PART 3. COSTING AND CONVENTIONAL ACTIVATED SLUDGE SYSTEMS (10 POINTS) Q. 3.1) List 3 capital costs (CAPEX) and explain 3 alternatives to reduce the total CAPEX of a wastewater treatment plant. Q. 3.2) List 3 operational costs (OPEX) and explain 3 alternatives to reduce the total OPEX of a wastewater treatment plant. Q. 3.3) What is the "Net present value" and how can it be applied for the economic assessment of an engineering project. Q3.4) What are the 3 most common shapes used for the design and construction of aeration tanks in activated sludge systems? What are their advantages and disadvantages between them? Q3.5) How the depth of the aeration tanks influence the selection of the aerators used in conventional activated sludge systems? What type of aerators will you suggest to select for water depths ranging between 23 m, 2.54.5 m and 4,08.0m?