| Polyformaldehyde(POM) is an high-performance engineering plastics widely used in automobile, medical equipment, agricultural machinery and military industry. The POM wastewater contained formaldehyde, s-Trioxan(TOX) and so will cause cancer and deformity, and is very hard to bio-degradation, which have great harmful effect on environment. A few studies about the treatment of POM wastewater were found and most of them focus on the process of Fenton oxidation, lime pretreatment, iron-carbon micro-electrolysis, and electric flocculation and so on. While the bioaumentation process with the advantage of mature technology, better treatment effect, small running expense and convenient management gain popularity. The formaldehyde and TOX will restrain the metabolism of microorganism thus make it hard for biological treatment. The bioaugmentation by the addition of strains which can metabolise target toxic pollutants such as formaldehyde and TOX and so on make it feasible for the effective biodegradation of POM wastewater.A strain(referred as Q1),which could utilize s-Trioxane(TOX) as sole carbon was isolated from the sediment in the equalization basin of a Polyoxymethylene WWTP and was identified as Bacillus methylotrophicus according to 16 S rDNA sequences analysis.Studies showed its optimized degradation was acquired as following:pH=7, T=30? at the rotate speed of 180r/min in incubator.The degradation effeceincy on TOX could reach 64.8% when the NaCl concentration is between 1% and 3%,while the metabolism on TOX was restrained and removal percentage slump to 32.7% and 7.1% when NaCl concentration rise up to 4% and 5% respectively. The TOX concentrations also have great effect on B. methylotrophicus. Degradation effeceincy is over 92.7% when TOX concetntation is between 100 mg and 400mg/L.And the percentage falled to almost 0 while its concentration gradually rose to 1600mg/L, which means the concentration reach the limit of upper tolerance. Study about the strains combination showed that the group constructed with B. methylotrophicus and Js(could metabolize formaldehyde) in the proportion of 2:1 is the optimal one(referred as FB) which got the greatest COD removal efficiency, and can be applied to the later research on the bioaugmentation in a pilot-scale reactor.Pilot-scale bioaumentagion research simulating the aerobic process of a POM wastewater treatment plant revealed that the formaldehyde, TOX and COD in effluent below 4mg/L, 10mg/L and 120mg/L respectively when the formaldehyde, TOX and COD in influent were170~250mg/L, 140~240mg/L, 1000~1600mg/L,and its reduction rate can reach to 97.8%,94.2% and 92.6%, respectively. Although formaldehyde degradagion rate is correspond with the plant, the COD and TOX reduction ability of the system rise to 9 and 10 times of the WWPT respectively which were not enhanced by strains and the pilot-scale system even showed greater stability when facing shock loading.The B. methylotrophicus was not found in original sludge, and was rooted in the system even became a dominant strain after bio-augmentation based on the polymerase chain reaction-temperature gradient gel electrophoresis technique(PCR-TGGE), thus the reactors gain high capability of TOX degradation, and the dominance of B. methylotrophicus did not change much even the system suffered the shock load. There are also synergy and antagonism between B. methylotrophicus and Proteobacterium sp., Pseudomonsa putida, Rhodpseudomonas sp. and so on., which combined with the variation of Shannon-wiener Index of sluge in different periods showed that B. methylotrophicus is indispensible in the maintenance of microbial community structure and diversity, and thus have the system gain high ability of degradation to formaldehyde, TOX, COD in POM wastewater. |
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