Study The Effect Of Reflux On Performance Of Scar Reactor Treating Printing And Dyeing Wastewater

Printing and dyeing wastewater is one of the largest pollution sources among variousindustries. According to incomplete statistics, there is about300~400million tons of dyeing andprinting wastewater produced in China every day. Dyeing and printing wastewater hasperformances of high pollutant concentration，heavy chromaticity color and changes of quantityand quality．Therefore, it is important to find efficent processes dealing with printing and dyeingwastewater with the advantages of simple operation, inexpensive operating cost and high removalefficiency.In this paper, the influence of effluent recycle on SCAR treatment of printing and dyeingwastewater was studied by adjusting the water recirculation flow and the optimal reflux ratio wasdetermined. The characteristics of anaerobic granular sludge in the SCAR reactor were analyzedunder different reflux ratio. And the influence of wastewater biodegradability by SCAR wasinvestigated by a biological contact oxidation device treating SCAR effluent water.The experimental results showed as follows:(1)The effect of reflux on performance of SCAR was investigated when the HRT was13.5hand the average volume loading rate of this system was4.1kg CODCr/(m3·d). The results showedthat the average removal rate of CODCrwas the highest when the reflux ratio was3and4, whilethe reflux ratio has small effect on the removal efficiency of PVA because of its hardbiodegradation properties. The condition of NH3-N concentration(generally200~600mg/L) hasno negative effects on the microbial activity in the reactor. The methanogenic metabolism and thehigh concentration of ammonia nitrogen generated in the reactor ensured the system usually keptalkalescent environment. The pH value of effluent was relatively higher than that of the inflowand the VFA in the system did not appear to accumulate.(2)SCAR reactor could achieve good effect on color removal and the removal rate peaked atabout70%when the reflux ratio of SCAR anaerobic reactor was4. Because of the hydrolyticacidification of the microorganisms, dyes in wastewater was decomposed into organic compoundssuch as conjugated double bonds or aromatic ring in the reactor and UV254of reactor effluentwater was increased. Reflux ratio not only strengthened the transfer function in the system but alsoaffected the distribution of microbial populations in the reactor. Both better mass transfer effect ofhydraulic conditions and more efficient distribution state of microbial populations were importantto the degradation of SCAR reactor for organic compound.(3)SCAR reactor also achieved obvious effect on improving the biodegradability of wastewater and created good conditions for the subsequent aerobic microbial degradation oforganic compounds. The biological contact oxidation device had the best removal effect on theeffluent of anaerobic reactor when the reflux ratio of SCAR anaerobic reactor was4. After thetreatment of SCAR reactor, B/C values of wastewater had a obvious increasing and the averagegrowth of value was0.16. Then the CODCrremoval rate changed at around50%, the averageremoval rate of PVA was37%.(4)During the experiment, the anaerobic granular sludge in the system presented black ovalor spherical, clear boundary, dense structure, smooth surface, and the average VSS/SS was0.7.The largest proportion of the granular sludge was medium size with diameter of2~3mm underdifferent reflux ratio. The particle size distribution was stable when the reflux ratio was3and4.The sedimentation velocity of granular sludge increased with the increasing of size. At the end ofthe experiment, the average particle size of the granular sludge was2.16mm and the averagevelocity was62.78m·h-1. In the course of the experiment, the content variation of coenzyme F420was similar to the dehydrogenase activity. In addition, the removal rate of CODCrwas closelyrelated to the dehydrogenase activity and the coenzyme F420concentration. The protein content inthe granular sludge had a growing trend with the progress of the experiment, while the content ofpolysaccharide changed little. The content of protein was higher than that of polysaccharide(PN/PS were greater than1) in EPS on the total amount of it. Then protein was the maincomponent of EPS in the anaerobic granular sludge, and PN/PS increased gradually over time.