Continuous Production Of Organic Acids From Palm Oil Mill Effluent And Kitchen Garbage

Waste materials such as palm oil mill effluent (POME) and kitchen garbage or refuse can be used as raw materials for organic acids production. In this study, POME and blended kitchen garbage were separately fed continuously into an anaerobic fermentation system in which they were converted to organic acids namely acetic, propionic, butyric and lactic acids, depending on the experimental conditions and type of microorganisms involved in the anaerobic treatment. The effect of two types of neutralizer, CaC03 and NaOH, on anaerobic treatment of POME was examined. The POME treatment was stabilized at pH5.0-5.5 when CaC03 was used to adjust the pH. Subsequently, anaerobic treatment of POME was performed at pH 5.0-5.5 with sludge recycle system. The major organic acids produced were acetic (5.0-5.6 g/L), propionic (2.0-2.6 g/L) and butyric acids (2.3- 3.3 g/L). Higher amount of butyric acid (average 2.8 g/L) was produced at pH 5.0. The sludge solids in the treated POME were separated by freezing-thawing technique and recycled into the reactor. More than 87% of the suspended solids in the treated POME were removed by this method.However, the clarified solution still contained more than 20,000 mg/L of total solids. Total microbial population stabilized at 108 cfu/mL in the reactor but reduced to 106 cfu/mL in the dewatered sludge upon freezing and thawing. The organic acids were fractionated to obtain more concentrated organic acids (22.4 g/L). In the case of kitchen garbage, Lactobacillus rhamnosus converted the carbohydrates to lactic acid with more than 87% selectivity. Glucoamylase with the activity of 60 U/mg was added during the fermentation at a dosage of 300 mg/L to enhance the hydrolysis of organic materials. Three sets of experimental conditions were studied, i.e. at pH 6.8 with RT 5 days, pH 5.5 with RT 5 days and pH 5.5 with RT 2.5 days which produced an average lactic acid concentration of 42 g/L, 53 g/L and 50 g/L respectively. The residual glucose and total sugars at steady state were less than 1 g/L and 20 g/L respectively. The optical purity of Llactic acid obtained was more than 90% under the optimum condition of pH 5.5 with RT 2.5 days.

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