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Effect of nitrite on accumulation of polyhydroxyalkanoates in aerobic granules treating palm oil mill effluent

Effect of nitrite on accumulation of polyhydroxyalkanoates in aerobic granules treating palm oil mill effluent / Eu Kean Wei
Berdasarkan teori, nitrit sebagai terminal elektron akseptor mempunyai peranan yang sama dengan oksigen dalam pembentukan granul aerobik dan pengumpulan PHA. Justeru, kesan nitrit terhadap pengumpulan PHA dalam granul aerobik mengunakan sisa air kilang minyak kelapa sawit sebagai makanan telah dikaji dalam berlainan nisbah COD:N dalam kajian ini. Pengurangan COD dalam reaktor induk tanpa penambahan nitrit boleh mencapai 90% dengan pengumpulan PHA sebanyak 0.6833mg PHA/mg biojisim. Asid propionik dan butirik dalam sisa air kilang kelapa sawit yang bertanggungjawab kepada pengumpulan PHA habis digunakan. Akan tetapi, pengurangan oksigen yang cepat pada permukaan granul aerobik mewujudkan zon anoksik dalam granul untuk denitrifikasi berlaku. Justeru, apabila nitrit ditambahkan ke dalam SBR, sebahagian COD digunakan untuk proses denitifikasi, jadi mengakibatkan pengurangan dalam pengumpulan PHA. Pada kepekatan nitrit yang rendah, 0.3380mg PHA/mg biojisim telah dikumpul dengan jauh lebih sikit asid propionik dan butirik digunakan berbanding dengan reaktor induk. Kekurangan dalam pengumpulan PHA mungkin disebabkan oleh perubahan laluan untuk pengumpulan PHA dalam granul aerobik akibat denitrifikasi proses yang berlaku dalam granul aerobik. Kesekatlakuan nitrit telah diperhatikan mula berlaku pada nisbah COD:N 15:1dengan pengumpulan PHA sebanyak 0.2823mg PHA/mg biojisim sahaja. Kepekatan nitrit yang tinggi menyebabkan persaingan yang lebih sengit dengan granul aerobik untuk COD. PHA yang telah dikumpulkan juga telah diurai dan digunakan oleh nitrit untuk denitrifikasi. Akan tetapi, penambahan nitrit yang lebih daripada nisbah COD:N 15:1 tidak menunjukkan kesekatlakuan yang lebih tenat dalam pengumpulan PHA disebabkan oleh kesekatlakuan nitrit ke atas dirinya sendiri apabila kepekatan lebih tinggi dari pengambilan biasa granul aerobik. Pengurangan COD juga semakin kurang apabila kepekatan nitrit semakin tambah. Pengurangan COD dalam SBR dengan 30:1, 15:1 dan 5:1 nisbah COD:N dicatatkan sebagai 80.95%, 72.28% dan 67.64% masing-masing. Lantas itu, kesekatlakuan nitrit menyebabkan nitrit tidak sesuai untuk menggantikan oksigen sebagai elektron akseptor untuk mengumpulkan PHA dalam granul aerobik. _______________________________________________________________________________________________________ Theoretically, nitrite, as terminal electron acceptor could have similar role as oxygen on the formation of heterotrophic aerobic granulation and accumulation of PHA. Therefore, the effect of nitrite on PHA accumulation in aerobic granules using palm oil mill effluent (POME) as feed was investigated in different concentration of COD:N ratio in this research. The COD removal in the parent reactor without addition of nitrite could reach 90% with 0.6833mg PHA/mg biomass accumulated. Both the propionic and butyric acids in POME were completely consumed to produce PHA. However, rapid oxygen depletion at the surface of aggregate making a significant anoxic zone in the core, where denitrification could occur. Thus, when nitrite was added to the SBR, part of the COD was used for denitrification process, resulting in reduction of PHA accumulation. At low concentration of nitrite, 0.3380mg PHA/mg biomass of PHA was accumulated with much lesser amount of propionic and butyric acids consumed than parent reactor. The reduction in PHA accumulation could be due to path way change for PHA accumulation since denitrification occur in the core of the aerobic granules. The inhibition effect of nitrite was observed to start at the COD:N of 15:1 with PHA accumulation of 0.2823mg PHA/mg biomass. The high amount of nitrite competed more vigorously with aerobic granules for COD. Accumulated PHA could be degraded and consumed by nitrite for denitrification purpose. However, further increased in nitrite concentration did not pose more severe inhibition effect on the PHA accumulation due to the inhibition effect of nitrite on itself when the concentration was higher than that to which the cells had been acclimated. The COD removal also reduced as the nitrite concentration increased. The COD in sequencing batch reactor (SBR) with 30:1, 15:1 and 5:1 of COD:N ratio were recorded as 80.95%, 72.28% and 67.64%, respectively. The inhibition effect of nitrite thus suggested that nitrite was not suitable as electron acceptor to replace oxygen to accumulate PHA in aerobic granules.
Contributor(s):
Eu Kean Wei - Author
Primary Item Type:
Final Year Project
Identifiers:
Barcode : 00003103382
Accession Number : 875005996
Language:
English
Subject Keywords:
nitrite; terminal electron acceptor; aerobic granules
First presented to the public:
5/1/2016
Original Publication Date:
5/21/2018
Previously Published By:
Universiti Sains Malaysia
Place Of Publication:
School of Chemical Engineering
Citation:
Extents:
Number of Pages - 57
License Grantor / Date Granted:
  / ( View License )
Date Deposited
2018-05-21 10:46:37.787
Date Last Updated
2019-01-07 11:24:32.9118
Submitter:
Mohd Jasnizam Mohd Salleh

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Effect of nitrite on accumulation of polyhydroxyalkanoates in aerobic granules treating palm oil mill effluent1 2018-05-21 10:46:37.787