Science AMA Series: I'm Kartik Chandran and I’m working to transform wastewater into a valuable resource. My approaches involve treating waste with the goal of producing useful resources such as fertilizers, chemicals, energy sources, and clean water. AMA!


Hi reddit!

I became interested in science because I grew up in India having access to clean water for only about a couple of hours each day, where we also had limited access to reliable power. Years later I realized that these were minor inconveniences compared to the ordeals faced by people in many parts of the world who travel many miles each day to get a few liters of clean water. In school I learned how to design large scale wastewater treatment systems to convert sewage into clean water, but then it dawned on me that such systems typical of the developed would not work very well for the majority of the developing world's population, which doesn't even have access to reliable electricity and power.

This gave rise to my work today as an environmental engineer and Professor at Columbia University linking clean water and sanitation to the resources needed to achieve them, such as energy and chemicals. Today, my focus is to develop solutions and technologies to address even more global grand societal challenges of our time such as clean water, sanitation and nutrients for agriculture in conjunction and not in isolation.

My research has involved approaching wastewater treatment with the goal of producing useful resources such as fertilizers, chemicals, and energy sources, in addition to clean water, in a way that takes into account the climate, energy, and nutrient challenges we face today. Me and my teams have tried to tailor solutions to be appropriate for the places we’re working in. For example, we’ve worked in rural Ghana to develop source-separation toilets to both provide sanitation and recover nutrients for use in agriculture. Recently, I have been collaborating with research groups in Brazil focused on facilitating energy efficient wastewater treatment there. Through our approach, sewage treatment plants can discharge better water quality to receiving water bodies such as Guanabara Bay, where sailing events for the 2016 Olympic Games will be held. Our technology, which involved using bioprocess technologies to enhance the capacity of the Alegria sewage treatment plant, was prototyped at Columbia University and demonstrated in Rio de Janeiro.

I’ll be back at 4 pm EST (1 pm PST, 9 pm UTC) to answer your questions, ask me anything!

Thanks for spending time with us today.

Large one-off projects are great for proof of concept but even in a country like the US we have a crumbling water and sewer infrastructure. What kind of behavior change in both the government and populace is being accompanied with these projects to ensure their sustainability from point of use to end product?


This is an excellent point.

There needs to be more widespread acceptance of such developments for maximizing impact. There is increasing recognition that the production of clean water requires energy, chemicals and other resources. As such there are global efforts to reduce the footprint of clean water production. From our interactions with the public and private sector, there is significant interest and actual work underway to connect these different sectors towards synergistic benefits. I am not suggesting that all systems look the same, but such synergies can be explored (are being explored) where they make sense. Some of these newer developments are not at the proof of concept any longer. During the past five years, recovery of resources and resource efficient wastewater treatment have been at the forefront of full-scale implementation in many parts of the States (and other nations).

I have no questions, I just want to thank you for your work.



Hello Mr. Kartik Chandran, thank you for doing this AMA! You and your teams are definitely doing some very important work!

My question: If you were the mayor of Rio de Janeiro and would have plenty of financial resources, do you think you can solve the huge environmental wastewater challenges of the city? Where would you start? Would it eventually be possible to even make profit out of this wastewater?


This would require a muti-pronged approach. First, I wold target the diffuse wastewater streams produced in the favelas around the city using decentralized treatment systems. A few years ago, I had traveled to Rio das Pedras, which is a prominent favela in the southwestern part of the city. I was pleasantly surprised to see a highly connected pipe network conveying the sewage out of the slums but right into the surrounding lagoon. A first step would be implement small-scale distributed treatment processes at this level. This is needed, since not all the favelas can be connected to the main wastewater treatment plant in the city.

Second, where possible in the city, I would improve connectivity to the centralized plant(s) in Rio. Currently, the plants are running far below capacity, partly due to lack of sewage inputs to them.

Third, I would pursue efforts to extract more from the existing centralized plants. Currently, the main objective at the Alegria plant, for instance, is organic carbon removal. However, significantly more benefits could be achieved (such as improved water quality in Guanabara Bay), if the plant to remove nutrients such as nitrogen and phosphorous as well.

In terms of profit (or at least better economics), there are a few options. First lowering the net operating costs by expending lower amounts of energy to achieve advanced treatment. Second, by converting the organics not just to biogas but to chemicals, which can help with sewage treatment itself and finally (if the market is there) by recovering some of the nutrients for agricultural reuse.

It is not commonly known, but cleaner water will also reduce the greenhouse gas footprint of the plant and with cap and trade, this could offset costs as well.

Thanks for doing the AmA! Till what extent can wastewater treatment solve the problem of water shortage in various regions of scarcity? How does the equation vary due to the effects of climate change in the future?

I understand this may not fall directly under the scope of Kartik's work, so I apologise if it violates any rules.


Direct and indirect potable reuse of wastewater could indeed contribute to overcoming water shortage. Currently, we use potable quality water for the most part not just for drinking (which is only about 2-4L per capita per day) but also for washing, flushing toilets and agriculture (among other end uses). The reuse of treated wastewater for non-potable uses could significantly reduce the overall societal water footprint. Further, through reuse, since we are not following a strictly linear model of once-use and discard, the overall water cycle becomes less exposed to externalities such as climate induced variability.

I recall hearing about using Thermal Depolymerization to create useful compounds out of waste (including organic matter) but it never seemed to take off. What makes the bioprocess technologies more practical, and how efficient is the process in term of creating usable resources?


I am not familiar with thermal depolymerization myself. However, with any such technologies, costs and other inputs (such as energy) are the primary deciding factor that dictate widespread use. Other factors also include ease of operation. Some of the bioprocess technologies that we work on are already part of or can be integrated into existing wastewater treatment infrastructure and some of them actually consume less energy than the current options.

Ultimately, both physical-chemical and biological processes (or a combination thereof) could be eminently suited for achieving the end goal- clean water and sanitation.

Hello Prof. Chandran,

I was wondering if you could explain more which bioprocess technologies you're implementing at the Alegria sewage treatment plant. Since most sewage treatment plants don't have the money/space to suddenly expand their processes, I'm interested as how you're increasing the BOD/nutrient removal without significant changes to the plant treatment scheme. Is this an anammox process or something different?


Last year, students at Columbia and UFRJ (in Rio) had modeled and prototyped as a first step biological nitrogen and phosphorus removal processes (somewhat conventional) at a variety of influent flows and optimized the system configuration and operation to maximize not just COD but N&P removal as well. We were careful not to suggest increases to reactor volume. Therefore, in a sense, this was a classic engineering effort to extract more from the existing process. No anammox (yet).

Hi! Thanks for doing this AMA!

Does the type of wastewater affect whether or not you're able to turn it into chemicals, fertilizer, etc.? Can you see this also working in developed countries and on smaller scales? I work at a brewery and wastewater (and water usage in general) is one of the biggest topics we talk about - especially for places like California. Most of us can't afford to treat our wastewater but I'm always interested in what kinds of technologies exist for it.



Excellent points.

The type of the waste stream (composition, concentration of constituents) indeed governs the practicality of the recovered endpoints. Industrial wastestreams could be a rich (concentrated) feedstock for conversion to chemicals or fuels. In fact brewery waste could be particularly applicable for recovering a wide spectrum of carbonaceous endpoints.

We really need to focus a lot more at developing and implementing systems, which are practical for application at the small scale (communities, buildings, households). In the developing world, this is less of a challenge due to concentrated streams (and ironically helped by a lack of pipe networks). In the developed world, if we could stop mixing black and grey water streams, smaller-scale systems would look more attractive. There are some examples of this in high-rises in Manhattan itself, where water is recycled and reused for non-potable purposes. In our building, we are further co-converting food-waste and sewage sludge to energy and fertilizer. For any of these to work, appropriate demand needs to exist.

To the general public, direct potable reuse sounds unsanitary and unappealing; when, in fact, it is a valuable and high quality resource for high water demand. How would you plan to change public opinion to be open to directly using the treated wastewater effluent for potable reuse?

Also, have you and your research team encountered pharmaceutical contamination in your studies?


This is a valid point. The fact remains that most of the States are not faced with the need for DPR (although this is changing). There are also some unknowns such as residual concentrations of trace organics (such as pharmaceuticals).

The co-evolution of improved DPR technologies and education could perhaps contribute partly towards removing the 'ick' factor associated with DPR. A good example is Singapore with NEWater.

To the general public, direct potable reuse sounds unsanitary and unappealing; when, in fact, it is a valuable and high quality resource for high water demand. How would you plan to change public opinion to be open to directly using the treated wastewater effluent for potable reuse?

Also, have you and your research team encountered pharmaceutical contamination in your studies?


Indeed, we have detected measurable concentrations of selected trace organics in our studies. However, on the positive side, we have also detected the capacity of the organisms present in treatment systems to metabolize some of these compounds.

Hello Mr Chandran

I work at DC Water Blue Plains, the largest wastewater facility in the world and I was wondering If you use some of the techniques and methods we use here and which ones that you use that you have found most effective.

For example we produce class A biosolids recycled to fertilizer and other soil enrichers. We also use microbes and bacteria to help breakdown wastes before returning them to their natural environment.

Unfortunately the most effective methods we have found are building digestors, green , grey and blue infrastructure assets. Unfortunately these along with a treatment plant have a large capital cost that many of the nations you work with can't afford or have expertise in. This is why micro level efforts such as yours are so important. Thank you for doing this AMA


Thanks, my group has worked with DC Water for quite a few years now. Our collaborative work has focused mainly on how to reduce the energy demand for biological nitrogen removal and understanding the impacts of thermal hydrolysis on the wastewater treatment process itself - ultimately directed towards meeting the water quality of the Chesapeake Bay. We ahad also worked on quantifying the greenhouse gas footprint of the biological process at Blue Plains itself.

I completely agree that some of the approaches used in the developed are not applicable in the developing or underdeveloped world for the following reasons. (1) Lack of reliable energy supply to run such plants, (2) lack of connectivity to sources of wastewater, sewage, or fecal sludge (3) operational cost and complexity.

This is exactly where the practice of resource recovery comes in- not to produce energy or chemicals to compete with the energy or chemical industry- but to drive the process of clean water and sanitation itself.

Many treatment plants already harvest solids for fertilizer and methane for energy... What are you doing that makes this process more efficient?


In the developed world, we focus on treatment processes that use less chemicals and energy while achieving water quality permits. Examples could range from shortcut nitrogen removal processes, anaerobic fermentation for producing volatile fatty acids to enhance nitrogen and phosphorus removal or converting the methane in biogas to chemicals ( such as methanol, that drive nitrogen removal). A lot of plants produce biogas and flare it, since they don't produce enough of it to justify clean up and use.

A lot of great organizations introduce novel ideas to better living conditions in low income areas, but often it is seen that a few years after they leave there are is no system in place to maintain and improve the projects, effectively making all progress null in the long term. What measures does your group implement to ensure the long term success of your projects?


Both in the developed and developing contexts, capacity building and education are key. We have visiting engineers and scientists who we host here in New York. We also have researchers in my group, who often work on site at different project locations.

This is a key issue, thanks for bringing it up.

It seems you're working toward systems for use by larger organizations and local governments. Do you think this would be available to a private home or individual in the near future? Of course, with time, it could be downsized, but how soon?


We have traditionally worked with systems applicable for both centralized and decentralized treatment. These range in scale from a billion gallons per day to about six individuals per day. We are at a point where it is not inconceivable to develop taliored solutions at the household level.

Difficult to say how soon this might be available more widely and commercially.

What obstacle(s) do countries typically face when attempting to mainstream sustainability (as far as recycling water, energy, ect)? In other words, why has this not become the global priority it should be? What's the problem?


This is a very complex issue, but I will try to provide some input. Some parts of the globe are simply not faced with the water pressures that others are. Therefore, the incentive for water reuse may not exist. On the other hand, the price of energy has been historically quite low.

More recently, there have been some shifts, which have led to a global explosion in energy efficient sewage processing and resource recovery. These include the following. 1. Increasingly stringent water quality limits being imposed on sewage treatment plants (which necessitates far higher energy and chemical usage and much bigger plants) 2. Varying price of energy and lack of access to petroleum derived chemicals

These factors have led the industry to significantly re-think the traditional models for producing clean water.

In the developing and underdeveloping world, the issues are somewhat more complex and include other pressures such as lack of food security and education. There are also alternate models for clean water (purchasing bottled water) and a systemic lack of sanitation. The absence of or absence of enforcement in environmental regulations is also a challenge. However, I see this as a big opportunity. There is increasing recognition that that lack of sanitation poses a significant detriment to the national GDP, which has led to increasing awareness and a demand for better sanitation practices (for instance, eliminating open defecation). Also, in communities, where sanitation has been traditionally lacking, we don't need to repeat all the mistakes we have made step-wise in the developed world. Rather, we can leapfrog directly to recovery technologies as applicable or to a combination decentralized and centralized systems for clean water, sanitation and more.

Technology alone won't do it however- education and regulatory support are key.

What can larger US based water and waste water companies do to help? Charitable contribution is encouraged and matched by my company.


Thanks for asking.

Larger water and wastewater companies could help not just in terms of technology development but could also act as a medium for connecting, translating and implementing the technologies with the appropriate end users and communities.

Hello Mr. Chandran, I'd like to know your opinion on low-energy, biological techniques for treating water, like those used by proponents of Permaculture, such as evapotranspiration basins for blackwater, wetlands for graywater, floating wetlands for lake/river cleanup, and fungi-innoculated bales for bacterial charge reduction (as proposed by Paul Stamets). Is it possible to upscale them? How do they compare to more complex, more engineered solutions?


I am not very familiar with this specific option. However, this is a fairly complex issue that we are discussing here, which is probably well served by an eco-system of solutions.

Hi! I have to ask. What were the challenges of doing your research? Are there any unintuitive side effects from such a sanitation system?


On the technical side, there are challenges associated with process development, implementation and optimization and especially linking conventional science and engineering to such an application (which is nevertheless needed). Another big challenge is to build local capacity to promote adoption and long term sustainability of the solutions. An unexpected positive impact has been a significant increase in interest from the financial and information technology fields towards some of our processes.

Hello Prof. This is quite a noble cause accompanied by great work and results. What has been the most rewarding part of building something that is effectively changing the world?


Thanks for your comment.

My biggest reward has been to work with some of the brightest minds and some of the most forward thinking individuals towards addressing this global challenge. I honestly think that this is just the beginning.

Good morning! When comparing your novel waste water treatments to existing treatments, do you often run tests against the uptake capacities and uptake kinetics of ion exchange resins? If so, what resins have you found to be the most commonly used in the current industry of waste water treatment. I am working on a project involving resins for water treatment, and am having trouble finding much literature on the topic. I hope you answer, and best of luck changing the world!


Sorry, we have not worked on the efficacy of resins for water treatment. Perhaps this is something that the resin manufacturers or treatment plants themselves could help with.

Hi Kartik thanks for the ama! Im always interested when it comes to quality of water and always a bit worried, specially because of fluoride and chlorine. By tour experiences are there any natural DIY ways of treating tap water for those chemicals, i read somewhere that ascorbic acid neutralizes clorine in water, but what about fluoride? Im from brasil and have also heard the use of plants to treat water in many ways, Moringa for instance can treat for bacterias and other bio contaminants. Any other info on this matter will be greatly welcomed.


Hello, I am anecdotally familiar with some of these alternate approaches for post-treatment. However, this is not my field of experience and therefore don't have any specific recommendations.

Less fertilizers and chemicals...more clean water and energy!


Perhaps all or some of the above based on local demand.


I'm currently an undergrad studying to be an environmental engineer because I share the same passion that you seem to have in improving the working relationship between our cities and the environment that supports them (via systems like wastewater treatment). My question to you is this: How can someone like me best prepare themselves to be a useful addition to this field of work?


You are already on your way - having identified the links between urban infrastructure and the environment. Personally, I always like to connect the fundamental research that we pursue to real-world applications. Additionally, sometimes the answers we look for are not always within our specific field of expertise. It is therefore good to try and integrate knowledge and information from other fields (for instance, biology and engineering). I would also strongly encourage you to gain some field-experience even during your formal education to be able to understand and appreciate real-world complexities and uncertainties. This cannot all be obtained from just classroom learning.

Good luck in your pursuits and let me know if I could help.

For all engineers interested in working in the water/wastewater development sphere full time:

  1. How would you recommend making the transition from industry in the United States into working in a developing world context? It seems like there are multiple routes: small social enterprise (business implementation), academic research and studies, large government agencies, and global and local NGOs.
  2. With the increasing number of highly educated and qualified local engineers, where do engineers from the US and other outside nations fit in without taking a local's job?

Extraneous personal info: Ever since I was in high school, I have wanted to work on water and sanitation improvement projects in the developing world. I went to college and focused on wastewater engineering, and for the past five years I've worked on a variety of water, wastewater, and stormwater engineering projects in the US and overseas in order to gain engineering design experience and get my Professional Engineering license. My plan was to get my PE license and then that would mean that I'd finally have enough engineering expertise to work full-time in a developing country designing wastewater treatment systems. Well, I received my PE license earlier this summer and am now looking into how to be the most effective engineer I can be.


Congratulations on getting your PE license.

Perhaps another way to look at your question is the following. The challenges associated with water, sanitation and environmental health are quite complex and need an amalgamation of expertise, backgrounds and training to be addressed. Therefore (as you rightly pointed out) partnerships with local bodies are key for the success of any implementation project and its longer term sustainability. The increase in local capacity is actually a positive in my opinion and could lead to more efficient and a more competitive workforce and industry not just in the developing world, but also in the developed world.

Do you think there is one technique/method which is currently being developed which will solve the clean water problem? If so, which one. If not, do you have any ideas in mind as to what this method may look like?


I don't believe that such a complex issue could be solved with a single technique or approach. There are also socio-economic and cultural aspects to this overall challenge, which means that technology alone won't provide a solution - it could be a component.

The ultimate objective is to protect human health. Whatever form the overall approach or technology assumes, this objective needs to be met, in an economic and context-specific fashion.

How can one invest to support this type of work?


Investments are direly needed in this field. We are in the process of organizing a think tank to help prioritize directions and level of support in the overall direction of global sustainable sanitation. (Happy to connect offline to discuss)

There are some major philanthropic foundations that have catalyzed significant activity, but a lot more is needed. Some specific investments are needed on technology development, field-testing and enabling full-scale implementation- this support could be directed towards technology developers, universities and to key public or private institutions to facilitate testing and scale up. Investments are also needed towards broadening education and capacity development in this sector - which could be directed towards educational institutions which excel in this field and also cater to global audiences.

Hi Dr. Chandran,

Thanks for the work you do. You neglected to point out your recent big-deal award in your bio (hey everyone, he's a certified genius!). It's really encouraging to me that people are paying attention to your work, and by extension to the entire field of wastewater treatment. This isn't a glamorous occupation, so we need all the good press we can get so people will realize how important it is to continue researching and improving.

We have a problem in this country and around the world getting people to fund water and wastewater infrastructure. It's expensive to build and expensive to maintain, and once it's built people take it for granted. Do you see any potential breakthroughs on the horizon that could radically change cost structures (maybe 5-10x cheaper than current CAPEX and OPEX) so that we can get over these cost hurdles?

Also, what are your thoughts on the new Ghostbusters movie?


Thanks for your comment.

There have been some really significant breakthroughs in the individual components that could potentially lead to the cost-structures that you point out. (I also agree, this is the scale of improvement that we should be targeting). The breakthroughs have been on the biological, physical, chemical, materials, sensing and monitoring aspects (I am sure that I am missing a few). This is all good. What we must now make sure to do is to use such breakthroughs for envisioning and implementing a radically new pathway towards clean water, energy and sanitation, rather than going back to just another version of the old model.

I was just thinking about this over the weekend - I'm wondering what currently happens with waste today... is it different from municipality to municipality, or region to region, or all the same? Is there anyone currently doing anything like this? Where does the fecal waste currently go?



The relative composition of domestic wastewater (sewage) in the context of piped sewers is largely similar. However, there is significant variability associated with fecal sludge quality, depending on community ablution and washing practices, the period of incubation and mode of conveyance. Additional inputs such as trash add more complexity to the composition and the processing techniques. There are different ways by which fecal sludge is handled including composting, treatment in anaerobic lagoons, anaerobic digestion, direct application for agriculture or just discharge to the environment. Conversion to biodiesel is somewhat novel.

Ap kaise hain, Chandran-ji.

I live in Pueblo, Colorado, which is home to just over 100,000 people. Our county commissioners have just won a $400 million case against Colorado Springs to the north of us, because the sedimentation from their urban expansion, and the growing amount of impermeable surfaces which contributes to run-off, is filling our Fountain Creek with toxic sediment and causing losses of land and property devaluation from mudslides and floods that inundate land along the Creek with high amounts of selenium and arsenic.

We are planning to build a damn with part of the money, which will mitigate the problem of land loss from mudslides and flooding, but we still have the problem of selenium and arsenic toxicity in the sediment. So even if we dredge the sediment from the river, we're not sure what to do with it, or how to reduce the toxicity so that it can be usable as a building, planting, or 3D printing resource.

I have suggested the idea of a large-scale micofiltration system, but am unsure of the total cost effectiveness of such a plan. Can you recommend that or anything else along those lines for extracting the selenium and arsenic? Some manner of permaculture process is preferable, but I'm curious of your best recommendations even if they are industrial and chemical-intensive processes. I'd like to be able to recommend dredging the river and using the sediment to shore up the river banks with mud-clay bulwarks + plants with strong root systems to keep land from washing away (preferably plants which are effective at extracting toxic substances from the soil, like hemp or sunflowers).


Sounds quite complex indeed. I'd have to learn and understand the specifics a bit more prior to coming up with recommendations. Thanks for bringing up this issue.

What was it like to receive the MacArthur "genius grant" and how has that impacted your work?


It was truly unexpected. The MacArthur fellowship has provided an excellent platform for me to bring to the public forefront issues relating to clean water, energy and sanitation. I see it as a significant validation for the field as a whole. On a lighter note, I can finally discuss some of these topics over dinner!

Professor Chandran, thank you for your time.

is there any bleed-through in your recapture techniques and the various processes being developed for seawater desalination? could your techniques work hand in hand with the desalination research community?

again, thank you for your work.


Hello, we are working on some processes that work at high TDS concentrations. One possible connection would be towards handling the brine that is generated from desalination.

Thank you for taking the time to think with us here on r/Science, Dr. Chandran!

Given your CV and your history in this field, I'm pretty sure you've already thought about this, but I feel compelled to ask anyway: have you considered what the feasibility of these bioprocess reclamation/purification technologies might be if they were scaled down?

I DO understand why it often makes sense to centralize purification processes, especially in large settlements and cities, but would there be any merit in developing a way for individuals to have micro-reclamation/micro-purification systems within/near their homes that accounted for the use of small groups of people (e.g. their families, maybe their neighbors)?


Thanks for posing this question.

Traditionally in engineering, a holy grail has been to scale up technologies and thus maximize impact. On the other hand, impact could be equally significant with multiple installations at smaller scale. The question you raise is of significant interest to us (as well as several others on this forum). Indeed, my group is working on efforts to 'intensify' processes for clean water and resource recovery that might find use at the community or household level. While some of these exist in some high-rise developments (for instance in New York), more work is needed to make these more efficient and perhaps even smaller. Another approach is to work with un-diluted waste streams.

What kind of filters do you use during your purification process?


Our focus is more on the upstream biological and chemical process to convert the constituents of the waste streams to energy, commodity chemicals or relatively benign products (such as N2 gas). We don't work specifically on the downstream filters and have used gravity based settling or just a sand filter (in some cases). That said, improvements in filter materials or filtration technologies could very well be integrated int our overall process.

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