Primary biodegradation

Biodegradation primary biodegradation rate constant k = 0.153 d and L, = 4.55 d in an acclimated shake flask CO2 evolution test (Sugatt et al. 1984)... 

Fig. 14.9 Energetic profiles in oxo- and hydro-biodegradables primary steps...

There are two types of biodegradability. Primary biodegradability, the loss of the original substance, is indicated by a change of a specific property such as colour or surface activity. Ultimate biodegradability refers to complete breakdown to carbon dioxide and water. 

Inherently biodegradable substances are those which show biodegradation (primary or ultimate) in a recognised test. 

APE Biodegradation. Primary biodegradation of APE, both linear and branched, occurs with proper time and acclimation of degraders. However, complete or ultimate biodegradation (mineralization) has not been consistently noted in biodegradation studies, and when mineralization is unequivocally observed, it is slower compared to many other surfactants. Even the linear APE show reduced rates of ultimate biodegradation. 

Oxidation of polysaccharides is a far more attractive route to polycarboxylates, potentially cleaner and less cosdy than esterification. Selectivity at the 2,3-secondary hydroxyls and the 6-primary is possible. Total biodegradation with acceptable property balance has not yet been achieved. For the most part, oxidations have been with hypochlorite—periodate under alkaline conditions. In the 1990s, catalytic oxidation has appeared as a possibiUty, and chemical oxidations have also been developed that are specific for the 6-hydroxyl oxidation. 

Sucrose reacts with fatty acids to produce esters with degrees of esterification (DE) from 1 to 8 and hydrophi1 ic /Iipophi1 ic balances that provide them with numerous appHcations. Primary producers are Japan and the Netherlands, with total production at 6000 t/yr. Sucrose esters are nontoxic and biodegradable, and are approved for use in the EC, Japan, and the United States. 

The primary biodegradation grades of secondary alkanesulfonates measured by different tests are distinctly above 90%. In the OECD Confirmatory Test (sewage treatment plant simulation test), the biodegradability is 99% (decrease in MBAS, the methylene blue active substance). 

Alcohol and alcohol ether sulfates are commonly considered as extremely rapid in primary biodegradation. The ester linkage in the molecule of these substances, prone to chemical hydrolysis in acid media, was considered the main reason for the rapid degradation. The hydrolysis of linear primary alcohol sulfates by bacterial enzymes is very easy and has been demonstrated in vitro. Since the direct consequence of this hydrolysis is the loss of surfactant properties, the primary biodegradation, determined by the methylene blue active substance analysis (MBAS), appears to be very rapid. However, the biodegradation of alcohol sulfates cannot be explained by this theory alone as it was proven by Hammerton in 1955 that other alcohol sulfates were highly resistant [386,387]. 

The first step in the complete biodegradation of primary alcohol sulfates seems to be the hydrolysis to yield alcohol. Sulfatases are able to hydrolyze primary alcohol sulfates. Different authors have isolated and used several sulfia-tase enzymes belonging to Pseudomonas species. The alcohol obtained as a result of the hydrolysis, provided that dehydrogenases have been removed to avoid the oxidation of the alcohol, was identified by chromatography and other methods [388-394]. The absence of oxygen uptake in the splitting of different primary alcohol sulfates also confirms the hydrolysis instead of oxidation [395, 396]. The hydrolysis may acidify the medium and stop the bacterial growth in the absence of pH control [397-399]. 

Linear primary alcohol sulfates can also be biodegraded under anaerobic conditions but the process seems to be limited to the hydrolysis of the sulfate [407]. 

Some enzymes isolated in studies of primary alcohol sulfate biodegradation are specific for these sulfates [390,396]. However, other enzymes are more versatile. A strain isolated by Payne et al. [408] was capable of hydrolyzing secondary alcohol sulfates and also primary alcohol sulfates. Similar results were found by Vaicum and Eminovici [409]. 

Linear primary alcohol sulfates often need only one day for 95 % primary biodegradation and degrade faster than other anionic surfactants, which usually need several days. This difference has been confirmed by Ruschenberg [412, 413]. 

Alcohol ether sulfates also biodegrade rapidly but not as rapidly as alcohol sulfates. Primary biodegradation of alcohol (2 EO) ether sulfates determined in the same conditions as primary alcohol sulfates in Table 30 is shown in Table 33 as reported by Borsari [414]. 

TABLE 32 Primary Biodegradation of Linear Alcohol Sulfates... 

TABLE 33 Primary Biodegradation of Alcohol (2EO) Ether Sulfates... 

Alcohol Linearity (%) Days for 95% primary biodegradation OCDE EMPA ... 

TABLE 34 Primary Biodegradation of C1214 and C12 14 Ether Sulfates... 

However, they behave similarly to alcohol sulfates since linear alcohol ether sulfates are more easily biodegradable than branched alcohol ether sulfates. Also linear secondary alcohol ether sulfates are poorer than linear primary alcohol ether sulfates [425]. 

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