Browsing by Author "Wijekoon, SLJ"
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- item: Conference-Extended-AbstractDesign of an industrial scale biofiltration system(2009) Wijayawardhana, AJ; Wijekoon, SLJ; Walpolage, S; Amarasinghe, ADUSAn industrial scale waste gas treatment system was designed and constructed at a Tobacco Processing Factory. The treatment system consisted of three units namely: condenser, scrubber and bio fdter, the latter acting as the major unit of the system. The major constituents of the foul smelling gas were found to be ammonia ( 400 — 500 ppm (v/v)) and hydrogen sulfide (> 100 ppm (v/v)). Complete removal of hydrogen sulfide and 95% removal of ammonia were achieved.
- item: Thesis-AbstractOptimization of the effluent treatment system (anaerobic/aerobic) for rubber industry by kinetec modelingHettiarachchi, IU; Wijekoon, SLJRaw rubber processing factories generate large amounts of wastewater containing organic pollutants & various process chemicals. Factory effluents exhibit high BOD (Biochemical Oxygen Demand) & COD (Chemical Oxygen Demand) concentrations, ammonia & suspended solids that are amenable to biological treatment methods. Rubber Research Institute (RRI) of Sri Lanka developed a novel & cost effective biological effluent treatment technique for rubber-processing effluents discharged by crepe rubber & centrifuged latex factories. Treatment system, based on high rate anaerobic digestion coupled with aerobic stabilization also consists of settling & sand filtration. The main feature of this technique is the use of a low cost, septic tank type anaerobic digester filled up with coir fibres for the attachment of useful microorganisms for effective biological conversion. Biological kinetic expressions have been derived for the design & control of effluent treatment plants where aerobic digestion is used commonly as the only treatment method. The kinetic coefficients in these expressions are widely used in design calculations. For a specified waste, a given biological community & a particular set of operating conditions the kinetic coefficients are fixed, Kinetic coefficients used for the design of domestic effluent treatment plants cannot be applied for the design of industrial effluent treatment plants as the waste composition & biological communities involved are different. Also kinetic coefficients for the anaerobically pretreated wastewater could be very different to those of the raw wastewater even for the same type of waste. No kinetic study has been carried out yet for the RRI developed treatment process for making possible improvements & modifications for optimal operation & performance of the aerobic treatment system to reduce, capital, operational & maintenance costs under low loading conditions. The objective of this study is to find out the kinetic coefficients required for the design of activated sludge process from anaerobically pretreated rubber industry wastewater. The obtained values of kinetic coefficients were used to model an existing treatment system. A pilot-scale continuously aerated stirred tank was used as a model reactor. Reactor was operated without a recycle stream & fed with a steady flow of anaerobically pretreated wastewater obtained from a full-scale rubber industry effluent treatment plant. Samples were taken for five different runs at five different mean-cell residence times (). BOD & MLVSS (Mixed Liquor Volatile Suspended Solids) of each sample for each run were measured according to Standard Methods for the Examination of Water & Wastewater. The following kinetic coefficients were estimated by a graphical method using measured data & the standard kinetic expressions. • Y = cell yield coefficient • kd= cell decay coefficient • Ks = half-velocity constant • k = maximum substrate concentration per unit mass of microorganisms • μm = maximum specific growth rate). The obtained kinetic.coefficients show significant differences to those of domestic wastewater reported in literature. Maximum substrate concentration per unit mass of microorganisms (k) is less than one-half of the corresponding value for domestic wastewater. This implies more than double the concentration of microorganisms is required to be maintained in the aeration tank than that for domestic wastewater. Half-velocity constant (Ks) is more than double the concentration of the corresponding value for domestic wastewater. It implies that the microorganisms have high affinity to anaerobically digested substrate. This could be expected because most anaerobically digested intermediate products & end products are considered good substrates for heterotrophic organisms. The cell yield coefficient (Y) is comparatively higher & the cell decay coefficient (kd) relatively lower than those for domestic wastewater leading to a higher μm. maximum specific growth rate. Therefore a richer microorganism concentration could be expected in the aeration tank. Obtained kinetic coefficients were used to model an existing activated sludge treatment system. The minimum mean-cell residence time calculated with the obtained kinetic coefficients lead to a value of O. 9 (d) with a safety factor of 3.33 & is within the accepted range for plant operation (2 - 20). Sludge washouts are very unlikely due to the fulfillment of the condition >1/ μm indicating a good waste stabilization. Calculations revealed significant difference between the predicted & operated condition of the plant. The obtained kinetic coefficients were used to optimize the plant operation by estimating sludge recirculation rate, aeration rate & sludge production rate. The findings will help improve the treatment system design & reduce the associated costs.
- item: Article-AbstractPerformance of peat/wood chips media as a biofilter packing material for the treatment of an industrial waste gas(2016-05-24) Wijayawardhana, AJ; Wijekoon, SLJ; Walpalage, S; Amarasinghe, ADUSA study was conducted to evaluate the removal efficiency of NH3 and H2S emitted from an industrial waste gas source by bio-filtration with peat/ wood chips media (50/50 (v/ v)) as a bio filter packing material. A pilot plant testing was carried out using peat samples from Muthurajawela, Sri Lanka and wood chips in the size range of 5 mm to 25 mm. The void age of the packing material was in the range of 50-70%. The experiments were carried out over an effective bio filter operational period of 45 days under intermittent loading (8 hours on weekdays only). Thin film micro sensors capable of sensing an array of industrial pollutants were used in measuring the concentration of NH3 and H2S in the contaminated air stream and found to be in the range between 43-90 ppm and 70-100 ppm, respectively. Results indicated that 100% removal efficiency of NH3 and H2S can be achieved for peat/wood chips medium. The maximum elimination capacity for NH3 was 5.59 gm^h1 and the H2S maximum elimination was 6.99 gm^lr1. The study was conducted as a preliminary evaluation of the suitability of peat/ wood chips media as a packing material for an industrial scale bio filter for the treatment of the same waste gas stream.
- item: Conference-Extended-AbstractStudy on the suitability of cation selective membrane and the effect 011 current density for electrodialitic removal of heavy metal joils(2003) Dissanayaka, DMDOK; Jaaweera, MW; Gunawardhana, WDDH; Wijekoon, SLJHeavy metal pollution of the environment is a major environmental problem facing the modem world. Their persistence in the environment and the difficulty in removal from wastewaters make them available for aquatic and terrestrial fauna. This would enable the transfer of heavy metals up in the food chain causing severe damages in the higher organisms due to bioaccumulation.