Effects of Changes in Heavy Metal Concentration on Effluent Quality in the Water Recovery Cycle Using the Storage-Recovery Technique
Declining water tables in groundwater aquifers and increased wastewater production are some of the important problems of our country today. This challenge could be converted into an opportunity through proper planning, in such a way that effluents and other surplus waters are used to implement the storage-recovery system of the aquifer, the quality of the effluent is improved using soil’s self-purification potential, the water level in the aquifer is raised and water is withdrawn from this source when needed. The present study was conducted to investigate the changes in the effluent and aquifer water quality by passing it through the unsaturated area and moving in the saturated area in the Chalous aquifer storage-recovery project. In simulating the study area for the measurement of the mentioned parameters, we first created a rectangular hole with specific dimensions of about 5 to 10 meters in the basement (depending on the conditions of the area). The effluent was injected into the hole by creating small pits on the surface. The volume of the hole was considered to be 5000 liters. To prevent water from penetrating from the bottom of the pit and to simulate using an aquifer, a layer of cement and sand mixture was directed into the hole to prevent water infiltration from the bottom of the pit. A daily volume of 1000 liters of effluent was injected for 5 days. After 60 days, recycled effluent and soil samples were collected for analysis from the outlet using a piezometer tube. Along the route, the content of heavy metals such as lead and cadmium was measured and the transfer of solutes was examined by the MODFLOW model in the saturated and unsaturated regions. The results showed that cadmium and lead were deposited in the first few centimeters of the route. The concentrations of nitrate, as well as microbial contaminants, were reduced to almost zero by denitrification and adsorption after a short distance.