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Waste Management
Published in Ronald Fayer, Lihua Xiao, Cryptosporidium and Cryptosporidiosis, 2007
Clarifiers work by simple settling, with solids sinking to the bottom and liquids staying on the surface. There are some special clarifiers that work in reverse, wherein particulates associated with air bubbles are caused to float to the surface while water drains from the bottom, but these are uncommon. Thus, clarifiers function mainly based on the buoyant density of the particulates being removed. The buoyant density of the oocysts of Cryptosporidium parvum based on ultracentrifugation in Percoll solutions is around a specific gravity of 1.08 (Jenkins et al., 1997). Because oocysts are very close to the density of water, they require a considerable amount of time to settle if they are not bound up in flock or adhering to other particulates.
VOCs In Wastewater
Published in Ralph L. Stephenson, James B. Blackburn, The Industrial Wastewater Systems Handbook, 2018
Ralph L. Stephenson, James B. Blackburn
The primary purpose of a clarifier is to separate solids from the wastewater through gravitational settling. Most clarifiers are equipped with surface skimmers to clear the water of floating oil deposits, grease, and scum. Clarifiers also have sludge raking arms that remove the accumulation of organic solids collected at the bottom of the tank. The depth and cross-sectional area of a clarifier are functions of the settling rate of the suspended solids and the thickening characteristics of the sludge. Clarifiers are designed to provide sufficient retention time for the settling and thickening of these solids.
Wastewater Treatment: Biological
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Water Resources and Hydrological Systems, 2020
Shaikh Ziauddin Ahammad, David W. Graham, Jan Dolfing
Clarifiers are used to separate the biomass and other solids coming out of the aeration tank by means of gravity settling. The flow rate of the liquid is maintained in such a way that the upflow velocity of the liquid is less than the settling velocity of the biosolids present in the liquid. As noted, some of the settled biosolids are returned back to the aeration tank to increase the solids’ contact time with the wastes and also maintain the desired biomass levels in the aeration tank.
Application of tracer technology in wastewater treatment processes: a review
Published in Chemical Engineering Communications, 2023
Metali Sarkar, Vikas Kumar Sangal, Harish Jagat Pant, Vijay Kumar Sharma, Haripada Bhunia, Pramod Kumar Bajpai
A large amount of sludge accumulates at the bottom of the primary and secondary clarifiers in the wastewater treatment process. This sludge needs further treatment, which is done in a sludge digester. A sludge digester reduces the amount of sludge by breaking down the organics into CO2 and CH4 gas. The sludge digesters usually have MRT in days, the RTD investigation of a solid-phase particle like sand and mud is done with radiotracers like Hafnium-175 (175Hf), Hafnium-181(181Hf), Iridium-191(191Ir), and Scandium-46 (46Sc) that have a half-life in days (IAEA 2011; Jung et al. 2004). It was found that in an efficient working sludge treatment unit, the presence of 10% and 30% of dead zone is acceptable. Borroto et al. (2003) performed an RTD study on the liquid phase in an anaerobic digester in a sugar mill WWTP using commercially generated radioisotope 99mTc. They found that the digester acted as a series of perfect mixing tanks and the RTD experiments provided sufficient information on the geometrical and physical behavior of the digester. Recent studies suggest that hydrodynamics study of anaerobic sludge treatment reactors can be conveniently carried out by 99mTc radiotracer (Luabanya et al. 2020). Summary of the literature available for radiotracer studies on wastewater sludge treatment processes have been given in Table 6.
Improving CH4/O2 energy ratio of meat processing wastewater treatment systems through micro-sieving
Published in Environmental Technology, 2022
The performance of primary clarifier and micro-sieving could be compared based on the design metrics proposed in Sustainable Environmental Engineering, as shown in Table 2 [10]. On the spatial scale, the land requirement of RBF is typically 10% of that of the primary clarifier [4]. Since the primary clarifier is open to the atmosphere, treatment efficiency is impacted by temperature, rain and wind effects. Micro-sieving is a modular and flexible design that could be installed indoor or outdoor to serve WWTPs at any capacity. In terms of materials, primary sedimentations are circular concrete tanks, and the major construction material of micro-sieving is stainless steel, while concrete and steel are recyclable materials. However, the quality of recycled concrete is 15–25% lower than that of the original concrete. Steel could be recycled repeatedly without loss of strength [29]. In terms of separation, the solids content of micro-sieving sludge is 3–8%, which is significantly higher than that of primary clarifier sludge [4].
Impact of activated sludge ozonation on filamentous bacteria viability and possible added benefits
Published in Environmental Technology, 2019
Filip Nilsson, Åsa Davidsson, Per Falås, Simon Bengtsson, Kai Bester, Karin Jönsson
Ozone has been shown to significantly improve the settling properties of activated sludge with a dosage of approximately 5 g O3/kg total suspended solids (TSS) [1–3]. As the secondary clarifier is a critical process stage at wastewater treatment plants (WWTPs) with activated sludge, a slow settling sludge can cause major problems at WWTPs. A secondary clarifier with slow settling sludge will not be able to separate sludge from the process as fast as a clarifier with normally settling sludge, possibly limiting the throughput of the entire plant. Additionally, surface floating sludge can be washed out of the settler, necessitating costly backwashing of tertiary filters such as sand filters. One cause of slow settling sludge is the excessive proliferation of filamentous bacteria that cause a phenomenon called filamentous bulking sludge [4–6]. To alleviate the problems with filamentous bulking sludge, ozone can be applied to the return activated sludge [6,7]. Ozone applied to the return activated sludge lowers the sludge volume index and increases the settling speed of the sludge [1–3]. However, the mechanism by which ozone interacts with the filamentous bacteria has not been widely studied. One proposed theory is that the large surface area of the filaments makes them more susceptible to ozone and other oxidants compared to the bacteria within the flocs [4].