THESIS
2014
xvii, 189 pages : illustrations (some color) ; 30 cm
Abstract
In the past decade nutrient removal and recovery by treatment of source separated urine has
received attention based on its high concentrations of nitrogen and phosphorus. In dense
urban environments nutrient removal via struvite precipitation, urine nitrification and in-sewer
denitrification allows phosphorus recovery, efficient use of sewer infrastructure and
wastewater-carbon, and a possible shift to high rate carbon removal at centralized plants.
Combination with seawater toilet flushing provides numerous additional benefits including
freshwater savings, an economical magnesium source and additional autotrophic
denitrification in sewer. To realize such a system a compact nitrification reactor such as an
aerobic granular sludge reactor is required, which due to unfavourable c...[
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In the past decade nutrient removal and recovery by treatment of source separated urine has
received attention based on its high concentrations of nitrogen and phosphorus. In dense
urban environments nutrient removal via struvite precipitation, urine nitrification and in-sewer
denitrification allows phosphorus recovery, efficient use of sewer infrastructure and
wastewater-carbon, and a possible shift to high rate carbon removal at centralized plants.
Combination with seawater toilet flushing provides numerous additional benefits including
freshwater savings, an economical magnesium source and additional autotrophic
denitrification in sewer. To realize such a system a compact nitrification reactor such as an
aerobic granular sludge reactor is required, which due to unfavourable chemical oxygen
demand to nitrogen ratio, high pH and free ammonia is difficult to achieve.
In this study a novel micro-granular sludge with size between 100 - 180 μm was cultivated for
nitrifying urine. Detailed characterization of the microgranules confirmed a compact structure
with specific gravity of 1.02 - 1.10 eligible to be termed aerobic granules. Granule
characteristics were improved when treating urine from seawater toilet flushing systems,
although 4-5 mg/L of bioavailable phosphorus was required to maintain biomass growth and
stable nitrification. Pulse feeding was the major operational parameter identified for granule
formation. Pulse feeding created low substrate gradients and reduced growth rates through
free ammonia inhibition. These two factors resulted in homogenous radial growth and dense
microcolonies giving the sludge its properties of high density and small size.
Microbial community analysis between reactors identified a common core of key bacteria
while activity measurements on various substrates indicated specific degradation niches.
Nevertheless, seawater toilet flushing selected for a number of unique organisms including an
ammonia oxidizer not typically found in wastewater systems, and potentially an unidentified
nitrite oxidizer.
Microgranules, as developed in this study bring a number of benefits over conventional
aerobic granules, possessing increased surface area, active biovolume and loading rates over
conventional aerobic granules (typically 0.2 - 6 mm). As a result they combine the benefits of
flocculent and granular sludge.
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