Evaluation of the effect of using artificial wetlands in domestic wastewater treatment

The increase in the human population and the growth in water consumption on one hand, and the rise in sewage production on the other hand, have led to the expansion of environmental pollution threats. The objectives of the present study include launching a pilot project for the localization of knowledge in the design of artificial wetlands in accordance with the quantitative and qualitative conditions of domestic sewage in Iran (specifically, the dormitory of the University of Agricultural Sciences and Natural Resources in Sari) and investigating the possibility of replacing wetland systems with conventional domestic sewage treatment systems in the country.

This study was conducted at the University of Agricultural Sciences and Natural Resources in Sari, involving the construction of six artificial wetlands, each with a length of 3 meters, width of 2 meters, and a height of 1.5 meters, using reinforced concrete. One of the ponds was excluded from the system due to leakage. Inside the ponds, artificial filters at different depths (1 meter: d1 and 1 meter and 30 centimeters: d2) and plant filters (Phragmites australis: p1 and Arundo donax: p2) were filled and planted. D10 and the coefficient of unifo rmity (CU) of the substrate materials were obtained as 2 millimeters and 3.625, respectively, from the grain size analysis. The hydraulic conductivity and porosity of the substrate were 2.523 cm/s and 39.2%, respectively. The specific surface area (SSA) of the substrate materials was calculated as 1.336 m²/kg (2245 m²/m³ of substrate materials). The effluent from the septic tank of the dormitory's baffled septic tank was injected onto the beds after a settling and dilution stage using a pump. In the initial loading, the beds were submerged below the surface, and a three-day retention time was allowed for the first sampling. Quality parameters of the wastewater, including biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), fecal coliform (FC), and total coliform (TC), were monitored to assess the performance of the treatment system.

Although the injected wastewater was diluted up to 25%, a significant removal efficiency of 51 to 55, 41 to 79, 74 to 89, 70 to 95.3, and 78 to 95 percent was achieved for BOD, COD, TSS, FC, and TC, respectively, in different treatments. Among the treatments, the weakest performance was associated with treatment P1D2, while the best purification performance was observed in treatment P2D1. This indicates the dominance of the physical characteristics of the systems at the beginning of the startup period on the purification performance. However, the initial performance of the treatment system was very promising and the removal of some parameters such as TSS and FC was at the average level of a full-fledged wetland treatment system.

This wastewater treatment technology is recommended for all managers and experts in the country's wastewater industry, especially in rural areas with inexpensive land and a population of fewer than 5000 people. These conditions encompass all towns, universities, military barracks, and military facilities as well.