Have you ever wondered what happens to the waste collected from your household? Or have you considered the impact of disposing waste into landfills or feeding it to piggeries, which is a common practice for bulk food waste generators like industrial canteens, apartment complexes, food processing industries, and many more?
Let’s start by comparing the commonly practiced traditional method of organic waste treatment or disposal and its impact on greenhouse gas emissions. This, in turn, affects the soil, climate, and poses a threat to the human race.
Greenhouse Gas (GHG) generation by 1 ton of food waste daily using various methods of disposal / treatment:
- Disposal to landfill: Food Waste sent to landfill undergo long term slow decay over a period of 10-12 years. As per the Clean Development Mechanism (CDM) guidelines of calculation of GHG by sending MSW waste to landfill, every 1 ton of waste sent to landfill for 1 year (365 tons total), generates 2650 tons of GHG over a 10 year period. Sending food / canteen waste / household kitchen waste to landfills has long term impact to global warming by emission of GHG over extended period of time.
- Disposal through piggeries: Food waste is categorised as calorie rich nitrogenous waste which can be used as food for pigs. As per estimates, each pig in its lifetime of 9 months consumes 1.8 tons of food and generates an estimated 3500 kg of GHG. From 1 ton of food waste, over 320 pigs can be fed each day which in its lifetime generates a whopping 970 tons of GHG in 9 months.
- Methane recovery through bio-methanation /anaerobic digestion (AD): AD is another process of treating food waste. However, AD as a process is useful only on the following conditions:
- Scale of treatment should be more than 20 tons per day using sophisticated bio-gas setup which requires constant monitoring of various bio-chemical parameters and corrections to input materials based upon the reactions in the digester.
- Bio-gas generated is utilized near the premises of generation. Botting of bio-gas under high pressure into cylinders consumes almost 70% of the energy equivalent that is put into a cylinder. So transporting bio-gas is not a sustainable option.
- For every 1 ton of food waste, over 3 tons of nitrogen rich sludge is formed. There should be a process to treat this sludge and convert into non-toxic soil friendly format (i.e. composting of the sludge needs to be done)
- For 1 ton of food waste treated through anaerobic digestion, approx. 200 cubic feet of biogas is produced. Out of this, 50% is methane and rest is CO2. However the utilisation of methane has to happen at source itself.
- Since 3 tons of semi-liquid sludge is formed for every 1 ton of food waste, the cost of composting is 3 times higher as the absorbent (carbon rich material) required will be more to absorb the moisture.
- Aerobic Composting Process: The carbon dioxide (CO2) emissions associated with composting 1 ton (1,000 kilograms) of food waste using the aerobic composting method are relatively minimal compared to other waste management methods, such as landfilling. In aerobic composting, microorganisms break down organic matter in the presence of oxygen, converting it into stable organic matter or humus, while releasing CO2 as a byproduct of the microbial activity. The CO2 emissions from aerobic composting primarily result from the decomposition of the organic carbon in the food waste. The amount of CO2 emitted can vary depending on factors such as the composition of the food waste, temperature, moisture levels, and the duration of the composting process. However, as a general estimate, the carbon dioxide emissions from composting 1 ton of food waste are approximately equivalent to the carbon content of the food waste and the carbon rich material added to the composting pile.For every 1 ton of food waste, we are adding 100 kg of dry carbon material for composting. We can assume about 50kg of carbon present in the food waste coming from vegetable waste. So in total, 150 kg of carbon per 1000 kg of food waste treated. Carbon has an atomic weight of approximately 12 atomic mass units (AMU), and carbon dioxide (CO2) has an atomic weight of approximately 44 AMU. To calculate the amount of CO2 emitted:150kg of carbon × (44 AMU CO2 / 12 AMU C) = 550 kg of CO2So, composting 1 ton of food waste can generate approximately 550 kilograms (of carbon dioxide (CO2) emissions. It’s important to note that these emissions are considered biogenic and part of the natural carbon cycle since the carbon released during composting was originally derived from plants through photosynthesis. Composting remains an environmentally preferable option for managing food waste compared to landfilling, as it reduces methane emissions (a potent greenhouse gas) and produces valuable compost that can enhance soil fertility and carbon sequestration in the soil.Carbon Sequestration potential of compost:
It is to be duly noted that only composting and a process and compost as the end product of the process has the potential to help in carbon sequestration and thereby helping in reversing climate change. The summary of the above claim is as follows:
Compost is carbon rich material and when applied to soil increases beneficial microbes population in the soil. One such beneficial microbe is mycorrhiza which uses CO2 as raw material to produce complex carbon compound called “glomalin”. This carbon compound does not degenerate back into carbon di oxide and there by becomes part of the mass of the soil. Every hectare of land when treated with compost can sequester 2 metric tons of CO2 from the atmosphere annually.
The above is the true potential of aerobic composting of waste and applying the compost generated to soil, which no other waste treatment process can provide.