Study On The Pwerformance Of Egsb For Anaerobic Bioiogical Treatment Tapioca Starch Wastewater With Cyanide

Tapioca starch wastewater containing cyanide is considered as a category of organic pollutants with the widest distribution and the largest effect which has become one of the most urglen problems to be resolved in the water treatment area in GuangXi Zhuang Autonomous Region.The anaerobic biological treatment is one of the most widely used wastewater treatment technologies at present. It is also a main technology to treat tapioca starch wastewater harmlessly in China. Expended granular sludge blanket (EGSB) reactor is suitable for many kinds of wastewater. It is a new kind of highly effiecient anaerobic biological treatment reactor which was developed based on UASB reactor over the past10years and is worthy of promotion. However, cyanide in tapioca starch wastewater have an inhibition on anaerobic microorganisms and can have a great impace on the anaerobic process. Therefore, further investigation and effective improvement on treatment technologies of tapioca starch wastewater should be of significance to control freshwater pulltion. In this study, the Expanded Granular Sludge Bed (EGSB) was used to treat tapioca starch wastewater containing low concentration of cyanide. Under the conditions of13.4h of HRT, the influence of cyanide concentration on the startup and stable operation of EGSB reactor was researched through the control of chemical oxygen demand (COD) and cyanide concentration in the influent, the performance of EGSB was assessed through the variation of COD, pH, alkalinity, volatile fatty acids (VFA) and methane variation during the process. In order to quantify the influence of cyanide on organic pollutants removal and to provide basic information reference for the engineering application, the inhibition kinetics of cyanide in anaerobic treatment of tapioca starch wastewater was investigated. The results were summarized as follows:During the startup period of EGSB reactor, cyanide had an inhibition on anaerobic microorganisms of the granular sludge in EGSB reactor, some operating rules in the EGSB reactor vary with the concentration of cyanide, the higer reactor volume loading rates, the more remarkable in inhibitory effects. Furthermore, the reactor required longer recovery period as the cyanide dosage tumed higher. When the feeding cyanide concentration was5mg·L-1, the reactor showed a good performance of biological treatment, with the removal rate of COD reached90%, biogas production reached approximately200mL·d-1, the influent VFA maintained blow the concentration of200mg·L-1. The removal rate of COD as well as biogas production decreased when the cyanide concentration increased to around10mg·L-1. However, removal rate of COD the production of biogas gradually recovered only in a few days. When cyanide concentration was increased from10to15mg·L-1, COD removal rate was decreased to70.4%, the production of biogas was affected drastically, the influent VFA maintained around700mg·L-1, VSS/TSS decreased from0.7618to0.7278, SMA decreased from946.00mLCH4·g-1VSS-1·d-1to196.94mLCH4·g-1VSS-1·d-1, indicating that the anaerobic sludge activity was decreased, in accordance with the obvious damage of the bacteria located in the inner part of some granules.The results showed that, during the process of maturation, some operating rules in the EGSB reactor vary with cyanide. When10mg·L-1of cyanide concentration was fed, the performance of biological treatment was still satisfactory, the removal rate of COD stayed at90%; when the cyanide concentration was increased around15-20mg·L-1, the removal rate of COD decreased with the increasing of cyanide concentration, and it decreased to70.1%by at the70th day; while the influent VFA was increased, the higher cyanide concentration, the more VFA was accumulated; when the cyanide concentration was increased to around20mg·L-1, the influent VFA was increased to around550mg·L-1and SMA decreased to83.19mLCH4·g-1VSS-1·d-1drastically. Furthermore, the methane production dropped to a value of105mL·d-1; pH of the medium varied in the range of7.8-8.5during the treatment of tapioca starch wastewater with the variation of cyanide concentration, and the influent shown slightly alkaline.Further investigation on inhibition kinetics of cyanide in anaerobic process for the treatment of tapioca starch wastewater showed that:cyanide inhibition complied with with the non-competition model,which can be written as q=qmaxS/Km+S·K1/K1+(I-6).The model parameters were estimated by non-line regression method,parameters were obtained and the value was determined as: qmax,Km and KI were1.6535mgCOD·d-1.mg-1VSS-1,793.1753mgCOD·L-1and15.5950mgCN-·L-1,respectively.The experimental data verification for the model equation is satisfactory.