Drying by Microwave Irradiation of Sewage Waste

도시 하수 폐기물의 고주파 건조

Dewatered digested sewage sludge were heated with microwave and their drying characteristics were investigated on the effect of their surface area, shape, diameter and thickness. The drying characteristics of identical samples in a conventional drying oven were studied. In conventional drying, constant rate period was not found and moisture was evaporated with capillary action. Moisture in the sludge was a bound water and free water was not exist. In microwave drying, the falling rate period was divided into two zones. In falling rate drying period, moisture movement occured by diffusion. The evaporation surface area was a significant variable, the greater heating surface area promoted water removal rate over wide region of water content. Drying rate was slow and constant rate drying period was found in wide moisture content region with increasing diameter. Drying characteristics appeared differently in various shape. In microwave heating, first of all temperature of sludge center was increased and was the highest. Temperature in the constant rate drying period was remained constantly at $80{\sim}100^{\circ}C$.

고주파를 이용한 오니의 건조특성에 대하여 살펴보고 재래식 건조특성과 비교 분석하였다. 고주파 건조는 빠른 속도와 높은 효율을 보였다. 재래식 건조에서는 항율건조기간이 나타나지 않았고 수분은 모세관현상에 의하여 이동하였다. 오니의 수분 중 자유수와 결합수는 존재하지 않았다. 고주파 건조에서 감율건조기간이 두 부분으로 나타났으며, 수분의 이동은 확산에 의하여 일어났다. 증발 표면적이 커질수록 수분의 제거가 촉진되었고, 오니의 지름이 커질수록 넓은 범위의 항율건조 기간이 나타났으며, 모양에 따라서도 건조특성이 다르게 나타났다. 고주파 건조에서는 오니의 중심부에서 가장 먼저 온도가 상승하였으며, 항율건조기간에서 $80{\sim}100^{\circ}C$로 일정하게 유지되면서 가장 높았다.