Investigation of organics and ammonium adsorption by activated sludge

The activated sludge process is one of the most important parts of conventional wastewater treatment plants. Wastewater is treated biologically in activated sludge basins. Activated sludge can remove soluble contaminants, primarily organics compounds and nitrogen, from the wastewater stream. The activated sludge is a mixture of microorganisms, inorganic and organic compounds aggregated to flocs. Nitrogen and organics can be removed from wastewater by oxidation or physical adsorption by activated sludge. Physical adsorption of organics and nitrogen by activated sludge takes place as soon as the wastewater has contact with the sludge mixture. The purpose of this thesis is to investigate the adsorption ability of different activated sludge. Three sequencing batch reactors (SBR) were operated in order to produce different kinds of activated sludge mixtures. Reactor one and two were fed with carbon source compound and reactor three was fed with nitrogen source compound. It was found that the flocs properties were changing significantly in these three reactors during three months of operation. The sludge in reactor three had finer and smaller flocs in comparison with the sludge in reactor one and two. Due to the different feed compounds, the dominant community of bacteria inside reactor one and two were heterotrophic bacteria and the major bacteria community in reactor three were nitrifying bacteria. The adsorption tests were conducted for the sludge mixtures of reactor one, two and three with glucose, ammonium, and milk powder as model compounds. Sodium azide was used to inhibit bacterial oxidation during the adsorption tests. The results showed that the sludge in reactor one was more capable of removing glucose and ammonium from synthetic wastewater. On the other hand, sludge in reactor three could remove higher concentration of milk powder in the first minutes of mixing in comparison with sludge in reactor one and two. Furthermore, the adsorption rate per unit of time for different adsorption tests show that higher concentration of organic and nitrogen were removed in the first minutes of contact in comparison with the next hours of mixing.