Treatment of Palm Oil Mill Effluent (POME) using Cassia obtusifolia Seed Gum Through Coagulation-Flocculation Process

2016-12-01T23:34:02Z (GMT) by Katrina Pui Yee Shak
With the economic upsurge and continuous industrial development of Southeast Asia’s palm oil sector, Malaysia alone produced an estimated 19 million tonnes of crude palm oil (CPO) in 2015. However, CPO production is in tandem with the high generations of both solid waste and effluent. Environmental issues related to the wellbeing of watercourses became a concern due to the discharge of palm oil mill effluent (POME). Governmental and international bodies have acknowledged the need to develop and implement sustainable effluent management strategies, especially concerns relating to the implementation of suitable treatment technologies with realistic pricing. Noted for its potential to treat organically polluted water and wastewater in major water utilities, coagulation and flocculation treatment using natural polymers can be an ecological and environmentally-friendly alternative to treat POME. In this study, the feasibility of applying natural seed gum and its derivative was investigated to treat POME by means of coagulation and flocculation processes as a sustainable alternative to ponding systems.
   
   The works which were conducted in the initial stage of research (Chapters 3 and 4) established and optimized the treatment of POME via coagulation-flocculation process using natural Cassia obtusifolia seed gum. Chapter 3 investigated the potential of C. obtusifolia seed gum as a natural coagulant in comparison with aluminium sulphate (alum) in treatment of POME. A series of batch experiments were performed under various factors: wastewater concentration, dosage of coagulant, initial pH of wastewater, settling time, slow stirring speed, and temperature. The removal of total suspended solids (TSS) and chemical oxygen demand (COD) were measured and used to assess the treatment efficiency. The findings of this study highlighted the negligible effect of wastewater temperature on the treatment efficiency when C. obtusifolia seed gum was used in comparison with alum. Based on the results, the recommended conditions to treat POME (TSS: 7500 mg/L) using C. obtusifolia seed gum were dosage, initial pH, and settling time of 1.0 g/L, pH 3, and 45 min, respectively. These treatment conditions enabled removals of TSS and COD up to 87 and 55%, respectively. After determining the key effects of the treatment process in Chapter 3, the influence of coagulant dosage and settling time on TSS and COD removals were optimized via response surface methodology. The treatment of POME using C. obtusifolia seed gum showed higher TSS (93.9%) and COD (61.2%) removals after undergoing optimization. In addition, the combined treatment using alum plus C. obtusifolia seed gum was examined and optimized to explore its synergistic effect on treatment of POME at natural pH (pH 4.8 – 5.0). The combined treatment using alum plus C. obtusifolia seed gum yielded high TSS and COD removals up to 81.58 and 48.22%, respectively using the following optimum conditions: alum dosage of 1.15 g/L, C. obtusifolia seed gum dosage of 2.47 g/L, and settling time of 35.16 min.
   
   To further improve the potential application of C. obtusifolia seed gum in the treatment of POME, a new derivative of the natural seed gum was developed in the following study (Chapter 5). Since POME contains countless colloidal particles which are negatively charged, the study was aimed towards developing a cationic C. obtusifolia seed gum with enhanced treatment capability. The natural seed gum was modified through an etherification process which leads to the substitution of reactive hydroxyl groups with cationic moieties from N-(3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC). The influence of cationic monomer concentration, catalyst concentration, reaction temperature, and reaction time were studied for the synthesis based on TSS and COD removals. The study showed that cationic C. obtusifolia seed gum, which was synthesized (at 50 °C and 5 h) using 19×10-3 mol of CHPTAC and 6×10-2 mol of sodium hydroxide (NaOH), removed 87% of TSS and 52% of COD from the POME. C. obtusifolia seed gum exhibited enhanced viscosity, higher magnitude of zeta potential (+6.41 mV) and changes in composition, thermal behaviour, and surface morphology after undergoing etherification.
   
   The final stage of this research (Chapter 6) optimized the treatment of POME using cationic C. obtusifolia seed gum. In addition, an integrated approach was investigated by employing ultrasonic technology to further assist coagulation-flocculation treatment of POME. The first stage of optimized coagulation-flocculation treatment required 0.4 g/L of cationic seed gum and 48 min of settling time. The performance of a subsequent coagulation-flocculation treatment using 0.22 g/L of cationic seed gum and 49 min of settling time was enhanced by the introduction of an ultrasound treatment lasting for 47 min at intensity of 49% prior to the subsequent treatment. Ultrasonic irradiation was found to improve subsequent coagulation-flocculation treatment by 27 and 3% in TSS and COD removals in comparison with unassisted and continuous coagulation-flocculation treatment. The overall study demonstrated the simple and effective use of modified natural polymers and ultrasonic-assisted coagulation-flocculation treatment systems to facilitate solid-liquid separation of POME.