Fatty acids, C16-18, sodium salts

Biodegradation in water and sediment: simulation tests

Description of key information

- completely biodegradable | OECD 303 A | sodium oleate, sodium laurate
- completely biodegradable | ISO 11734 | potassium cocoate, C12-16 
- 69% degradation | no guideline followed | sodium oleate
- 67% degradation | no guideline followed | Palm kernel soap 
- 60% degradation | no guideline followed | Tallow soap

Additional information

In the OECD confirmatory test according OECD Guideline 303A, sodium laurate and sodium oleate are completely eliminated, if spiking concentrations of 10-50 mg/l are used. The tests were run with activated sludge from municipal sewage treatment plants for 21-29 days. The sludge retention time was 12-16 days. In comparison to a control elevated fatty acid concentration could be detected neither in the outflow nor in the sludge of the simulation plant by GC analysis. Overall, the cleaning effect of the plant was on its overall performance degradation unchanged. The test substances in the activated sludge process have been largely eliminated entirely via an oxidative degradation. Hence degradation of fatty acid was concluded to be 100%.

Also the potassium cocoate, C12 -16 is ,according to the ISO 11734 guideline, almost completely biodegradable (99% ThGP theoretical gas production).

In a simulation test (fermenter) the anaerobic degradation of sodium oleate and other soaps such as tallow soap and palm kernel soap was examined. The evaluation was determined mainly by the amount of methane.
The measurement of gas production results for the different soaps are the following levels of degradation:

Sodium oleate	69%
Palm kernel soap	67%
Tallow soap	60%

At a concentration of 200 mg/l and 6.15 mg/g dry weight relative to the fermenter, the soaps causes no interference or inhibition in a discontinuous fermeter infeed in the sludge digestion process.

There is no influence of the pH-value, rather than even the reduction phase. In the sludge water only acetic acid at concentrations of ca. 70 - 170 mg/l and in some samples propionic acid at concentrations of 10 - 13 mg/l can be detected. The methane content in biogas corresponds to the theoretical values of 70 - 73%. Therefore the sensitive reduction of the methanation step runs unimpeded.

The anaerobic degradation is no different from the aerobic. An increase in degradation can be determined with decreasing carbon chain length, even under anaerobic conditions.

From the available test results, it can be deduced that the fatty acid C16 -18, sodium salt has a very high biodegradability.