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Dick published a classic paper in the mid-1970s illuminating popular final settling tank beliefs as folklore with little factual or logical support. Unfortunately, some of that folklore persists in an evolved form and new folklore developed along with technology development. Secondary clarifier folklore examined in this paper include: (1) scraper mechanisms outperform suction pickup mechanisms; (2) surface overflow rate accurately dimensions secondary clarifiers; (3) secondary clarifiers should not be used for sludge storage under any operating conditions; (4) solids flux theory and state point analysis does not predict secondary clarifier failure; (5) dye studies always indicate secondary clarifier deficiencies; (6) rectangular clarifiers outperform circular clarifiers; (7) flocculator center wells encourage density currents; and (8) the sludge volume index must be high to produce low effluent suspended solids.

The trickling filter solids contact (TF/SC) process is now over 20 years old, having been first demonstrated successfully in 1979 at Corvallis, Oreg. Design and operating concepts have evolved significantly since the first generation of plants. The purpose of this paper is to document the changes that have occurred since prior reviews. Data from four large plants (Santa Cruz, Littleton/Englewood, Central Valley, and Annacis Island) are used for illustration. The basis of the original peer reviewed U.S. EPA definition of the TF/SC process is reviewed. Pilot-scale and plant-scale research coupled with advanced analysis tools had allowed the overall horizons of the TF/SC process to be expanded, such that higher loadings have been obtained. For instance, use of modern plastic media has allowed the criterion that the majority of the biochemical oxygen demand be removed on the trickling filter while sustaining high total organic loadings. Owing to the features of the flocculator-clarifier and the superior thickening and compaction qualities of TF/SC solids, high solids loading rates can be obtained. As a result, current advanced designs occupy less footprint, and it is axiomatic that costs have been reduced. Furthermore, there is considerable potential to rerate, optimize, and debottleneck existing TF/SC plants to release low cost capacity.

The classification of chemical reactions based on shared characteristics is at the heart of the chemical sciences, and is well exemplified by Langmuir's concept of isovalency, in which 'two molecular entities with the same number of valence electrons have similar chemistries'. Within this account we further investigate the ramifications of the isovalency of four radicals with the same χ²Σ+ electronic structure -- cyano (CN), boron monoxide (BO), silicon nitride (SiN), and ethynyl (C2H), and their reactions with simple prototype hydrocarbons acetylene (C2H2) and ethylene (C2H4). The fact that these four reactants own the same χ²Σ+ electronic ground state should dictate the outcome of their reactions with prototypical hydrocarbons holding a carbon--carbon triple and double bond. However, we find that other factors come into play, namely, atomic radii, bonding orbital overlaps, and preferential location of the radical site. These doublet radical reactions with simple hydrocarbons play significant roles in extreme environments such as the interstellar medium and planetary atmospheres (CN, SiN and C2H), and combustion flames (C2H, BO). [ABSTRACT FROM AUTHOR]

The classification of chemical reactions based on shared characteristics is at the heart of the chemical sciences, and is well exemplified by Langmuir's concept of isovalency, in which 'two molecular entities with the same number of valence electrons have similar chemistries'. Within this account we further investigate the ramifications of the isovalency of four radicals with the same χ²Σ+ electronic structure -- cyano (CN), boron monoxide (BO), silicon nitride (SiN), and ethynyl (C2H), and their reactions with simple prototype hydrocarbons acetylene (C2H2) and ethylene (C2H4). The fact that these four reactants own the same χ²Σ+ electronic ground state should dictate the outcome of their reactions with prototypical hydrocarbons holding a carbon--carbon triple and double bond. However, we find that other factors come into play, namely, atomic radii, bonding orbital overlaps, and preferential location of the radical site. These doublet radical reactions with simple hydrocarbons play significant roles in extreme environments such as the interstellar medium and planetary atmospheres (CN, SiN and C2H), and combustion flames (C2H, BO). [ABSTRACT FROM AUTHOR]