Influence of the Pyrolysis Temperature on Sewage Sludge Product Distribution, Bio-Oil, and Char Properties

Fast pyrolysis may be used for sewage sludge treatment with the advantages of a significant reduction of solid waste volume and production of a bio-oil that can be used as fuel. A study of the influence of the reaction temperature on sewage sludge pyrolysis has been carried out using a pyrolysis centrifugel reactor (PCR) at 475, 525, 575, and 625 °C. Maxima of both organic oil yield of 41 wt % on a dry ash free feedstock basis (daf) and a sludge oil energy recovery of 50% were obtained at 575 °C. The water-insoluble fraction, molecular-weight distribution, higher heating value (HHV), and thermal behaviors of sludge oils were found to be considerably influenced by the applied pyrolysis temperatures. The sludge oil properties obtained at the optimal temperature of 575 °C were a HHV of 25.5 MJ/kg, a water-insoluble fraction of 18.7 wt %, a viscosity of 43.6 mPa s at 40 °C, a mean molecular weight of 392 g/mol, and metal concentrations lower than 0.14 wt % on a dry basis (db). Less optimal oil properties with respect to industrial applications were observed for oil samples obtained at 475 and 625 °C. Char properties of the 575 °C sample were an ash content of 81 wt % and a HHV of 6.1 MJ/kg db. A total of 95% of the sewage sludge phosphorus content was recovered in the char. The solid waste amount (char compared to sludge) was reduced to 52% on a bulk volume basis at the pyrolysis temperature of 575 °C

Comparison of Lignin, Macroalgae, Wood, and Straw Fast Pyrolysis

A fast pyrolysis study on lignin and macroalgae (nonconventional biomass) and wood and straw (conventional biomass) were carried out in a pyrolysis centrifugal reactor at pyrolysis temperature of 550 °C. The product distributions and energy recoveries were measured and compared among these biomasses. The fast pyrolysis of macroalgae showed a promising result with a bio-oil yield of 65 wt % dry ash free basis (daf) and 76% energy recovery in the bio-oil while the lignin fast pyrolysis provides a bio-oil yield of 47 wt % daf and energy recovery in bio-oil of 45%. The physiochemical properties of the bio-oils were characterized with respect to higher heating value (HHV), molecular mass distribution, viscosity, pH, density, thermal behaviors, elemental concentrations, phase separation, and aging. The lignin and macroalgae oil properties were different compared to those of the wood and straw oils with respect to carbon and oxygen contents, HHV, thermal behaviors, and mean molecular weight. The HHV of wood, straw, lignin, and algae oils were 24.0, 23.7, 29.7, and 25.7 MJ/kg db, respectively. The distributions of metals, Cl and S in char and bio-oil were investigated for the biomasses. Almost all the metals (Al, Ca, Fe, K, Mg, Na, P, and Si) were contained in the chars at the pyrolysis temperature of 550 °C. The char properties were characterized, and their potential applications are discussed