Iranian Journal of

Backgrounds and Objectives: The Atrak River is an important water supply resource in the Razavi Khorasan, Northern Khorasan and Golestan provinces. This river is the line border of Iran and Turkistan countries. Unfortunately, lack of water quality and quantity data due to nonexistence of a proper surface water quality monitoring station network is one of the main problems for water quality evaluation in the Atrak River. The main objective of the research is to offer a proper framework for surface water quality evaluation regarding to the mentioned limitations.
Materials and Method: In the first step, proper surface water quality monitoring stations along Atrak River are selected and water quality conditions are indicated using water quality index (WQI) model. The second step is allocated for determining trophic states of the river. Finally, the river water quality modeling is carried out for one of the most important index of water quality in the Atrak River i.e. total dissolved solids (TDS) based on proposed method by Oconnor (1976).
Result: Results of WQI model showed that most of the stations were in the moderate class. The result also showed that most parts of this river had trophic condition. Finally, based on findings of O'Conor model it is demonstrated that the salinity status observed in these four stations originated from the base flow and therefore, salinity is affected by the natural sources.
Conclusion: This methodology in the research can be used in rivers which don't have the proper surface water quality monitoring stations and therefore encountered with lack of water quality data. It can provide the proper strategy and management tasks to reach the good water quality conditions.

Background and Objective: Phosphorus (P), as one of the agricultural, industrial and urban wastewater pollutants, plays an important role in eutrophication of surface waters. Use of cationic sorbents for removal of anions including phosphate from aqueous environments is a well-known and effective method. Meanwhile, layered double hydroxides (LDHs) are known as effective anion exchange sorbents. In this study, the efficiency of Mg-Al layered double hydroxide (Mg-Al-LDH) for P removal from aqueous solutions was investigated.

Methods and Materials: The Mg-Al layered double hydroxide (Mg-Al-LDH) was synthesized by co-precipitation method and used for removing of P from aqueous solutions. The kinetics and equilibrium studies of phosphate adsorption by Mg-Al-LDH were performed using a batch experiment at different contact times, initial phosphate concentrations, pH values, ionic strengths and doses of sorbent.

Results: The results of the kinetics experiments showed that sorption of P with LDH reached equilibrium after 30 min. The highest correlation coefficient was obtained for the pseudo-second order model, indicated that chemical sorption controlled the rate of phosphate sorption by LDH. The results showed that the sorption experiments data were in good agreement with Langmuir model and the maximum adsorption capacity predicted by this model was 37.83 mg P/g LDH.

Conclusion: The current study revealed that P adsorption by LDH was increased by increasing contact time and concentration of LDH, but decreased by increasing initial concentration of P, pH and ionic strength. The optimum conditions for phosphate anion adsorption by Mg-Al-LDH were determined as P initial concentration of 20 mg/L, contact time of 120 min, pH of 3.0, sorbent dose of 10 g/L and ionic strength of 0.03 mol/L.