Characterization of Oily and Non-Oily Natural Sediments in Palm Oil Mill Effluent

Hindawi Publishing Corporation Journal of Chemistry Volume 2013, Article ID 298958, 11 pages http://dx.doi.org/10.1155/2013/298958 Research Article Characterization of Oily and Non-Oily Natural Sediments in Palm Oil Mill Effluent Reem A. Alrawi,1 Nik Norulaini Nik Ab Rahman,2 Anees Ahmad,3 Norli Ismail,1 and A. K. Mohd Omar1 1 Environmental Technology Division, School of Industrial Technology, Universiti Sains Malaysia, 11800 George Town, Malaysia School of Distance Education, Universiti Sains Malaysia, 11800 George Town, Malaysia 3 Division of Analytical and Environmental Chemistry, Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India 2 Correspondence should be addressed to A. K. Mohd Omar; Received 21 June 2012; Revised 16 October 2012; Accepted 17 October 2012 Academic Editor: Ali Nokhodchi Copyright © 2013 Reem A. Alrawi et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Palm oil is one of the many vegetable oils widely consumed around the world. e production of palm oil requires voluminous amount of water with the concurrent generation of large amount of wastewater known as palm oil mill effluent (POME). POME is a mixture of water, oil, and natural sediments (solid particles and �bres).ere is a dearth of information on the physical properties of these POME sediments. is study intends to distinguish the physical properties of oily and non-oily POME sediments which include sediment size, particle size distribution (PSD), sediment shape, sediment surface morphology, and sediment density. ese characterizations are important for future researches because these properties have signi�cant effects on the settling process that occurs either under natural gravity or by coagulations. It was found that the oily and non-oily POME sediments have different sizes with nonspherical irregular shapes, and because of that, the aspect ratio (AR) and circularity shape factors were adopted to describe the shapes of these sediments. e results also indicate that the density of oily POME sediment decreases as the sediment size increases. 1. Introduction Raw palm oil mill effluent (POME) is a thick, brownish, highly concentrated, and colloidal slurry with pH ranging from 4.0 to 4.5. It contains mainly water (95-96%), suspended solids (2–4%), and oil (0.6-0.7%) [1]. Freshly discharged POME has temperature between 80 and 90∘ C. Palm oil production process does not utilize any chemical; hence, POME is considered as non-toxic wastewater. e chemical characterizations of POME that include biochemical oxygen demand (BOD), chemical oxygen demand (COD), total solids (TSS), oil and grease (O and G) and other chemical properties are shown in Table 1 [2]. Many studies are focused on raw POME physicochemical treatments like sedimentation by coagulation and �occulation [3], adsorption [4], electrocoagulation [5] and membrane �ltration [6], and they characterized the raw POME in their studies. But there is no information about the physical properties of the suspended solids (or can be called natural sediments) that exit in the raw POME and play an important role in the separation processes like sedimentation, �ltration and separation processes by the membrane. Allen (2003) mentioned that the particle settling behaviour is dependent on the particle density, particle morphology (shape, texture, etc.), size and particle size, distribution [7]. e most natural particles in industrial processes are nonspherical and irregular in shape which means it is impossible to accurately describe their sizes [8]. e size determination of the natural particles is considered a difficult task, and to overcome this, various approaches are suggested to determine their average diameter such as sieving and microscope image analysis [9]. Furthermore, there is a relationship between the average particle diameter and its shape. is can be done by multiplying the mean diameter by the shape factor to obtain the equivalent diameter [10, 11]. Bouwman et al. [12] de�ned the shape factor as a number which could characterize the particle’s shape, and it is derived from a microscopic image of the particle. Many different shape factors are being used in 2 Journal of Chemistry T 1: Chemical properties of palm oil mill effluent (POME). Property Range pH BOD COD Oil and grease 4.15–4.45 21,500–24,500 45,500–65,000 ∗ 1077–7582 Property Total nitrogen Suspended solid Total solid Total volatile solids Range 300–410 15,660–23,560 33,790–37,230 27,300–30,150 Unit for all parameters is mg/L except pH. previous studies to describe the particles, such as Corey shape factor (cfs) [13], aspect ratio (AR) [9], circularity [9], new projection shape factor, Stokes’ shape factor, and new roughness factor [12]. It was reported that the AR and circularity shape factors are suitable to describe the particle’s shape in different aspects [14]. Particle aspect ratio is expressed by the ratio of the maximum diameter to minimum diameter, and the �bre aspect ratio is expressed by the ratio of mean length to the mean diameter. On the other hand, the circularity shape factor is based on the projected area of the particle and the overall perimeter [12, 15]. Another important property is the particle density which plays a signi�cant role in the particle settling rate combined with the �uid density. Actually, the particle settling depends on the difference between particle and �uid densities. e volume determination of non-spherical irregular natural sediments can be done directly by either pycnometer or by a liquid or a gas sample displacement [16]. e objectives of this study were to investigate the main physical properties of oily and non-oily natural sediments in raw POME. ese properties include particle size, particle size distribution (PSD), particle density, and particle surface morphology. In addition to these properties, this study examines the suitability of aspect ratio (AR) and circularity shape factors to describe the POME particles and �bres. e output of this characterization is considered as a source material for future researches because these properties play an important role and more signi�cant impact on the separation processes like sedimentation, �occulation, �ltration and separation process by membrane. 2. Experimental 2.1. Separation of Oily and Non-Oily Sediments from Raw POME. Raw POME was allowed to naturally settle for 24 to 48 hours to obtain POME sludge. e upper clear layer “supernatant” was drawn out by a pump, and the bottom layer “POME sludge” was taken and dewatered using �bre materials with pore openings <20 𝜇𝜇m. e dewatered POME sludge was freeze-dried completely using a freeze dryer (Model LABCONCO, USA) to get oily POME sediments. A portion of the oily POME sediments was treated with n-hexane (C6 H14 , min 99.0%, QReC) in a Soxh (...truncated)