Contaminants of emerging concerns (CECs) have been detected in surface water ranging from several nanograms to micrograms per liter, and the high exposure to these chemicals may cause toxicity to human’s cerebral, cardiovascular or respiratory system. For example, amitriptyline (ATT) is a tricyclic antidepressant mainly used for the treatment of depression and various pains from neuropathic pain to migraine. However, conventional water and wastewater treatment system cannot remove ATT efficiently, and the catalytic ozonation process, producing powerful hydroxyl radicals (∙OH), are also limited to treating ATT due to recovery issues of powder catalysts and fast decay of ∙OH before reacting with ATT. To overcome these limitations, copper-nickel oxide (CuNiO) catalysts were synthesized and incorporated on the surface and pore walls of 3D-printed ceramic membranes to enhance the advanced oxidation process with ozone.
CuNiO nanoparticles were successfully fabricated via hydrothermal methods and exhibited the elevated first-order kinetic constant (k) from 0.020 $s^{-1}$ to 0.028 $s^{-1}$ when 10 mg/L CuNiO catalyst was applied during removal of 2 mg/L ATT with 0.5 mg $O_3$/L in batch mode. Moreover, the ATT removal was increased as pH increased, while the presence of natural organic matter (NOM) scavenged the reaction of hydroxyl radicals with ATT.
In order to overcome the recovery issue of powdered catalysts, and to increase the contact between hydroxyl radicals and ATT, CuNiO catalyst was incorporated by a precursor filling-calcination method on the surface and pore walls of the ceramic membrane. The hybrid system of catalytic ozonation with CuNiO incorporated ceramic membrane enhanced ATT removal by about 10% compared to the system without catalyst. Also, ATT removal increased about 20% in the hybrid system than the batch system, leading ATT removal to more than 70% only in ten seconds of contact time.
3D-printed ceramic membrane (3DP CM) was developed due to its simple printing with complex design applicability, which is expected to increase oxidation efficiency with lower applied pressures. The 3DP CM showed 27,500 $L/m^2/h/bar$ of water permeability. Although catalytic ozonation with CuNiO incorporated 3DP CM did not achieve a better ATT removal efficiency than $O_3$-CuNiO/CM due to some issues such as the low resolution of 3D ceramic printing, crack formation during the sintering process, and difficulties in sintering temperature scheme, it required much less pressure compared to conventional CM system, thus, 3DP CM could be regarded as one of the potentially applicable technologies in catalytic ceramic membrane fabrications.
In conclusion, CuNiO catalyst incorporated ceramic membrane enhanced ATT removal by the elevated generation of ∙OH and the reaction in confound pores. CuNiO catalyst incorporated 3D-printed ceramic membrane is expected to increase ATT removal in case the resolution and crack issues are overcome.
난분해성 미량오염물질은 지표수 내에서 리터 당 수 나노그램에서 마이크로그램으로 검출되며 이러한 물질에 대한 노출은 인간의 심혈관계, 신경계, 호흡기계 등에 독성을 유발한다. 이 중 아미트립틸린은 주로 우울증, 편두통 등 여러 통증 치료에 사용되는 삼환계 항우울제이다. 그러나 기존의 수처리 및 폐수처리 시스템은 아미트립틸린을 효율적으로 제거할 수 없고, 강력한 수산화 라디칼을 생성하는 촉매적 오존 산화 공정 역시 분말 촉매의 회수 문제와 수산화라디칼의 빠른 붕괴로 아미트립틸린 처리에 한계가 있다. 이를 극복하기 위해 구리니켈산화물 촉매가 합성되고 3D 프린팅된 세라믹 분리막의 표면과 기공 벽에 담지되어 오존촉매산화-세라믹 분리막 융합 공정을 운영하였다. 그 결과, 오존촉매산화-세라믹 분리막 융합 공정 운영 시 수산화 라디칼의 생성 증가와 분리막 공극 내에서의 반응에 의해 아미트립틸린 제거 효율이 향상되었다. 3D 프린팅 기술의 해상도 및 균열 문제가 극복된다면 구리니켈산화물 촉매를 3D 프린팅된 세라믹 분리막에 담지하여 융합공정을 운영할 때 신종 미량오염물질의 저감 효율이 더욱 극대화될 것으로 예상된다.
