The composition of sludge organic matter is mainly influenced by the origin of
wastewater. The biochemical composition of sludge could, however, alter from post
wastewater treatment drying techniques. Such changes have a direct effect on the N
fertilizer value of sludge because the biochemical composition of sludge dictates its
decomposition rate. Therefore, proper understanding of the effect of wastewater
treatment methods and post treatment drying techniques on a) the C and N contents as
well as organic matter composition of sludge, and b) C decomposition and N
mineralization is crucial for N management in sludge amended agricultural lands. The
aim of this study was to investigate the effect of selected wastewater treatment and post
treatment drying techniques on a) the N, C, and organic matter composition, as well as
b) C decomposition and N mineralization of municipal sewage sludge. The study also
investigated the compounds responsible for C and N release during a decomposition process. Two consecutive incubation studies (100 days each) were conducted to
determine N release, C decomposition and sludge organic matter decomposition using
different sludge types namely: Thermally hydrolysed sludge (THS), Activated sludge
(Activated), and anaerobically digested sludge. The anaerobically digested sludges
were collected from two different drying techniques (concrete beds and earth paddy) as
well as two sludge drying depths on beds ( 10 cm and 25 cm). Inorganic N was
determined by the steam distillation method. Sludge organic matter composition was
analysed using Van Soest method. Total N and total organic C were determined using
Carlo-Erba method. A parallel sludge alone incubation study was conducted from which
organic compounds degradation and transformation analysis were conducted. The anaerobically digested sludge dried in thin layers of 10 cm (ADS3) had higher total N
(4.95%) than similar sludge types dried in thick layers of 25 cm in concrete beds
(ADS1= 2.81%N) and in earth paddy (ADS2 = 2.83%N). Large fraction (>60%) of the
organic C in all sludge types was in soluble compounds form (SOL). Thermally
hydrolyzed sludge (THS) had the highest (90%) SOL. ADS3 and Activated had lower
lignin fraction (<3%) than THS, ADS1 and ADS2. Net N mineralization per kg C applied
was highest for activated (77 g kg-1 C) and was lowest for ADS2 (23 g kg-1 C). Despite
having highest SOL, THS had relatively lower net N mineralization per kg organic N
applied (350 g kg-1 organic N) than Activated sludge (449 g kg-1 organic N) mainly due
to the relatively higher lignin fraction. It was apparent from this study that the soluble
compounds were responsible for about 90% of the organic matter decomposition. The
Van Soest method was also successfully used to determine residual compounds at intervals during the incubation study from the sludge alone study but not with the soilsludge
mixture. / Dissertation (MSc)--University of Pretoria, 2014. / National Research Foundation (NRF)
Water Research Commission (WRC), East Rand Water Care Company (ERWAT) / Plant Production and Soil Science / MSc / Unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/84065 |
| Date | 11 1900 |
| Creators | Malobane, Mashapa Elvis |
| Contributors | Tesfamariam, Eyob Habte, euob.tesfamariam@up.ac.za, De Jager, P.C. (Pieter Christiaan) |
| Publisher | University of Pretoria |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | © 2021 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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