Q1
API separator uses the principle defined in Stokes’ Law to separate oil from wastewater. It operates by suspending the mixture of the waste above a gravity tank and letting the oil settle on top from the waste when the difference in gravity between the substances act via the tank.
The solid waste in the mixture would settle at the bottom acting as sedimentation and the water would be suspended between the oil and solids at the bottom. The benefits of using an API separator is that is it cost effective in large scale uses and an extremely beneficial multipurpose tool for industries that operate with bulk amounts of oil and waste disposal however, if the oil droplets area less than 150 micron or the density of the oil increases then the efficiency of API separator becomes null and void (Bahadori, 2014)
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Contrastingly, the Rotary Drum oil Skimmer is a not built for large scale industrial use but the main attraction is the ease of use and the cost effective nature in which it can be setup. That said, rotary drums cannot function at varying high temperatures and in places that might require a fast large scale turn around. For a small municipality with a residential community it can be used however for an industrial complex API separators are to be preferred.
Q2
To achieve a constant flow rate or to induce damping in flow rate variations, flow equalization is periodically used. This is achieved by constant mixing and aeration in the equalization basin, furthermore the equalization basin would need to have an in line arrangement so that all the flow passes through the basin without hindrance.
Using flow equalization biological treatment is enhanced and shock loadings are minimized. Additionally, effluent quality and thickening performance are enhanced as well along with reducing filtration surface area requirement. Conclusively, if flow equalization is used in the treatment of chemicals then damping of mass loadings critically improve chemical feed control and reliability of process (Bahadori, 2014).
There are certain necessary volume requirements for Flow equalization and categorically speaking they are as follows:
The depth of the liquid should be sufficient enough to allow continuous aeration and mixing
The total volume should be sufficient enough to maintain 16 hours of retention of the waste water flows.
There should be additional volume for unforeseen circumstance or changes in diurnal flow or BOD mass loading rate damping.
Finally, sufficient volume should be catered for plant recycle streams.
Q3
In sedimentary theory sedimentary rocks are classified into three distinct groups; clastic (siliciclastic) rocks, chemical rocks and biochemical rocks. The nature of these sedimentary rocks or particles can be prescribed via their solubility in waste water and how much sedimentation they cause when they are induced in any waste management system (Guerrero, 2013).
Clastic rocks have a relatively rather large particle size which is why they can be siphoned out via simple filtration process. The particles in this category are visible to the naked eye therefore they are fully filtered using either decanting process or letting these suspended solids settle in the bottom of the body of water.
In contrast chemical rocks are soluble and hence need to be separated via distillation or evaporation. Substances such as chalk are prime example of particles of chemical rock and are separated from a waste water reserve using heat and the process of evaporation. Finally biochemical rocks are substances such as coal and lead which can be significantly toxic in nature if not disposed of properly (Bahadori, 2013).
The most imperative process in determining biochemical particles is to reduce their toxicity which implies that the waste water has to be chemically treated before being exposed to heat or before we can increase the overall temperature of the basin. Once inert we can filter off or decant the waste water as similar to clastic particles biochemical waste is visible to the naked eye.
Q4
DAF (Dissolved Air Filtration) refers to the process of removing hydrocarbons and petrochemicals from streams of wastewater. This process is employed to reduce overall toxicity of the waste water before they are released downstream again. DAF systems are a high rate process and have an extremely efficient return for clearing solid particles from a waste water stream. These systems are scalable and offer flexibility in design and implementation (Bahadori, 2013).
In a contemporary DAF system air bubbles are attached to solids in a waste water stream when they are introduced during the upstream of the process. This causes the bubbles and the solids to form an air-solid agglomerate that is later removed using surface skimmers. A normal DAF unit will always be located downstream of the API separators and upstream of the biological oxidation units.
Limitations of DAF include operating variables, design variables, pH value, surface activity and suspended solid concentration in a waste water stream. The temperature of water is also a key factor in determining the efficiency of DAF.
References
Schultz, P. W., Large, L. B., Tabanico, J., Bruni, C., & Bator, R. (2009). Littering behavior in America: Results of a national study. San Marcos, CA: Action Research/Keep America Beautiful.
Bahadori, A. (2014). Waste management in the chemical and petroleum industries. Chichester: John Wiley & Sons.
Guerrero, L. A., Maas, G., & Hogland, W. (2013). Solid waste management challenges for cities in developing countries. Waste management, 33(1), 220-232.
Sharholy, M., Ahmad, K., Mahmood, G., & Trivedi, R. C. (2008). Municipal solid waste management in Indian cities–A review. Waste management, 28(2), 459-467.
