Comparative Experiment of Coagulant for the Pretreatment of Coagulation Air Floatation for Slaughter Wastewater

As a kind of high concentration organic wastewater, coagulation pretreatment for slaughter wastewater should be carried out before biological treatment process.For optimal treatment effect, the choice of coagulant was crucial.In this paper , FeSO4.7H2O , FeCl3 , Al2(SO4)3 , PAC were taken as coagulant and PAM was taken as coagulant aid. The effect of coagulation was analyzed under different conditions.Results showed that the PAC was the best coagulant for slaughter wastewater pretreatment .This study provided reference for coagulation air floatation of slaughter wastewater pretreatment . Introduction The wastewater from slaughter industry present high concentration, serious pollution, the waste water produced in composition is complex and the characteristics of volatility.According to the characteristics of slaughter wastewater, there are a lot of pollutants in the form of slurry, which is the main object of physical and chemical treatment to remove [1-2]. Coagulation precipitation and coagulation air floatation are necessary to choose the appropriate coagulant and flocculant is a lot of more phyletic, the existing coagulant has two kinds of inorganic and organic.Of applied inorganic coagulant in water treatment, mainly iron and aluminium salt and its polymer [3].Aluminum salt coagulant used mainly for Al2 (SO4) 3, PAC.Iron salts commonly used mainly FeCl3, FeSO4.7 H2O and PAF.This experiment through the beaker experiment considering the removal rate of COD and turbidity and cost to determine the use of coagulant.Coagulant aid PAM for nonionic organic polymer flocculant, plays a role of bridge can be.This experiment selected coagulants can better play and colloid particle surface charge, electric double layer compression, to reduce the potential role.But coagulant bridging ability is weak, the formation of flocs is loose, and not easy sedimentation, PAM is just made up for the inadequacy of them [4].Selection of coagulant and coagulant aid are shown in table 1: Table1 The types of flocculant and coagulant aid Flocculant Coagulant aid FeSO4.7H2O PAM FeCl3 Al2(SO4)3 PAC Comparison of Coagulants Six 1000 ml beaker were numbered from left to right with 1, 2, 3, 4, 5, 6, 6 cup which all added 1000 ml of raw water. The water was adjusted by 0.1 mol/L NaOH and HCl solution to maintained the pH slightly greater than 7.0.All of the five brakers remained at about 15 °C.1, 2, 3, 4 beaker added FeSO4.7 H2O, FeCl3, Al2 (SO4) 3, and solid PAC potions in turn which quantity were all 0.5 g/L as 5 and 6 beaker were taken as comparison test.Under the six league blender, will lower position in central impeller into a beaker, make the raw water can be fully mixed with the coagulant, 2nd International Conference on Machinery, Materials Engineering, Chemical Engineering and Biotechnology (MMECEB 2015) © 2016. The authors Published by Atlantis Press 467 with 120 r/min intensity of stirring 20 s, add 2 ml coagulant aid after 0.1% PAM, among them, add 2 5 ml distilled water (alternative to join the amount of PAM solution), 6, don't add any potions, again slowly stir 5 min.Then stir 20 min with observing he amount of time, size, density and other reference of alum grain .Take the clear liquid COD as indicators to detect water effect.Experimental apparatus as shown in figure 1. Fig 1 The drug coagulation precipitation reaction conditions after joining the drug In the test number 1 to 4 beaker in adding flocculant and coagulant aid,the alum grain began to form after 30 s which appeared to about 1 min alum grain, a large number of suspended matter in raw water to precipitation to the bottom, the water in the beaker stratification gradually, the upper begin to clarify, after 20 min, 4 state of the water in the beaker are to clarify.Testing water quality with extracting different location of the water with a syringe, the result shows in figure 2. Fig 2 The influence of coagulant on COD removal Based on the analysis of figure 2, the same original water quality was taken tested which COD was 2385 mg/l. raw water after joined the flocculant, COD removal rate is over 50%, PAC, FeCl3, FeSO4.7H2O removal effect is more obvious and very close.Based on the four beakers that determination of the supernatant fluid, removal rate of Al2 (SO4)3 is 54.3%;the PAC removal rate is 67.8%;removal rate of FeCl3 is 66.4%;removal rate of FeSO4.7 H2O was 67.2%.From the result , all these iron salts were similar, the coagulation effect between FeSO4.7 H2O in water ionization of Fe2 + only produce mononuclear complex than FeCl3 coagulation effect.But the coagulation constantly stir to dissolve in water more oxygen to accelerate its oxidation, the pollutants in the water as the generated Fe (OH) 3 precipitation to the bottom of the cup, although longer time than FeCl3, but the upper water effect is better also. PAC and Al2(SO4)3 are of aluminium salt whose coagulation effect are more obvious differences.Their basic principle of coagulation, Al2(SO4)3 hydrolysis to produce Al3 ions, Al(OH)3 gel and a variety of forms of hydrolysis of the polymer.For slaughter wastewater is not high negative charges that exist in the colloid, can take advantage of the positive charge lower