Explain critical path method and idea, Other Engineering


Problem 1

Case Study - Development of a new sewage secondary treatment plant Context and location:

Consideration is being given to the development of a new major sewage secondary treatment plant. The plant is to complement existing primary treatment for a city of half a million people and be designed with a capacity of 200 mega litres per day. The appropriate authority plans to acquire the land necessary for the complex as close as possible to the city. The objectives of the authority are:

  • To develop a world class environmentally friendly facility
  • To develop a facility that returns best value to rate payers
  • To commission the proposed secondary treatment plant as soon as possible


A number of viable technical solutions exist. Four new options have been considered in detail. Proposed options are:

Option 1: Intermittently Decanted Extended Aeration (IDEA) treatment system

Land area required:            20 ha

Construction cost:               $150 million

Construction duration:         3 years

Operating cost:                  $1.5 million per annum

Operating features:

  • Plant relies on natural biological action
  • Plant removes liquid pollutants and cuts industrial contaminants
  • Reliable and flexible
  • Almost no odour

Option 2: Activated sludge treatment system

The activated sludge system relies on a combination of mechanical and biochemical processes. After screening and sedimentation, naturally occurring micro-organisms are fed oxygen so they vigorously feed on organic material in the sewage. Sewage is treated to a secondary standard and effluent is chlorinated prior to discharge. A thick black sludge is produced as part of the process and is died in shallow drying pans.

Land area required:            500 ha

Construction cost:               $700 million

Construction duration:         3 years

Operating cost:                  $5 million per annum

Operating features:

  • Proven technology
  • Some treated effluent is used in nurseries, market gardens, golf courses and sports grounds
  • Some odour
  • Environmental concern in terms of the volume of chlorine used

Option 3: Lagoon treatment system

In lagoon treatment, sewage travels slowly through a series of connected ponds which contain high concentrations of naturally-occurring bacteria. The bacteria convert the organic and inorganic nutrients in the incoming sewage into bacteria cells and inorganic products like carbon dioxide, water, ammonia and phosphate. Algae then consume these inorganic products.

The ponds are constructed so that the water flows from one pond to the next under gravity. It is possible to cover the lagoons to collect gases from the bacterial breakdown of the solids settled from the sewage. These gases contain methane and odorous compounds and may be combusted to produce electricity and non-odorous gaseous by-products.

Land area required:                            200 ha

Construction cost:                               $100 million

Construction duration:                         7-10 years

Operating cost:                                  $1 million per annum

Operating features:

  • Technical process still under development
  • Potential for commercial income for sale of energy
  • A time significant odour
  • Good environmental outcomes

Option 4: Reed bed lagoons treatment system

In a reed bed lagoon treatment system the reed bed lagoon provide secondary treatment through naturally-occurring bacteria and the environmental balance achieved through the action of the reeds feeding on the effluent. Reed beds require cleaning about every 10 years.

Land area required:                1,000 ha

Construction cost:                  $100 million

Construction duration             2 years

Operating cost:                     $4 million per annum

Operating features:

  • Significant area of land required
  • Some odour
  • Good environmental outcomes whilst plant is well maintained
  • Process has limited scope for expansion


You have been appointed as a Project Engineer by the water authority which is carefully considered all aspects of the options prior to deciding its preferred option.

One of your tasks is to perform stakeholder analysis and propose strategies to manage those stakeholders. The Project Management ask you to prepare a brief report which should include:

a) List of ten stakeholders who are interested in this secondary treatment plant, and brief description on why they are interested

b) Analysis of their influence to the project and strategy to manage each of them

c) Brief discussion on how would you go about evaluating which of the four sewage treatment options would meet the water authorities' objectives. Your discussion should include issues relating to:

  • Finances
  • The environment
  • Ratepayers of the water authority
  • Other stakeholders

Problem 2

Your company has been awarded a contract to construct a combination plant-officewarehouse for a small industrial form. As a project engineer you are responsible for the interior work for the plant and warehouse. The activities which are needed to complete the interior work can start once the building is closed in (note: this part is done by other). The activities required to complete the interior work can be described as follows:

  • Once the building closed in, you can: Set electrical load centre (2 days), a package unit located on the slab of the warehouse; install Power panel backing boxes (10 days), which can be mounted on the masonry walls and structural steel; install Masonry partitions (10 days); install Exterior door (5 days) which must be installed prior to the drywall; install heating and ventilating units (15 days); erect boiler and auxiliaries (25 days); Fabricate piping systems (30 days); Install fuel oil tank (3 days); Install monorail (5 days), which can be done anytime between the closed in and completion of the building.
  • Once electrical load centre is set, you can install Power conduit (20 days).

This will be followed by installing branch conduit (15 days), which also needs a completion of Power panel backing boxes. The branch conduit needs to be installed for you to Pull wire (15 days) and install Outlets (5 days).

However, to install Outlet, need to complete drywall.

After the wire is pulled, you can install panel internals (5 days), followed by terminate wire (10 days), then Ring out (10 days). Energise power (1 day) can start once the ring out is completed. However, you also need to have Electrical fixtures (10 days) installed to energise the power. To install electrical fixture you need to complete the outlet.

  • To Drywall (10 days), you need to have Exterior door installed, as well as

Frame ceilings completed (5 days). To Frame ceilings, you need to have Masonry partitions installed.

  • Drywall completion is very important, as it is required to: install the Outlets; hang Interior doors (10 days); install Ceramic tile (10 days); and install Ductwork (25 days). Once Ceramic tile is installed, you can Paint rooms (5 days), followed by installing Floor tile (10 days), then Install furnishing (10 days). Plumbing fixtures (10 days) can be installed after you Paint rooms.
  • To install Ductwork, you need have both the Drywall and Heating and ventilating units installed. Once the Ductwork installed, you can Insulate heating and ventilating system (15 days).
  • To Light off boiler and test (5 days), you need to have Fuel oil tank installed, perform Preoperational check (5 days), and Test piping system (10 days). To perform Preoperational check, you need to have boilers and auxiliaries erected. And to Test piping system, you have to complete Piping system fabrication.

Your Project Manager wants to know how many days that the interior work for the plant and warehouse can be completed. He also needs to know the critical activities in that work, which he should monitor closely. As a Project Engineer, you are asked to provide the required information by preparing and analysing a schedule using the Critical Path Method (CPM)

Posted Date: 2/16/2013 4:37:45 AM | Location : United States

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