. A total of, 12 rectangular concrete reactor in parallel was built at the desired location. The overall dimensions of 12 reactor is sized length 220, width 75 and height 50 cm. in 6 reactor of coarse gravel and was used in six other reactor of fine-grained sand that 4 ponds as control and other ponds were working with Carex plant. Horizontal flow pattern done through a split pipe and valve controls. The data from this study indicates that the maximum lead removal of reactor No. 8 was 51 percent and the minimum the removal of related to wetland No. 9 by 35 percent. The most remove done by increasing the hydraulic detention time. As a result, we can say that the removal efficiency when the lead initial concentration was Equal in all cells, detention time high, with plant cells and as well as fine bed material used, Removal rate is the highest value, It is obvious that such high efficiency without the high cost and adverse environmental effects is highly desirable.

Background: Natural methods of wastewater treatment, such as wetlands, are simple, cheap and acceptable for developing countries, especially small and remote cities. The aim of this study was to evaluate the efficiency of Typha Latifolica in subsurface flow constructed wetland for wastewater treatment in Yazd city, Iran.Methods: In this experimental research, the efficiency of Typha Latifolica in subsurface flow wetland for removing chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids (TSS), nitrate-N (NO3-N), ammonia-N (NH3-N), orthophosphate (PO4-P), total coliform and fecal coliform was evaluated. Two reactors (without and with the plant) were made, as a pilot study, by subsurface flow constructed wetland with the dimensions of 2 × 1.5 × 0.6 m and with a retention time of 4 days. In two months, samples were taken from the incoming and outgoing flow of the reactors and were analyzed according to standard methods.Results: The efficiency of Typha Latifolica wetland for removing COD, BOD5, TSS, NO3-N, NH3-N, PO4-P, total coliform and fecal coliform was 72, 72, 85, 31, 25, 40, 94 and 59 percent, respectively, and 44, 34, 77, 15, 0.3, 1, 17 and 29 percent for the control wetland; all the differences were statistically significant, except for NH3-N and fecal coliform.Conclusion: According to the result of this study, Typha Latifolica has a high efficiency in removing organic material and suspended solids; and the treated wastewater by Typha Latifolica can achieve the national environmental standards for agriculture and irrigation use.

IntroductionPopulation growth and changes in the pattern of needs in accordance with economic growth and lifestyle changes have increased the need for suitable water sources. Treatment and reuse of wastewater is very important in order to reduce the water crisis and prevent the pollution of surface and underground water sources and ecological destruction caused by the discharge of sewage and preserv human health. Conventional wastewater treatment methods have many implementation limitations, including high cost, complex operations and maintenance, etc. For this reason, it is not possible to implement conventional and high-tech methods everywhere. While natural wastewater treatment systems have lower technology and less need for trained labor and at the same time have high efficiency. Among the solutions for green wastewater treatment, we can mention phytoremediation and artificial wetland system. An artificial terrestrial wetland that removes pollutants by creating a saturated porous environment and providing the conditions for the occurrence of physical, chemical and biological processes. Phytoremediation is a biological treatment method in which a plant reduces the pollutants by selective absorption of pollutants and accumulation of them in its tissues. In this method, various factors such as retention time, pollutant concentration, environmental factors (acidity, temperature) and plant characteristics (species, root system, etc.) are important. Since the artificial wetland is similar to a black box whose processes cannot be predicted, simulation models are used to design them with the aim of achieving the highest pollutant removal efficiency. The HYDRUS-2D model is an advanced two-dimensional model related to the simulation of water movement and solute and heat transfer in saturated and unsaturated porous media. In this model, Richards and dispersivity-diffusion equations have been used respectively to simulate water movement and solute transport, as well as features such as spatial distribution of plant roots, water absorption by plant roots, various equations of hydraulic properties of porous media and various initial and boundary conditions, the possibility to provide the simulation of an artificial wetland with plants. MethodologyExperimental site and Measuring TDSTo collect the information from the model, six artificial wetland systems, including three vertical subsurface flow systems and three horizontal subsurface flow systems were constructed at the sewage treatment plant located in Fakhb, Rasht. From the three systems that were constructed, one system was considered without plants and the other two systems contained Reed and Typha plants.  The wetlands were filled with Gravel in diameter of 5 to 25 mm. To adapt Plants with the cultivation environment and wastewater quality, the plants were irrigated by wastewater about three months. After the three months, the main data collection was done by sampling and checking the performance of the systems. Collecting data was for 9 months. During experiment, the raw wastewater sample was entered into the wetland systems and after the hydraulic retention time (about one month in winter and one week in spring and summer), were sampled from the outlet of the wetlands and the parameter of total dissolved solids measured.  Calibration and Validation HYDRUS-2DIn this research, the HYDRUS-2D model was used to simulate the processes governing the movement of water and transport of solutes and its absorption by plants. S-ship model was used to estimate water absorption by Reed and Typha plants. The effective parameters of water movement and transport of solutes, including saturated hydraulic conductivity, longitudinal and transverse dispersivity, and diffusion of the wetland bed, were estimated using the inverse solution method, respectively, using the output flow data and the total dissolved solids of the output wastewater. Statistical indices were used to evaluate the accuracy of the model in the simulation of the purification process in the wetland. The data of days 112, 125, 131, 140, 146 and 152 from the start of the experiment were used for calibration and the data of days 187, 208, 215 and 222 from the start of the experiment were used to validate the wetlands. Results and discussionComparison of the saturated water conductivity value estimated by the HYDRUS-2D model with Sheykhan et al.'s research (2019) showed that the model was able to estimate the hydraulic properties of the bed properly. The longitudinal and transverse dispersivity coefficients in the horizontal wetland were found to be almost half of the vertical wetlands, which is in line with the lower saturated water conductivity and as a result, the lower velocity of the wastewater in the pores in these wetlands compared to the vertical wetland. Dispersion coefficient was a more important factor in solute transport than dispersivity coefficients. On average, in vertical wetlands, the model was able to estimate the amount of reduction of total dissolved solids with about 2% less than the values measured in wetlands under plant cultivation, while in the horizontal wetland, this amount was between 3 and 5 percent. ConclusionsAccording to the results of statistical indices, the estimated values of the total dissolved solids of the artificial wetland system under Reed cultivation were more consistent with the measured values than other wetlands. The results showed that the model has a suitable ability to simulate the movement of solutes and total dissolved solids, which means that it can be used in the design process of treatment in the wetland.

The influent concentration has a great effect on nutrients removal efficiency in vertical subsurface flow constructed wetland systems, but treatment performance response to different C: N: P ratios in the influent are unclear at present. At the first growing seasons, the effects of the plants present or not, season, the different C: N: P ratio in influent condition and their interaction on treatment performances were studied in the planted or the unplanted wetlands in greenhouse condition. Each set of units was operated at hydraulic loading rates of 40 L/d. Low, medium and high-strength (100, 200, 400 mg/L of chemical oxygen demand or 20, 40, 80 mg/L total nitrogen) synthetic sewage were applied as influent. According to the first growing season results, the average removal efficiencies for the unplanted and the planted wetlands were as follows: chemical oxygen demand (44-58 % and 55-61 % respectively), total nitrogen (26- 49% and 31-54 %) and total phosphorus (36-64 % and 70-83 %). The both wetlands system was operated as an efficient treatment system of highest average removal rates of both chemical oxygen demand and total phosphorus when medium-strength synthetic sewage were applied. When high strength synthetic sewage was applied, the planted wetlands usually had a higher nutrients removal rates than the unplanted over the study period. The plants grew well under any high loading treatment over the study period. Anyhow, it also proved that the wetland systems have a good capacity to treat different strength wastewater in greenhouse condition.

Treatment capability of a constructed wetland is heavily dependent on the uniformity of flow moving inside the wetland. This modeling study was performed to evaluate the effect of flow distribution on internal hydraulic behavior of horizontal subsurface flow constructed wetland. To accomplish this objective of the study, three different inlet flow configurations including (1) midpoint, (2) corner and (3) uniform while keeping a fixed midpoint outlet flow for all configurations. The model used in this study was based on COMSOL Multiphysics platform for subsurface flow differential equation in porous mediums (Darcy law). Hydraulic head zoning indicated uniform flow distribution in form of parallel streamlines from inlet to outlet in configuration 3 while substantial number of shortcuts and a noticiable difference between high and low pressure areas were observed in configuration 1 and 2. Results obtained from the simulated streamlines and pressure contours throughout the wetland confirmed the field observation results. Hydraulic head range at each configuration is 14. 35, 15. 25 and 13. 05 cm, respectively. Results indicated an appropriate hydraulic performance of the uniform inflow configuration to use the whole capacity of constructed wetland for treatment process. Meanwhile, midpoint inlet configuration had a proper performance by considering some criteria to reduce dead volume and shortcuts.

Introduction: Wetlands are classified into four kinds of flows as subsurface, surface, vertical, and hybrid flows. Usually, wetlands are planted with common reed (Phragmites Australis), a rhizomatose plant of the Graminae which produces a good yield in green biomass and whose roots can reach a considerable depth and plays a significant role in the wetland self-purification. The treatment efficiency of these systems mainly depends on the wetland design, hydraulic loading rate (HLR), and type of contaminant, microbial interactions and the climatic factors. For best treatment efficiency these systems require a low hydraulic loading rate and a long hydraulic retention time. The hydraulic retention time, including the length of time the water is in contact with the plant roots, affects the extent to which the plant plays a significant role in the removal or breakdown of pollutants. Whereas plants significantly affect the removal of pollutants in horizontal subsurface systems with long hydraulic retention times used to clean municipal wastewater, their role is minor in pollutant removal in periodically loaded vertical filters, which usually have short hydraulic retention times. With respect to the necessity of the research and above descriptions, the main purpose of this study was to evaluate the effect of reed and the increasing hydraulic retention time from 1 day to 10 days on lead removal efficiency in horizontal subsurface-flow constructed wetland to reduce the negative impact generated by lead in the environment.

Background: Constructed wetlands are systems designed based on the utilization of natural processes, including vegetation, soil, and their associated microbial assemblage to assist in treating different types of wastewater. Methods: Two local Appalachian plants (Louis latifolia and Phragmites australis) were planted into smallscale constructed wetlands to treat domestic wastewater in the North of Iran. The influent wastewater and the effluent from each wetland were sampled daily for 120 days. Experiments were conducted based on the mean ± standard deviation (SD) by analysis of variance (ANOVA). Results: It was found that nitrate, phosphate, fecal and total coliforms were reduced by 84. 4%, 94. 4%, 96. 3%, 93. 9% for P. australis and 73. 3%, 64. 0%, 94. 4%, 92. 1% for L. latifolia, respectively. Conclusion: According to the results, by using the HF-CW technology with L. latifolia and P. australis plants, the treated wastewater fully meets the wastewater discharge parameters of WHO standards.

Background and Aim: Constructed wetlands and conventional treatment methods have a same duty in wastewater treatment، but they have different methods and mechanisms. The aim of this study was to investigate the removal of phenol from synthetic wastewater using horizontal sub-surface flow constructed wetland and the aeration and hydraulic retention time effect on phenol removal efficiency. Materials and Methods: This study was an interventional study that was carried out on a laboratory scale in horizontal sub-surface flow constructed wetland. In order to determine the effect of aeration on the efficiency of phenol removal، one reactor was aerated and another one was non-aerated. Pumice was used as a media. The wetlands were planted by Phragmatis australis. Results: The results showed that phenol degradation in both aerated and nonaerated wetland was influenced by organic loading rate and hydraulic retention time. It was also found that the removal of phenol was completely accomplished in both aerated and non-aerated wetlands. This is while the phenol removal rate is higher in aerated wetland، and in order to achieve the same results، the hydraulic retention time in non-aerated reactor should be about twice as high as the aerated one. Conclusion: Horizontal sub-surface flow constructed wetland has a high efficiency in phenol removal and if the conditions of operation especially hydraulic retention time are optimized، can be applied as an effective system for phenol removal from wastewater.