Optimization of hybrid coagulation / flocculation-sand filtration system for decolourization of anaerobically digested palm oil mill effluent

• Main Author: Nasimah Asmuran
• Format: Thesis
• Language: English; English
• Published: 2015
• Subjects: TP670-699 Oils, fats, and waxes
• Online Access: https://eprints.ums.edu.my/id/eprint/40642/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/40642/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/40642/

The oil palm conventional biological ponding system was unable to fully decolourize the effluent due to the presence of lignin particles which are difficult to be biodegraded. The aim of this study is to propose coagulation/flocculation-depth filtration system as a pre-treatment for the decolourization of AnPOME. A non-toxic and biodegradable chemical i.e. calcium lactate was utilized as a coagulant/flocculants. During coagulation/flocculation studied, two types of condition had been conducted (i) calcium lactate as a destabilizer in a two tank system with an addition of different flocculant aids i.e. polydimethyldiallyl ammonium chloride (polyDADMAC), anionic polyacrylamide (APAM) and magnesium hydroxide. (ii) polyDADMAC as a destabilizer in a single tank system with an addition of different flocculant aids i.e. APAM, calcium lactate and magnesium hydroxide. The best combination had been identified at (i) 0.7 g/L of calcium lactate and (0.5-1.0) mg/L of APAM with ~64% of lignin removal. (ii) 8 mg/L of polyDADMAC and 6 mg/L of calcium lactate with ~68% of lignin removal. Based on removal and cost estimation studied, the combination of polyDADMAC and calcium lactate at a single tank system shown the best performance. To model and optimize the application of single tank system, an experiment was conducted using response surface methodology (RSM). Through a central composite design (CCD) method, the optimum pH, mixing speed, polyDADMAC dosage and calcium lactate dosage achieved were 6.66, 56.72 rpm, 5.27 mg/L and 2.78 mg/L, respectively. The optimum parameters had been investigated by varying the initial lignin concentration and additive, i.e. calcium chloride and ferric chloride. Different initial lignin concentration indicated different mechanism occured during coagulation/flocculation. While, calcium lactate can be used in replacement of traditional coagulants to be use with polyDADMAC. To enhance the performance of removal, the coagulated solution then was treated in a sand media. At 40 cm of sand bedheight and 767 m3/(d.m2) loading rate, lignin achieved 71% of removal. The used of new sand shows 12% lignin removal higher compared with the use of recycled sand. The effect of different initial lignin concentration could achieved until ~90% of lignin removal. To evaluate the whole pre-treatment system, the experiment was conducted by using the real anaerobically digested palm oil mill effluent (AnPOME). At single coagulation/flocculation-sand filtration system, AnPOME achieved ~74% of colour removal. Finally, an integrated system which consisted of 2 stages of coagulation/flocculation-sand filtration and 1 stage of sandash- sand filtration able to treat AnPOME and achieved ~97% colour, ~90% lignin and ~74% ammonia nitrogen removal, respectively for non-filtered sample. It can be concluded that coagulation/flocculation-depth filtration system with polyDADMAC-calcium lactate as hybrid coagulants in a single tank system was suitable to be applied in a pre-treatment for the decolourization of AnPOME.