Measurement of oxygen uptake rate (OUR) during start-up phase of aerobic granular sludge (AGS) formation in leachate treatment
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Date
2019-06
Authors
Nurul Najihah Binti Ahmad
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Abstract
Sanitary landfill is the most common method to dispose municipal solid waste
due to such advantages as simplicity, low price and landscape-restoration of holes from
mineral workings. Treating and managed safely landfill leachate is very important to
avoid environment hazard to surface and ground water as it can percolate throughout
soils and subsoils causing adverse impacts to receiving waters. Aerobic granular sludge
(AGS) is one of the technologies that use activated sludge from Indah Water Konsortium
(IWK) and it has a great potential in reducing footprint and improving efficiency of
municipal and industrial wastewater treatment plants. AGS is a novel microbial
community that allows simultaneous removal of carbon, nitrogen, phosphorus and other
pollutants in a single sludge system. The AGS method provides unique characteristics,
including compact structure, high settling velocity, ability to sustain high biomass
concentration and simultaneous nutrient removal capability. On the other hand, oxygen
uptake rate (OUR) defined as the rate at which microorganisms use oxygen is an indicator
of the biological activity of the system. While for specific oxygen uptake rate (SOUR),
it described the amount of oxygen used by the microorganisms to consume one gram of
food. Both OUR and SOUR were used as the parameters to characterised the leachate
during AGS formation. This research aims to cultivate AGS using leachate as a substrate.
After 50 days operation, a small and compact sludge with size 25 - 163 µm were obtained.
It decreases in size from 219 - 1612 µm on the first day operation, which has a flat, loose
and irregular structure. The analysis on the relationship between OUR and AGS
formation based on mixed liquor suspended solid (MLSS), mixed liquor volatile
suspended solid (MLVSS), sludge retention time (SRT), food to microorganism (F/M)
ratio and also removal effectively in suspended solid (SS) with maximum removal of
80%. While for chemical oxygen demand (COD), maximum removal of 67% is obtained.
Next, F/M increased from 0.65 g COD/g MLVSS d on day 15 to 3.52 g COD/g MLVSS
d on day 30. This is followed by simultaneous increment of SOUR on day 22 to day 30
which are 130 mg O2/g MLVSS h and 263 mg O2/g MLVSS h, respectively. It shows
that SOUR increases when F/M increases. Due to a low organic loading rate (OLR),
which was from 0.84 kg COD/m3d on day 12 to 0.62 kg COD/m3d on day 15 has resulting
in lower MLSS to 0.72 g/L on day 22. The disintegration that occurs on day 12 resulted
in lower SRT (4 days) reducing the OUR value (0.63 mg O2/ L min ) which should be it
is higher than SOUR (177 mg O2/ g MLVSS h). Also on day 12, lower OUR is because
of higher F/M ratio (3.77 g COD/g MLVSS d). This is due to lower consuming of oxygen
by the lower microorganisms.