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Characterizing municipal wastewater sludge for sustainable beneficial agricultural use
Expanded Title:The main aim of the study was to establish quantitative relationships between sludge fertilizer value (nitrogen release rate) and wastewater sludge treatment processes, drying techniques, sludge nitrogen (N) composition and use these to refine the current South African sludge guidelines. This was achieved through comprehensive literature study, liquid municipal wastewater sludge characterization, laboratory incubation studies, field experiments and model scenario simulations. The study showed that the pH and trace metal content of most wastewater sludges used in the study were within acceptable ranges for use in agricultural lands. Although most anaerobically digested sludges had exceptionally high salinity (EC), exceeding the agricultural threshold value of 200 mS m-1, and Total Suspended Solids (TSS) values exceeding the threshold value of 25 mg L-1 making them not feasible for use in agricultural lands, the aerobically digested sludges had EC values of less than 200 mS m-1 and TSS values of less than 25 mS m-1. Wastewater sludge treatment and dewatering techniques were observed to affect the N content of sludge thus influencing the fertilizer value. In this regard sludge dried in thin layers of 10 to 15 cm thickness generated higher total N and N fertilizer value than sludge dried in thick layers of 20 cm and higher. Inter-comparison of a six-year cumulative N mineralization rate (%) among years in which a single 10 t ha-1 sludge was applied during the lowest rainfall year, an average rainfall year, and the highest rainfall year showed little variation. Similarly, cumulative N mineralization rate (%) from a single sludge application rate of 10 t ha-1 for sludges with a range of N contents (2% to 6%) showed significant variation during the first and second year after application. Cumulative N mineralization at a specific site, however, was generally higher under irrigation compared with dryland farming. From this it can be deduced that a single N release rate per farming system (dryland vs irrigated) could be used at a specific site for agricultural lands that use sludge in the long term. This should be synchronized with crop nutrient requirements because crop nutrient requirements also vary, depending on the availability of water. Hence, sludge guidelines for beneficial land application ought to be synchronized with the South African fertilizer guidelines as presented in the fertilizer handbook.
Date Published:01/07/2018
Document Type:Research Report
Document Subjects:Agricultural Water - Small holder irrigation, Wastewater Management - Sludge management
Document Format:Report
Document File Type:pdf
Research Report Type:Technical
WRC Report No:TT 756/18
ISBN No:978-1-4312-0997-2
Authors:Tesfamariam EH; Badza T; Demana MT; Rapaledi MJ; Annandale JG
Project No:K5/2477
Originator:WRC
Organizations:University of Pretoria
Document Size:1 151 KB
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