Drying of Activated Sludge Under Partial Vacuum Conditions—An Experimental Study

Abstract

A typical wastewater treatment system in a pulp and paper mill in Finland treats wastewater both mechanically and biologically. Sludges resulting from these processes have to be disposed of. One possible way of doing this is to incinerate them with solid fuel in the power plant of the mill. To minimize the amount of sludge and to make the use of the sludge energy efficient, it has to be dried before incineration. Mechanical drying of the sludge from biological wastewater treatment is difficult to carry out. Using secondary energies may provide a competitive way of arranging drying: a method of doing this by using partial vacuum evaporation to utilize the low temperature secondary heat in sludge drying is under development. A laboratory study to examine the behavior of activated sludge ORDER REPRINTS under partial vacuum evaporation conditions was carried out using a laboratory rotating evaporator to analyze the drying of activated sludge from three mills at 40-80 C boiling temperatures. This article presents the results from the tests. These are promising; it was possible to reach high dry solids content. Also, no boiling point temperature rise was detected, fouling of the evaporator seemed low and easily avoidable, condensate from the evaporator weas relatively clean and returnable to the processes of the mill.

Pretreatment of recycled paper sludge with a novel high-velocity pilot cyclone: Effect of process parameters on convective drying efficiency

“…Sludge dewatering is generally managed by centrifuges, filters or various pressing machines, which however are unable to remove intracellular and chemically bound water present in the sludge suspensions [6,7]. Hence, although mechanical dewatering has been seen as http://dx.doi.org/10.1016/j.apenergy.2014.06.057 0306-2619/Ó 2014 Elsevier Ltd. All rights reserved.…”

“…Wastewater treatment processes generally consist of mechanical primary treatment by, e.g., gravity settling followed by secondary treatment using chemical or biological methods [1,4,6]. In the case of paper recycling, recycled fibers are potentially deinked depending on the characteristics of the raw material and subsequently pulped after which residual fibers unsuitable for further utilization are separated.…”

Response surface optimization of a novel pilot dryer for processing mixed forest industry biosludge

“…The original axial distance of sludge feeding rate (5/3), and included first-order and second-order terms in the E fan model, resulted in more stable variance behaviour around the design centre, which can be seen in the more symmetric shapes of the E fan contours ( Figure 6). Optimization of a novel pilot dryer for mixed biosludge M. Mäkelä and P. Geladi According to the acquired model results, the presented cyclone technology shows promise for energy efficient drying of mixed sludge using secondary energies potentially available in industrial environments [11,35]. 10-fold higher than that of the DSC model, which significantly increased the size of confidence intervals relative to actual predicted values (Figures 4 and 6).…”

“…Sludge is generally dewatered by centrifuges, filter or various pressing machines, which are, however, unable to remove intracellular and chemically bound water present in the sludge suspensions [4,5]. Sludge is generally dewatered by centrifuges, filter or various pressing machines, which are, however, unable to remove intracellular and chemically bound water present in the sludge suspensions [4,5].…”

“…As evaporation temperature is a function of prevailing pressure, potential low-temperature secondary energies are best utilized for sludge drying under partial vacuum conditions [11]. Hippinen and Ahtila [11] used a rotary laboratory evaporator coupled to a vacuum pump to dry activated sludge under partial vacuum with evaporation temperatures of 40-80°C.…”