Eight kilos a day behind the school wall
A high school in Puri has 640 students and 22 staff. A waste audit shows about 8 kg a day: 4 kg of cooked food, vegetable peel and midday-meal leftovers, 2 kg of paper and cardboard, 1 kg of plastic (wrappers, broken buckets, some PVC pipe offcuts) and 1 kg of glass and metal. Everything is thrown into one heap behind the boundary wall and burnt each evening. The smoke drifts into a slum of 60 households next door, whose residents complain of coughs, eye irritation and clothes that smell of smoke. The headmaster has ₹15,000 and an unused patch of ground 4 m by 3 m. He proposes to 'burn only the plastic, since that is the smelly part' and to compost the rest in a pit.
1. Evaluate the headmaster's plan to burn only the plastic fraction.
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Burning only the plastic is the worst possible choice, because plastic is the fraction that should never be burned in the open.
The heap contains PVC offcuts. PVC is about 57% chlorine by mass, so its combustion releases hydrogen chloride, which with atmospheric moisture forms hydrochloric acid; at the low, uneven temperatures of an open heap (roughly 300–600 °C, with poor air supply) it also produces dioxins and furans, which are persistent, bioaccumulative and toxic at very low concentrations. Every plastic produces carbon monoxide, soot and polycyclic aromatic hydrocarbons when starved of air, and the visible smoke contains fine particles small enough to reach the alveoli - which is exactly what the neighbours are coughing on.
Open burning of waste is prohibited under the Solid Waste Management Rules, 2016, which require segregation at source and channeling of plastic to recycling. Recycling also makes financial sense: wrappers and rigid plastic have scrap value.
The correct advice is: stop burning immediately; do not incinerate, since a compliant incinerator costs far more than ₹15,000 and would still need pollution control; segregate and hand plastic to a recycler; reduce single-use plastic in the canteen.
2. Design a workable plan for the 8 kg a day using the ₹15,000 and the 4 m × 3 m patch, and estimate the compost produced.
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Segregate at source first, before any equipment. Two bins per classroom and one at the kitchen: green for food and peel, blue for paper, a sack for plastic, a crate for glass and metal. Appoint two student monitors per week.
Compostable fraction = 4 kg food + 2 kg paper = 6 kg a day, about 180 kg a month. Aerobic composting loses roughly 60–70% of the mass as water vapour and carbon dioxide, so expect 50–60 kg of finished compost per month, ready in six to eight weeks.
The 12 m² patch easily holds three pits of 1 m × 1 m × 0.75 m, used in rotation: one filling, one maturing, one being emptied. Food waste alone is too wet and too low in carbon (C:N near 15:1), so each 10 cm layer of food waste should be covered with shredded non-recyclable paper or dry leaves to bring the mix towards 30:1, and the top should be covered with dry leaves to keep flies away. Turn every 5–7 days; keep it as damp as a wrung sponge.
Budget: 3 pit liners or brick edging ₹3,000; 20 colour-coded bins ₹6,000; gloves, rake, spade, moisture meter ₹2,500; mesh covers ₹1,500; signage and student training ₹2,000. A scrap dealer will take the glass and metal, and often pays a little, which can fund the consumables. The compost goes to the school garden and is given to parents.
3. The compost pit starts to smell of rotten eggs, attracts flies, and a dark liquid seeps from its base. Explain the causes and corrections.
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The smell of rotten eggs is hydrogen sulphide, and it is a sign that the heap has gone anaerobic. If food waste is piled wet and left unturned, the microbes consume oxygen faster than it can diffuse in from the surface. Decomposition then switches to anaerobic pathways, producing hydrogen sulphide, ammonia, organic acids and methane. Anaerobic heaps also stay cooler, so weed seeds and pathogens are not killed, and they release methane, a gas with a much higher warming potential than the carbon dioxide that aerobic composting would have produced.
Corrections: turn the heap to admit air; add dry carbon-rich material - shredded paper, dry leaves, sawdust - to soak up excess moisture and open the structure; keep the moisture at the wrung-sponge level and cover the top with a layer of dry leaves or a mesh to deny flies a landing surface. Do not compost meat, fish, dairy or heavily oily food in a school pit, as these are the worst offenders.
The dark seepage is leachate, carrying dissolved organic matter, nitrate and possibly pathogens. If it percolates into the soil it can reach groundwater, so the pit should be lined or sited well away from any well or borewell, with a small collection channel. Diluted several times with water it can be poured on plants, but it should not be discharged into a drain or a pond.