(583e) Degradation Behavior of Palm Oil Mill Effluent in Fenton Oxidation

Authors: 
Gamaralalage, D., The University of Tokyo
Sawai, O., The University of Tokyo
Nunoura, T., The University of Tokyo
Palm oil is a major crop production in Asian region which covers 2% of world cultivated lands and its production generates large amount of wastewater as palm oil mill effluent (POME), around 180 million tons annually. Among palm oil wastes, POME is considered as the most harmful waste to discharge untreated. It is very thick, brownish and odorous liquid with a high chemical oxygen demand (COD), N and P. Ponding systems, anaerobic digestion and membrane technologies are applied for POME treatment, but most are unsuccessful. Fenton oxidation is capable in producing intermediates with improved biodegradability, degrading hardly decomposable organics with no electrical energy requirement. In Fenton oxidation, peroxides react with iron ions to form hydroxyl radicals (OH.). These radicals and potential reactive intermediates (HO2., [Fe(OH)]+, [Fe(OOH)]+, [Fe(OH)]2+, [Fe(OH)(OOH)]+) formed in Fenton process attack on organics in wastewater. Even though Fenton oxidation is a potential candidate, behavior of POME in Fenton reaction is yet to study.

Considering above issues, this study applied Fenton oxidation for POME with objectives of its effective treatment and understanding its degradation behavior on Fenton process. Batch mode Fenton oxidation experiments were performed for diluted POME at adjusted pH of 2-5. Throughout reaction period, pH was kept constant and continuous magnetic stirring at 500 rpm was performed. Samples were withdrawn at predestined time intervals. Right after each sampling, potential reactions were quenched by adjusting samples’ pH to >9. Samples were analyzed for TOC, TN, residual [H2O2], [Fe2+], [NO2--N], [NO3--N], [NH4+-N], TP, [PO43--P], change of compounds and generation of intermediate products.

Composition of POME indicated high COD of 50000 ppm, TN of 516 ppm, TP of 509 ppm and total solids of 66300 ppm and suspended solids of 44000 ppm. Presence of carboxylic acids (acetic, propionic, butanoic, pentanoic, hexanoic) and phenol in POME contributed for over 71% of its TOC. NO2--N, NO3--N & NH4+-N contributed for 62.5% of TN in POME. Fenton oxidation showed greater TOC reductions of over 85% with relatively low oxidant consumption of 1:1.88 molar ratio of COD to H2O2. C balance indicated complete degradation of propionic, butanoic, pentanoic, hexanoic acids and phenol, and partial decomposition of 27% in acetic acid after Fenton oxidation for as less as 15 minutes. Formic acid, phthalic acid and acetamide were identified as main intermediate products and inorganic carbon (liquid phase) increased by 5.2 times within 15 minutes. Rapid consumptions of H2O2 and Fe2+ were observed within a few minutes of Fenton oxidation. Increase of hydrogen peroxide concentration promoted TOC reduction. Change of pH above and below 3 decreased TOC reduction and optimum pH was identified as 3. Performing Fenton oxidation in a closed system revealed formations of N2 and CO2 gases during POME degradation. Liquid fraction analysis indicated the drop of NO2--N by 36%, NH4+-N by 95.6% and TN by 21% after 15 minutes. Behavior of P revealed comprehensive removal of PO43--P by 99.9% within 15 minutes.

This study verified the possibility of applying Fenton oxidation in treating POME effectively by eliminating majority of TOC, TP and adequate TN. The study on C, N, P behaviors, change of compounds and generation of intermediate products provided a detailed degradation behavioral study of POME in Fenton oxidation. These outcomes will provide important information for future research in Fenton oxidation and POME, as well as for oil palm production industries on effective treatment of POME.

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