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Case Study I: Application of the Divalent Cation Bridging Theory to Improve Biofloc Properties and Industrial Activated Sludge System Performance—direct Addition Of Divalent Cations
Author(s) -
Higgins Matthew J.,
Tom Lou Ann,
Sobeck David C.
Publication year - 2004
Publication title -
water environment research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.356
H-Index - 73
eISSN - 1554-7531
pISSN - 1061-4303
DOI - 10.2175/106143004x141933
Subject(s) - chemistry , effluent , divalent , dewatering , calcium , wastewater , activated sludge , settling , suspended solids , magnesium , chemical oxygen demand , industrial wastewater treatment , pulp and paper industry , chromatography , inorganic chemistry , nuclear chemistry , environmental engineering , organic chemistry , environmental science , engineering , geotechnical engineering
The objectives of this study were to examine the application of the divalent cation bridging theory (DCBT) to improve settling, dewatering, and effluent quality in pilot‐scale reactors and a full‐scale system treating an industrial wastewater. This was accomplished by lowering the monovalent‐to‐divalent (M/D) cation ratio by direct divalent cation addition. Research has shown that the M/D ratio is a potential indicator for settling and dewatering problems at wastewater treatment plants, and M/D ratios above 2 have been associated with poor settling, dewatering, and effluent quality. The M/D ratio of the wastewater in this study ranged from 6 to 20. The cations studied were calcium and magnesium. Results showed that the addition of calcium improved floc properties compared to control reactors with no calcium addition. The reductions in sludge volume index, effluent chemical oxygen demand (COD), and effluent total suspended solids (TSS) were approximately 35, 34, and 55%, respectively, when the M/D ratio was decreased to approximately 2:1. In addition, the cake solids from a belt filter press simulator increased by 72% and the optimum polymer dose required forconditioning was reduced by 70% in the reactor fed the highest calcium concentration when compared to control reactors with no calcium addition. The addition of calcium also decreased the negative effect of high filamentous organism numbers. In general, the addition of magnesium (Mg 2+ ) had similar effects on effluent quality and dewatering properties, although some differences were measured. A full‐scale test using calcium addition was performed. Measurements of effluent quality and floc properties were performed before, during, and after the calcium (Ca 2+ ) addition period. The average M/D ratio during these periods was 6.2, 4.6, and 14.0, respectively. The addition of Ca 2+ decreased the effluent five‐day biochemical oxygen demand, effluent TSS, and effluent COD. The increased Ca 2+ concentration also improved dewatering measured by a decrease in specific resistance to filtration and capillary suction time. Overall, the addition of divalent cations to the pilot‐ and full‐scale activated sludge systems improved floc properties and the data fit well with the DCBT.