Monitoring of methylated naphthalenes in sludge-derived pyrogenic carbonaceous materials

Abstract

Methylated analogues of polycyclic aromatic hydrocarbons (PAHs) represent important environmental contaminants produced often at process of feedstock thermochemical conversion. In the present study, we determined and compared levels of 1-methylnaphtalene and 2-methylnaphtalene in municipal sewage sludge (MSS), sludge-derived pyrogenic carbonaceous materials produced at 350 °C (PCM350) and 500 °C (PCM500) in process of slow pyrolysis. The highest extraction efficiency of both aromatic structures from MSS, PCM350 and PCM500 for toluene as extraction agent and 36 h of extraction time was revealed. The total concentrations of 1-methylnaphtalene reached values 8.7 mg/kg for MSS, 14.6 mg/kg for PCM350 and 18.1 mg/kg for PCM500.2-methylnaphtalene was quantified in concentrations 12.5 mg/kg for MSS, 19.3 mg/kg for PCM350 and 23 mg/kg for PCM500. Available levels of 1-methylnaphtalene and 2-methylnaphtalene determined by Tenax resin desorption test during 36 days showed decreasing trend in order PCM500 > PCM350 > MSS. In summary, pyrolysis treatment of sewage sludge can increase total amount of methylated PAHs in produced carbonaceous materials but decrease their available forms. This fact can contribute to global ecotoxicological assessment of organic pollutants in biochars and pyrogenic carbonaceous materials applied in agronomy as soil amendments.

Keywords: 1-Methylnaphtalene; 2-Methylnaphtalene; Organic pollutants; Pyrolysis; Sewage sludge.