REMOVAL OF FLUORIDE FROM INDUSTRIAL WASTE WATER

Abstract

Water is an essential natural resource for sustaining existence of humans and their surroundings that are perceived to be free and unlimited gift given to us. As regards the chemical composition of surface or subsurface, it can easily be seen as one of the most significant factors having a great effect on the usefulness of water for all kinds of life as well as industrial or agricultural purposes. Freshwater is found as surface as well as groundwater. On one hand groundwater constitutes barely 0.6% from the overall water available on this planet; on the other hand it is the most reliable and the most recommended source of water for domestic purposes everywhere. This is more so especially in countries with sufficient potential to achieve the status of developed nations, such as India, as processing of this groundwater, with disinfection, is generally not needed. Groundwater covers 80% of the total requirement of water for domestic use and 50% of in rural India for agrarian purposes. In the present age of economic and industrial development, groundwater is becoming more and more polluted because of industrialization and urbanization. During the last few decades, the continually-increasing population, urbanization and industrialization, as well as exploitation of available resources have yielded a kind of decline in the quality level of water and also decrease in the amount of water available per capital in various developing countries. When it comes to considering health detriments due to fluoride, it can be seen as a grave concern related to our environment everywhere in the world. These detriments can happen owing to changes in nature as well as due to human activities. Drinking water containing fluoride may be beneficial or detrimental depending upon its concentration and total amount consumed. Fluoride concentrations between 0.5-1.5 mg/L are beneficial, especially to infants for the prevention of dental caries or tooth decay, but concentrations above 1.5 mg/L cause mottling of teeth in mild cases but fluorosis (dental or skeletal) and several neurological disorders in severe cases. Defluoridation is usually done through absorption, chemical as well as electrochemical processes, and dialysis or the ion-exchange process. When it comes to choosing the most effective, eco-friendly and cost-effective process, absorption can be found as the best one. Among various treatment procedure used for defluoridation, batch adsorption process gives satisfactory results to an extent. In this study, we have studied fluoride removal using citrus iv limetta peel, Java Plum Seed (Syzygium cumini), banana peel, groundnut shell, Neem leaves (Azadirachta indica) as it serves as a low cost, easily available and a highly effective adsorbent. These adsorbents were collected from local market of Roorkee, Haridwar, Uttarakhand, India. It was washed with distilled water several times, crushed and sieved to get a particle size range of 0.5 – 2.0 mm. The adsorbents so developed were used for removal of fluoride and further the batch process is optimized by varying the adsorbent dose, pH, fluoride concentration and time of contact. The detailed characterization pertaining to physiochemical, structural and morphological properties of agricultural waste were also carried out. The adsorption capacity of all adsorbents was compared to that of GAC. GAC was chosen as the control since a considerable work has been reported in the literature. On the basis of result obtained, we can conclude that java plum (Syzygium cumini) seed is the best adsorbent in the present list of adsorbents for defluoridation process for same biological conditions. Equilibrium and kinetics and modeling of adsorption and SAB process were also done. To study the mechanism of adsorbate transfer from the solution to the surface of the adsorption particles Weber-Morris’s equation was applied. It was observed that macropore diffusion rate is greater than micropore diffusion rate. The kinetic of the process has been studied using pseudo first order, pseudo second order and Elovich model. The isotherm equation including the conventional Freundlich, Langmuir and Temkin isotherm have been fitted with the equilibrium adsorption and SAB data. The fitness of the isotherm towards the prediction of specific uptake was analyzed by computing standard deviation to calculate squared sum of errors (SSE) function. Column and continuous studies are done so as to study the defluoridation capacity of the adsorbent in continuous mode. The effect of flow rate, fluoride concentration and bed height is studied. The Empty Bed Residence Time, Thomas model and bed Depth Service Time design model were used to inspect the effect of the different operating variables such as bed depth; flow rate and initial concentration. The performances of the column were tested on these simple fixed bed design models. To evaluate the possibilities of regeneration and reuse of the adsorbents, desorption experiments were conducted. We also examined the effects of co-existing ions on the adsorption capacity in batch mode. Bioaccumulation studies have been carried out for studying the effectiveness of single microorganisms. The single cultures of nitrogen fixing bacteria Acinetobacter baumannii v (MTCC No.-11451) were used for fluoride bioaccumulation from water and soil. Initially the microorganism acclimatized to grow at higher fluoride concentration and their ability to accumulate fluoride was measured. The effect of initial fluoride concentration and sucrose (as second carbon source) concentration on the removal efficiency was studied for single microorganism. It was found to have maximum efficiency at about 20 mg/L of fluoride concentration. Acinetobacter baumannii (MTCC No.-11451) was found to be most efficient bacterial strain on the basis of fluoride removal capacity. Simultaneous adsorption and bioaccumulation studies were conducted in SBB reactor using Acinetobacter baumannii (MTCC No.-11451) immobilized on java plum seed (Syzygium cumini). Optimum condition, estimated by adsorption and bioaccumulation studies was maintained in SAB process. SAB process was used for removal of fluoride at higher concentration than 20 mg/l from synthetic simulated waste water and real industrial effluent, both in batch and continuous reactor. To overcome the drawbacks and adsorption and bioaccumulation integration of adsorption in the form of immobilized cell technology and bioremediation is carried out in the present study. The recent development, commonly known as, simultaneously adsorption and bioaccumulation (SAB) has been used by a few researchers and results was found to be better than individual adsorption or bioaccumulation. Due to the biolayer formation on the adsorbent bed simultaneous adsorption and bioaccumulation occurs simultaneously. Adsorption and bioaccumulation have successfully supplemented to each other here microbial mass bio accumulate toxic substance into simpler product as well as biosorbes some of them on the other hand. Adsorption of toxic substances on to a adsorbent reduces the inhibitory effect of the substance on the microbial growth. Accordingly, simultaneous adsorption and bioaccumulation (SAB) is expected to be more efficient as compared to adsorption and bioaccumulation alone. Granular/powdered activated carbon is most widely used adsorbent for fluoride removal. The surface chemistry of activated carbon on the chemical characteristic of adsorbate such as functional group, ionic nature, polarity and solubility determine the nature of binding mechanism as well as the extent and strength of adsorption. GAC has good adsorption capacity and biolayer formation capacity. In the search of more effective and economical adsorbents agriculture byproducts e.g. citrus lemetta peel, banana peel, groundnut shell, neem leaves, turmeric, GAC and java plum seed, etc. were used in present work for the removal of fluoride compounds. These adsorbents have been successfully used for the adsorptive vi removal of many other toxic substances. However SAB process along with this agriculture waste based adsorbent for fluoride removal has not been reported yet. Continuous studies were carried out using packed column along with Acinetobacter baumannii (MTCC No.-11451). The effect of bed height and flow rate on fluoride removal capacity of the column was studied. The continuous processes were found to be feasible and effective for removal of higher concentrations of fluoride pointing towards development of new and efficient technology for fluoride removal. We had taken two aquatic plant species which were selected for the studies were Ipomoea aquatica [Water spinach] and Eichhornia crassipes [Water Hyacinth] in the phytoremedation of fluoride study. These were very common aquatic plants which can easily found in water bodies like pond, lake, river etc. They were grown in plant growth chamber and studied for 10 days exposure period to fluoride of different concentrations and pH. The removal efficiency of Ipomoea aquatica [Water spinach] was found 40.988 % and for Eichhornia crassipes [Water Hyacinth] it was found 58.894 %. Results show that water hyacinth had better removal efficiency to remediate fluoride. In pH study for both the plants shows negative results, as we increase or decrees the pH of the solution the removal efficiency was decreased for both the plants. Accumulation of fluoride was found mainly in the roots for both plants. It was found 872.866 μg/g Dw for Ipomoea aquatica and 1148.479 μg/g Dw for Eichhornia crassipes. Both the plants show the biomass degradation due to the fluoride exposure.