Aerobes and Effluents - Environmental Biotechnology: Theory and Application - page 127

Table6.3 Horticulturalwasteprocessliquoranalysisbeforeandafter85day
aerationtreatmentandtheassociatedpercentagereductionsachieved

Determinant Baseline Post treatment % reduction

pH 5.8 8.8 -

Conductivity @20 ◦ C 6 950 6320 9.1

BOD total + ATU 15 800 198 98.7

COD 27 200 1990 92.7

Solids particulate 105 ◦ C 6 200 28 99.5

Total dissolved solids 13 700 293 97.9

Ammoniacal nitrogen 515 316 38.6

Total oxidised nitrogen 1.7 0.3 82.4

Kjeldahl nitrogen 926 435 53.0

Nitrite 0.79 0.04 94.9

Nitrate 0.9 0.3 66.7

Sulphate 194 63.4 67.3

All in mg/l except pH (in pH units) and conductivity (in mS/cm).
ResultscourtesyofRobHeap,unpublishedprojectreport.

Other variants on this theme are brush aerators, which are commonly used to
provide both aeration and mixing in the sewage industry and submerged turbine
spargers, which introduce air beneath an impeller, which again mixes as it aer-
ates. This latter approach, shown in Figure 6.2, can be considered as a hybrid
between mechanical and diffused systems and though, obviously, represents a
higher capital cost, provides great operational efficiency. A major factor in this
is that the impeller establishes internal currents within the tank. As a result the
bubbles injected at the bottom, instead of travelling straight up, follow a typi-
cally spiral path, which increases their mean transit time through the body of the
liquid and hence, since their residence period is lengthened, the overall efficacy
of oxygen diffusion increases.

Figure6.2 Turbinespargeraerationsystem