Agriculture Reference
In-Depth Information
Fig. 12.9 Hydraulic
cleaning for NF flux
recovery
Furthermore, the changes in the total number of bacteria showed a surprising trend.
The total bacteria removal rate of nano-MgO and NF membrane was
99.99 %,
whereas that of the filter column was 80-98 %, which may be owing to the
microorganisms in the filter using nano-MgO organic compounds for growth and
metabolism. Therefore, it can be concluded that nano-MgO does not have any
bactericidal effect and that NF membrane could intercept bacteria. In addition,
according to the results obtained, by regulating the level of KH
2
PO
4
, the pH of
water could be maintained at about 7, thus meeting the standard of irrigation water.
For cleaning, we used the physical method of hydraulic cleaning as follows: the
outlet of the NF membrane permeation liquid was closed, and the liquid was used
for washing. As a result of closing of the outlet, the pressure of the inner membrane
filtrate increased and caused the liquid to reverse-flow through the roll film at a high
speed, thus removing the dirt deposited on it.
From Fig.
12.9
, it can be observed that after hydraulic cleaning for 5 min, the
membrane flux increased from 4.53 to 8.87 L/(m
2
h) and that with the increase in
the period of cleaning, the membrane flux slightly increased. These findings
indicate that through hydraulic cleaning, the pollutants can be effectively removed
from the NF membrane surface, and the processing ability of the NF membrane can
be restored. At the same time, the results also suggest that we can apply “batch
processing mode for 1 h and cleaning for 5 min” to NF membrane components to
effectively prevent membrane pore blockage and maintain high membrane flux.
>
12.14 Conclusion
In this chapter, the applications of three kinds of nano-materials (nano-iron, nano-
TiO
2
, and nanofiltration) for the treatments of fertilizer-polluted groundwater,
livestock wastewater, and irrigation water for greenhouse vegetables, respectively,
were described. Based on the discussion above, some conclusions could be drawn:
