Costo del proyecto

The wastewater generated by our cities is normally treated in a wastewater treatment plant before it is discharged, usually into the sea or into inland streams. Traditionally this treatment was implemented in three stages: primary treatment removes grit and other solids; secondary treatment removes organic material through biological digestion in ponds, trickle filters or through activated sludge methods; and tertiary treatment removes various forms of nutrients such as nitrogen and phosphorus, since these nutrients can have harmful effects on waterways, encouraging algal blooms.

In the last decade, as water shortages have become more acute, serious attention has shifted to further treatment processes that would render the resulting water suitable for human consumption or for specialist industry usage. These processes include micro-filtration, nano-micro-filtration, reverse-osmosis, oxidation and ultraviolet disinfection (National Water Commission 2007). These processes are designed to remove any harmful organisms such as bacteria and viruses, which are not able to pass through the very fine membranes used to filter the water. These membranes also intercept a range of complex molecules such as hormones, which might also be harmful if allowed to return to the drinking water system.

Naturally there is considerable community unease about such systems. This may be an instinctive understanding that such systems would need to be foolproof — operated at very high levels of reliability. For example, how would a membrane filtration system cope with the sudden rupturing of one of the membranes, allowing the polluted wastewater to mix with the pure water on the downstream side? To manage this

eventuality the engineers would need to create a control system that could immediately isolate the ruptured filtration module from the rest of the plant so that the cleaned water would not be contaminated by such a failure.

63 Such systems are already operating in the USA, particularly on the west coast, where population growth is quickly exceeding the available water supply from natural sources.

In Singapore, the government has funded the development of NEWater, where used water is treated by micro-filtration and reverse-osmosis before being transferred back to mix into existing water storages (Singapore’s National Water Agency — PUB 2008).

This water is also supplied to some industry users, such as the semiconductor industry, who benefit from its very low level of dissolved solids.

City West Water in Melbourne has recently opened a new water recycling plant in Altona that produces two grades of water for irrigation and industrial purposes (City West Water 2011). The plant uses reverse osmosis to produce up to 9ML/day or more than 3 GL/year. This will reduce demand on Melbourne’s drinking water supply by an equivalent amount. The plant cost $46 million and uses technology from Spain.

As the reliability of these systems becomes better understood, it is likely that such systems will operate routinely in Australian cities. These plants will be designed by chemical engineers who have the process engineering skills for the task, together with control engineers, electrical engineers, mechanical engineers and civil engineers who will design the various subsystems.

Critical thinking

How would you convince attendees at a community meeting that water from such a treatment facility is safe to drink, and how would you present it?

Step 3. Evaluating alternative solutions

Having identified a range of solutions, either through research or through creative thinking, the next step is to evaluate each solution against the performance criteria.

As you gather information about each alternative solution on a project, you will be able to start identifying the attributes of each alternative. This will assist you in completing the third step of the engineering method for problem-solving, which is evaluating alternative solutions.

For the car scenario, the attributes of each car may be different, including its fuel efficiency, noisiness, power rating and embodied energy. Some of these measures may require detailed calculations or careful investigation.

The attributes of each alternative can be documented in a table. An example of how this information might be shown is given in table 2.2. Many car magazines use similar tables to compare vehicles. You might like to analyse suitable alternatives for the engineering project now, using this table or your own comparative document. You can include this table or document in your project file.

64 Table 2.2 Comparing the feasibility of alternatives

You will need to consider the feasibility (the need, value and practicality) of each alternative. Some alternatives may be viable, while you might reject others quickly for different reasons (such as cost or environmental impact). An option becomes infeasible when it fails to satisfy a basic design requirement. In the car scenario, if the client has specified they require a four-wheel-drive car, then a two-wheel-drive car will be an infeasible option. There is no point providing a collection of alternatives that do not match this basic requirement.

A feasibility check allows engineers to ‘prune the solution tree’, or to quickly eliminate a number of options by declaring them infeasible. This is a natural process that is very helpful. It allows engineers to deal with complex problems despite the limitations of short-term memory mentioned earlier in the chapter. If there are a small number of available solutions (say

between five and nine) then these can be kept in an ‘engineer’s head’ while they work. If there are many more, it will be likely that writing them all down and keeping careful records will be vital. Grouping solutions is another way of dealing with short-term memory problems. The range of solutions could perhaps be grouped into small cars, medium cars and large cars. In each category, there might then be five to nine different car types. This reduced number makes it easier to think about or compare them and be less overwhelmed by the range of solutions.

In modelling the alternative solutions to an engineering problem, it is important to rate feasible alternatives against decision criteria. This can be done using a spreadsheet program that uses simple mathematical formulas to work out the best alternative. Table 2.3

demonstrates how this could be done for the car scenario.

Table 2.3 Rating feasible solutions: a hypothetical comparison

Key

Size: prefer small-medium, so small-medium = 5, large = 4 Fuel: consumption — less consumption means a higher rating

Audio: availability of sophisticated equipment as standard (higher rating indicates more likely) Safety: Australasian New Car Assessment Program (ANCAP) rating

Doors: availability of hatchback option = 5; else = 4

65 Based on this analysis, the Subaru WRX and the Toyota Yaris seem to be better suited to the client’s needs. However, the scores are all quite close together, suggesting that any of the choices might be suitable with the right options.

The approach documented is simplistic. Most of us weight some factors more than others.

For example, a client might be very concerned about fuel consumption for environmental reasons and also concerned about personal safety. Someone else might be more concerned about the make or colour of the car. An easy way of doing this on a problem is to add a weighting factor to each criterion, in consultation with the client. The weights can be any magnitude. In our car-buying scenario, a weight factor of 0 to 5 has been used, with fuel efficiency having the greatest weight.

The final score, shown in table 2.4, is calculated by multiplying the appropriate weight by the rating and adding them together. In mathematics, this is called the dot product.

Table 2.4 Rating alternatives with weights

score = ΣWiri

Where wi = weight i and ri = rating i.

These calculations are easily handled in a spreadsheet program such as Microsoft Excel.

Note that as a result of this process, the scores in our car-buying example are now more variable, and the Yaris is a clear choice.

Having evaluated the range of solutions, it is now time to check that the client’s needs have been met.

Step 4. Engineering decision-making

At all stages of the engineering method, and particularly before the final report is released, it is important to monitor, check and review the recommendations. Engineering decision-making ensures that obvious errors have not been made. For example, are the calculations correct? Is the formula in the spreadsheet correct? Is the answer realistic?

A quick calculation on one of the rows in table 2.4reveals it is correct (for example, the Yaris score = 4*5 + 4*5 + 3*4 + 5*5 + 3*5 = 92). A check of the second row confirms the formula is also followed in this column (for example, the Holden score = 4*3 + 4*4 + 3*5 + 5*5 + 3*4 = 80 is correct). The last row of the column is correct, which implies the first row should also be correct. This is an additional revision of the outcomes. In large projects, independent consultants are enlisted to check calculations.

66 This is a vital check that helps protect the safety of both the public and the workforce. As such, it is part of the quality assurance process.

Ideally a co-worker should check your work on a project when you are employed as an engineer. Your boss might want a report on progress once or twice a week. You will want to check progress and direction with the client at strategic stages as well. Some strategic checkpoints include when the project is 15 per cent complete, 50 per cent complete, 85 per cent complete, and finished. Hopefully the client will be 100 per cent satisfied with your efforts. If you are working on a large project, you will need to report your progress to other team members so their efforts complement your work. Engineering failures have occurred from team members not keeping each other informed. Once it is clear that you have met the client’s needs, then you can communicate your recommendations more formally.

Step 5. Communicating your recommendation

The fifth step in the engineering method involves communicating recommended solutions. In order to communicate recommended solutions, you need to have access to the collected documentation for the engineering project, including the research, the alternative solutions proposed, evaluation of the alternatives and the recommended course of action.

Communication of the recommendations is often conveyed in multiple ways. Firstly, a report could be drafted outlining the recommendations. This report would be followed up by a meeting where the recommendations are presented and discussed with the client. There may then be negotiation around a final set of preferred options. This is a complex process requiring a range of communication skills — writing, speaking, listening and negotiating. These skills are discussed further in chapters 5, 6 and 11.

Reaching agreement on a set of preferred solutions is the final step in the engineering method as it has been described here. Surrounding this core problem-solving process is a range of project management processes, which will be discussed later in this chapter. Before considering project management, further consideration will be given to properly understand the problem. Before we do that, let’s compare the engineering method with the scientific method.

The scientific method

Science has transformed our world in the last 300 years, and it has certainly transformed engineering practice, particularly in the last 100 years. But, what is science? Is it what we learn from textbooks, or is it a process of creating new knowledge in a systematic way? Since the seventeenth century, science has placed an emphasis on the empirical collection of

evidence as its fundamental principle. This evidence must be observable, measurable and reproducible if we are to have any confidence in it.

How does the scientific method work? How is it similar to and different from the

engineering method? Both methods start with a problem or a need. For example, the problem could be to explain the climate changes we are observing of rising global temperatures and sea levels. Scientists begin by forming hypotheses about the cause (of climate change in this case).

Competing hypotheses could be (i) climate change is induced by human activity, such as burning fossil fuels; and (ii) climate change

67 is a naturally occurring process that has been observed throughout the life of the planet. This is similar to the ‘generate alternative solutions’ phase of the engineering method.

Scientists address this kind of problem by carefully collecting data such as temperature, tree growth rings, atmospheric CO2 levels and so on. These data are correlated in an attempt to confirm one hypothesis and reject the other. This is the evaluation part of the process, using empirical data to test the alternative hypotheses. Although it is impossible to prove a theory, it is much easier to disprove or reject a competing theory or hypothesis. Despite the work of thousands of climate scientists, there is still considerable doubt expressed, particularly by politicians, that the case for climate change has been proven.

Finally, conclusions must be drawn and communicated to the intended audience through reports, papers and presentations. So, it can be seen that the scientific method is quite similar to the engineering method, as shown in table 2.5.

Table 2.5 Comparison of the engineering method and the scientific method

Engineering method Scientific method

Begins with a problem or a need The problem or need is often a question to be answered

Requires research to better understand the problem and to define suitable criteria and constraints for a problem solution

Likewise requires a research phase to better understand the question and to define its boundaries

What are some suitable solutions to this problem? This can require creative and divergent thinking

What are some suitable hypotheses to answer the question? This can also require creative and divergent thinking

Evaluate the solutions against the criteria and constraints using available data and modelling tools

Evaluate the hypotheses using data and modelling tools, with data either collected first-hand or derived from other reliable sources

Choose one or more suitable solutions Choose the hypothesis that is best supported by the evidence

Make a recommendation for further action, such as to implementing one of the

solutions

Make a recommendation for further action, which might also include the need for further data collection and analysis