Co-Pyrolysis of Sewage Sludge and Wetland Biomass Waste for Biochar Production: Behaviors of Phosphorus and Heavy Metals.

Ilham Gbouri,Junxia Wang,Xutong Wang,Beibei Yan,Xiaoqiang Cui,Yanjun Hu,Fan Yu,Guanyi Chen

doi:10.3390/ijerph19052818

Abstract

Large amounts of sewage sludge (SS) and wetland plant wastes are generated in the wastewater treatment system worldwide. The conversion of these solid wastes into biochar through co-pyrolysis could be a promising resource utilization scheme. In this study, biochar was prepared by co-pyrolysis of SS and reed (Phragmites australis, RD) using a modified muffle furnace device under different temperatures (300, 500, and 700 °C) and with different mixing ratios (25, 50, and 75 wt.% RD). The physicochemical properties of biochar and the transformation behaviors of phosphorus (P) and heavy metals during the co-pyrolysis process were studied. Compared with single SS pyrolysis, the biochar derived from SS-RD co-pyrolysis had lower yield and ash content, higher pH, C content, and aromatic structure. The addition of RD could reduce the total P content of biochar and promote the transformation from non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP). In addition, co-pyrolysis also reduced the content and toxicity of heavy metals in biochar. Therefore, co-pyrolysis could be a promising strategy to achieve the simultaneous treatment of SS and RD, as well as the production of value-added biochar.

Highlights

Sewage sludge (SS) is a byproduct of wastewater treatment plants (WWTPs) consisting of a considerable amount of inorganic nutrients [1]
Sewage sludge generated from WWTPs contained some toxic substances such as heavy metals, polycyclic aromatic hydrocarbons, and pathogenic microorganisms, which could increase the risk of secondary pollution [5,6]
Sewage sludge was obtained from a wastewater treatment plant with a daily processing capacity of 30,000 m3 located in Tianjin, China, where an anaerobic-anoxic-oxic (A2 /O) system was operated for the residential wastewater treatment

Summary

Introduction

Sewage sludge (SS) is a byproduct of wastewater treatment plants (WWTPs) consisting of a considerable amount of inorganic nutrients (i.e., phosphorus, nitrogen, and potassium) [1]. The annual generation amount of sewage sludge in China has reached approximately 39.04 million tons in 2019 with a moisture content of up to 80%, and more increases are expected in the few years based on economic and population growth [2,3]. Sewage sludge has good potential to be applied to agricultural lands as it can improve soil fertility and promote organic carbon storage [4]. Sewage sludge generated from WWTPs contained some toxic substances such as heavy metals, polycyclic aromatic hydrocarbons, and pathogenic microorganisms, which could increase the risk of secondary pollution [5,6]. The common disposal methods of sewage sludge include landfill, incineration, and land application [7]. Landfill and land application have been restricted due to the poisonous leachate and limited soil area, while incineration is limited by high operational cost and emission of hazardous gases [8]. Pyrolysis (the process of thermochemical decomposition of organic matter under anoxic conditions) is a promising alternative as it can

Methods

Results

Conclusion