Humic protein content

The microorganisms in sewer biofilms are embedded in a matrix of EPS that consists mostly of polysaccharides produced by the bacteria (Characklis and Marshall, 1990). The EPS fraction is the largest organic fraction in the biofilm, i.e., up to about 90% of the total organic content. Only limited studies of the total composition of sewer biofilms in terms of carbohydrates, proteins and humic substances have been undertaken (Figure 3.12). Corresponding information on the composition of anaerobic biofilms in pressure mains does not yet exist. 

Acid hydrolysis has been used extensively to remove ash, protein, and carbohydrate from humic substances (see reviews by Schnitzer and Khan, 1972, 1978 Stevenson, 1982 Kononova, 1961). In theory, this method should remove peripheral groups and co-precipitated materials and leave the core of humic or fulvic acid. What actually happens may be quite disconcerting. Structural changes may take place, as well as the removal of contaminants. Depolymerization may occur, but acid-catalyzed condensation may also take place. These changes can be seen by the loss of hydrogen content and by a decrease in the E IEf, ratios. All of these events are best summarized in Table 5 (Stevenson, 1982). 

This structure does not account for the nitrogen and sulfur content of humic substances. It has been suggested that these elements are derived from parts of other types of molecule, for example, proteins, which are associated with the humic substances. Indeed it has been proposed that humic substances consist of an aromatic core to which peptides, carbohydrates, metals, and phenolic acids are chemically or physically attached. It can be seen that the structure in Fig. 5-9 is an "open" network. In fact, there have been suggestions that organic and inorganic materials associated with humic substances are trapped inside these "holes" in the humic substance structure. " ... 

It is estimated that nearly 30 g of dry mixed sludge (from aerobic and anaerobic treatment) are produced per day per inhabitant [53] in municipal treatment systems alone. This suggests that for a city of 1 million inhabitants, this constitutes approximately 30 tonnes of dry sludge produced every day. Wastewater biosolids can be an important source of carbon-based compounds [54], The most important components of wastewater biomass are polysaccharides and proteins, either in pure form or in associations with other compounds, such as glycoproteins, lipopolysaccharides, lipoproteins, and so on. Other constituents include humic substances, deoxyribonucleic acid (DNA), lipids and uronic acids [54]. In the case of lipids, the content of lipids can vary from 2 to 30% [55]. 

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