Abstract
Phenol is a major pollutant in the wastewater because of its presence in the effluent of more processing and refining plants. It has severe effect on human being, both short term and long term. Various methods are used for removal of the phenol from wastewater such as adsorption, photodecomposition, volatilization and other various biological and non-biological methods. In the present study attempt is done to present the survey of the research on the phenol removal by various methods. The methods such as Polymerization, electrocoagulation, extraction, photodecomposition, advanced oxidation and ion exchange were used effectively by various investigators. These methods are reported to be efficient for the phenol removal. But suitable method for phenol removal can be selected based on availability of the material, extent of separation required and properties of phenolic effluent.
Locally available sawdust, a very low cost and promising material was tested experimentally as an adsorbent, after carbonization, for the removal of phenol from industrial waste waters for a safe disposal. The experiments were performed in batch wise to remove phenol from synthesized aqueous solutions. The equilibrium of adsorption was determined as a function of the solution pH, temperature, contact time, adsorbent dose and the initial adsorbate concentration. Adsorption isotherms of phenol for adsorbents were determined and correlated with the usual isotherm equations such as Langmuir and Freundlich.
From equilibrium model analysis the results indicates that the fitness of Langmuir Isotherm model (R2=0.9943) to Sawdust adsorption system. In case of sawdust carbon, the result indicates the fitness of Langmuir Isotherm model (R2=0.9954) for adsorption of Phenol from wastewater.
Key Words: Phenol, Sawdust, Langmuir and Freundlich, Adsorption
01. INTRODUCTION
Fast population growth, industrial expansion, rapid urbanization, use of energy and generation of wastes from domestic and industrial sources have rendered many water sources unwholesome and hazardous to man and the environment in most countries including India. Wastewater is characterized in terms of its chemical, physical and biological composition. In South Africa, typical industries which produce significant volumes of wastewater include textile, steel mills, mineral processing, paper and fiber plants, chemical and fertilizer plants, breweries, refining and petrochemical operations, poultry processors and meat packers, fruit and vegetable packing operations and many more. Wastewater treatment can be done using three methods: primary, secondary and tertiary/advanced processes. Primary treatment separates suspended solids and greases from water and a secondary treatment such as biodegradation process is used in the removal of biodegradable compounds whilst tertiary/advanced treatment methods are largely used to remove non-biodegradable wastes.
Phenol is the priority pollutant since it is toxic and harmful to organisms even at low concentrations. Beside the toxic effects, phenolic compounds create an oxygen demand in receiving waters, and impart taste and odor to water with minute concentrations of their chlorinated compounds. Surface and ground waters are contaminated by phenolic as a result of the continuous release of these compounds from petrochemical, coal conversion and phenol producing industries. Therefore, the waste waters containing phenolic compounds must be treated before their discharging into the water streams. Conventional methods for the removal of phenolic pollutants in aqueous solutions can be divided into three main categories: physical, chemical and biological treatment. Among them, physical adsorption method is generally considered to be the best, effective, low-cost and most frequently used method for the removal of phenolic pollutions. Therefore, the search for low cost and easily available adsorbents has led many researchers to search more economic and efficient techniques of using the natural and synthetic materials as adsorbents. Recently, using the inorganic materials as adsorbents has become one hot research field. Adsorption, as a simple and relatively economical method, is a widely used technique in the removal of pollutants. Although the adsorbents used may vary due to the change in adsorption conditions depending on the type of pollutants, the properties affecting the efficiency of an adsorbent are; a large surface area, the homogeneous pore size, well defined structural properties, selective adsorption ability, easy regeneration, and multiple use. Since the synthetic adsorbents satisfying most of these conditions are relatively expensive, use of natural adsorbents is an active area of research. The aim of the present work is to investigate the capability of industrial sawdust used as an adsorbent for removal of phenol from wastewater and to study the effects of initial phenol concentration, adsorbent dosage, pH value and contact time on the adsorption process, then, find then optimum conditions. In addition, the equilibrium isotherms Langmuir and Freundlich models were determined using the optimum conditions selected from the statistical design of experiments.
Non-biodegradable contaminants pose a serious health and environmental hazard and removal of these wastes cannot be achieved using secondary methods. Hence, tertiary/advanced wastewater treatment methods such as ion exchange, precipitation, membrane separation, electrolysis and adsorption can be used to remove these recalcitrant wastes. However, most of these methods are costly and require high level of expertise; hence they are not applied by many end-users. For these reasons, adsorption technology has gained a wider application due to its inherent low cost, simplicity, versatility and robustness. The success of an adsorption process starts with the choice of an adsorbent. Several adsorbents can be used to treat industrial wastewater. A few of such adsorbent materials are commercial activated carbon, zeolites, silica gel and activated alumina. Unfortunately, most of these adsorption media are very costly. Thus, the use of low cost adsorbents derived from agricultural and industrial solid wastes for wastewater treatment has attracted a vast amount of attention in recent years. These waste materials are underutilized and hence they are readily available. Consequently, the use of these low cost adsorbents forms the main focus of this study. Formerly looking in to allowable levels of phenol below are the concentration of phenol which is reported in numerous industrial wastewater is given in table 1.1 below.