Research On Aerobic Biodegradation Of Vegetable Tanning Agents

In the leather production process, vegetable tanning agents can not be absorbedcompletely by the leather, the remaining part will be discharged with the tannerywastewater. Because the chemical structures of the major components of vegetabletanning agents are complex, they are difficult to be degraded by microorganisms. Andthen a large number of studies have shown that vegetable tannins take a broad-spectruminhibitory effect on microorganisms, so the tannery wastewater rich in vegetable tanninshave strong biological toxicity, discharging directly to the environment will causeserious environmental problems. The studies about the biodegradation of vegetabletannins are still not much, which mainly focus on the hydrolytic tannin. While thestructures of vegetable tannin agents are complex, the biodegradation mechanisms arenot yet clear. The study of vegetable tannins biodegradation will not only bring benefitsto the treatment of tannery wastewater, but also the preparations and applications ofvegetable tannins degradation products, such as catechin, ellagic acid and gallic acid.The biodegradation of the vegetable tanning agents is a process that themicroorganisms secrete a variety of enzyme to decompose the vegetable tanning agentsfor their growth. In this paper, the activated sludge was used as the source ofmicroorganisms to research the biodegradability of four kinds of vegetable tanningagents, of which the chestnut tanning agent belongs to hydrolytic tanning agent, thequebracho tanning agent, wattle bark tanning agent, betel nut tanning agent belong tocondensed tanning agent. In the paper the conditions of Folin-Ciocalteu colorimetrywere optimized by orthogonal test and the Folin-Ciocalteu colorimetry was used todetermine the concentrations of vegetable tanning agents, then the standard curves ofthe concentration and absorbance of the four kinds of vegetable tanning agents wasdrawn. The removal efficiency of vegetable tanning agents can be determined by thechange of absorbance according to the curve of the concentration and absorbance ofvegetable tanning agents.In this paper, the optimal conditions for biodegradation of vegetable tanning agentswere studied, the results showed that the optimal conditions for biodegradation: pH=6.0, temperature30℃. The paper took a preliminary study by agar dilution method onthe antibacterial properties of four kinds of vegetable tanning agents, and thecomprehensive evaluation of the biodegradability of four kinds of vegetable tanning agents were made by the BOD₅/COD and kinetic constants. Studies have shown thatchestnut tanning agent is degradable organic matter, while the remaining threecondensed tanning agents were difficult to be degraded. The quebracho tanning agentwas the most difficult to be degraded, the wattle bark tanning agent was in the secondplace, and the betel nut tanning agent was easier to be degraded. The biodegradability offour kinds of vegetable tanning agents related to the chemical structures of their majorcomponents.In the paper the effects taken by glucose and phospholipids fatliquor as theco-substrate on biodegradability of the four kinds of vegetable tanning agents werestudied, the results showed that glucose and phospholipids fatliquor can both promotethe biodegradations of the vegetable tanning agents.The phospholipids fatliquorimprove the biodegradation rate of the vegetable tanning agents obviously than glucose.These two easily degradable organic matter can both increase the removal efficiency ofthe four kinds of vegetable tanning agents, the efficiency of phospholipids fatliquor wasbetter than that of the glucose. The promoter action to the more difficult degradabletanning agent was more obvious, phospholipids fatliquor could enhanced the removalrate of quebracho tanning agent as high as40.997%. The paper raised a hypothesis onthe biological degradation pathways of the condensed tanning agents with theco-substrate, which the condensed tannins were mainly degraded by the iron-sulfurprotein and the role of polyphenol oxidase system.