Sewage Sludge Dewatering Process Using Liquefied Dimethyl Ether as Solid Fuel

Dewatering of sewage sludge is an essential step required to obtain a dry solid that can be used as a fuel. We, therefore, focused on a method to remove water from sewage sludge by using dimethyl ether (DME) as an extractant, which liquefies under moderate pressures at room temperature; it is primarily applied to dewatering low-grade coal with high water content. This study evaluated the applicability of the DME dewatering method to sewage sludge cakes by using a DME flow-type experimental apparatus.It was found that sludge cakes could be dried absolutely under a linear velocity of 0.48 m/h and a liquid DME-sludge ratio of over 115 mL/g. It became clear that a high dewatering ratio was achieved by increasing the liquefied DME/sludge ratio and lowering the liquefied DME linear velocity.As the liquefied DME/sludge ratio increased, the content of volatile total solid (VTS), fixed total solid (FTS), Hydrogen, Nitrogen and other metal in dewatered sludge did not decreased, but carbon content in dewatered sludge decreased slightly. And the total organic carbon (TOC) concentration in separated liquid increased significantly. Therefore, when DME dewatering process is introduced to existing wastewater treatment plant, it should be necessary to pay attention to organic load of TOC in the separated liquidFinally, we estimated the input energy per kg of H2O removed from the sludge: Es, in the both the DME dewatering method and the conventional drying method. In the calculation result, Es of DME dewatering process is a third of Es of direct drying process as conventional method.