טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAlfiya Yuval
SubjectInvestigation of the Clogging Mechanism, and Development of
Operation Parameters for a Passive-Aeration Novel
Biological Vertical-Bed
DepartmentDepartment of Agricultural Engineering
Supervisors Professor Ori Lahav
Professor Emeritus Michal Green


Abstract

A semi-intensive wastewater treatment system, based on unsaturated flow through porous media, and a “passive aeration” concept was developed at the Technion. The passively aerated vertical bed enjoys the advantages of a conventional vertical bed, but with a much higher oxygen supply rate. Experiments were centered round determining an “optimal” media size, which maximizes air suction into the bed. In order to choose a plausible media diameter-range, a model for predicting the passive air pump efficiency was developed, given the average diameter of the media particles and the aeration tube diameter. Model results show that large diameter particles reduce the pump’s efficiency, while larger pipe surface area has an opposite effect.

Using the model equation two different types of media were selected, a fine particle media (4-6 mm) and a coarser media (8-10 mm). Operation with the fine particles resulted in organic and mineral matter accumulation in the media, and irreversible clogging occurred, mostly at the upper end of the reactor. The experiments with the coarse media were run with two hydraulic loads: a “low” hydraulic load of 9 m3/m2/d, and a “high” hydraulic load of 18 m3/m2/d. The average removal rate using the coarse media was 1,280 g CODt/m2/d, 940 g BOD5/m2/d and 330 g TSS/m2/d.

The passive air pump improved significantly the COD removal rates (as compared with a conventional VB) for the two media types tested. Although the fine media showed somewhat better removal results, the conclusion was that coarse media was preferable for long-term operation, provided that the operational hydraulic load does not exceed 9 m3/m2/d.