Sewage Sludge Dewatering Process Using Liquefied Dimethyl Ether as Solid Fuel

Abstract

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 liquid Finally, we estimated the input energy per kg of H 2 O 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.

Dewatering of Biomass Using Liquid Bio Dimethyl Ether

“…Future work should focus on developing a continuous DME dewatering system, similar to that of the group of Kanda et al [17][18][19][20] For comparison, a laboratory system where a continuous flow of DME was used has in fact been reported for dewatering of, e.g., sewage sludge, which also could be considered as a biomass sample [20] and for dewatering of coal. [19] That system consisted of several different vessels and a pressurized N 2 supply.…”

“…[19] That system consisted of several different vessels and a pressurized N 2 supply. [19,20] In the work by Oshita et al, [20] a storage vessel of liquid DME, an extraction vessel containing the sample to be dewatered, a storage vessel for the separated water and DME, a trap column for organic vapors and a condensation vessel for gaseous DME were used. [20] RESULTS AND DISCUSSION Figures 2 and 3 show optical microscopy images of wet and dewatered saw dust and wood chips, respectively.…”

“…1270 Ö HRMAN AND PETTERSSON assumption that equilibrium was not reached. In another work, Oshita et al [20] investigated the dewatering rate of sewage sludge and found that increasing the external area (by decreasing the diameter) of the sludge balls increased the dewatering rate. The diffusion path length will be lower for smaller sludge balls, in addition to increased contact area of sample and DME, resulting in an increased dewatering rate.…”

“…[19] DME has also been used for dewatering of sewage sludge, which can be considered as a biomass sample. [20] The DME dewatering process separates water in liquid form using liquid DME. Thus, the process differs from traditional technology based on drying where water is evaporated.…”

“…Approximately 15% of Sweden's industry heating can be related to drying, [22] of which a large portion is for drying related to bioenergy production. Different drying and dewatering techniques are described in references [12,20,[22][23][24][25] and drying techniques for production of second-generation biofuels have also been discussed. [12] Available drying technologies of woody biomass feedstock to a bioenergy plant have also been carefully reviewed.…”