Chemical Engineering

Share this article:

Chemical Engineering

  • Join our comunity:

Classic Mistakes in Water and Effluent Treatment Plant Design and Operation #1

By: , Posted on: April 18, 2018

My new book “ An Applied Guide to Water and Effluent Treatment Plant Design” is available for preorder now. It covers all of the things you need to know about designing water and effluent treatment plants which were previously hard (or in many cases impossible) to find in the public domain. This lack of availability of know-how has led to certain mistakes appearing again and again in my troubleshooting/expert witness practice. I include a chapter on these in the book, and in this post I will cover errors commonly made by design teams.

Academic Approaches 

The main problem I have observed with academic approaches to water treatment plant design is the lack of grasp of the key constraint: price. Engineers are never asked how to solve a problem as if money were no object. Balancing cost, safety and robustness are the essence of engineering.

The next most important academic mistake is to assume that a full-scale plant will outperform a lab scale plant. I have known this to happen on just one occasion, and the opposite situation is vastly more common. It is very common indeed that a full-scale version of a lab experiment will not work at all. Never assume that scale-up is even possible. I have experience of many cases from my expert witness practice where it was not.

Separation of Design and Costing

I once worked for a large UK water company on the conceptual design of a major extension to a large municipal sewage treatment plant. This company had an approach where process scientists chose the “best process”, civil engineers designed the plant around the selected process elements, and civil engineering estimators carried out a costing exercise based upon the design produced.

This resulted in the selection of a too-novel process which was both expensive and unreliable. The process scientists took no responsibility for this, as they assumed engineers would deal with the nuts and bolts of making the plant work. Their brief was to select the “best process”, based upon a simple and naïve cost/benefit analysis.

The scientists had no access to accurate costing data, nor knowledge of how to generate it, as they were not engineers. They had no brief to ensure process robustness, and they lacked the engineer’s conservatism and dislike of novelty. They were not trained in the analysis of safety as all engineers are. The civil engineers who used their process recommendations as the basis of their design were not able to examine them critically.

The outcome of this exercise will be unsurprising to experienced engineers. The novel process made it to the final decision stage, even though the process economics were bogus, and the process too novel to be used for the first time at such a large scale. The decision to use the wrong process was however sealed when a senior manager expressed an interest in the novel approach. The decision was made to go with the “HiPPO” (Highest Paid Person’s Opinion).

Following the HiPPO

Professional engineers use a combination of explicit and tacit knowledge, founded in any given design case by as thorough an analysis of the design envelope as is practically possible to make their design decisions.

Their line management, the managers of various disciplines within the company they work for, and their fellow engineers and technicians within and outside that company may all have opinions on these decisions. Within the engineer’s field of expertise, they should rely upon their own analysis, reasoning, and experience, neither unreasonably rejecting any suggestions nor wasting time on ones they know to be inappropriate.

It Is common for a higher-ranking engineer or manager to want to make their own mark on the process. Managers are generally less risk averse than professional engineers. Engineers from other disciplines or from outside the designer’s organization have different priorities and may well not grasp the full picture. The process designer cannot see the whole picture themselves unless they are willing to listen to these opinions, but they should insist on making decisions rationally.

Whilst relevant experience should be respected, it is important not follow the HiPPO blindly. Sometimes, however, it may be wise to stand aside from HiPPOs to avoid being trampled.

Running from the Tiger

I once undertook an expert witness case where an undergraduate had been allowed to design a full-scale plant worth millions of dollars. None of the several layers of senior engineers who should have been checking the student’s work corrected it, nor even asked why a student was leading the job and offering such an unusual design. When I questioned this, I was told “She is like a tiger!”

This was clearly quite a formidable student. However, no amount of force of personality can be an effective substitute for a grasp of the facts, together with the training and experience to know what to do with them. It is our job as engineers to ask the difficult questions, and many tigers are just paper.

Believing Salespeople

Mostly, technical sales staff in firms selling well-established products are the designer’s best source of reliable information for detailed design of plant. They will also know how their equipment has been used by others – information not in the public domain. They may even, in a competitive bidding situation, know how your competitors are using their equipment.

Good engineering salespeople do not tend to lie, though what they say may be incorrect for several reasons. They may pass on – in good faith – bad information which they have been supplied with by their company. The bad data is more likely to be selective or statistically insignificant than false. Never take someone else’s data analysis at face value.

Salespeople may also omit key facts. They may genuinely lack knowledge of superior alternative competing products or, more commonly, they may withhold any knowledge like this which they do have. The best salespeople will however give you this information if they have it, if only because they know a competent engineer will find it eventually and think less of them for withholding it.

Some salespeople may offer advice on matters they do not fully understand. Their knowledge of the manufacture, operation and testing of their products and how they might be adapted to suit your design should be highly detailed. Their other knowledge may be secondhand, anecdotal, ill-understood and unsupported by their training or experience. Always ask questions until you are sure that you understand where they are offering opinion as opposed to knowledge.

Then there are the minority of salespeople whose ethics are questionable, most commonly found in the world of novel products and processes.

In my next post I will discuss other kinds of common error

Read more articles from Sean Moran, The Voice of Chemical Engineering

About the author

Professor Sean Moran is a Chartered Engineer with over twenty years’ experience in process design, commissioning and troubleshooting and is regarded as the ‘voice of chemical engineering’. He started his career with international process engineering contractors and worked worldwide on water treatment projects before setting up his own consultancy in 1996, specializing in process and hydraulic design, commissioning and troubleshooting of industrial effluent and water treatment plants.

Whilst Associate Professor at the University of Nottingham, he coordinated the design teaching program for chemical engineering students. Professor Moran’s university work focused on increasing industrial relevance in teaching, with a particular emphasis on process design, safety and employability.

Connect with Sean on LinkedIn here, check out his Facebook page here and stay up-to-date on his thoughts, research and practice at his personal blog here.

Sean’s latest books are also available to order on the Elsevier Store. Use discount code STC317 at checkout and save up to 30% on your very own copy!


Connect with us on social media and stay up to date on new articles

Chemical Engineering

Most of the major scientific challenges of the 21st century — including sustainable energy resources, water quality issues, and process efficiency in the biotechnology and pharmaceutical industries — revolve around chemical engineering. Elsevier’s broad content in this area examines topics such as bioprocessing, polymer nano-composites, biomass gasification and pyrolysis, computational fluid dynamics, industrial proteins, catalysis, and many others with great significance and applicability to researchers today. Our books, eBooks, and online tools provide foundational information to students, and cutting-edge coverage to advance corporate research and development. Learn more about our Chemical Engineering books here.