Browsing by Author "Samarathunga, IR"

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    item: Conference-Abstract
    Effect of Chemical Oxygen Demand (COD) to Sulfate (SO4-2) ratio on sulfate reduction in anaerobic digestion of sulfate rich wastewater
    Samarathunga, IR; Rathnasiri, PG; Hansaka, MAR; Kawinda, UGYS; Ananda, RYB
    Effluents discharged from some industries are both high in chemical oxygen demand. If sulfate is not treated up to the standards before discharging, it will contaminate with the surface or ground water bodies. Although sulfate does not cause any direct impact on the environment, biological transformation of sulfate under anaerobic conditions produces toxic hydrogen sulfide. There exists a competition between Sulfur Reducing Bacteria (SRB) and Methanogenic Bacteria (MB) for same available substrate. COD/SO4-2 ratio represents the fraction of electron flow for SRBs and MBs, which determines the sulfate reduction. This research study, investigates the influence of COD/SO4-2ratio on the performance of the sulfate reduction in anaerobic digestion. Laboratory experiments were conducted for high and low concentrations of substrate loading at COD/SO4-2ratioof 7 and 3. Total percentage sulfate reduction for high and low concentrated synthetic wastewater at same COD/SO4-2 of 7 and 3are 50.5%,48.9%, 24.8% and 4.8%respectively. The average sulfate reduction rates for high and low concentrations at COD/SO4-2 of 7 and 3 are 111 ± 11.1 mg/l/d and 55 ± 5.8 mg/l/d, 62 ± 5.4 mg/l/d and 10 ± 1.6 mg/l/d respectively. Experimental results indicated that percentage sulfate reduction is efficient at COD/SO4-2 of 7 than at 3 and rate of sulfate reduction is high in high concentrated influent than low concentrated influent, while the COD/SO4-2 is kept at a constant. Therefore when these results are commercialized, for sulfate rich wastewater treatment, precautions have to be taken to add sufficient amount of electron donors to maintain the COD/SO4-2ratio for complete sulfate reduction.
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    item: Conference-Full-text
    Effect of Influent Volumetric Loading of Skim Latex Wastewater on Anaerobic Sulfate Reduction
    (IEEE, 2021-07) Samarathunga, IR; Rathnasiri, PG; Adhikariwatte, W; Rathnayake, M; Hemachandra, K
    Wastewater generated in skim latex industry is rich in high sulfate concentrations, ammonia and protein. This research study investigates the effect of influent volumetric loading of Skim Latex Wastewater (SLW) on anaerobic sulfate reduction. Experiment was conducted using two semi-batch reactors operated under completely anaerobic condition. Operating volume and the temperature were 2.5 litre and 35 ±1°C respectively. This experiment was conducted in three phases VL01, VL02 and VL03 by feeding the reactor at 33.2 l/m 3 .d, 50.0 l/m 3 .d and 100.0 l/m 3 .d respectively. SLW contained influent COD/SO 4 −2 ratio of 2.7, whereas the influent COD/TKN (Total Kjeldahl Nitrogen) ratio was 10.1. Complete sulfate reduction was observed in all phases under anaerobic condition. However, the least average rate of sulfate reduction and overall percentage sulfate reduction was observed for the 100.0 l/m 3 .d. During this phase, anaerobic reactor showed symptoms of overloading, unstable and most affected with shock load. In VL03, time taken for complete sulfate reduction increased by 77.5% as a result of the high rate of ammonia formation. For SLW, sulfate degradation reduces at higher volumetric loading, but for moderate volumetric loading sulfate reduction was efficient, and ammonia inhibition could not be observed.
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    item: Conference-Abstract
    Effect of pH and external electron donor on mesophilic sulfate reduction during start-up of anaerobic digesters treating skim latex wastewater
    Samarathunga, IR; Rathnasiri, PG
    Effluent of skim latex industry contains high concentrations of sulfate, together with ammonia, protein and organic matter. This research study investigates the influence of pH and addition of external electron donor on improvement of sulfate reduction in anaerobic digestion under high ammonia concentrations, using Skim Latex Wastewater (SLW) during initial start-up period. Experiment was conducted using two 3- liter reactors fed semi continuously at 35 ±1 ̊C. The influent COD/SO4-2 ratio and the pH of real skim latex wastewater was 2.8 and 5.9 respectively. The experiment was conducted in three phases. During phase I and II, the pH of the reactors was not controlled whereas the influent pH of the sample was adjusted to 7, and influent pH was adjusted to 3 in phase III. The influent COD/SO4-2 ratio was 2.8 in phase I, while in phase II and III it was increased to 10 using acetate. In phase I, average sulfate reduction per cycle was only 33 ± 2 %. When the influent COD/SO4-2 ratio was increased to 10 using acetic acid during phase II, average sulfate reduction per cycle increased to 64%, but it gradually decreased to 30%, 8% and 0% within next three feeding cycles, this is because the pH of the anaerobic digesters increased steeply to 8.85 ± 0.3. Although sulfate reduction increased with addition of external electron donors such as acetate, according to results, the sulfate reduction was adversely affected due to free ammonia formation at the end of the phase II. Sulfur reducing bacteria (SRB) withstand high pH values as 8.8. Even though the anaerobic reactors inhibited, they did not completely fail. But when the Free Ammoniacal Nitrogen (FAN) of the system reached 679.5 ± 12.2 mg/l, the system completely inhibited. The completely inhibited sulfate reduction process was recovered by decreasing the pH of the digester by decreasing the pH of the influent feed sample to 3, while influent COD/SO4-2 ratio was at 10. Thus, sulfate reduction again increased in phase III. In the first cycle of phase III, after the low pH influent fed to the reactors, percentage sulfate reduction per cycle increased to 76%, decreasing the accumulated sulfate in the reactors. But within next three cycles of phase III, average sulfate reduction was 58 ± 3%. When the pH of the digester was controlled at 7.5, the FAN concentration was able to be maintained 92% lower. Thus, the system inhibition could be avoided by controlling the digester pH at 7.5 by controlling influent pH and enhancing sulfate reduction with increasing influent COD/SO4-2 ratio to 10.
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    item: Article-Abstract
    Investigation on Sulphide inhibition of anaerobic digestion for Sulphate rich wastewater
    Samarathunga, IR; Rathnasiri, PG
    Skim latex processing wastew iter is enriched with both organic materials and sulfates the environment as it is a nontoxic, non-volatile -Abstract: (SCV2). Sulfate does not cause any direct impact on and chemically inert compound. But biologinil transformation of sulfate under anaerobic conditions produces toxic sulfide, which inhibitory to ethanogenic microorganisms. Toxic, odorous and corrosive free hydrogen sulfide causes reduction in methane yield, significant reduction in overall treatment efficiency or complete failures in anaerobic process. According to the case study conducted, anaerobic reactor of skim latex processing wastewater treatment facility is evaluated.Its daily - wastewater generation is 100m3/day and the average COD and the BOD levels are 5,000 mg/1 and •1000 mg/1 respectively. The COD/SOp2 of the feedstock is 6.25. Although the expected efficiency of the reactor is 50%-80%, the actual COD removal efficiency is only 42% due to sulphide inhibition. Therefore, conventional anaerobic treatment cannot be applicable to skim latex wastewater without taking sufficient precautions to minimize sulfiti 2 inhibition and hydrogen sulfide emission. Microaeration is proposed as an option for treatment c: sulphate rich wastewater.