Research On Electro-dewatering For The Sewage Sludge In Ring Electric Field And Device Development

With the steady growth of sludge production in our country and the gradually improvement of sludge disposal regulations, we need to use some economic and effective sludge depth dewatering methods in order to achieve the sludge disposal standards prescribed by the state. Sludge electro-dewatering technology is a kind of sludge depth dewatering technology and has some advantages such as highly efficient rapid dehydration and adding no reagents, etc. It causes the attention of the scholars.In this paper, we aim at the problems of the existing sludge electro-dewatering devices such as the complexity of the devices and the difficulty of continuous operation. To improve the sludge electro-dewatering devices, we put forward the ring electric field sludge electro-dewatering device. This device has some advantages such as simple, easy operation and can realizing continuous running electro-dewatering, etc. Experiments use mechanical dewatering sludge in municipal sewage treatment plant as research object, to study the sludge dehydration in the ring electric field electro-dewatering device under the static and dynamic running state and to text the dewatering performance of the device. We should determinate the basic property index of the electro osmosis filtrate and analyze the energy consumption of the device and operating costs at the same time.Static dewatering experiment on the ring electric field sludge electro-dewatering device shows that: the power supply voltage gradient and the residence time of sludge dewatering are concerned with the static electro-dewatering effect. Considering the electro-dewatering effect and the energy consumption, we determine the optimal operating conditions for static sludge electro-dewatering: the power supply voltage gradient chooses 40 V/cm(sludge thickness is 1 cm always), the residence time of sludge electro-dewatering chooses 9 min. In this condition, the sludge moisture content reduces from 84.5% to 68.1% and the volume reduces by more than half, the unit taking-off water weight of wet sludge is 510 kg per ton and the unit energy consumption of wet sludge treatment is 109.2 kWh per ton.Dynamic dewatering experiment on the ring electric field sludge electrodewatering device shows that: the power supply voltage gradient, the power supply form and the residence time of sludge dewatering are concerned with the dynamic electro-dewatering effect. Considering the electro-dewatering effect and the energy consumption, we determine the optimal operating conditions for dynamic sludge electro-dewatering: the power supply voltage gradient chooses 50 V/cm(sludge thickness is 1 cm always), the power supply form chooses intermittent form and the residence time of sludge electro-dewatering chooses 5 min(the sludge pressure is 0.04~0.1MPa and the length of the electro-dewatering unit is 30cm). In this condition, the sludge moisture content reduces from 77.4% to 51.0% and the volume reduces by 53.9%, achieving the purpose of sludge deep dewatering. By the calculation, the energy consumption treating unit wet sludge is 117.6 kWh per ton, the energy consumption of unit dewatering is 0.218 kWh per kilogram and the operation cost is 107.6 Yuan per ton.Some properties of electro osmosis filtrate are determined in the experiment. The results show that: the electro osmosis filtrate is alkaline with the pH value of 10~12, the COD concentration is 1200~1600 mg per liter, the TN concentration is 150~230 mg per liter and the Carbon-Nitrogen ratio(COD/N) is 6.6~7.7. Electro osmosis filtrate after electro-dewatering belongs to wastewater with low Carbon-Nitrogen ratio. If we use the traditional biological denitrification technique to deal with it, we need to add some carbon source form outside.