Study On Cattle Manure Wastewater Treatment By Using The Integrated Thermophilic Anaerobic Digestion-SBR-Flocculation Process

The pollution of the dejection wastewater discharged from breed farms become severely and needed to be solved urgently in China. Based on the characters of the wastewater, the technology of thermophillic anaerobic digestion-SBR-flocculation was studied to treat them in this paper. Not only the reproducible energy was obtained but also the environmental pollutions were treated, it has important social and economic benefits.The thermophilic anaerobic digestion of cow manure wastewater was the kernel part of this paper. In order to make the biochemistry reaction running smoothly and quickly, the inocula used in the experiments were selected and cultivated firstly, and the effects of the inocula's species, the cultivating conditions etc on the process of the wastewater thermophilic anaerobic digestion were discussed. Results showed that the anaerobic digestion reaction inoculated with the inocula cultivated with mixed sludge start up more quickly, biogas production more steady and last longer than that of the anaerobic digestion inoculated with inocula domesticated with single sludge, and the pH was more steady, COD removal efficiency higher too.On the basis of the effects of inocula on the biochemistry's reaction, the selected incula was adopted and the effects of temperature, COD concentration and trace elements were studied. Results indicated that the temperature has greater impact on the system's operation. The biogas production, the percentage of methane in the biogas (63%) and the COD removal efficiency (57%) of thermophilic anaerobic digestion were higher than that of room temperature.There wre some effects of COD concentration on the biogas production. With the increasing of COD concentration, total biogas production increased, while the biogas produced by per-unit quality of COD was decreased. The addition of trace elements had little effect on the lower COD concentration wastewater, but it could improve the treatment efficiency of higher COD wastewater. The appropriate quantity of Fe²⁺, Mg²⁺ or Ni²⁺ was about 0.5 mmol/L to the higher COD wastewater.Combined with the results of thermophilic anaerobic digestion of cow manure wastewater, a kinetics equation based on the Stover-Kincannon model was obtained with the maximum reaction rate constant U_max as 13.18 gCOD/(L_溶液·d) and the saturation constant K_b as 13.77 gCOD/(L_溶液·d). In the same way, the maximum constant of methane production rate (M_max=18.11 L_gas/(L_溶液·d)) and coefficient of methane yield (M_b= 49.31 gCOD/(L_溶液·d)) were obtained too by studying the dynamics of the methane production rate. These research results have very important theoretical significance on the design and operations of anaerobic digestion reactor.The concentration of COD, suspended substance were still higher than that of the discharge standard after the wastewater was treated by thermophilic anaerobic digestion and the SBR made by ourselves was used to treat them furthermore. The cultivation of popular active sludge and granular sludge, the COD removal efficiency of the two types sludge, the factors that affect the disposal efficiency of popular active sludge and the SBR kinetics were studied in this stage. Results showed that the SBR have a certain ability to resist the impact of organic loading rate when the COD concentration ranged from 0.5 g/L to 1.6 g/L. Both of the two types sludge have high removal efficiencies on organic compounds of the wastewater. The difference between them was that the suspended substance was lower, the removal efficiencies of COD and TKN a little higher of the water treated by granular sludge than that of treated by popular active sludge. In addition to that, the kinetics equation of SBR was established based on the actual situation of treating the effluent of the cow manure wastewater treated by the method of thermophilic anaerobic digestion.Because the water treated by SBR still contained lots of celluloses and other tiny suspended substances, a process of flocculation as the secondary treatment was adopted to decrease the color, the suspended substances and the organic compounds concentration. The effects of the coagulant categories, dosage of coagulant, stirring speed, stirring time and settlement time were investigated, and the better flocculation conditions were obtained as coagulant dosage 1.5 g/L, stirring speed 120 r/min, stirring time 2.5 min and settlement time 20 min. After being treated under these conditions, COD concentration lower than 400 mg/L, suspended substance about 144 mg/L and the color about 50.Not only the reproducible energy was obtained but also the ideal treatment effects of cow manure wastewater were obtained by the process of thermophilic anaerobic digestion combined with SBR and flocculation. The COD, suspended substances and color all met the discharge standard of water pollutants for farm breeds (GB18596-2001) after being treated by this method. A new integrated technology and theoretical basis were provided for the treatment of the similar wastewater.