Q1:
A secondary settlement tank is utilized when the majority of suspended material in the body of wastewater is categorically removed. The remaining liquid of the wastewater flow over a weir and into the secondary settlement tank. Primarily speaking, chlorination of the effluent takes place in this tank and that is done via the chlorination FAC residual where the effluent is maintained for 30 mins or more, based on the statuary laws in that particular municipality.
When the wastewater is treated, the effluent is discharged into a body of water that is maintained in a large reserve basin known as humus tank. The secondary settlement tanks have various design considerations and they are noted to have the following specifics:
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The use of an upward flow tank where surface area should not be less than:
Where:
A = minimum area of the tank top
P = design population
This particular design specification allow for 180 litres of dry weather flow and increased variability of flow rates in small proportions
Additionally, Secondary horizontal flow tanks can be expressed in the latter equation:
Where:
C = Gross capacity in Tank
P = design population
This calculation is based on the number of persons to be served in dry weather flow.
Q2:
According to Bahadori (2014) in his book ‘Wastewater management in chemical and petroleum industries’ hydrocarbons are compounds that contain two distinct elements, Hydrogen and Carbon. Even though generic waste management techniques duly remove visible hydrocarbons from a body of wastewater (these residuals are mostly organic), lighter organic compounds such as ethane and methane still persistently remain in the body of the wastewater (Bahadori, 2014).
These saturated hydrocarbons, have very low solubility in water and these compounds emphatically pose a great threat to the working environment of the process of wastewater management due to their low flashpoint and their ability to combust if not handled with care.
According to Bahadori ‘dissolved organic carbons (DOC) can be anticipated in units of percentage by weight for each petroleum related compound’ and then these hydrocarbons subsequently be correlated as a ratio to the DOC to chemical oxygen demand (COD). Once these calculations have been appropriately completed methane and ethane can be separated from the effluent wastewater and the discharge would be a low risk recyclable product that can be stored in any given reserve basin. The following representation of the above calculation can be taken as a very progressive starting point in the removal of methane:
Q3:
As mentioned in the above equation, historical measurements of DOC concentration from various refinery effluents fundamentally showcase that an increased concentration of hydrocarbons can effectively stagnate the recycling process of a body of wastewater. To fundamentally make use of the DOC concentration and calculations is to mitigate hazardous environmental conditions that offer lacklustre support on treating biologically contaminated waste.
Bahadori argues that one of the critical variables related to the safety of a treatment system is the air quality surrounding the process and methane and ethane concentration as displayed in the subsequent equation (Fig 1) shows that undissolved hydrocarbons are dangerous to the working environments of the individuals associated with this process.
(Fig 1)
Using this figure we can categorically place the concertation of the dissolved organic compound and the pressures exerted by such system on the overall treatment process.
Q4:
A biological filtration unit enables the removal of suspended solids from a body of wastewater. To achieve this, air is blown via the bottom of the filter to create a biofilm on the surface of the filter. The process enables the removal of biodegradable organic solids as they are dissolved and removed and the water is treated to be cleaner. According to Bahadori, biological filter in a conventional system bring the primary settlement tank into contact with suitable medium. Through this process the surface is coated with a biological film which oxidizes the polluting matter with the help of various microorganisms.
The design specification of a biological filter requires significant ventilation and should be distributed in a proportioned way. The filters need to be circular or rectangle and should be placed via small installation units. Volume of the filtration process should be kept at a medium interval and necessarily speaking the latter can be defined by the following equation:
Where:
V = minimum area of the tank top
P = design population
With the above equation volumetric capacity of the biological filtration unit and the design specification provided can ideally enable us to treat biologically toxic wastewater in multiple capacities.
References
Bahadori, A. (2014). Waste management in the chemical and petroleum industries. Chichester: John Wiley & Sons.
Pakdel, P. M., & Peighambardoust, S. J. (2018). A review on acrylic based hydrogels and their applications in wastewater treatment. Journal of environmental management, 217, 123-143.
Bourgin, M., Beck, B., Boehler, M., Borowska, E., Fleiner, J., Salhi, E., ... & McArdell, C. S. (2018). Evaluation of a full-scale wastewater treatment plant upgraded with ozonation and biological post-treatments: Abatement of micropollutants, formation of transformation products and oxidation by-products. Water research, 129, 486-498.
