Livestock wastewater which contains excrement and urine of livestock and washing water has not only high density and viscosity but also particulate solid materials. To achieve high removal efficiency in a biological treatment process for this wastewater, it is necessary to separate solid materials f...
Livestock wastewater which contains excrement and urine of livestock and washing water has not only high density and viscosity but also particulate solid materials. To achieve high removal efficiency in a biological treatment process for this wastewater, it is necessary to separate solid materials from liquid wastewater in the pretreatment process. In this study, pretreatment system for solid-liquid separation and optimum operation conditions of each pretreatment system was searched by investigating the characteristics of livestock wastewater generated from G city of Gyeongnam and pretreatment system of public livestock wastewater treatment plants in Korea. The livestock wastewater amounts generated from G city were 2,733 m3/d and 89% of them were from pigs. This wastewater contained high level of dissolved and persistent organic matter such as VSS/SS 74%, SCODCr/TCODCr 74%, and CODMn/TCODCr 22%. And the most of public livestock wastewater treatment facilities had composed of total impurities remover and centrifugal separator system, but had not kept constant removal efficiency. To improve biological treatment efficiency, three stages of pretreatment system has been recommended as : total impurities remover to remove impurities for first stage, centrifugal separator for solid-liquid separation for second stage, and coagulation, flotation, and Fenton oxidation for the third stage. In this study, the optimum operational conditions were investigated for the third stage solid-liquid separation such as coagulation, flotation, and Fenton oxidation by using laboratory scale batch experiment and continuous pilot plant research. The results were summarized as follows ; 1. Coagulation precipitation efficiency had the following order ; FeCl3 (1000mg/L)> PAC(1500mg/L) > Alum(1500mg/L) for their optimum dosing amount. In case of polymer coagulant, only cationic polymer coagulant had an effect on coagulation with 200 mg/L of optimum dosage amount. Combined coagulant mixed with inorganic and cationic polymer coagulants showed the highest removal efficiency. The optimum combined coagulant amounts were 500 mg/L of inorganic coagulant and 25 mg/L of cationic polymer coagulant. 2. The optimum operational conditions for flotation using DAF were 400% of recycle ratio, 4 atm and pH 4. In addition to 500 mg/L of Alum, 50 mg/L of cationic polymer coagulant had proper operational condition for the flotation followed by coagulation with combined coagulants. 3. Fenton oxidation to achieve removal of persistent organic materials and separation of solid-liquid had the optimum efficiency at the condition of initial pH 4, 10:1 of H2O2/Fe2+ dosing rate, 5,000/500 mg/L of H2O2/Fe2+ dosing amount, and Ca(OH)2 as counteragent. 4. As results from laboratory experiments, the removal efficiency of SS and CODCr were 79% and 50% for coagulation-precipitation, 87% and 61% for flotation, and 84% and 43% for Fenton oxidation, respectively. Flotation showed the highest efficiency but all of these three processes might be applied for the pretreatment of livestock wastewater as solid-liquid separation. 5. In the pilot plant research using Fenton oxidation, the removal efficiency of BOD and COD was about 50%. TS increased after Fenton oxidation due to the addition of chemicals. Sulfate ion causing the increase of TS seems to have disadvantage for degradation of organic matter because of low ratio of COD/SO42-. On the other hand, ferric ion might not have adverse effect on the next step anaerobic biological process by making precipitation from reaction of iron reducing bacteria and other iron oxides and improving activation of anaerobic microorganism.
Livestock wastewater which contains excrement and urine of livestock and washing water has not only high density and viscosity but also particulate solid materials. To achieve high removal efficiency in a biological treatment process for this wastewater, it is necessary to separate solid materials from liquid wastewater in the pretreatment process. In this study, pretreatment system for solid-liquid separation and optimum operation conditions of each pretreatment system was searched by investigating the characteristics of livestock wastewater generated from G city of Gyeongnam and pretreatment system of public livestock wastewater treatment plants in Korea. The livestock wastewater amounts generated from G city were 2,733 m3/d and 89% of them were from pigs. This wastewater contained high level of dissolved and persistent organic matter such as VSS/SS 74%, SCODCr/TCODCr 74%, and CODMn/TCODCr 22%. And the most of public livestock wastewater treatment facilities had composed of total impurities remover and centrifugal separator system, but had not kept constant removal efficiency. To improve biological treatment efficiency, three stages of pretreatment system has been recommended as : total impurities remover to remove impurities for first stage, centrifugal separator for solid-liquid separation for second stage, and coagulation, flotation, and Fenton oxidation for the third stage. In this study, the optimum operational conditions were investigated for the third stage solid-liquid separation such as coagulation, flotation, and Fenton oxidation by using laboratory scale batch experiment and continuous pilot plant research. The results were summarized as follows ; 1. Coagulation precipitation efficiency had the following order ; FeCl3 (1000mg/L)> PAC(1500mg/L) > Alum(1500mg/L) for their optimum dosing amount. In case of polymer coagulant, only cationic polymer coagulant had an effect on coagulation with 200 mg/L of optimum dosage amount. Combined coagulant mixed with inorganic and cationic polymer coagulants showed the highest removal efficiency. The optimum combined coagulant amounts were 500 mg/L of inorganic coagulant and 25 mg/L of cationic polymer coagulant. 2. The optimum operational conditions for flotation using DAF were 400% of recycle ratio, 4 atm and pH 4. In addition to 500 mg/L of Alum, 50 mg/L of cationic polymer coagulant had proper operational condition for the flotation followed by coagulation with combined coagulants. 3. Fenton oxidation to achieve removal of persistent organic materials and separation of solid-liquid had the optimum efficiency at the condition of initial pH 4, 10:1 of H2O2/Fe2+ dosing rate, 5,000/500 mg/L of H2O2/Fe2+ dosing amount, and Ca(OH)2 as counteragent. 4. As results from laboratory experiments, the removal efficiency of SS and CODCr were 79% and 50% for coagulation-precipitation, 87% and 61% for flotation, and 84% and 43% for Fenton oxidation, respectively. Flotation showed the highest efficiency but all of these three processes might be applied for the pretreatment of livestock wastewater as solid-liquid separation. 5. In the pilot plant research using Fenton oxidation, the removal efficiency of BOD and COD was about 50%. TS increased after Fenton oxidation due to the addition of chemicals. Sulfate ion causing the increase of TS seems to have disadvantage for degradation of organic matter because of low ratio of COD/SO42-. On the other hand, ferric ion might not have adverse effect on the next step anaerobic biological process by making precipitation from reaction of iron reducing bacteria and other iron oxides and improving activation of anaerobic microorganism.
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