Stabilization of aerobic granules
Date Issued
2010
Date
2010
Author(s)
Chen, Yu-You
Abstract
There are three objectives in this study: to obtain stable aerobic granules in high organic loading rate (OLR) wastewater; to enhance its mechanical strength of aerobic granules and to find proper conservation approaches of the aerobic granules.
To obtain the stable aerobic granules, nitrogen source, ammonium (NH4-N) and nitrate (NO3-N), are prepared in three ratios (i.e. 100/0, 40/60, 20/80) while carbon source (propionic acid and ethanol) are fixed as feed. Following the three nitrogen ratios, aerobic granules are generated after two weeks in three sequence batch reactor (SBR), namely R1, R2 and R3. OLR in the three SBRs are gradually increased from 2.5 to 14 kg COD.m-3.day-1 in 25-days continuous operation. Broken of R3 granules are firstly observed at OLR= 6.87 kg COD.m-3.day-1, while R2 granules are then broken at OLR= 14.24 kg COD.m-3.day-1. R1 granules are not found any broken and still survive at the highest OLR (21.85 kg COD.m-3.day-1) till the end of the experiment. The result shows that nitrate (NH4-N) as the sole nitrogen source (R1) is the most stable among the three SBR experiments. Consequently, R1 granules are transfered to continuous stirred tank tractor (CSTR) and continuously running till a new-record (220 days) at the highest OLR forever (39 kg COD.m-3.day-1).
To increase mechanical strength of aerobic granules, two coating techniques, namely inside and outside coating, are developed. Inside coating are found easier fabricated and more stable than outside-coating granules. Among seven tested oversaturation solutions, Mg3(PO4)2 and CaSO4 achieved the highest mechanical strength. For granules coating by MgCO3, the strcture of granules are observed rigid in alkalne condition (pH=12) and its bioactivity in acid condition (pH=3) is better than the uncoated granules. Residual numbers of the MgCO3-coated granules in CSTR are found existing more than the uncoated ones during long-term CSTR operation (220 days). Diversity of microbial community in the aerobic granules is getting three uniform bacterial species (i.e. Rhizobium sp., Brevundimonas sp., Nitratireductor sp.) at 160-days continuous running.
Drying granules are carried out in order to reserve the aerobic granules. It is found the recovered granules still remian its bioactivity (i.e. COD degradation). Three drying approaches, i.e. drying by acetone, in dark and after coating, are found better than the other five drying approaches in terms of bioactivity recovery. Bioactivity of the recovered aerobic granules storaging after 22 days and 78 days are both the same as undried ones. Molecular biological techniques, i.e. DGGE, are applied to charaterize bacterial species of aerobic granules. Three species, Flavobacterium sp., Trigonala sp., and Arthrobacter sp., are found in the dried and recovered aerobic granules.
Subjects
aerobic granules
stabilization
SBR
dry
coating
Type
thesis
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