Sorption and Release of Organics by Primary, Anaerobic, and Aerobic Activated Sludge Mixed with Raw Municipal Wastewater

Abstract

New activated sludge processes that utilize sorption as a major mechanism for organics removal are being developed to maximize energy recovery from wastewater organics, or as enhanced primary treatment technologies. To model and optimize sorption-based activated sludge processes, further knowledge about sorption of organics onto sludge is needed. This study compared primary-, anaerobic-, and aerobic activated sludge as sorbents, determined sorption capacity and kinetics, and investigated some characteristics of the organics being sorbed. Batch sorption assays were carried out without aeration at a mixing velocity of 200 rpm. Only aerobic activated sludge showed net sorption of organics. Sorption of dissolved organics occurred by a near-instantaneous sorption event followed by a slower process that obeyed 1st order kinetics. Sorption of particulates also followed 1st order kinetics but there was no instantaneous sorption event; instead there was a release of particles upon mixing. The 5-min sorption capacity of activated sludge was 6.5±10.8 mg total organic carbon (TOC) per g volatile suspend solids (VSS) for particulate organics and 5.0±4.7 mgTOC/gVSS for dissolved organics. The observed instantaneous sorption appeared to be mainly due to organics larger than 20 kDa in size being sorbed, although molecules with a size of about 200 Da with strong UV absorbance at 215–230 nm were also rapidly removed.

Nitrogen Removal From Municipal Wastewater Using a Two‐Sludge Denitrification/Nitrification Batch Reactor: Performance and Mechanisms

“…In addition, the PHA in the sludge did not increase. Therefore, the sorption of organics by sludge flocs was a physical‐chemical process, which was consistent with previous studies . Moreover, NO 3 − ‐N in the three flasks did not decrease, indicating that the reduction of NO 3 − ‐N was based on the denitrification, but not the sorption process.…”

Introductory Chapter: Biosorption

“…For the modeling and optimization of processes using sorption on the activated sludge, the necessary is knowledge about the sorption of organic matter to the sludge. Modin et al [47] compares primary, anaerobic, and aerobically activated sludge as biosorbent materials. Biosorptive capacity values were determined, process kinetics was studied, and some characteristics of sorbed organic matter were studied.…”

Nonoxidative removal of organics in the activated sludge process

“…There is no clear definition of what each term mean. For example, many researchers refer to organic compounds passing through a 0.45-μm pore size filter as being soluble or dissolved whereas compounds retained by the filter are called particulate (e.g., Jorand et al., 1995 ; Modin et al., 2015 ). Another method for defining soluble compounds was developed by Mamais et al.…”

“…The commonly used mathematical models developed by the International Water Association (IWA) for activated sludge processes assume that slowly biodegradable organic matters such as particles and colloids are instantaneously sorbed to the activated sludge flocs (Henze et al., 2000 ). However, research has shown that not all particulate organics are sorbed (Alexander et al., 1980 ) and the process could be described using both instantaneous sorption and first-order kinetics (Jorand et al., 1995 ; Modin et al., 2015 ). Several studies have shown that sorption primarily affects the colloidal and particulate fraction of the wastewater organics (i.e., >0.001 µm) (e.g., Bunch and Griffin Jr., 1987 ; Jimenez et al., 2005 ).…”