Measurement of pools of protein, carbohydrate and lipid in domestic wastewater

A more detailed characterization of organic matter in domestic wastewater than given by the bulk parameters BOD, COD and TOC is needed to increase the knowledge about transformations in sewer systems and the quality of wastewater as input to the wastewater treatment processes. In this paper results of various selected methods optimized for analysing pools of carbohydrate, protein and lipid in domestic wastewater were described and discussed. The most suitable method for measurement of protein was the method of Lowry et al. (1951), for carbohydrate it was the anthrone method originally introduced by Dreywood (1946) and for lipid it was an infrared method modified from Standard Methods (APHA et al., 1985). The modified methods showed high precision and compounds in the wastewater did not seem to interfere. The results of the methods were, however, slightly influenced by the choice of standard. A case study was performed using the methods for characterization of wastewater from catchment areas of different characteristics. The fractions of total protein, carbohydrate and lipid of total COD were, on average, 28, 18 and 31% with standard deviations of 4, 6 and 10%, respectively. The dissolved carbohydrate fraction varied considerably—10% as an average of dissolved COD, and 7% as standard deviation, presumably due to degradation in the sewers influenced by differences in residence times.