The integrated fixed-film activated sludge (IFAS) process has been widely used in the upgrading of wastewater treatment plants (WWTPs). The oxygen transfer efficiency (αOTE) is of great significance to the design and operation of the IFAS process. The carrier filling ratio (CFR) and aeration type are two critical factors affecting αOTE and standard oxygen transfer efficiency (αSOTE). However, the distribution and changing laws of αOTE and αSOTE in the full-scale IFAS process areunclear. To optimize the operation of a WWTP and to improve the αOTE of the aeration systems, several off-gas tests were conducted under different aeration types and different CFRs. The results show that for the aerobic tank investigated (the ratio of length and width was 8:1), the αOTE and the αSOTE of the middle of the aeration systems were higher than those of the other two sides. However, the reason for the low αOTE at the beginning and the end of the tank may be different. Coarse-bubble aeration systems had a lower αOTE and almost the same oxygenation capacity (αSOTE) as the fine-bubble aeration systems under constant CFR (43%). The average αSOTE (18.7–28.9%) of the hybrid aeration systems increased with increasing CFR (7.7–57.7%), and different locations exhibited different degrees of change. The results reveal the distribution and changing law of the αOTE of aeration systems in the IFAS process, and attention should be paid to the improvement of the OTE of the plug-flow IFAS process.
Assessing liquefaction potential, in situ screening using cone penetration resistance, and liquefaction-remediation of non-plastic silty soils are difficult problems. Presence of silt particles among the sand grains in silty soils alter the moduli, shear strength, and flow characteristics of silty soils compared to clean host sand at the same global void ratio. Cyclic resistance (CRR) and normalized cone penetration resistance (q c1N) are each affected by silt content in a different way. Therefore, a unique correlation between cyclic resistance and cone resistance is not possible for sands and silty sands. Likewise, the response of silty soils subjected to traditional deep dynamic compaction (DC) and vibro-stone column (SC) densification techniques is influenced by the presence of silt particles, compared to the response in sand. Silty soils require drainage-modifications to make them amenable for dynamic densification techniques. The first part of this paper addresses the effects of silt content on cyclic resistance CRR, hydraulic conductivity k, and coefficient of consolidation C v of silty soils compared to clean sand. The second part of the paper assesses the effectiveness of equivalent intergranular void ratio (e c) eq concept to approximately account for the effects of silt content on CRR. The third part of the paper explores the combined effects of silt content (viz effects of (e c) eq , k, and C v) on q c1N using laboratory model cone tests and preliminary numerical simulation experiments. A possible interrelationship between q c1N , CRR, accommodating the different degrees of influence of (e c) eq , k, and C v on q c1N and CRR, is discussed. The fourth part of the paper focuses on the detrimental effects of silt content on the effectiveness of DC and SC techniques to densify silty soils for liquefaction-mitigation. Finally, the effectiveness of supplemental wick drains to aid drainage and facilitate densification and liquefaction mitigation of silty sands using DC and SC techniques is discussed. This has sparked numerous research on the effects of fines on cyclic liquefaction
The silt has the properties, such as low strength and slow drainage; so it is usually treated by precompression method. For short construction period and low cost , a new drained consolidation method-drainage consolidation due to excessive pore water pressure for silt is tested: fist, the sand is replaced in the surface of silt for horizontal drain; and then, the plastic drain boards is applied for vertical drain; finally, the excess pore water pressure is generated by surcharge loads and dynamic consolidation and the drainage consolidation is fast under the excess pore water pressure. The result of the settlement observation and acceptance test shows that the result of drainage consolidation due to excessive pore water pressure for silt soft soil is remarkable.
Fast drained and consolidated mechanism of soft soil under excessive pore water pressure generate excessive pore water pressure in the soft soil through the addition of vertical and horizontal drainage channel as well as the applied load, because the drainage path is significantly reduced, the seepage velocity speed up and water excreted rapidly under the excessive pore water pressure, also, the effective stress increase rapidly between the soil particles and accelerate consolidation of soft soil so as to improve the strength of soft soil.
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