Whole-Plant Simulations for Two Pure-Oxygen Activated Sludge Plants in San Francisco

Sierra, Natalie; Huang, Guohe; Jones, B.; Velasco, A.; Haddad, Djamel; Chan, Rick L.; Chu, Irene; Feng, Yu; Jolis, Domènec

doi:10.2175/193864706783779302

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“…With predicted sea‐level rise, municipal wastewater treatment plants situated along coastal areas will be impacted by saltwater intrusion problems, which will negatively affect mixed liquor settling characteristic as measured by increased SVI. State point analysis of secondary clarification (Sierra et al., 2006) clearly demonstrates the dependence of the activated sludge process efficiency on the ability of mixed liquor to separate from wastewater. Poor settling characteristics require the secondary system to operate at low solids inventory to keep the clarifier operating rate below the gravity flux and avoid any detrimental effects on effluent quality.…”

Section: Addition Of Cacl2 and Naclmentioning

confidence: 99%

Effect of saltwater intrusion on activated sludge flocculation

Berde

Jolis

2020

Water Environment Research

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Saltwater addition negatively impacted the settling properties of the activated sludge in a sequencing batch reactor, which in turn caused the effluent quality and the dewatering properties to deteriorate. Experiments showed that increasing sodium ion concentrations above 1 meq/L interfered with bio‐flocculation by ion exchange of calcium ions displaced by sodium in mixed liquor flocs, causing increases in the sludge volume index, total suspended solids, and chemical oxygen demand concentrations of the final effluent and in the times of the time to filter test of the mixed liquor. Experiments were also conducted to reverse mixed liquor de‐flocculation by adding calcium ions in wastewater with different sodium chloride concentrations and a positive relationship was found between calcium ion added and improved effluent quality. Calcium ion concentrations above 1.6 meq/L proved to be beneficial for adhesion of microbial aggregates leading to the formation of stable flocs and improved sludge dewatering by reversing the ion exchange phenomenon observed with sodium concentrations above 1 meq/L. Monovalent‐to‐divalent ratios did not provide predictive information on de‐flocculation. Hence, individual ion concentrations in addition to monovalent‐to‐divalent cation ratios are important in the onset of de‐flocculation effects while a system‐specific concentration threshold was measured under which no adverse effects were observed. Practitioner points The adverse effects of varying concentrations of sodium chloride on the biological process affecting bioflocculation and effluent quality. Impact of sodium on the health of the mixed liquor as well as on dewatering processes. Prediction of sea level rise due to climate change will impact utilities situated along the coast with saltwater intrusion problems. Management of dewatered flows containing saltwater from onsite construction Identify management practices to reduce the impact of saltwater on the wastewater treatment plant.

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Section: Addition Of Cacl2 and Naclmentioning

confidence: 99%