Activated sludge influent and effluent from five municipal wastewater treatment plants were analyzed to further elucidate the roles of aluminum, iron, and the monovalent to divalent cation ratio (M/D) on the influent and effluent characteristics of the systems. The size distribution of organic nitrogen, organic carbon, protein, humic acid, and polysaccharide was examined with respect to the concentration of cations in the activated sludge influent. It was found that the majority of organic nitrogen, organic carbon, protein and polysaccharides were found in material larger than 0.45μm in activated sludge influent. Humic acids were mostly found in material smaller than 0.45μm. Protein was the largest contributor to organic nitrogen and humic acids were the largest contributor to organic carbon. Using 0.45μm as a division between particulate and soluble material, the ratio of soluble to particulate material in activated sludge influent was found to be negatively correlated with the ratio of iron to aluminum.

In activated sludge effluent, the majority of the organic nitrogen and protein was found in material larger than 0.45μm, while the majority of the organic carbon, humic acid, and polysaccharide were found in material smaller than 30kDa. Influent aluminum concentration had no observable effect on the concentration or distribution of organic nitrogen or organic carbon. Influent iron appeared to play a role in the flocculation of organic nitrogen and protein containing material between 0.45μm and 1kDa in size. A high monovalent to divalent cation ratio appeared to play a role in deflocculating organic nitrogen containing material larger than 1.5μm and increased the concentration of TOC smaller than 1kDa and the total polysaccharide concentration. Tertiary depth filtration removed all organic nitrogen and protein in material larger than 0.45μm, but a poor job of removing organic carbon from and an inconsistent job of removing polysaccharide from effluent

Eight lab-scale activated sludge reactors were also run, but the data was not consistent enough for analysis and comparison with the municipal wastewater treatment plants. This thesis contains a series of four papers that each deal with a different aspect of the role of cations on activated sludge influent and effluent. The first paper focuses on activated sludge influent characteristics, the second on effluent organic nitrogen and organic carbon, the third on effluent EPS, and the last on the lab-scale reactors. The papers were divided in this way because of the unique analytical obstacles that were encountered with each set of data.