Effect of nitrite and pH on the accumulation of polyhydroxyalkanoates (PHAs)
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Date
2018-06
Authors
Hairiady Hindwan
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Abstract
Synthetic plastic which is made from fossil fuel is commonly used in human life due
to its advantages in term of strength, lightness and durability. Producing plastics from bio based materials such as polyhydroxyalkanoate (PHA) is one of the method that are able to
replace conventional petroleum-derived polymers. However, there are some factors that can
affect the accumulation of PHA. The purpose of this study is to investigate the effect of pH
and nitrite concentration on the accumulation of PHA. Experiment are conducted for 6 hours
operation cycle by using 2 L bioreactors. 1 L sample which consists of PHA-accumulating
microorganisms in granules form are taken from 8 L parent reactor and dilute with 1 L water
to form mixed liquor. 2 L of mixed liquor are added into the 2 L bioreactor together with the
specific concentration of nitrite starting from 30 mg/L, 60 mg/L, 90 mg/L, 120 mg/L and 150
mg/L for each cycles by controlling the value of pH at 7.5. Sample are taken at 0, 0.5, 1.0,
1,5, 2,0, 4.0 and 6.0 h for COD, nitrite (NO2
-
), FNA, and PHA analysis. Similar step is
repeated by changing the pH of the mixed liquor from 6.0, 6.5, 7.0, 7.5 and 8 for each 6 hours
cycle without any addition of nitrite. Stock solution of sodium hydroxide, NaOH and acetic
acid, CH3COOH were used to control pH value. Accumulation of PHA is observed to be
higher at pH of 7.0 and nitrite concentration of 30 mg/L. Effect of nitrite and pH were
determined by the presence of free nitrous acid (FNA) in the sample. Hence, the effect of
nitrite and pH value on the accumulation of PHA will be determined by the presence of FNA.
The lower the value of FNA in the sample, the highest the PHA will be accumulated in the
microorganism.