Application of Reverse Osmosis and Ultrafiltration

EPA has for several years performed experiments to determine the feasibility of membrane techniques in treatment of municipal waste water. The results can be summarized in the following 5 points (EPA, 1969, Feige and Smith, 1974 and Bilstad, 1989):

1. The flux decreased over a period of 20 days and was then stabilized.

2. The quality of the influent was important for the flux. Chemical precipitation seems to be an appropriate pretreatment to use in this context.

3. It is technically feasible to separate nitrogen and other compounds from the waste water.

4. The major problems are concerned with the material-technology. These problems may be solved in the very near future.

5. It is possible to remove impurities on the membranes chemically to obtain the same flux as for new membranes.

The results obtained by EPA at the Pomona waste water treatment plant are shown in Table 10.4. The shown results were obtained with the spiral technique used at a pressure of 31 kg / cm2. The waste water was pretreated on activated carbon.

Similar experiments have been performed in Tokyo, using different types of membrane processes. The aim was to find suitable methods to recover waste water. A final report from these experiments is expected soon, but the provisional results have indicated that it is possible to obtain a certain removal of nitrogen compounds by ultrafiltration.

The widest application of membrane processes for removal of nitrogen compounds from waste water or waste has been the use of ultrafiltration to remove water from whey (rich in proteins) and municipal sludge. Whey was previously used as pig feed, but due to the high dilution, the transportation to the farms became uneconomical. It is, however, possible to obtain protein concentrations 4-6 times higher by ultrafiltration, which reduces the transportation cost correspondingly and makes it again profitable to utilize whey as pig feed. The discharge of nitrogenous material by dairies may thereby be reduced correspondingly.

As seen from this review on the application of membrane processes for the removal of nitrogenous material, the present use is limited, but many waste water engineers and scientists in the field of membrane processes expect a rapid growth in the use of these technologies in the very near future. It seems therefore appropriate to include the presentation of membrane processes in a review of nitrogen removal techniques.

Table 10.4.

Results obtained by reverse osmosis after pretreatment of municipal waste water by biological treatment and activated carbon adsorption. 75% of the water was recovered by the process.

Parameter Influent Effluent % separation

Table 10.4.

Results obtained by reverse osmosis after pretreatment of municipal waste water by biological treatment and activated carbon adsorption. 75% of the water was recovered by the process.

Parameter Influent Effluent % separation

COD mg/l

8.7

1.0

88.5

Ammonium-N

10.1

1.1

89.2

Phosphate-P

10.9

0.2

98.4

TDS

750

59

92.1

0 0

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