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Treatment of Palm Oil Mill EffluentAn Insight by Green Wastewater Engineering Sdn Bhd (www.greenwastewater.com.my) (This article is published in Asia Palm Oil Magazine Vo.1 No. 1. April - June 2012) Decades into the history of modern palm oil milling, during which period much progress and breakthroughs have been made, it is still lamented that “New technology for effluent treatment is urgently needed to overcome the effluent problem.” [International Palm Oil Congress, PIPOC 2011 (CP19)]! This is a worrisome scenario and may be our last wake-up call to address the problem. Watercourse pollution has reached alarming levels with many rivers and river basins in the country being badly affected, impacting the livelihood of people and their habitation. Large quantities of mill effluent from the ubiquitous ponding system, of varying strength, end up in waterways unabated, year in year out. The pollution sources’ cumulative loads are probably close to or may have already exceeded the assimilative capacity or limits of rivers and other receiving water bodies. Unfortunately, a present shortcoming of the existing Regulation-based command-and-control environment monitoring strategy is its inability to adequately take cognizance of this fact. The initial massive destruction of organics in fresh POME from anaerobic digestion is critical to the production of an effluent that is more tractable and amenable to treatment downstream to achieve discharge compliance quality. Although we have come a long way in R&D on anaerobic reactors, including the so-called high-rate varieties, what is missing and most needed is a powerful digester which, when used alone or in a simple setup upfront of the ponding system, can drastically ameliorate the biological liquid train, thus holding out the possibility of purifying the final effluent using cost-effective and sustainable technologies. A net energy credit in the form of biogas plus environmental impact reduction (for both air and water) and a greater imprint of greenness, consequent upon the elimination of a lingering stigma, for the palm oil mill being the bonuses! It is necessary, perhaps, for us to take a cue from chemists with their expert views on the colloidal nature of POME and its treatment, to enable us to examine the subtler aspects of the design of truly high-end digesters. “Palm oil effluent can be considered as a colloidal system with high suspended solids. Colloidal particles consists of distinct types of disperse units apart from oil droplets, constituting the homogeneous phase that is distributed in the other homogeneous continuous or bulk phase. Suffice to say, these palm oil effluents are rather complicated in their colloidal behaviour.” “The effluents from palm oil mills are essentially colloidal in nature. Certain aspects of these effluents such as biochemical assay on the sludge solids, B.O.D. and C.O.D. are relatively well-investigated. However, their basic colloidal nature seems to have been overlooked. This is perhaps because the oil palm industry is urgently looking for an economically viable method for its effluent treatment in the shortest possible time; the more fundamental studies on the colloidal particles themselves are therefore of low priority or are even neglected altogether. From a colloidal chemist’s point of view, however, information on the characteristics of these disperse units are valuable in the understanding of their stability and hence in their subsequent treatment.” — From the Proceedings of a
Symposium titled “IMPROVING THE QUALITY OF LIFE IN MALAYSIA: THE ROLE OF
CHEMISTRY” – Kuala Lumpur 24-26 March 1977 (Organised by the Malaysian
Institute of Chemistry, INSTITUT KIMIA MALAYSIA)
We should seriously consider migrating to the ‘biomass retained reactors’ which operate on the ‘sludge immobilization’ principle which involves the sessile bacteria attachment to ‘thickened’ cellular biomass. This breed of reactors, which represents a major breakthrough in the development of newer anaerobic digesters, effectively delinks the solid retention time (SRT) from the hydraulic retention time (HRT), extending the former while greatly reducing the latter, thereby substantially increasing the concentration of bacteria in the reactor and leading to marked increased rates of conversion of organic materials to methane. [BIOTECHNOLOGICAL SOLUTIONS TO ENVIRONMENTAL PROBLEMS – Biochemical Engineering Division, Department of Chemical Engineering, University of Malaya, June, 1998] Reactor design and engineering which incorporates selective rheological appropriation to differentiate it from the quiescent fluid regime that is associated with this type of reactors, of which the UASB may be regarded as the forerunner, greatly facilitates the sequential breakdown of liquid film resistance for bacteria ‘bombardment’ and removal of the ‘colloidal barrier’, thereby accelerating the degradation process. The process of destabilizing the colloidal particles facilitates the growth of bacterial particles by charge neutralization (colloidal particles almost invariably carry an electrostatic charge, i.e. they have an excess or deficit of electrons compared with the neutral state, and thus their surfaces differ in potential from the bulk of the soluble substrate). Since entry of influent waste is at the inclined bottom of the reactor where concentrated sludge bed is present, this overcomes an inherent and major disadvantage of anaerobic microbial processes, which is the low biomass production and very slow rate of digestion. The propensity of bacteria, especially methanogen, to form self-immobilized granular structures is employed in the reactor. Lower loading rates and low strength wastes can, therefore, be accommodated with this type of reactor which if used in series, can circumvent the law of diminishing returns in anaerobic digestion and provide for a more mellow liquor for subsequent treatment by aeration where oxygen transfer through both surface renewal and diffusion through interfacial resistances is facilitated and end products of bacterial metabolism (the aerobic biosolids and the water content) will be more easily segregated and removed. It is important that Malaysia, being the Cradle of the palm oil industry, maintains her lead in the technological advancement of the industry. In the case of POME we should strive to raise the bar above the treat-to-discharge criterion to a higher level where the focus of treatment will move away from one of preserving public and environmental health at the end of the pipe and towards the recognition of the waste as a resource. With the spectre of a global water crisis looming, treatment of POME to a quality suitable for reuse in the mill will assuredly be a milestone achievement and contribution to the industry. |
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