Influence of cations on activated-sludge effluent quality

Laboratory experiments and field tests were conducted to determine the effe ct of inorganic cations. on effluent from activated-sludge systems. Laborat ory experiments showed that monovalent cations tend to, increase the concen tration of solution biological polymers (biopolymers), whereas divalent cat ions tend to retain the biopolymers in the floe. Biopolymers in solution af fect effluent chemical oxygen demand (COD). Coagulation tests were performe d on the effluent with ferric chloride. Ferric hydroxide can coagulate prot ein through possible adsorptive interactions and may be responsible for som e biopolymer retention in the floes. In the field study, it was found that sodium ions in the influent wastewater caused an increase in proteins, and polysaccharides in solution, thereby increasing the effluent COD concentrat ion of the treated municipal wastewater. The attachment or release of these microbially derived organic biopolymers and recalcitrant influent substrat e may depend on the monovalent-to-divalent cation ratio and the concentrati on of iron. Modeling of effluent organics in the activated-sludge process, can be enhanced through incorporation of concepts that take into account th e partitioning (between floe and solution) of microbial biopolymers and inf luent recalcitrant substrate.