Question 2 [34 marks] A small village in the west of Ireland has 200 domestic residences (with an average occupancy per

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Question 2 34 Marks A Small Village In The West Of Ireland Has 200 Domestic Residences With An Average Occupancy Per 1 (50.3 KiB) Viewed 51 times

Question 2 34 Marks A Small Village In The West Of Ireland Has 200 Domestic Residences With An Average Occupancy Per 2 (89.03 KiB) Viewed 51 times

Question 2 [34 marks] A small village in the west of Ireland has 200 domestic residences (with an average occupancy per house of three people) and five businesses, each employing on average six people. There is also an abattoir located just outside the village. A recent Annual Environmental Report (AER) estimated that the average daily volume of untreated wastewater exiting the abattoir was 20 m³ d- 1 and that its average BOD concentration was 4000 mg L-1. You are part of a team responsible for the design of a wastewater treatment plant (WWTP) capable of treating wastewater from the residences, commercial properties and abattoir. The WWTP should have a capacity to treat wastewater until 2040 (15 years from the time of the design).
(a) Estimate the dry weather flow (DWF) and peak flow (total design inflow, Qmax) in 2040 assuming that 10 domestic residences per year are constructed (with the same average occupancy per house as currently exists), a new business (employing on average two people) opens each year over the 15-year design life, and the flow and concentration from the abattoir remains unchanged. [8] (b) Listing any other assumptions made, calculate the grit channel dimensions (depth, width and length) assuming the horizontal flow velocity of a particle is 0.4 m s¹ and its settling velocity is 0.05 m s1. [8] (c) Estimate the dimensions of a single-sided, broad-crested weir used to separate the flows greater than three times the DWF as it enters the WWTP. [8] (d) An aeration basin will be used to treat the wastewater. As part of the process to select a suitable aeration unit, preliminary tests were conducted to assess its aeration efficacy. The unit was filled with tap water, which was de-aerated using Na2SO3. The aeration unit was then started and measurements of dissolved oxygen were carried out in 5-min intervals over a 30-min period. The temperature of the water was 8 °C. The data are tabulated in Table 1. Calculate the KLa and comment on what implications this may have on the selection of the aeration unit. [10] Time (mins) 5 10 15 20 25 30 Table 1 Observed DO (mg L-¹) 0.2 1.4 3.3 3.9 4.2 5.8