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Use of carbohydrate, protein and fat to characterise wastewater in terms of its major elemental constituents and energy

Yao, Yao

[Thesis]. Manchester, UK: The University of Manchester; 2014.

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Abstract

A method has been developed to determine the elemental composition, ThOD and heat of combustion of a simulated wastewater sample, based on the analysis of its carbohydrate, protein and fat components. According to the human dietary habits, the empirical contributions of carbohydrates, proteins and fats from selected types of food to the wastewater are considered. Their generic formulae are hereby calculated as CH1.826O0.913, CH2.063O0.626N0.282S0.008 and CH1.838O0.118, respectively. Carbohydrates are sub-grouped into mono-, di- and poly-saccharides and their heats of combustion are studied separately. Considering the constituents of the three groups in food, the overall heat of combustion of carbohydrates is calculated as 16.51 kJ g-1. Furthermore, a relationship between functional groups in amino acids and the heats of combustion has been summarised and consequently a protein with its generic formula can be deconstructed as a combination of glycine and extra functional groups. The heat of combustion of protein is thus obtained as 18.20 kJ g-1. Moreover, the linear relationship between heats of combustion and the number of carbons for both saturated and unsaturated fats are provided individually. The fat with its generic formula can be considered as a specific combination of saturated and unsaturated fats and the heat of combustion calculated as 38.93 kJ g-1.The generic formulae are applied to calculate the ThOD values of wastewater samples. The results are compared with the experimental measurements of COD and the results of calculated generic formulae previously reported[1]. It shows the generic formulae in this project are able to provide a closer estimation of the experimental results than the previous formulae, giving an average ratio of 0.96 compared with 0.84.The heat of combustion of NESCAFÉ® Coffee-Mate Original has been measured experimentally and the energy value is also simulated by the overall heats of combustion of the three categories. A measurement after dissolving and drying samples is also conducted to mimic the experiment for wastewater sample. It is found the simulation only give 1.7% difference to the original measurement, while the dissolved-dried process significantly underestimates the energy value of the product because of the removal of volatile components and partial oxidation of the samples.