응집과정에서 알루미늄 가수분해종의 특성 및 유기물제거 메카니즘 규명

Abstract

알루미늄 가수분해종 분포실험결과 급속교반 조건과 응집조건에 따라 알루미늄 가수분해종 분포는 다르게 나타나며 가수분해종 동역학 특성도 차이가 발생하였다. 이러한 가수분해종 분포와 가수분해종 동역학 특성에 따라 유기물 및 탁도 제거 메카니즘도 차이가 발생하였다. 응집제를 급속교반조에서 단시간에 골고루 확산시키는 목적을 가진 급속교반공정을 설계할 경우 다양한 변수를 고려해야 하지만 그중 급속교반시간, 급속교반강도, 응집제 종류, 응집 pH, 원수수질특성에 대한 변수는 가장 중요한 고려해야 될 변수라 알려져 있다. 하지만 교반강도와 교반시간, 응집제종류와 응집 pH 그리고 수질특성에 따라 생성되는 알루미늄 가수분해종 분포의 차이가 발생하였으며 생성된 알루미늄 가수분해종 분포에 따라 유기물 제거율 차이가 나타났다. 특히, 높은 교반강도를 유지하며 교반시간이 짧은 급속교반공정의 경우 유기물 제거에 효과적인 알루미늄 가수분해종 분포을 유도하였다. 따라서 급속교반공정의 설계시 이러한 가수분해종 분포특성 및 동역학 특성을 고려한 급속교반공정의 설계가 이루어져야 할 것이다. 이러한 결과를 바탕으로 설계된 급속교반공정은 급속교반강도를 강하게 하여 응집제의 분산을 빠르게 유도하여 응집제 주입량을 감소시켜 응집제 비용과 슬러지 발생량을 감소시키는등 경제적인 운전을 유도할 수 있다.

The overall objective of this research was to find out the role of rapid mixing conditions in the species of hydrolyzed Al(Ⅲ) formed by Al(Ⅲ) coagulants and to find out the interrelation of coagulant and organic matter in rapid mixing process and to identify the change of organic matter by mixing condition and to evaluate the distribution of hydrolyzed Al(Ⅲ) species by coagulant dose and coagulation pH. When an Al(Ⅲ) salt is added to water, monomers, polymers, or solid precipitates may be formed. The color intensity of monomeric Al was read 3min after mixing. With standard Al solution containing monomeric Al only, the Al-ferron color intensity slightly increased with until about 3min. During the rapid mixing period, for pure water, formation of dissolved Al(Ⅲ) (monomer and polymer) constant by rapid mixing condition, but for raw water, the species of Al hydrolysis showed different result. During the rapid mixing period, for high coagulant dose, Al-ferron reaction increases rapidly. Different Al(Ⅲ) coagulants (alum and PSOM) show different Al(Ⅲ) species distribution over a rapid mixing condition. During the rapid mixing period, for alum, formation of dissolved Al(Ⅲ) (monomer and polymer) increases, but for PSOM, precipitates of Al(OH)3(s) increases rapidly. The kinetic constants, K_(a) and kb, derived from Al-ferron reaction. The kinetic constants followed very well the defined tendencies for coagulation condition. For pure water, when the rapid mixing time increased, the kinetic constants, k_(a) and kb showed lower values. Also, for raw water, when the rapid mixing time increased, the kinetic constants, k_(a) and kb showed lower values. At A/D and sweep condition, both Al(OH)3(s) and dissolved Al(Ⅲ) (monomer and polymer) exist, concurrent reactions by both mechanism appear to cause simultaneous precipitation. During the coagulation, substantial changes in dissolved organics must be occurred by coagulation due to the simultaneous formation of microflocs and NOM precipitates. Increase in the organic removal efficiency should be mainly caused by the removal of microflocs formed during coagulant injection. That is, during the mixing period, substantial amount of dissolved organics were transformed into microflocs due to the simultaneous formation of microflocs and NOM precipitates. The results also showed that 40 to 80% of dissolved organic matter was converted into particulate material after rapid mixing process of coagulation.