Modelling with Parsimony and Living with Prudence


[A bit of a technical blog – but with messages for you to decifer]

I went to see my Professor Friend at IIT Bombay. I had not taken his appointment. He was in the class teaching Water Quality Modelling to the postgraduate students.

When Professor saw me waiting outside, he paused and asked me to join.” Come in Dr Modak” he said, “I have just begun the first class”.

I took a seat in the last row.

Professor was introducing the basics of Streeter-Phelps model for modelling Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD) in rivers.

For those who don’t know about the Streeter and Phelps  DO-BOD Model. The Streeter and Phelps model describes how DO decreases in a river or stream along a certain distance by degradation due to presence of BOD. The equation was derived by H. W. Streeter, a sanitary engineer at Cincinnati in the US, and Earle B. Phelps, a consultant for the U.S. Public Health Service. The model was built in 1925 based on field data from the Ohio River. The model makes use of two parameters viz. reaeration rate that depends on the hydraulic variables like depth and velocity and the deoxygenation rate that depends on the level and type of the organic matter present in the river.

Professor used few slides to explain the Streeter-Phelps model and the governing equations that attempted to explain the oxygen deficit. The model looked simple and rather straightforward asking for minimalistic data to help predict the outcomes.

“You can use this model for deciding the concentration of BOD that you could allow to ensure that we do not run into situation of high DO deficit that could affect the aquatic life”.

Professor solved one example problem the showed how limits to BOD can be set on this basis. He then expanded the problem statement to the case of multiple discharges of wastewater over a long river stretch with water withdrawals and tributaries joining.

He explained how the model can be used to decide not just the level of treatment of BOD but also decide on the minimum flow needed in the river to ensure dilution and assimilation of the wastewater.

Students enjoyed the application potential of the Streeter-Phelps model. Models must be taught with application perspective I said to myself.

Professor then paused and asked the students to critique the model. “Are we missing anything?” He asked one of the brighter students.

“Sir, I think the model misses the fact that wastewater contains suspended solids. These solids when settle in the bottom, the particulate BOD will reduce. We must include a sedimentation rate in the model. This rate  will depend on the river velocity at the point of wastewater discharge”

I thought he was right.

Another student commented “Well, whatever settles will still remain part of the system – the sediments at the bottom will continue exert an oxygen demand, albeit at a different degradation rate perhaps because the organisms responsible could be different”

“You are right” Professor said – we will recognize this aspect as Sediment Oxygen Demand (SOD).

A girl with spectacles got up and said – “How about the process of nitrification Sir?”

Professor said “Dr Modak, can I ask you to elaborate on this very important point?”

I liked this idea of participatory teaching. So, I walked to the blackboard and wrote the following

Ammonium in the wastewater is oxidized to nitrate under aerobic conditions as

NH4+ + 2O2 → NO3− + H2O + 2H+

Ammonium oxidation can be treated as part of BOD, so that BOD = CBOD + NBOD, where CBOD is the carbonaceous biochemical oxygen demand and NBOD is nitrogenous BOD.

The change in oxygen deficit due to oxidation of ammonium can be described with help of the nitrification rate and ammonium-nitrogen concentration. The model must expand.

The original humble Streeter-Phelps model thus started to look more complicated. And as if this was not enough, Professor introduced the role of photosynthesis and respiration. Photosynthesis and respiration are performed by algae and by macrophytes. Respiration is performed by bacteria and aquatic animals. Inclusion of photosynthesis brought the role of sunlight.

After some more brainstorming, all of us developed a bit monstrous water quality model (QUAL II) as shown below

Architecture of QUAL II model

“You can if you wish even further complicate this model – Professor said. “Maybe you like to build a model for a lake that is tending to be eutrophic (i.e. overloaded with nutrients and algae) and partially stratified during winter. This can be challenging” Professor winked.

The class was now about to end.

While summing up, Professor said “And friends, we can continue building more and more complex  water quality models for the interest of completeness. But remember that there is an optimal model complexity that we must recognize. Simpler is the model, more is the model uncertainty in prediction due to its frugal structure. But more is the model complexity, more are the parameters that come into play and hence predictions can become uncertain due parameter uncertainty. Imagine the complex model like QUAL II that requires data on more than 20 parameters (rates). Our poor understanding on these parameters can  lead to a “chaos” or “noise”, leading to a performance close to the simple  Streeter Phelps model. You must realize that your degradation rate in the simple Streeter and Phelps model will now become a surrogate with sedimentation and the reaeration rate will factor contribution due to photosynthesis on a “lumped basis”

I did know how much of this philosophy of modelling was understood by the students, but I was sure at least few did as the Professor projected his last slide.

When we reached Professor’s office, I asked for a coffee. Professor lighted his cigar.

“The most important message is understanding the Parsimony. The parsimony principle is basic to all science and tells us to choose the simplest scientific explanation that fits the evidence i.e. involves fewest entities. When scholar William Ockham wrote “Pluralitas non est ponenda sine necessitate” which later became known as the Law of Parsimony, it wasn’t to describe tightfisted stinginess but to say that all things being equal, the simplest explanation may times tends to be the right one. This realization is most important for a happy, successful and sustainable life”

I realized the topic had transcended the subject of water quality modelling

Professor took a deep puff

“I’m not saying that we don’t try to push ourselves to do the difficult or complex things in life. What it means is that we should look for the simplest way to achieve our goals and focus on the minimum but relevant tasks … while still doing them well. Remember – sometimes Streeter Phelps model can lead to same management decisions as arrived by a complex QUAL-II model”

He continued

“Some say parsimony means being stingy. I disagree. By saying “No, I can’t do that” may allow us to do what we want – that is really must be done or we would rather do – with our available time and energy. It has taken me many years to get my head around to “listen to myself”, look at my health and priorities of life”

“So, Professor, are you now living life on the principles of parsimony – that is hovering between complexity (due to your inherent curiosity) and a modest completeness (just good enough for your inner satisfaction?”. Professor did not answer. He looked outside the window.

I could not hesitate but ask “And have you reached the optima?”

“Well, Dr Modak, we will talk on this some other time. Needs another round of coffee” Professor got up from the chair. “I have to leave now as I have reach the meeting point for carpooling. See, I haven’t given up the comfort of riding a car but I am taking a simple step of sharing resources to reduce travel costs, curtail emissions and converse with new friends on topics other than environment. Its parsimony with prudence that makes life worth living and interesting

I understood now the significance of Streeter-Phelps equation. “Professor, when is the next lecture on water quality modelling?” I asked.

Professor smiled

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Lift Kara De (LKD) is a carpooling initiative taken up by the enthusiastic residents of Whispering Palms Society in Kandivali, Mumbai, India. The group consists of about 256 carpoolers so far with numbers increasing every few months. Santosh Shetty, one of the key members of the Lift Kara De group had approached Ekonnect (my section 8 company) for calculating their individual/group emission reductions, fuel and money savings achieved so far from their ongoing carpooling activity.

Ekonnect team members estimated these values based on the data received from the LKD group members which comprised of number of rides, distance traveled, number of individuals in a car, type of fuel and years of carpooling.

The results showcased that in a short duration of 5 years LKD members had achieved 1, 91,000 Kg of Carbon dioxide emission reductions.

If you want to read this fascinating story , then do download this presentation

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Sustainability Considerations while Making Technology Choices


Technologies are always evolving and present several options while making decisions. Generally, costs are given prime consideration as a selection criterion while meeting the required target of efficiency and yields. Costs include the capital and operating costs on a life time basis.  We calculate the Present Worth of the two options by amortizing the operating costs and help us to make a comparison to select the technology of the least life cycle cost.

It has been now realized that costs alone may not be the sole criteria. While cost could be one of the critical and deciding factor, there could be other considerations as well, especially on the environmental and social frontiers.

One of the important environmental factors is the generation of wastes and emissions. We consider this perspective by adding the costs of pollution control and monitoring to the base costs of the technology. These costs include installation as well as operating costs. A technology may not be preferred when costs of pollution control are added to the base costs. We see this situation when comparing biological processes with those following the thermal or chemical routes.

Use of technologies that have low Material Intensities or MI (including embodied energy as well as factoring virtual forms of water) is sometimes preferred. These decisions are taken by performing Life Cycle Assessment (LCA) to helps to arrive at the estimates of MI. You may like to visit “databases” created by Wuppertal Institute in Germany. A paper on Assessment of wastewater treatment technologies: life cycle approach by Pradeep Kalbar, Subhankar Karmarkar and Sham Asolekar will be an interesting read.

Another criterion is the emissions of Greenhouse gases (GHG). While there are no emission limits legally prescribed, most would like to choose technology option that has minimum emissions of GHG. Such technologies are often called as low carbon technologies. Technologies that use more of renewable energy get preferred as compared to those which may use of fossil fuels. You may find Buyers Guide to Renewable and Low Carbon Technologies as an interesting read published in the UK.

is another environmental criterion that could decide the choice of technology. For example, we may not like to prefer technologies that use mercury or chlorine in any form. On the other hand, there could be preferences. We may prefer technologies that can make maximum use of the locally sourced materials to avoid transportation and boost local entrepreneurs.

We also need to factor the costs of disposal of the end of life of the equipment. In some cases, because of the use of non-biodegradable or potentially hazardous materials –costs of disposal of the used or abandoned equipment could be substantial. This aspect could influence the final decision between technology options.

Environmental risk
is another perspective. Some technologies may be compliant to the waste/emission standards that are legally prescribed but may pose risks of process upsets even leading to disaster during operations. These risks may arise due to process abnormalities that may occasionally arise – albeit rarely, posing certain restrictions on continuous operations or requiring on-line monitoring with process control or investments on the back-up systems. These considerations could add to the total costs.

Social considerations could also play an important role in the selection of technologies. These considerations include local employment. When one of the objectives of investment is to improve livelihoods of people, then technology options that generate local jobs may be preferred. Here low to moderate scale of technology and associated investments, especially in offering decentralized solutions get preferred. These technologies should be easy to understand and operate.

Generation of odor and noise and safety become additional considerations in the interest of workers and the neighborhood. Technologies that lead to nuisance during operations, shut down and startup operations are not preferred

When we address all the above considerations, we generally come up with design of a “system” that incorporates a “mix or combination of technologies”. In this system design, we ensure that technologies are in place for pre-treatment (that may include separation), main processing, with add on pollution control and recovery units and process control instrumentation (monitoring and interlocks) for ensuring safety during operations.  This entire system then needs to be assessed based on economic, environmental and social parameters.  For this purpose, quantitative or qualitative schema are used such as weighted scoring and Analytical Hierarchical Process (AHP). You may like to read paper by Tung  Nguyen Nhu on Application of Analytical Hierarchical Process Method to Select a Technology Option for Water Treatment in Rural Settings. 

When investments are sourced from public funds, a transparent process of technology assessment needs to be followed. I developed for the International Environment Technology Center (IETC) at the United Nations Environment Programme (UNEP), a methodology called Sustainability Assessment of Technologies (SAT). Figure below shows the steps followed.


Methodology for Sustainability Assessment of Technologies


SAT methodology operates in tiers such as screening, scoping and detailed assessment. It follows a PDCA cycle as implemented in the most management systems to ensure that feedbacks on the use of technology is factored. Importantly it involves expert and if appropriate a public consultation. Lastly, the methodology could be used to select options at both strategic and operational level e.g. whether decentralized solutions are better suited than the centralized option.  More details on SAT can be accessed from the manual available online.

Applications of SAT methodology have been carried out for making choice of technologies across sectors such as water treatment, wastewater recycling, waste recovery etc. The SAT manual cited above includes a solved example that could be perused for better understanding.

I spoke to my Professor Friend about how sustainability could be factored in the technology selection. I told him that the “costs” incurred due to wrong selection of technology could be more than the apparent savings! Professor let me speak while enjoying his cigar. After I finished, he extinguished his cigar and said “Dr Modak, what you said is worth in a conference. The world would have been different or the research would have changed its course – if sustainability considerations were actually considered while making the right choice on technologies.

He then paused, smiled and said while patting my back

“Don’t forget Dr Modak, today it is the L1 that counts!

I realized that there are hardly any choices to make!!

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“Global Carbon Footprint”

An infographic is a popular form of content communication that can simplify a complicated subject or turn an otherwise boring subject into a captivating, learning and inspirational experience. Ideally, an infographic should be visually engaging and contain a subject matter with organized or processed data that is appealing to your target audience.

Today, we prefer to make reports and presentations using infographics. The infographic speaks thousands of words and provides an insight more than just the data. In creating infographics, we often “crunch” the data and present associations between various data elements. This analyses  with right visualization leads to astonishing interpretations. Unfortunately, not many are skilled or experienced in creating meaningful and captivating infographics.

I asked my Professor Friend for an example. He was completing a report on water quality data analyses on river Godavari in Maharashtra, India.

“Well, Dr Modak. The Maharashtra Pollution Control Board gave me water quality data on 18 stations over 10 parameters sampled every month over 8 years. The interest was to know whether the water quality in Godavari was improving between 2012 and 2013. So, I thought of creating an infographic. The first step I had to do was to crunch the 10 parameter water quality data into a single parameter. I selected  for this purpose a Water Quality Index (WQI). I looked at many options and chose a structure recommended by the Central Pollution Control Board. I generated a time series of WQI at all the 18 stations for 2012-2013”. Professor showed me an MS Excel sheet where all the required number crunching was done.

He then lit his cigar.

“The main interest was to know whether the water quality was improving or worsening. So, I realized that I had to do some quantitative trend analyses. I applied Kendal-Tau test to assess for each station the trend in WQI which gave me the direction of the trend (upward or downward) and its significance. So, the time series data on WQI was converted into a single number at each station viz. trend”

“Clever – Professor. So, you essentially reduced 24 x 10 data points into just one number for each station” I exclaimed

“Well, that was not enough. I had to bring in visualization now to help understand the changes” Professor projected a slide that depicted river Godavari with locations of monitoring stations and the results of the trend. So, this was the infographic. It not only communicated the trend but opened discussions on why the trend reversed in the adjoining stations and possible field investigations that were needed. Showing on the map the key points of wastewater discharges would be have been very useful but MPCB did not have such data”


The example of infographics for water quality in Godavari showed how techniques of data crunching and spatial visualization were used for effective communication and actioning.

Let us now look at the power of data association in creating infographics.

Figure below shows a construct of time series of data collected at two automatic air quality monitoring stations (BT4 and HR1) for parameters PM10 and NOx .  The time series can be viewed to see the outliers (values crossing four times of standard deviation per Dixon’s test) as well as spot values crossing the applicable ambient air quality standard. But it is perhaps more interesting to find instances when both PM10 and NOx   are simultaneously exceeding over the standard.   These instances (red dots) tell us more about the associativity of PM10 and NOx emissions for better source diagnosis.

Similar extensions could be made. The time series of stack emission data can be plotted and “associated” with time series of ambient air quality data. Hourly observations on wind directions could be then used to estimate the “stack influence” and a time series plot of stack influence could be generated by setting an “influence function”. A time series of stack influences can be used to assess the relevance of ambient air quality monitoring station (i.e. siting) and importantly take actions for controlling the stack emissions. See Figure below.

The data association approach can be effectively used to communicate “causation”, especially to the non-scientific community by preparing striking visualizations. I remember Professor showing me a map where concentrations of PM10 were plotted along with information on sale of inhalers at the shops of chemists. We could see here interesting association between PM10 concentrations and the sale of inhalers – wherever PM10 was found to be high, there was high sale of the inhalers. See Figure below.


Sometimes we run into a situation where the management is interested to get a top view of the “situation” and then go into the details for actioning. In a typical Environmental, Health and Safety (EHS) audit, the Team after the plant visit writes a report, generally in the form of table that states the Non-Compliances (NC). While such tables are needed, an infographic that presents a quick snap shot in the form of a summary is always useful as the first slide of the presentation. Figure below shows application of a Fish-bone diagram where NCs are shown in perspectives, in a manner easy to grasp and importantly help prioritize and take actions.  The strategy in creating such infographic is to capture the key perspectives of the “problem” (or the eye of the fish) and then overlay on the fish-bones the “highs or lows” or “good or bad” performance against the benchmark or standard.



Sometimes, we need to prepare “popular” and easy to understand infographics, especially when conducting awareness events in schools and for citizens. These infographics follow the principle of cascading information where issues are flagged in a step-wise manner, material/energy flows are shown and outcomes or impacts on health for example are stated with damage in economic terms. Here icons, colors and data points in large fonts are used to get the needed focus or attention of the eye. Two examples of such infographic are shown below.


Finally, there are challenges when we create infographics for concept communication. Such infographic is generally hard to make. Couple of years ago, I created an infographic to communicate the concepts of Project EIA, Regional EIA and Strategic EIA. See Figure below

The crux of this infographic are the three baloons shown for each category of project, Category A for most sensitive, B – moderately sensitive and C – Not sensitive. The infographic communicates EIA at project level, for plans and for policies using the impact typology of direct, indirect, cumulative and induced impacts. The most important communication was to bring out limitations of project EIAs for area wide projects and need to use Environmental & Social Management Framework (ESMF)

“Dr Modak, creating infographic is more of an art or creativity than just data and science. It is a stimulating exercise. Our environmental students should learn this art of science” Professor was ordering some coffee.  “Data crunching, data association, structuring infographic based on perspectives and cascading information in the form of cause-effect or input-outcome are some illustrations. But there are numerous other possibilities, especially in the complex and multidisciplinary subject of environment”

I couldn’t disagree with Professor.  I wish we did with students, group sessions on how to create the infographics from seemingly drab data into something exciting and innovative– These teaching sessions will certainly lead to some out of the box thinking – I thought

“Should we  run a competition on infographics in environmental management Professor” I suggested

“Oh, clever idea. But call the competition as Enfographics” Professor said while finishing his coffee. I realized that he just coined a new term!!

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Sustainability Literacy


Sustainability education is essential today. It is required at all levels but more so in schools, colleges and at the institutions with higher learning. We also need continuing education programs on sustainability for professionals, regulators and bankers.

In India, we are not yet focusing on sustainability education.

But let us first start with the basics. Everyone should be sustainability literate.

What does Sustainability Literacy means? I asked my Professor Friend

“Well there is no formal universally accepted definition” he said. The Sustainability Literacy Test (SuLitest) defines “Sustainability Literacy” as the knowledge, skills and mindsets that help compel an individual to become deeply committed to building a sustainable future and allow him or her to make informed and effective decisions to this end”.

(Hearing this kind of definition, I thought I was attending some UN Conference)

Then Professor said with a smirk “Dr Modak, don’t you think we need to focus on the basic literacy first? According to me this Sustainability Literacy is a luxury and all humbug. A 1990 study estimated that it would take until 2060 for India to achieve universal literacy from the present 74.4%. We better work on achieving this target”

“But then we are simply missing the boat. What is the use of making people literate – as by 2060, if we don’t change our lifestyles the warming of the planet will cross 4 0C. I said in despair “I expect Sustainability Literacy will help us to bring in the behavioral change and at least delay the global warming”

What is definition of literacy? I asked the Professor

Professor said that the National Literacy Mission defines literacy as acquiring the skills of reading, writing and arithmetic and the ability to apply them to one’s day-to-day life. The achievement of functional literacy includes (i) awareness of the causes of deprivation and the ability to move towards amelioration of their condition by participating in the process of development, (ii) acquiring skills to improve economic status and general well-being, and (iii) imbibing values such as national integration, conservation of environment, women’s equality, observance of small family norms. So, we do include aspects such as conservation of environment”. He lit his cigar.

“Oh” I said. I did not know that the National Literacy Mission addressed environmental perspective in the very definition of literacy. “Not many may know” I muttered to myself.

“I hope that those who implement the Mission know this environmental perspective” I said. I must have sounded sarcastic or unsure but the Professor continued.

So we are fine when it comes to inclusion of environmental aspects in the definition of literacy. To move on however I suggest that we focus on the English Language Literacy” He said this rather emphatically.

English language literacy in India is “estimated” around 10%. But the people who speak, read and write it well enough to be considered acceptable in England and USA are probably only about 2 percent of the population. The rest (8 %) can merely understand simple English and speak broken English with an amazing variety of accents. We need to escalate this percentage to at least 50% by 2060. Remember Dr Modak, much of the sustainability related seminars we hold, reports we write and read are essentially in English. 90% of India’s population that is not English literate and so will never get involved in Sustainability.

“Well Professor – I don’t buy this argument. If this was the case, then the Americans would not have led this planet to a situation so unsustainable – and they wouldn’t have elected Donald Trump as their President.” This was now my turn to checkmate the Professor. Professor smiled.

OK, let us look at the global initiative on Sustainability Literacy. Professor said. The Natural Step has launched a program on Sustainability Literacy at 2 levels complemented by E-learning

Under the efforts to reach Sustainable Development Goals (SDGs), we have Sustainability Literacy Test (SULITEST) of the Higher Education Sustainability Initiative (HESI)

The Sustainability Literacy test (SULITEST) is an online multiple choice question assessment. It assesses, in 30 minutes, the minimum level of knowledge in economic, social and environmental responsibility, applicable all over the world, in any kind of higher education institution (HEI), in any country, for students from any kind of tertiary-level course (bachelors, masters, MBAs, PhD).

All the questions in this assessment will ensure that future graduates have basic knowledge on sustainable development and both individual and organizational sustainability and responsibility. For this purpose, the scope of this assessment covers 2 types of questions: Questions on challenges facing society and the planet i.e. general knowledge on social, environmental and economic issues, basic understanding of the earth e.g. water and carbon cycles, greenhouse effect, etc. And questions on the organization’s responsibility in general and on corporate responsibility i.e. questions on practices for integrating social responsibility throughout an organization and questions on the responsibility of individuals as employees and citizens.

The target by 2030 is that 200,000 tests get carried out per year, out of which 50,000 are done by professionals.

There is now a Handbook of Sustainability Literacy: A Multimedia version edited by Poppy Villiers-Stuart and Arran Stibbe. This two-part Handbook has several interesting topics. You can browse this Handbook online resource by chapters from the paperback, additional chapters as well as Video interviews.

In this ground-breaking book, leading sustainability educators are joined by literary critics, permaculturalists, ecologists, artists, journalists, engineers, mathematicians and philosophers in a deep reflection on the skills people need to survive and thrive in the challenging conditions of the 21st century. Responding to the threats of climate change, peak oil, resource depletion, economic uncertainty and energy insecurity demands the utmost in creativity, ingenuity and new ways of thinking in order to reinvent both self and society. The book covers a wide range of skills and attributes from technology appraisal to ecological intelligence, and includes active learning exercises to help develop those skills.

“This sounds rather too sophisticated or elevated – whom are we making sustaibility literate – those already converted or an uneducated slum dweller or a farmer?” I wasn’t happy with the topics covered in the Handbook. Perhaps, for India, we will need to address the rural and urban segments separately for introducing Sustainability Literacy capturing their lifestyles

Professor lit his second cigar and took a deep puff

I think we need to think differently. You should read paper by Dr. John J. Kineman, University of Colorado, USA and Dr. Deepak Anand, Sri Sathya Sai Institute of Higher Learning, India – titled Roots of Sustainability in Ancient India 

In this paper, the Authors quote and interpret as follows

“Most ancient cultures have grown in the lap of Nature with reverence for nature in which all of its elements, mountains, rivers, forests, animals, etc., may be considered sacred. The Hindu scriptures like the Upanishads, Srimad Bhagavatam, Puranas, Vedas, and Bhagavad Geeta have also expressed the sacredness of various aspects of the environment and its conservation. Ancient texts like Kautilya’s Arthasastra have an immense amount of information on environment, natural resource management and prevention of pollution. The realization of this fundamental and ultimate Truth is that there is unity of all life and existence and the goal of human life is to merge one’s little self in the Divine to experience this unity.

The Vedas are the primary sources of not only moral enhancement for the economic progress but also guide to address ecology to achieve a true sustainability. The Vedas view human perfection and happiness from integrated perspectives, which embraces both material and spiritual values in individual and harmonious unity. The Vedas provide guidance to enlighten the inner human soul in order to preserve moral values, true purpose of life and care for Nature.”

I thought the Professor was right. We in India already had sustainability embedded in our culture – we need to revisit, unfold and recommunicate.

Integration of sustainability concepts with spirituality – anchored with the culture will make us understand the true Sustainability Literacy. Sustainability Literacy explained in the Handbooks or assessed through on-line tests is not going help– all we will get there is just the “information” but not the “messages and realization” that will bring in the behavioral change.

So are you Sustainability Literate in this perspective?

Professor asked me this question, extinguished his cigar and left.


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Blending Strategy, Design and Operations


In the university education, we are taught engineering designs with first principles.

In practice, we rarely attempt to design units applying these principles that we learn from the textbooks. This is probably because we know that there are stark differences between the principle based design and the design we put in practice.

Stoke’s law is customarily taught when we teach our students the theory of sedimentation. Stokes’ law makes the following assumptions for the behaviour of a particle in a fluid:

  • Laminar Flow
  • Spherical particles
  • Homogeneous (uniform in composition) material
  • Smooth surfaces
  • That particles do not interfere with each other.

We do not therefore design a sedimentation tank following Stoke’s law. We know its limitations. Instead, we use design criteria such as overflow rate, weir loading rate and retention time to size and arrive at the diameter and depth of the sedimentation tank. But remember that these design criteria make use of the first principles taught in our textbooks as the foundation.

We estimate the likely removal of Suspended Solids (SS) and the Biochemical Oxygen Demand (BOD) based on “performance equations” or “design graphs” where we link performance with overflow rates and retention time. For sewage treatment, these graphs are developed based on actual experience of removals of SS and BOD in practice from data pooled from several installations. So, we tend to believe them and rightly so. (Pity it is that we still do not have in India our “home-grown” national performance equations for designing sewage treatment plants)


Graph indicating BOD and SS Removal for Raw Sewage in a Sedimentation Tank as a function of Overflow  Rates and Retention Times

The design of the sedimentation tank is however not complete as all we now have are the outline dimensions of the tank based on design overflow rates and retention time.

For the design that we can implement, we need much more details. We need to decide on the type of influent well, hopper slope, type of scraper mechanism (single or double arm, straight or helical), skimmer, positioning of the motor drive (e.g. at the center or at the periphery) etc. These details are with the manufacturer/supplier of the mechanism or the equipment. Based on the outline dimensions, the manufacturer provides these details along with General Assembly drawings and preliminary cost estimates. The cost estimates include mechanical, civil and electrical works with specifications.


Typical Equipment in the Sedimentation Tank

You learn about these essential elements of design only when you reach the stage of implementation or practice and not in the classroom at the university. We however need to make student understand this important extension.

When I worked with Dorr-Oliver, we were shown videos of installation of equipment for the sedimentation tank (Dorr-Oliver Clarifiers). This made us understand both design features and the procedure of installation – including commissioning. This kind of training helped me to understand link between principles and practice.  

To increase the efficiency of sedimentation, chemical assist sedimentation is practiced. Designing chemical assist sedimentation tank requires laboratory studies where we attempt to use different chemicals and arrive at an optimum recipe. The recipe is often a concoction of alum, lime and polyelectrolytes. Based on observations made in the laboratory in a settling column, we come up with the dose of chemicals, estimate the generation of chemical sludge (specially to work out “K factor” (resistance) of the scraper arm, volume of the sludge hopper and the desludging schedule). We then guestimate improved efficiency of SS and BOD based on laboratory experience.

This “base design” however needs to be tweaked in the operational phase, as the experiments made on the settling column do not mimic the hydraulics of the real sedimentation tank. With a “reasonable” base design we adjust the recipe of chemicals during operation. The design process thus extends from first principles (e.g. stoichiometry, understanding flocculation and coagulation), to laboratory trials and finally arrives at the operational design. The students at the university do not get exposed to such a process where principles and operational designs are developed as a logical sequence.

There are situations when it is not possible to arrive at the outline dimensions – especially when designs are proprietary.  The textbooks we use do not contain the proprietary information. So, if we want to design a lamella separator instead of a circular sedimentation tank, then we need to reach out to the suppliers of the lamella separator, examine the catalogues, talk to the users or clients and gather the operational experience. Sometimes we need to invite the technology provider or equipment supplier to set up a pilot on the site and demonstrate the performance as Proof of Concept (PoC). With the advent of several types of proprietary equipment, we often land up with discussions with commercial vendors to take final decision. We try to open the “black box” as much possible through questions (based on first principles) and by checking the operational experience.

In all above, we often overlook or underplay the strategy part that should ideally precede the design. We limit ourselves to the engineering design. In the strategy, we need to ask questions such as

  • Why do we generate so much wastewater in the first place?
  • What is the source of SS?
  • Do we need a separate unit for removal of SS at all?
  • If yes, then do we use sedimentation or flotation?
  • If we use sedimentation, then do we adopt a circular tank or a rectangular tank?
  • How will we be addressing situations of increased flows or increased SS concentration?
  • How do we handle the sludge?

These questions require a discussion and making of scenarios. We need case studies and a dialogue with the “client”, potential vendor and the practioners. If we follow “flip method” of teaching, then strategy should form the core of the class room sessions.

How should we teach then the engineering design to make it interesting as well as effective?

We clearly need to blend strategy with design and operations. The subject needs to cover the process starting from first principles, laboratory work, outline designs, detailed design (focusing on equipment) followed by tweaks needed based on the operational experience. We need to “teach” in a narrative style.

The lectures will need to include case studies, videos and field visits with faculty drawn from both academia and practice. This is a difficult task and needs good planning and coordination.

I would propose that we conduct Winter/Summer schools of say 2 weeks on engineering design for pollution control following a blended approach. This school may do the necessary blending. I used in this post, illustration of design of sedimentation tank – but indeed we need to cover gamut of major unit operations especially those that have emerged in the last decade where the practice experience has still to mature in India. Examples could be membrane based processes and processes using nano-technology and those operations which use advanced biological processes.

These Winter/Summer schools may not limit to university students but also include professionals. If undertaken as a campaign say across 4 locations in the country, we will be able to train 250 students/professionals every year. A couple of years of experience of running such schools will guide us on how to replicate and scale up.

I wanted to speak with my Professor Friend about my point on blending strategy, design and operations. Professor was at a Sewage Treatment Plant that he frequently visits and conducts field research on what he calls as “operational optimization”.

Professor heard me while we walked towards the aeration tank. He seemed to agree but I saw him not listening to me very attentively.

He inhaled a deep breath near the aeration tank (like a sniff) and turned to the Supervisor “Avinash, I think you need to ramp a bit on the sludge recycling pump, the odor tells me that we are falling short on the MLSS (Mixed Liquor Suspended Solids)”. “Yes Sir” said Avinash.

With this instruction, Professor turned to me.

I decided to block the dates of my proposed Winter/Summer school based on the availability and convenience of my Professor Friend.

Let me know if you are interested to join me.

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Whats your Story?


In our profession, we are often required to tell a “story”.  We use presentations and summaries to communicate.

In order to be effective, we need to be good in making a presentation that is remembered. When we write couple of pages as a summary to our report, it must communicate that is the essential and serve as a “teaser” to make the reader go through the entire report.

I often tell my students and colleagues to master the skill of effective story telling. Unfortunately, these skills are not imparted in the universities and are just let go.

In making presentations, we need to have creative capability to organize our thoughts and presenting to the audience in a limited time. The presentation must convey the “substance” and engage the audience.

In writing an Executive Summary of a report we want to be sure that we don’t miss out anything that we want our reader to know. Most people are not interested to do a “full read” and many a times stick only to the Executive Summary.

Technique of PechaKucha 20×20 is an example of the first skill that I highly recommend. This technique should be experimented, experienced and mastered. PechaKucha is a presentation format where you show 20 images (slides), each for 20 seconds. Every speaker has thus only 400 seconds (approximately 6.75 minutes) for presentation.

The images in a PechaKucha “show” advance automatically and your talk should “flow” along to the images. Once you start, the slides move and you don’t have any control. You cannot stop, “rewind” or “skip”. You have to simply “perform” resonating with the moving slides. A simple format of PechaKucha can be therefore deceiving. You need to take PechaKucha presentation very seriously and rehearse.

PechaKucha format was devised by Astrid Klein and Mark Dytham of Klein Dytham architecture. PechaKucha in Japanese means “chit-chat”. The first PechaKucha Night was held in Tokyo in the gallery “SuperDeluxe”. Today, PechaKucha Nights happen in over 900 cities around the world, taking inspiration from Tokyo. The PechaKucha get-togethers are often held in fun spaces (essentially places for “thinking and drinking”) where people can show and share their work in a relaxed manner. (Alas! when do we get time and space to relax now-a-days!)


A PechaKucha Night

I feel that PechaKucha format is best suited when we hold conferences that often get crammed with speakers. Many a times, we stack too many speakers in a session (just to oblige) and the first speaker hogs the time by showing some 50 slides – ending with apologies. There is hardly any time left for the last speaker and for Q&A. The situation of the Chairman of the session is like the Speaker of the Indian Loksabha – helpless and hopeless.

Here imposing PechaKucha format can make wonders.

I remember attending a session at the IAIA (International Association for Impact Assessment) event where we could comfortably “accommodate” six presentations in just one hour. More than management of time, the presentations turned out to be very engaging and sometimes hilarious.

I will recommend you to read guidance materials on how to prepare a PechaKucha.

Take a look at presentation by industrial designer Dave Bramston. Follow him during one of his journeys in China to understand Upcycling and innovative product design.  Or watch David Gunawan’s presentation on his ideas on sustainability and healthy eating as a chef. In his talk on “Promoting Sustainability and Consciousness in Food” you can see  that David strives to find local, organic foods by creating a healthy and viable relationship with farmers.

Few years ago, I started experimenting PechaKucha format in my office with my colleagues. And wow, it opened new doors to creativity and composing – leading to confidence in communication (my 4c’s). I witnessed some outstanding and bold presentations.  I am sure my colleagues gained significantly by preparing, making and listening to such presentations.

Imagine if conferences in India start holding one PechaKucha session to start with.  It will be something so effective and transformational! Let us demand such PechaKucha sessions.

The second skill I urge my students and colleagues is to master writing of an Executive Summary. Executive Summary is often the toughest piece to write. Some people read the Executive Summary to find out if they need to read the full report.  It’s this group that you really need to worry about, because they’re likely to include the Board or executive team of your organisation, as well as journalists. What goes into the Executive Summary, therefore, is the message that they’re going to take away, that may be spread more widely. For these people, the Executive Summary is their window to your full report.

So, when you are writing your Executive Summary, you should always keep your intended audience in mind and write your summary for them. Unfortunately, Executive Summary is given a low priority by many and is written at the “last moment” and generally with less attention than it deserves. I have seen umpteen number of instances where a report, painstakingly prepared, gets abused or misunderstood because of the poorly written Executive Summary.

Broadly, an Executive Summary summarizes the main points of the underlying paper, and draws out the key points. A good way to think about the key content of the Executive Summary is to imagine meeting your boss or CEO in the car park or at the coffee machine. These conversations are generally difficult! You often miss the point.


Ensuring Clarity, Maintaining Relevance and Using the right Keywords is Important

An Executive Summary has typically three sections: introduction, main body and conclusion. The main body of the Executive Summary needs to be stand-alone without the reader having to refer to the main report. But remember that the Executive Summary should not be stuffed with overwhelming Data or Tables. You only provide a top view and make a reference. Please refer to the Guidelines

There are how a few commercial software tools available to “generate” a summary. Visit Some tools are even online. See

Do try these tools and have some fun. Indeed these tools are not a substitute for writing an Executive Summary. There is no option but to sweat.

In the field of Environmental Impact Assessment (EIA), a Non-Technical Summary (NTS) is considered as a special form of an Executive Summary. In countries like United Kingdom, NTS is asked as a requirement in the preparation of an EIA.

A NTS is not equivalent or substitute to an Executive Summary. It should be written in a local language. But a NTS is not a translated version of the (Technical) Executive Summary.

Writing a NTS is an art where we use less technical jargon and use more easy to understand words or expressions. We should not take the reader for granted. For example, we should know that an ordinary citizen does not know the term BOD and the abbreviation may imply to him/her as Board of Directors and not Biochemical Oxygen Demand.

IAIA has come up with guidelines on how to write a NTS. In India, we do not have such a requirement. We should ask MoEFCC to specify so by amending the EIA Notification.

So, while selecting a new Team member in your organization, it is a good idea to ask for a PechaKucha presentation and give an exercise of  writing an Executive Summary. I guarantee you that anyone doing good in these two “tests”, will be an asset to your organization for effective “story telling”.

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Who do you want to be?


For the past few years I have been organizing a Career Counseling event called “Disha” (means “direction or guidance” in Sanskrit) for the interest of students and young entrepreneurs. Visit Disha for more details.

I was very keen to have my Professor friend to speak at the Disha event but he was simply not available.  Finally, due to my persistent coaxing, he agreed to join.

In Disha, we do an interactive session where we discuss with the students what they want to be. I thought moderation of this session by the Professor will make a big difference

When we got into the auditorium, the hall was already packed with students. I went to the dais and introduced the Professor. His bio-data was 10 pages long and I faced difficulty to condense it in 2 minutes. But the students looked impressed.

Professor thanked me for the invitation. He spoke a few words on how important it is to decide what you want to be in the early phase of life. He then proposed that the session should be run in an interactive manner.   All agreed.

He asked the girl in the fourth row wearing spectacles “So what do you want to be”. The girl stood up and said “I want to be like Wangari Maathai or like Vandada Shiva or Kate Stohr or Safia Minney. I am really inspired with the great humanitarian work they have done and shown leadership”


Wangari Maathai


Vandana Shiva


Kate Stohr


Safia Minney

Professor took a deep puff from his cigar and said “That’s not the right choice. All these women have done is essentially a PR work, have sought publicity with no measurable impact and have in fact created obstacles in the development pathways. I suggest you rethink and dream of becoming like Kiran Shaw Muzumdar or Naina Lal Kidwai who are shining examples of women guiding India’s business – with (apparent?) interest in the sustainability e.g. application of biotechnology or sustainable finance”

I had reservations on what Professor said. So I pointed out that Wangari Maathai, was a woman of many firsts: not only she was the first African woman and first environmentalist to bring home a Nobel Peace Prize but being the frontwoman of the United Nations Billion Tree Campaign. Vandana Shiva has always been an outspoken campaigner for protecting seed biodiversity against biotech-profiteering and genetic engineering. Her grassroots approach has helped to redefine food security and the green revolution as a movement that empowers local food growers, rather than big agribusiness. She is the founder of Navdanya, a NGO based in Dehradun, India that promotes organic farming and seed-saving. Kate Stohr worked hard to provide disaster relief and reconstruction services during the Hurricane Katrina and Southeast Asian tsunami crises. In 2005, her organization AFH won the TED Prize which allowed them to develop “The Open Architecture Network”, a unique open source platform for sharing sustainable and humanitarian design solutions. Safia Minney is as one of the world’s foremost social entrepreneurs, establishing World Fair Trade Day (observed every second Saturday of May).Her  work strives to change the fashion business by addressing integral issues of fair wages, gender equity, transparency, accountability, capacity building, improved working conditions and environmentally sound practices. These women are examples of careers to follow

Professor did not like my intervention.

He turned to the boy sitting in the last row with a full white shirt and a red tie. “How about you Sir” He asked in all politeness.

“Well, I am an engineer and want to study more to take a Doctoral degree from a reputed University in the United States. Then I want to be a Practicing Professor like Prof S J Arceivala of India or Prof W W Eckenfelder of the United States or Professor Ryoichi Yamamoto of Japan”

Professor said “Well, let me be honest with you, all these Professors you cited were or are essentially consultants in “disguise”. Indeed, they are excellent in the class rooms, writing books etc. but half of their energies are or were directed in grabbing consulting projects or running consulting outfits (sometimes remotely)  while taking shelter at the universities or international bodies.


W W Eckenfelder


Professor Yamamato


S J Arceivala

I simply did not like Professors caustic remarks on these outstanding Professors. I said that’s not true. Professors must get into consulting to bring the perspective of real world to the students. Professor Ryoichi Yamamoto is the Professor at the Institute of Industrial Science, University of Tokyo. A highly respected expert in environmentally conscious materials and design, as well as in Life-Cycle Assessment.  He is currently the Science Advisor for the Ministry of Education, Culture, Sports, and Science and Technology, the President of The Institute of Life Cycle Assessment Japan, the President of The Eco-Efficient Forum of Japan, the President of International Green Procurement Network, and a member of steering committee of Eco Products Exhibition. His talks in the class room are therefore laced with his rich policy experience.

Professor Eckenfelder was known internationally as a pioneer in the field of water treatment and a leading authority in industrial wastewater management. He was an environmental engineering professor at Manhattan College, the University of Texas-Austin, and Vanderbilt University. Eckenfelder was a prolific writer and he influenced countless numbers of engineers through his many textbooks, hundreds of journal articles, and courses. Among Eckenfelder’s more than 30 technical books, his second book, Industrial Water Pollution Control published by McGraw-Hill, is a classic text initially intended for the classroom. Eckenfelder was the founding principal of several companies, including AWARE, Inc. in Nashville, Tenn., which was later named Eckenfelder, Inc. in his honor. AWARE merged in 1998 with Brown and Caldwell, a California-based full-service environmental engineering firm.

After his studies at the Harvard University, Professor Soli Arceivala was Professor at VJTI in Mumbai, then Director of National Environmental Engineering Research Institute, Nagpur and finally Advisor at WHO. He established and operated Associated Industrial Consultants (AIC) in Mumbai successfully that was later acquired by Montgomery Watson. Prof Arcievala published several classic books on wastewater treatment, water reuse and natural wastewater treatment systems where case studies have come from his practice experience.

My Friend Professor did not pay much attention to my defense of these distinguished Professors cum Consultants. He continued his questioning. He now asked a student sitting in the front row who was holding an iPad in his hand. He seemed to be googling the personalities that were getting mentioned. “How about you?” Professor asked him.

The student got up from his seat holding his iPad, put on his spectacles, took some time and said in a very thoughtful voice “I believe that you cannot mainstream sustainability unless you sit at the top of the organization or at least hold an anchor position and “shake” or “inspire” the system. I want to be Anand Mahindra of Mahindra & Mahindra or Jochen Zeitz of Puma or the like”

Professor laughed. “Strange, how you young minds don’t see the chameleons in the business. All these names you mentioned are actually businessmen focusing on making profits and getting on the top of the markets “somehow”. Sustainability is just a clever strategy that they discovered and they were smart to project and claim that the sustainability is now in the DNA of their organizations. Go and ask folks working for them – you will see a totally different picture”


Jochen Zeitz


Anand Mahindra

I thought that Professor was very biased and negative in all his judgements. The poor iPad student sat down in despair. I butted in immediately and said.

Friends, let me tell you a bit about Jochen Zeitz. He began his professional career with Colgate-Palmolive in New York and Hamburg and later joined PUMA in 1990. In 1993 he was appointed Chairman and CEO of PUMA becoming the youngest CEO in German history to head a public company at the age of 30. Zeitz managed to turn PUMA from a low priced, undesirable brand into one of the top 3 brands in the sporting goods industry. In 2008 Zeitz introduced PUMAVision, an ethical framework defined by the four key principles of being Fair, Honest, Positive and Creative as applied to all professional behavior, business procedures and relationships throughout and outside of PUMA. Zeitz conceived the Environmental Profit & Loss Account (E P&L) and coined the term and in May 2011 he announced PUMA’s Environmental Profit & Loss Account that puts a monetary value to a businesses use of ecosystem services across the entire supply chain. In 2008 Zeitz founded the not-for-profit Zeitz Foundation of Intercultural Ecosphere Safety to support creative and innovative sustainable projects and solutions that balance conservation, community development, culture, and commerce (the “4Cs”) in a quadruple bottom line approach, promoting an inclusive, holistic paradigm of conservation that enhances livelihoods and fosters intercultural dialogue while building sustainable businesses.

Zeitz has received the Strategist of the Year three times from the Financial Times “Entrepreneur of the Year”, “Trendsetter of the Year” and “Best of European Business Award 2006″. In 2010, the German Sustainability Foundation gave Zeitz an award for Germany’s most sustainable future strategies. In 2015 Jochen Zeitz was awarded the Special Advocacy Award for Responsible Capitalism.

Anand Mahindra is included by Fortune Magazine among the ‘World’s 50 Greatest Leaders’ and featured in the magazine’s 2011 listing of Asia’s 25 most powerful business people. Anand is a staunch advocate of promoting girl child education and in 1996, founded Project Nanhi Kali, which provides sponsorship to underprivileged girls across India including, material support (e.g. school uniforms, school bag, shoes, socks, stationery etc.).

A student of the arts and culture, Anand believes that the study of humanities is essential in shaping leaders of the future. In November 2010, he donated $10million to support the Harvard Humanities Center in honor of his mother, Indira Mahindra. It is the largest gift for the study of humanities in Harvard’s history.

Anand is co-founder of Naandi Danone, which is the largest safe drinking water provider to rural areas of India, catering to nearly 3 million customers. Founded in 1998, the Naandi Foundation works in 4 broad sectors: safe drinking water, support for urban school children, work training for unemployed youth and agricultural marketing.

The iPad student seemed to be convinced.

The Professor frowned.

The interactions continued and the students proposed several role models of India such as M C Mehta, the Environmental Lawyer, Dr Deepak Apte, Director of BNHS, Sunita Narain of Centre for Science & Environment and for each proposition, Professor continued finding faults and I kept on pointing the good work done by these leading personalities.

By then, most students realized the negativism and an attitude of finding faults with the Professor. One girl from the sixth row who was wearing a bright Tee shirt that had a slogan “We Dare”, got up, faced the classroom and spoke in a tone of leadership. She said

“Well Sirs, we now at least know what we don’t want to be. We don’t want to be like the Professor Friend of yours. And we want to be positive like you”

My Professor Friend was shocked with this statement. There was a silence in the class. He extinguished his cigar in the tray that was placed on the table and exclaimed.

“You mean you want to be like Dr Modak? He is a shining example of a thoroughly “kaleidoscoped” personality, with career profile showing utmost confusion and a complete lack of clarity. He has been a Professor, a Consultant, a Corporate Honcho, An Author and Editor, an Entrepreneur and an International Adviser to Governments & Financing Institutions. He also works as an NGO for spreading awareness and conducting training on environmental management & sustainability. I could never understand what this gentleman wanted to be. He has simply been a “free radical”. You will waste your time and career following him

I thought this time Professor was absolutely right. So I kept shut

I ended the class thanking the Professor.

I will be organizing the next Disha event in third week of June in Mumbai. Will keep you all posted. Stay tuned at

Cover image sourced from