Biological treatment of source separated urine in a sequencing batch reactor
Date
2014-12
Authors
McMillan, Morgan
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Urine contains up to 80% of nitrogen, 50 % of phosphates and 90 % of potassium of the total
load in domestic wastewater but makes up less than 1% of the total volume (Larsen et al.,
1996). The source separation and separate treatment of this concentrated waste stream can
have various downstream advantages on wastewater infrastructure and treated effluent
quality. The handling of undiluted source separated urine however poses various challenges
from the origin onward. The urine has to be transported to a point of discharge and ultimately
has to be treated in order to remove the high loads of organics and nutrients. Wilsenach (2006)
proposed onsite treatment of source separated urine in a sequencing batch reactor before
discharging it into the sewer system.
This study focused on the treatment of urine in a sequencing batch reactor (SBR) primarily for
removal of nitrogen through biological nitrification-denitrification. The aim of the study was to
determine nitrification and denitrification kinetics of undiluted urine as well as quantification of
the stoichiometric reactions. A further objective was to develop a mathematical model for
nitrification and denitrification of urine using experimental data from the SBR.
The SBR was operated in 24 hour cycles consisting of an anoxic denitrification phase and an
aerobic nitrification phase. The sludge age and hydraulic retention time was maintained at 20
days. pH was controlled through influent urine during volume exchanges. Undiluted urine for
the study was obtained from a source separation system at an office at the CSIR campus in
Stellenbosch. Conditions in the reactor were monitored by online temperature, pH and ORP
probes. The OUR of the system was also measured online. One of the main challenges in the biological treatment of undiluted urine was the inhibiting
effect thereof on nitrification rate. The anoxic mass fraction was therefore limited to 17 % in
order to allow longer aerobic phases and compensate for the slow nitrification rates. Volume
exchanges were also limited to 5% of the reactor volume in order to maintain pH within optimal
range. Samples from the reactor were analysed for TKN, FSA-N, nitrite-N, nitrate-N and COD. From the
analytical results it was concluded that ammonia oxidising organisms and nitrite oxidising
organism were inhibited as significant concentrations of ammonia-N and nitrite-N were present
in the effluent. It was also concluded that nitrite oxidising organisms were more severely
inhibited than ammonia oxidising organisms as nitrate-N was present in very low
concentrations in the effluent and in some instances not present at all.
Ultimately the experimental system was capable of converting 66% of FSA-N to nitrite-
N/nitrate-N of which 44% was converted to nitrogen gas. On average 48% of COD was
removed.
A mathematical model was developed in spreadsheet form using a time step integration
method. The model was calibrated with measured online data from the SBR and evaluated by
comparing the output with analytical results. Biomass in the model was devised into three
groups, namely heterotrophic organisms, autotrophic ammonia oxidisers (AAO) and
autotrophic nitrite oxidisers (ANO). It was found that biomass fractionation into these three
groups of 40% heterotrophs, 30% AAO and 30% ANO produced best results.
The model was capable of reproducing the general trends of changes in substrate for the
various organism groups as well as OUR. The accuracy of the results however varies and nearexact
results were not always achievable. The model has some imperfections and limitations
but provides a basis for future work.
Description
Thesis (MScEng) -- Stellenbosch University, 2014.
Keywords
Urine treatment in sewage, Nitrification, Denitrification, Sequencing batch reactor, Sewage -- Purification -- Sequencing batch reactor process, Sewage -- Purification -- Nitrogen removal, UCTD