Analysis and optimization of coagulation and flocculation process

V. Saritha 0 N. Srinivas 0 N. V. Srikanth Vuppala 0 0 V. Saritha (&) N. Srinivas N. V. Srikanth Vuppala Department of Environmental Studies, GITAM Institute of Science, GITAM University , Visakhapatnam 530 045 , India Natural coagulants have been the focus of research of many investigators through the last decade owing to the problems caused by the chemical coagulants. Optimization of process parameters is vital for the effectiveness of coagulation process. In the present study optimization of parameters like pH, dose of coagulant and mixing speed were studied using natural coagulants sago and chitin in comparison with alum. Jar test apparatus was used to perform the coagulation. The results showed that the removal of turbidity was up to 99 % by both alum and chitin at lower doses of coagulant, i.e., 0.1-0.3 g/L, whereas sago has shown a reduction of 70-100 % at doses of 0.1 and 0.2 g/L. The optimum conditions observed for sago were 6 and 7 whereas chitin was stable at all pH ranges, lower coagulant doses, i.e., 0.1-0.3 g/L and mixing speed-rapid mixing at 100 rpm for 10 min and slow mixing 20 rpm for 20 min. Hence, it can be concluded that sago and chitin can be used for treating water even with large seasonal variation in turbidity. - Because of its ability to solubilise, pure water is not found in nature. Dissolved impurities comprise minerals, organic compounds and gases that alter the physical (turbidity, color, temperature, electrical conductivity), chemical (chemical and biological demand for oxygen, pH, alkalinity, total organic carbon) and biological characteristics of water, whose effect depends on the composition, concentration and chemical reactions between pollutants (Richter 2009; Theodoro et al. 2013). Safe drinking water is essential to the health and welfare of a community and water from all sources must have some form of purification before consumption. Various methods are used to make water safe and attractive to the consumer. The method employed depends on the character of the raw water. One of the problems with treatment of surface water is the large seasonal variation in turbidity (McConnachie et al. 1999). The efficiency of suspended solid (colloid) separation from water has been achieved by the application of chemical coagulants such as alum, ferric chloride, and polyelectrolyte. This process highlights a water treatment mechanism that stimulates the aggregation of suspended particles to settleable flocs by the destabilization of the charged colloids thus, neutralizing the forces that keep them apart. The factors that influence coagulationflocculation are, among others, temperature, pH, effluent quality, dosage and coagulant type (Nnaji 2012; Jin 2005; Ma et al. 2001). The suspended particles vary considerably in source, composition charge, particle size, shape, and density. Correct application of coagulation and flocculation processes and selection of the coagulants depend upon understanding the interaction between these factors. It is imperative for relevant stakeholders to fully comprehend the technicalities involved when considering the coagulants for rural domestic water treatment. Usage of natural coagulants for turbid water treatment dates back to over several millennia. So far, environmental scientists have been able to identify several plant types for this purpose. While it is understandable that these coagulants are meant as simple domestic point of use (POU) technology, there have also been numerous studies focused on their usage for treatment of industrial wastewaters. The mechanisms associated with different natural coagulants are varied as well (Babu and Chaudhuri 2005). To address these issues, the present work focuses on the understanding and optimisation of various factors that govern the process of coagulation by natural coagulants, so that environmental experts can tailor its usage for copious water contaminants. The coagulants nominated in this study are a plant-based coagulant, sago and the other derived from non-plant source chitin (widely produced from exoskeleton of crustaceans). Optimization of coagulant dosage The study was initialized by testing the efficiency of the coagulants in removal of turbidity. The results from this stage of study encouraged us to proceed further to second stage, with the coagulant dosage optimized at 0.1, 0.2, 0.3 and 0.4 g/l. Optimization of pH The optimized dosages of coagulants were further examined at various pH conditions to test their efficiency and suitability at a wide range of pH. The observations from the study revealed the optimum pH conditions to be 6, 7 and 8. Optimization of mixing speed and time Coagulation is performed in two stages: first the coagulant is rapidly mixed and then flocculation is enhanced by slow mixing. Hence, the optimized dosages were further optimized for varied mixing speed and time for each stage of coagulation. Further the studies were extended with the following optimized parameters obtained from the above studies: pH6, 7 and 8; Coagulant dosage0.05, 0.1, 0.15 and 0.2 g/500 ml; Mixing speedrapid mixing at 100 mixing speed for 10 min and slow mixing at 30 mixing speed for 20 min; rapid mixing at 80 for 2 min and slow mixing at 20 for 20 min. Tapioca is a productive crop in poor soils and requires the least labor in cultivation and can tolerate drought, but the labor requirement in processing after harvest is high (Radhakrishnan 1996). Indian sago starch is extracted from Manihot esculenta belonging to family Euphorblaceace. It is also known as SAGO (SABUDANA in Hindi or JAVVARISHI in Tamil). This sago is native to Brazil, Amazon, Colombia, Venezuela, West Indies, Cuba, and Puerto Rico. In India it was introduced in later part of nineteenth century. Kerala, Andhra Pradesh and Tamil Nadu are the major producers of sago starch (Sabuindia 2013; Renu and Garima 2013). Dry tapioca root consists of 8090 % carbohydrate out of which the most important is starch. Starch content in tapioca ranges from 78.1 to 90.1 % on dry basis. Tapioca is mainly processed into starch and sago. There are more than 1,000 tapioca processing units in India producing starch and sago in cottage and small scale sectors (Manickavasagan and Thangavel 2006). Chemical structure of (starch) amylose and amylopectin (Buleon et al. 1998) Like cellulose, chitin is a fiber, and in addition, it presents exceptional chemical and biological qualities that can be used in many industrial and medical applications. Chitin is one of the most abundant renewable biopolymer on earth that can be obtained as a cheap renewable biopolymer from marine sources (Feisal and Montarop 2010). It is biocompatible, biodegradable and bio-absorbable, with antibacterial and wound-healing abilities and low immunogenicity; therefore, there have been many reports on its biomedical applications (Muzzarelli 1977). Chitin is a long-chain polymer of N-acetyl glucosamine, a derivative of glucose, and is insoluble in wate (...truncated)