The aim of this study was to investigate the possibility of using rice bran as a natural adsorbent for the removal of citric acid from water and the effect of temperature, time, initial concentration of adsorbate and adsorbent concentration on the adsorption process. Fitting experimental data was performed using several adsorption models. Also, the thermodynamics and kinetics of adsorption have been studied. The equilibrium was reached after 60 minutes. The results showed that removal of citric acid decreased as temperature and initial concentration of citric acid increased in contrast, it increased as adsorbent concentration and time increased. In addition, the optimum adsorbent weight was obtained to be 4g. Freundlich isotherm was found to be a better fit than other isotherms. The thermodynamic study showed that the adsorption process was exothermic and spontaneous in nature. The adsorption of citric acid on the rice bran followed reversible second-order rate kinetics. This study showed that rice bran efficiently removed the citric acid from aqueous solutions.

This investigation was carried out to evaluate Indole acetic acid (IAA) production by isolated bacteria from drought and salinity affected soils. Four hundred bacteria were isolated from soils with different levels of electrical conductivity (EC) and sodium adsorption ratio (SAR). Then the ability of these bacteria to produce IAA and the effects of different amounts of tryptophan and drought-salinity tensions on IAA production were analyzed. Results indicated that the effects of drought and salinity tensions on variability of IAA production were statistically significant. One of the bacterial species isolated from saline-sodic soils, Arthrobacter siccitolerans, was IAA producer and data comparison indicated that under drought stress conditions it produced IAA 84.3% higher than isolate RS11. While isolated RS11 produced highest rate of IAA (10.42 µg.ml^-1) under normal conditions. Also, A.siccitolerans continued to produce IAA until the EC was 40 dS.m^-1 and OP (Osmosis pressure) was -20 bar. The amount of IAA production per unit of applied tryptophan in this bacterium was 0.1 and in others it was lesser. According to experiments, the relative preference of this bacterium was verified and proposed for field experiments in drought, salinity and salinity-sodicity affected soils.