Optimizing drying of municipal dewatered sludge using heat-assisted microorganisms and pig manure addition: A process and economic analysis

Abstract

Sludge drying is an important pretreatment step for municipal dewatered sludge (MDS) treatment and disposal, but the time-consuming and high cost of existing processes have hindered the development of MDS treatment and disposal. In this study, a novel sludge drying technology was proposed on the basis of the characteristics and treatment needs of MDS in China. Pig manure (PM) addition and multisource heat assistance together assisted hyperthermophilic bacteria in achieving rapid drying of MDS. Mechanical factors were optimized via orthogonal experiments, and the optimum PM addition ratio was determined. The relationship between energy input (generation) and output in the system was explored to reveal the reasons why the novel drying technology exhibited superiority. Compared with the traditional biological drying technique and the thermal drying technique, the novel technique has the advantages of high efficiency, time savings and low cost. After 24 h of drying, the moisture content, organic matter content and net calorific value on an air-dried basis (Q_{net, V,Mad}) of the dried products were 31.43 ± 0.91 %, 72.47 ± 1.89 % and 16.94 ± 0.35 MJ/kg, respectively, which met the requirements of heat recovery and utilization for subsequent thermal treatment. The energy input (generation) to the system exceeded the energy output, indicating that the drying process was positively spontaneous. Multisource heat assistance accounted for 81.6 % of the total generated (input) energy, and 86.43 % of the energy was used for moisture evaporation, indicating high energy utilization of the drying system. In addition, cost savings of US $11.46–16.84/ton (¥83-122.10/ton) were achieved when MDS was treated via the novel drying technology. Overall, the novel drying technology proposed in this study provides feasible, efficient and cost-saving pretreatment technology and ideas for MDS treatment and disposal engineering.