Abstract
Chemical conditioning has been used for enhancing wastewater sludge dewaterability for many years, but the characteristics of odorous pollutants emission in sludge conditioning were still unclear. In this work, the transfer behavior of different odorous pollutants between air, liquid and solid phases under typical chemical conditioning processes for high-pressure dewatering was systematically investigated. The results indicated that that besides hydrogen sulfide (H2S) and ammonia (NH3), 21 kinds of volatile organic contaminants (VOCs) were identified and quantified by gas chromatography-mass spectrometry (GC-MS), while the concentrations and composition of odorous pollutants varied greatly for different conditioning processes. VOCs were composed by three main constituents including benzenes, halogeno benzene and hydrocarbons. According to mass balance analysis, about 50% of VOCs adsorbed within sludge extracellular polymeric substances (EPS) fraction. Since EPS was damaged and/or flocculation in different chemical conditioning processes, VOCs distributed in solid phase transformed into liquid phase and then released into air. The discrepancies in mass of odorous pollutants before and after chemical conditioning were likely to be related to chemical conversion under acidification, oxidation and precipitation in the presence of ferric ions.
Highlights
With development of urbanization and growth of population, huge amount of sludge is produced in municipal wastewater treatment
It was reported that addition of inorganic coagulants could eliminate the negative surface charge of the sludge particles by charge neutralization and interparticle bridging, resulting in particle destabilization and aggregation, they were not able to break extracellular polymeric substances (EPS) and reduce bound water in sludge flocs[14]
This study indicated that a large amounts of odorous pollutants (H2S, NH3 and volatile organic contaminants (VOCs)) were released a under different conditioning processes
Summary
With development of urbanization and growth of population, huge amount of sludge is produced in municipal wastewater treatment. Microorganisms in sludge system are highly active, inorganic salts, organic matters and microorganisms in sewage sludge might break down into a variety of small molecules and volatile gas in the wastewater and sludge treatment process. These gaseous contaminants were easy to release into air environment, disturbing healthy and normal lives of residents around wastewater treatment plant (WWTP)[1,2,3]. EPS accounts for 60–80% of the mass of waste activated sludge, they play important roles in the removal of pollutants from wastewater, bioflocculation, settling and dewatering of activated sludge[18,19,20]. Advanced treatment processes were developed to destroy sludge EPS fractions and convert the bound water within sludge flocs into free water[25, 26]
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