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Showing posts with label Waste water Treatment. Show all posts
Showing posts with label Waste water Treatment. Show all posts

Wednesday, May 31, 2017

Waste water Treatment of BGP containing TAR


Tar Removal through Physical Processes Physical processes will continue to play a very important role for the successful commercial implementation of gasification. They constitute the basic arm for removing most of the raw gasifier contaminants, including “tar.” “Tar” is removed mainly through wet or wet-dry scrubbing. Coalescers, demisters, and cold filtration are also necessary supplements. These well-known commercial methods are easily designed and applied, depending on the specific needs of any gasification process. The main problem arising from “tar” scrubbing is that condensed “tar” components are merely transferred into another phase (water or solids such as scrubbing lime), which then has to be disposed of in an environmentally acceptable manner. The problems associated with the management of these wastewater or solid residues are summarized as follows: • “Tar” and “tar”-contaminated solid-waste streams are considered as a special waste; consequently, their disposal is usually cumbersome and costly. • “Tar”-bearing wastewater is usually a bi-phasic mixture requiring various steps of treatment before final disposal. Water insoluble “tar” skimming • Most water-soluble “tar” components are refractory to the usual biological wastewater treatments. The applied methods for “tar” and “tar”-containing waste streams include solid waste stabilization and landfilling, organic phase skimming off the bi-phasic wastewater-free surface, wastewater incineration, wet oxidation, adsorption on activated carbon, and final biological treatment. Wastewater contaminants include dissolved organics, inorganic acids, NH , and metals. 3 Typical values of COD, BOD, and phenols for wastewater from fixed-bed gasifiers are given in Hasler et al. (1997). The new BIOSYN design proposes a continuous skimming-off of insoluble “tar” from the surface of the wastewater. tar-containing wastewater was treated using lime and alum for the removal of in-organics, followed by adsorption on powdered activated carbon (PAC) for the removal of organics. At optimum concentrations, both lime and alum individually proved to be capable of removing color, total suspended solids (TSS) and total dissolved solids (TDS), but in both cases, pH adjustment had to be carried out after treatment. The combination of lime and alum at the dose ratio of 0.8:0.8 g/L was found to be optimum for the removal of inorganics. The removal efficiency achieved at optimum concentrations were 78.6, 62.0, 62.5 and 52.8% for color, alkalinity, TSS and TDS, respectively. Coagulation-precipitation followed by adsorption on PAC resulted in 92.3% chemical oxygen demand (COD) removal and 100% phenol removal at equilibrium. This technology may prove to be one of the fastest and most techno-economically feasible methods for the treatment of tar-containing wastewater generated from BGPs. biomass gasification plant.
The specific technical objectives of this study are: 1. Identify the optimum individual doses of lime and alum (coagulant) required to achieve the best treatment efficiency. 2. Identify the optimum and minimum dose of the coagulant-combination (lime and alum) required to achieve good treatment efficiency without having to conduct final pH adjustment. 3. Determine the efficiency of the coagulationflocculation process at optimum coagulant dosage followed by adsorption on powdered activated carbon (PAC). The iodine value of PAC was 1050 mg/g. The optimum dose of lime was found to be 0.8 g/L, with maximum removal efficiency for color, TSS and TDS, and minimum amount of sludge generation. The optimum dose of alum was observed to be 0.8 g/L with maximum TSS, TDS and minimum amount of sludge generation. However, the optimum dose of alum for maximum color removal was found to be 1.0 g/L. Lime was found to remove ammonia more efficiently than alum. In the lime-alum combination, lime:alum dose of 0.8:0.8 g/L was found to demonstrate maximum removal of TSS, TDS, alkalinity, and minimum amount of sludge generation. However, the lime:alum dose of 0.9:1.0 g/L provided maximum removal of color and ammonia. The coagulation-flocculation process was found to be more efficient for the removal of color, TDS, TSS and alkalinity than for the removal of COD and phenol.
CHARACTERISTICS OF EFFLUENT FROM BIOMASS GASIFICATION PLANT Parameter Unit Values pH -- 7.49 (±0.015) Color Co-Pt unit 1076.5 (±38.5) TDS mg/L 1875 (±75) TSS mg/L 82.5 (±2.5) Alkalinity (as CaCO3) mg/L 537.5 (±12.5) Ammonical Nitrogen mg/L 242.55 (±12.45) Nitrate nitrogen mg/L 0.62 (± 0.02) Phosphate (as PO4 3-) mg/L 0.12 (±0.03) CODtotal mg/L 3599.5 (±57.5) CODsoluble mg/L 3499.5 (±57.5) Phenol mg/L 465 (±10) Oil and Grease mg/L 36 (± 4.0) Note: Values in parenthesis are standard deviation