Mineralization biodegradability tests

In many inherent biodegradability tests only the disappearance of the test substance is measured. Such a result only demonstrates a primary biodegradability and not a total mineralization. Thus, more or less persistent degradation products may have been formed. Primary biodegradation of a substance is no indication of ultimate degradability in the environment. 

Nutrient-Mineral-Buffer (NMB) Solution. Table 1 lists the composition of the nutrient-mineral-buffer (NMB) stock solution used as recommend by ASTM 5271. A trace element solution was also added in order to support biological growth. These solutions were used for all biodegradation tests. Each compound in column one was dissolved in distilled water and diluted to 1L at the concentrations listed in column two. The test medium was formed by adding the volumes listed in column three to 1 L of high-quality reagent water and adjusting the pH to pH 7.0 0.1 with HC1 and NaOH. Approximately 400 mL of the test... 

As described above, esterquats differ structurally from DTDMACs by the presence of ester linkages in the alkyl chains. These linkages allow a rapid and complete biodegradation of esterquats. For example, DEEDMACs reached about 80% CO2 evolution in the modified Sturm test. With respect to the other criteria, DEEDMACs can be classified as readily biodegradable. In addition, a rapid and high anaerobic biodegradability of DEEDMACs was found (22). Similar results were reported from biodegradation tests with esterquats, DEQs and DTIEs. There was almost a complete mineralization and stable metabolites were not formed. 

Several other norms for aquatic, aerobic biodegradation tests have been published as well but are not frequently used for biodegradable polymers. Mostly the conditions of incubation (mineral medium, inoculum, temperature, concentration, etc.), are identical or at least similar to the Sturm and MITI methods. The differences lie in the parameters that are being measured and the method for calculating the biodegradation. The following different tests can be used ... 

Biodegradation tests do not in themselves demonstrate complete mineralization or ultimate biodegradation of the surfactant, that is complete breakdown into carbon dioxide, water and mineral salts. For this metaboUc studies have to be conducted. Metabolic studies also eliminate the possibility of toxic metabolites being formed as a result of the degradation pathway. 

Table 4. Batch tests measuring mineral oil biodegradation under biostimulation by air and nutrient supplementation.

Anaerobic conditions often develop in hydrocarbon-contaminated subsurface sites due to rapid aerobic biodegradation rates and limited supply of oxygen. In the absence of O, oxidized forms or natural organic materials, such as humic substances, are used by microorganisms as electron acceptors. Because many sites polluted by petroleum hydrocarbons are depleted of oxygen, alternative degradation pathways under anaerobic conditions tend to develop. Cervantes et al. (2001) tested the possibility of microbially mediated mineralization of toluene by quinones and humus as terminal electron acceptors. Anaerobic microbial oxidation of toluene to CO, coupled to humus respiration, was demonstrated by use of enriched anaerobic sediments (e.g., from the Amsterdam petroleum harbor). Natural humic acids and... 

Pentachlorophenol, a widely used wood preservative, is considered to be moderately biorefractory with a biodegradation rate constant of 3 x 1012 L/ cell/hr, a log of 5.01, and a vapor pressure of 1.1 x 10-4 mmHg at 20°C. Watts et al. (1990) carried out completely mixed batch tests by treating penta-chlorophenol-contaminated soils with Fenton s reagent. Mineralization of pentachlorophenol (PCP) was studied in commercially available silica sand and two natural soils by removal of parent compound and total organic carbon with corresponding stoichiometric recovery of chloride. The soluble iron concentration decreased over the first 3 hr of treatment, and the concentration remained relatively constant thereafter. A possible mechanism for iron precipitation was proposed as follows ... 

---