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Why are cities overflowing with waste – Part 1: Material balance of a city, The organic waste

© Ajay Phatak, Think2Transform, Pune India

Remember: Mass cannot be created nor be destroyed– Law of conservation of mass.

One of the most challenging problem that every city faces today is that of Solid Waste Management.  May that be organic wet waste, plastic and packaging dry waste or eWaste.  The quantity of solid waste continues to increase as much as the local governing bodies are trying to address the disposal and clearing of such solid waste.

Every citizen is most concerned that no waste should sit in her backyard.  Seldom a citizen cares about the ‘life cycle’ of this waste.  How is waste generated and why do cities have this ever-expanding problem.   Generally, citizens blame the city government, themselves or just accept the situation and live through it.   Why is it so that this problem has not been satisfactorily solved in any of the large cities worldwide in the last 100 years since the consumerist society was born in the roaring ‘20’s. 

Let us use the law of conservation of mass to understand this problem better, let us take a simple first-principle approach:

material in = material out + material stored

This is a the basic law of conservation of mass.  Once we start looking at this equation carefully, solution might start dawning on us.  Stored quantity of material will only grow a bit, however, it can be considered constant over a period. Only way for any new input material through purchase of new goods not to accumulate in our houses is to move the older goods move out of our houses – and that happens as we discard this as trash day in and day out.  Whether that trash is in the form of plastic dumping, or dumping the vegetable and fruit remains, or additional cooked food not consumed is disposed, is immaterial.  All the excess material being put out of our houses very day will certainly appear as waste. 

Once we realize that simple material (im)balance is the reason why this waste appears all over the city, we should turn our attention to basics again to understand the possible remedies.  We will focus on the organic waste part of this equation in this blog.  Considering we should never mix the 2 streams – something that can be absorbed and used by the biological cycle and once that should remain ideally in a closed loop – the loop of technical nutrients, emanating from the Industrial world.

We as a question why does such imbalance occur? 

The simple equation:

Input = Waste + accumulation + Consumption

Provides a good insight into solutions as well.   We have 3 levers to play –  Input, Consumption and Accumulation to try and minimize waste. 

Unfortunately, there is almost no material, which gets consumed.  We land up generating sewage as we continue to consume food.  We also throw away excess food cooked and refuse, part of the biomass that we cannot process. The sewage, which has much of the nutrients required for our food to grow again, in principle must go back to the soil, from where the food was produced.  This will ensure that the nutrients are returned to the soil for the next cycle of food to be produced.  That, this feedback loop is absent, we need to feed the soil with external nutrients. Typically, these will come from chemical fertilizers.  Any excess fertilizer input to the crop means that the excess input gets carried through in  agricultural run-off and into the water streams while the rest is assimilated in the crops we produce.

All the food items that come into the city are typically imports from the nearby villages. The aftermath of our food consumption in terms of fruit and vegetable refuse or sewage, which has the organic matter imported from the villages is rarely given back to villages.  We try and find urban solutions to something which must be returned to villages if we want to ensure material balance and natural cyclicity of material movement.  If this output in terms of food waste, fruit & vegetable refuse as well as sewage is returned to the soil and to the village which grew the food for you in the first place, there is a good chance that the additional nutrient required by the soil in the villages in terms of chemical fertilizers can be reduced substantially.  It is important to understand that the NPK and other micronutrients circulating in the part of the food web today, are far more than anytime what has been in the history.  This is simply by looking at the chemical fertilizers used to boost the productivity of the crops consumed by humans.  With amount of food produced exceeding the needs of humans already (even while just distribution is certainly a question mark) the nutrients available and circulating in our food is already enough should we use all of these nutrients in closed loops.  This also means that there may be little need of additional chemical fertilizers if these nutrients are returned to the soil which produced the food in the first place. 

At this juncture, it might be worthwhile to look at how the nutrients flow was in the preindustrial agriculture era and how that has changed as of today.  We will use these diagrams to explain the end impact of these flows as well.  The picture is put in only to ensure that we get a good collective look to understand the challenges we face in terms of organic waste for now and convert that understanding into possible solution pathways!

Fig. 1 Material Flows in pre-industrial agriculture

The simplified diagram clearly illustrates that in the absence of external chemical fertilizer input, all the excess biomass and food-refuse and waste is returned to the soil.  This means that the solution to the current problem can well be envisioned in this flow diagram. 

We can now look at the current flows of Nutrients in the era of rampant fertilizer use and explore ways to identify problems.

Fig 2: Nutrient flows in the industrial era – use of chemical fertilizers

We realize that in the modern world most of the nutrients supplied to our Modern Industrial Agriculture come through chemical fertilizers and very little through manure route.  We also realize that we are feeding excess fertilizer to our plants than what is necessary.  Having said that a good part of these nutrients is absorbed by the ‘additional’ produce – directly attributed to the additional input.  We realize that we now have our additional food, which has metabolized these nutrients (via the Chemical fertilizer route) and there is a great potential to continue and keep these external fertilizer inputs in the biological cycle.  This can only happen if we use the waste and food-refuse effectively. Return of this material to the producer can save the need for additional fertilizer input and still maintain sufficiently high yield.  Another observation is the linear nature of nutrient flows, leading to the seemingly unsurmountable problems of waste.  If we can indeed create the required circularity and precision in terms of nutrient flows, there is an opportunity to address multiple sticky problems in one go.

  1. We ensure that ALL the nutrient flow is available for our agriculture and can indeed go back to the fields
  2. We can substantially eliminate the need for additional nutrient stream – which is going into agricultural runoff and avoid the downstream pollution and health problems as well.  If some runoff is inevitable, we can capture the NPK nutrients and bring these back into the circular system by using hyper accumulator plant species.

Take a close look at Nutrient inflows and outflows in the city.  Some observations are as under:

Fig 3: The linear flow of nutrients today

Current method demonstrates that the nutrients flow into the environment outside of agriculture, where these create pollution in the form of land pollution, associated water pollution through the leachates (which enter the ground water near landfills) and pollute these water bodies. Such pollution leads to serious health problems for the village folk.  In fact, these pollution problems, again raises new questions and leads to pushing you into trying to find new downstream answers.  This model of waste management also requires substantial transportation, which is responsible for further local air pollution and global carbon pollution.  The landfills generate Methane in an anaerobic reaction, which is multiple times as potent a Green House Gas as CO2. 

In the ideal case the nutrients should go back to where they come from.  That is, these should go back to the producers in the villages, where the food is grown.  This will work only when we look at producing only as much as the village needs and all the output is recycled right in the farms.  However, in the modern world, where villages produce far more food to be sold and consumed by the city dwellers using chemical fertilizers as a nutrition boost.  These additional nutrition does not come back to the producers.  This cycle is broken and we land up with multiple problems as we see in the diagram depicting nutrient flows in the city centric consumption model.

If we must eliminate the challenges of pollution, we will need to look at the polluting elements and explore how the food waste & refuse can be converted to usable nutrients, which can go back into our food production cycle.  We can reduce the transportation necessary to the best possible extent by nurturing villages close to the cities to supply the city’s needs.  In near ideal scenario, cities should eat whatever is produced within the city and by the nearby villages based on their agroclimatic situation and the types of food, fruits, and vegetables they can ideally produce.  This could even be supplemented by forest foods if there are any forests nearby.  If otherwise, some restoration might be necessary. 

Another important aspect is to understand that all the food waste as it is called today is not waste but a source of nutrients for the producers.  In fact, any urban food production can be a good way to reduce transportation on both sides – food that comes into the city and waste that goes outside the city.  This way of handling the waste OR resource dilemma can solve multiple problems at the same time. 

  1. Significant reduction is the scale of waste in the city.  Cities of course must manage waste to resource conversion and return such resource where it belongs – to the producers. Consider urban farming as an option wherever feasible.
  2. No need for landfills – substantially eliminates the leaching and associated water pollution and ever-increasing need for land to be used as landfills.  This in turn will keep clean water sources available and can minimize the health issues connected with bad drinking water.
  3. Reduce or eliminate black water – If Sewerage can also be converted to resource – much of the issues of water pollution will vanish.  Even while science has solved the problem and technology has the solution, such implementation is still looked at sceptically.  There may be a need of how society may look at at this ‘resource’ scientifically and positively.
  4. Reduce transportation – On priority the manure output derived from Food refuse and sewerage should first be consumed in a cyclical fashion within urban agriculture initiatives.  This will further reduce transportation. 
  5. Considering the pure material balance, if all the inorganic nutrients (NPK and other trace elements), which are part of the food we produce today, can go back as natural manure to the producers we will eliminate or significantly reduce the need for additional fresh chemical fertilizer.  This will also reduce the cost of inputs to agriculture and increase viability of agriculture.  Cost of agriculture is not so much because of the nature of business, but also because of lack of cyclicity in resource flows. This is a significant issue worldwide.

Here is how the desired flow of nutrients will look like in this new world of closed loop nutrient flows:

Fig. 4: The circular flow of nutrients – capturing all the nutrients out there

Considering, we make accumulation equal to Input– we would solve this problem of waste.  While true, it is impossible to accumulate material – whether food or discretionary goods, all the time.  Moreover, accumulating anything in large quantity or volume will call for space, which is not available in the city (or for that matter anywhere).  If this solution is ruled out, other solution could be to reduce the input to a level where there is very little waste.  This too seems impractical in the current economic paradigm and the scale of population we have reached, thanks to boost in productivity through fertilizer use and other advances in technology.

In the context of this imbroglio, there is a great opportunity to use the fundamental principle of material balance and law of conservation of mass to address part of the waste problem through circularity.

Note: The excess fertilizer eventually lands into our rivers and oceans causing serious nutrient ‘overload’.  Excess nutrients land up in rivers and cause algal bloom or excessive growth of water hyacinth or Pistoia like invasive vegetation and renders the water completely devoid of oxygen.  This phenomenon called eutrophication leads to substantial loss of aquatic biodiversity. The invasive species create new set of problems for the local governing bodies to deal with.   (There is also an opportunity to recoup this NPK using hyper accumulator plant species before such nutrient loaded water is released to the river, as also practice precision agriculture)

Using organic resource in a circular fashion could be a sustainable solution to addressing the problem of solid waste management – organic waste addressed in this blog – in cities.

Ajay Phatak is a Trustee and Faculty at the Ecological Society. He advices early-stage companies in the spaces of Healthcare, Environment on strategy and writes on subjects of energy, sustainability and circular economy.

One Response to “Why are cities overflowing with waste – Part 1: Material balance of a city, The organic waste”

  1. Simple solutions are always available if we approach the problem from first principles instead of being blinded by the obsessive need to use technologies – hi tech- to fix problems. you bring out this aspect very well in the case of organic solid waste management.


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