Nickolas J. Themelis, Professor of Earth and Environmental Engineering, Columbia University, Talks to TNH

Nickolas J. Themelis, Professor of Earth and Environmental Engineering, Columbia University. (Photo:

Professor Nickolas J. Themelis finished high school in Athens, and then went on to obtain his BS in  Engineering and PhD degrees from McGill University in Montreal, Canada. In the first part of his career he developed metallurgical processes for the extraction and refining of copper and other metals, including the Noranda Process which did away with the emission of millions of tons of sulfur into the atmosphere.

After 20 years in the metallurgical industry, he joined Columbia University’s School of Mines, which was first such in the United States. In 1997, the School of Mines was transformed into a school for the new discipline of Earth and Environmental Engineering.

At Columbia University, he was the first Chair of the Department of Earth and Environmental Engineering and founder of Columbia’s Earth Engineering Center. He is Chair of the Global WTERT Council (, which has sister organizations in several countries, including the United States, China and India.

Themelis has been honored with several awards, including those received from the Canadian Chemical Engineering and Metallurgical Societies, the British Institute of Metallurgy, the American Institute of Mining, the U.S. Metallurgical Society, the Japan Institute of Metals, the Confederation of European WTE Plants (CEWEP), and the Materials and Energy Recovery Division of the American Society of Mechanical Engineers. He is a member of the U.S. National Academy of Engineering.

Catherina Ploumidaki: What was your most important achievement during your years of industrial research?

Professor Nickolas J. Themelis: Inventing a process for extracting copper from copper ore that reduced sulfur emissions into the atmosphere by millions of tons (Noranda Process). This process is also used today for recovering metals from used electronics, [reducing electronic waste.]

CP: Tell us about your current field of research.

NT: Waste management is a major environmental problem and I am applying my knowledge of materials science and process engineering to sustainable waste managementthat is, with least possible environmental impacts. Since the beginning of history, humans have generated solid wastes and disposed them in makeshift dumps or set them on fire. After the industrial revolution in the 18th century, the amount of goods used and then discarded by people increased so much that it was necessary for cities to build landfills and incinerators for disposing waste. The management of municipal solid waste (MSW) has become a major problem of cities since the middle of the 20th century, when the consumption of goods, and the corresponding generation of MSW, increased by as much as six times!

CP: What was the response of scientists and engineers?

NT: In response, the most advanced countries developed various means and technologies for dealing with solid waste. They range from reducing waste by better designing products and packaging, to recycling of usable materials, composting of green wastes, combustion with energy recovery – commonly called “waste to energy” (WTE) – and sanitary landfilling that prevents aqueous and gaseous emissions to the environment.

CP: How big is the problem of managing waste?

NT: It has been estimated that the urban solid waste even after recycling (post-recycling MSW) exceeds1.5 billion tons, of which over one billion tons are landfilled and the rest are treated in waste-to-energy (WTE) power plants which generate electricity and also recover metals and building materials.

CP: Is there a difference between regulated landfills and waste dumps?

NT: Yes, a lot. However, of the MSW landfilled globally, less than 20% are disposed in regulated (“sanitary”) landfills that reduce aqueous and gaseous emissions to the environment.

CP: What is the Hierarchy of Waste Management?

NT: The order of priority and the applicability of waste management methods is represented graphically by the Hierarchy of Waste Management

In this Hierarchy, sanitary landfilling is given a lower priority than waste-to-energy, although it is less costly to implement. One reason for this is that sanitary landfilling requires a lot of land and also has much higher environmental impacts than WTE including the transformation of greenfields to landfills. For example, we have estimated that the nearly eight billion tons landfilled in the United States in the last forty years have covered an area of four billion square feet of land, or 91,000 acres.

What is the Ladder of Sustainable Waste

CP: Management Hierarchy of Waste Management?

NT: The environmental performance of waste management of a city or country can be rated by comparing the tonnage of materials recovery (i.e., recycling and composting) and of energy (i.e., WTE) to the tonnage of MSW landfilled. The “ladder of sustainable waste management” rates nations according to how little they landfill and how much they recycle and combust with energy recovery.

This figure shows that several nations have already reached the goal of very little or no landfilling. The United States, one of the wealthiest nations, is behind many developed countries, such as Austria, Germany, Japan, and the Netherlands. Europe as a whole is doing a good job: It has gone from 60% landfilling in 1995 to 25% in 2015 by a combination of recycling and WTE. The United States is stuck at about 63% landfilling and only 7% WTE, most of it on the east coast. China is moving fast and becoming a leader in WTE, from 40 plants in 2000 to over 350 by 2018.

CP: What about Greece?

NT: As for Greece, regrettably the “cradle of western civilization” in the last two decades hasn’t moved much from 80% landfilling (vs 65% for the United States and 28% average for the EU). This is despite the fact that the per capita GDP in Greece is higher than other countries who are progressing in sustainable waste management. Also, the price of electricity in Greece is relatively high so that WTE plants would be both environmentally and economically much preferable to landfilling.


CP: What other problems is Greece facing now with respect to waste management?

NT: The worst thing is the practice of setting fires to waste dumps, to create more landfill space, which is prevalent at several Greek islands. Columbia’s sister organization in Greece (WtERT-Greece) is headed by Professor Kostas Aravossis of the Athens Polytechnion and is trying hard to reverse the existing situation in Greece.

CP: Is there a climate change advantage of WTE, over regulated landfilling?

NT: WTE eliminates landfill methane emissions and, therefore, one ton of MSW going to WTE, instead of a sanitary landfill, reduces carbon emissions by one ton.

CP: What are your future goals and ambitions?

NT: To reduce and eventually eliminate the use of landfilling of urban wastes.

CP: What do you consider to be your most important achievement during your academic career at Columbia?

NT: Educating young people from all over the world as to the need for sustainable waste management. By now, Columbia is one of the foremost academic groups in this field of study, with sister organizations in other countries, including China, India, and Greece; also, being elected as member of the U.S. National Academy of Engineering.

CP: Which are the wisest words you were taught and from whom?

NT: “Enjoy today but plan for tomorrow” Epicurus and Plato!

CP: If you could turn time back what would you change?

NT: Really, nothing!

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