New M.Tech. Thesis Submitted from Environmental Sc.

COMPARISON OF ADSORPTION CAPABILITY OF WHEAT STRAW AND RICE STRAW FOR THE REMOVAL OF CUTTING OIL FROM WASTEWATER by Simran Kaur 

Abstract

Metal cutting and metal working operations make use of Metal Working Fluids (MWFs) for controlling temperature through cooling and lubrication. These MWFs are of various sorts. They might be straight oils, synthetic, semi-synthetic or soluble oils. The most commonly utilized MWFs are soluble oils which are used after dilution with water. With repeated usage, the characteristics of these fluids are lost and they have to be discarded and replaced. There are various methods for the treatment of such emulsion waste streams like membrane filtration and electrocoagulation but these are not used in small scale commercial enterprises as they require high instalment and operational costs. So these spent fluids are drained into sewers, ultimately entering the wastewater treatment plants where they cause damage to the microorganisms responsible for biological processes. Oil has a capability to penetrate the ground as well, hence becoming a grave threat to the groundwater. Therefore, there is a requirement of a cost-effective technique to treat the spent MWFs. Many research studies propose adsorption as one of the most cost effective treatment techniques for oily wastewater emulsions. This work investigates the adsorption capability of two agricultural waste materials- Wheat Straw and Rice Straw for their oil removal efficiency and the parameters at which they demonstrate maximum oil adsorption. Oil-inwater emulsions were prepared and the impact of variables like adsorbent dosage, contact duration, pH and mixing rate on the removal efficiency of oil using Wheat Straw and Rice Straw was analysed. A UV-Visible Spectrophotometer technique was created to quantify the residual oil content in the emulsions and the ideal conditions for maximum adsorption were derived.  It was found that a dosage of 8 g/L, a contact period of an hour, a mixing speed of 75 rpm, and pH 2 showed maximum oil removal when Wheat Straw was used as an adsorbent at an initial oil concentration of 6% by volume. On the other hand, a dosage of 6 g/L, a contact time of 45 minutes, mixing speed of 50 rpm, and pH 3 resulted in maximum oil removal when Rice Straw was utilized at the same initial oil concentration. The outcomes of the experiments conducted showed that the kinetics of cutting oil adsorption on both the adsorbents closely follows Langmuir isotherms. The maximum amount of oil adsorbed per unit mass of the adsorbent was 0.588 g/g for Wheat Straw and 0.667 g/g for Rice Straw. Although rice straw has a slightly more adsorption capability than wheat straw, but both of them are equally suggested to be used for removing cutting oil from wastewater.