| Sewage treatment plant biological sludge dewatering is an important operation in wastewater treatment processes. The degree of sludge dewatering is directly related to the cost of disposal and the value of utilization. As an emerging technology of sludge dewatering, electro osmotic dewatering has many advantages compared with the traditional dehydration technology. But with the dehydration rate increases, the dehydration efficiency decreases and the energy consumption increases significantly because the sludge of the anode is becoming drying. Biodrying is based on bio energy as the only source of heat to dewater the sludge economically. But for the high water content of sludge, it will increase the cost and reduce the drying efficiency. The paper combines the respective advantages of the electro-dewatering technology and biological drying technology, to establish the system of “electro osmosis-biodring”, which makes sludge be dewatered quickly to the moisture content of 60-70% by electro-dewatering technology at first, then be dried by biodring technology. The paper summers the design essentials of “electro osmosis-biodring” system, which contains the design of process, drying tank, inlet and outlet, aeration, mixing and deodorization. Take the sludge after mechanical dewatering of Xianyang Road sewage treatment plant in Tianjin as the research target, to study on the optimization and characteristics of operating parameters.The influences of voltage and pressure on electro osmotic dewatering, current and energy consumption were investigated. The results show that the voltage has a positive correlation with the amount of water removing and current. 18 V was chosen as the best voltage, because the dehydration increased slowly when the voltage was higher than 18 V. Increasing the mechanical pressure can compact the sludge to enhance the effect of dewatering. But the excessive mechanical pressure would need higher bearing capacity of the equipment, and reduced the flow water passage in sludge. So we chose the mechanical pressure of 0.10 MPa in this experiment. The electro osmotic time should be 9 min because the speed of dehydration became slow significantly after 9 min.The study of the optimization of operation parameters of the bio-drying indicates that the products reflux play the role of microbial inoculation to reduce the start time of the bio-drying system. Conditioner will adjust the ratio of C/N and porosity, which makes the microbial activity more intense. And the reflux and conditioner added the higher ratio, the effect of drying is better. The temperature of treatment of turning per 48 h compared to 72 h recovered obviously. It shows that the pile should be turned when the temperature dropped first to reduce the inactivation effect of high temperature on the strain. The excessive ventilation rate would make the pile temperature too low, which weaken the water holding capacity of air. The low ventilation rate would make the less water removing due to the lower aeration rate. So the ventilation rate should be moderate. The temperature management of the bio-dying system can keep the microbial activity. And the heat generated by the microbial metabolic activity was fully used in the high temperature stage to evaporate moisture rapidly. The optimal operation parameters of the “electro osmosis-biodrying” system was: ventilation rate 0.08 m~3/(h·kg), mstraw: msludge=1:5, mreflux: msludge=1:5, 2d turning frequency, temperature control points 55 ?. The result of heat balance indicated that under the optimal condition the system ran normally, while the heat loss was more. Suggestions were given according to the heat balance. The results of control group confirmed that the sludge after electro osmosis is more suitable for biological drying than the sludge after natural drying. |
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