# Session 6: Productive Use of Biogas ## Learning Objectives By the end of this session, you will be able to: 1. Identify surplus biogas potential in your digester and explain why many owners underutilise it. 2. Evaluate at least three productive use applications — chicken brooding, fodder chopping, food drying — and determine which might suit your farm or community. 3. Assess the basic economic viability of a productive use investment using real field data. --- ## The Untapped Resource Most biogas owners use their gas for **3–5 hours of cooking per day** — then the digester continues producing gas that builds up pressure and vents to the atmosphere. **Methane is 28–36× more potent than CO₂ as a greenhouse gas.** Venting it unused is harmful to the climate and a waste of a valuable resource. --- ## Four Common Underutilisation Patterns | Pattern | Description | |---|---| | 🍳 Cooking only | 3–5 hours daily; remainder vents | | 📅 Seasonal mismatch | Intensive use some seasons, surplus vented in others | | 💧 Fertiliser-first mindset | Biogas seen as a by-product of slurry production, not a primary resource | | ❓ Don't know what else to do | Many owners unaware of productive use options | --- ## Case Study 1: Chicken Brooding ### My Passion Farm, Wakiso District, Uganda **Background:** A farm with a 9 m³ biodigester rearing ~1,000 chickens per year. Biogas was only used for cooking (~5 hours/day). During the critical 4–5 week brooding period (when day-old chicks need constant warmth at 30–33°C), the farm burned briquettes — taking 40 person-hours per week to produce.

**The intervention:** A biogas-powered brooder installed for **UGX 806,500 (~$220 USD)**, consuming 0.3 m³/hour. | Economic Result | Value | |---|---| | Installation cost | UGX 806,500 (~$220 USD) | | Briquettes available for sale (year 1) | UGX 1,200,000 | | New income: brooding services to neighbours | UGX 2,000,000/yr | | **Total first-year benefit** | **UGX 3,200,000** | | **Payback period** | **~4 months** | | **5-year ROI** | **1,729%** | **Key lesson:** The brooder converted a labour-intensive cost centre into a new income stream. The 40 person-hours previously spent making briquettes is now free for other activities. --- ## Case Study 2: Fodder Chopping ### ECHO East Africa, Arusha, Tanzania Petrol-powered fodder choppers were converted to run on biogas by replacing petrol carburettors with gas carburettors and adding a simple purification system (water container → silica gel → activated carbon → desulfuriser).

**The circular loop:** > Livestock produce waste → waste feeds the digester → digester produces biogas → biogas powers the fodder chopper → chopped fodder feeds the livestock. Zero external fuel cost for fodder processing. --- ## Case Study 3: Hybrid Solar-Biogas Food Dryer ### Eden Primary School Farm, Masaka District, Uganda A 30 kg capacity **Sparky dryer** with biogas heating was connected to the school's existing biodigester. The system is solar-biogas hybrid: - **Daytime:** solar provides free heat. - **Nighttime/cloudy:** biogas provides backup.

| Product | Traditional drying | Sparky dryer | |---|---|---| | Coffee | 3–5 days | **24–36 hours** | | Maize | 3–5 days | **1–2 days** | ```{warning} **LPG ≠ Biogas.** The initial burners supplied with the dryer were designed for LPG pressure and could not generate sufficient heat from biogas. Always test equipment with actual biogas before full installation. ``` **Drying performance:** | Crop/metric | Traditional sun-drying | Sparky dryer | |---|---|---| | Coffee | 3–5 days (longer in poor weather) | **24–36 hours** to correct moisture | | Maize | 3–5 days | **1–2 days** | | Maize moisture target | — | 12–13% for safe storage | | Coffee quality outcome | Variable | Independent test: excellent flavour, smell, texture | | Aflatoxin risk (maize) | Higher | Significantly reduced through faster, controlled drying | Other high-potential drying applications: fish (near lakeshores), medicinal herbs, vegetables (tomatoes, onions, leafy greens), fruits (mango, pineapple, banana), seeds. **Economic viability:** | | | |---|---| | Total investment (dryer + pipeline) | ~$800–1,100 USD | | Service fee model | UGX 500–1,000 per kg dried | | Per batch (30 kg) | UGX 15,000–30,000 | | Weekly capacity (3–4 batches) | UGX 45,000–120,000/week | | Annual revenue potential | UGX 2–6 million (depends on volume) | | Premium from quality (high-value crops) | +20–40% on coffee, spices | | Payback period | 1–3 years depending on volume and pricing | | User type | Verdict | |---|---| | Farmer cooperative (high-value crops) | ✅ Viable — premium pricing + sufficient volume | | Individual smallholder | ⚠️ Marginal alone — viable if offering services to neighbours | | School / community institution | ✅ Viable — service + training model, diversified income | --- ## Which Productive Use Suits Your Context? | Application | Typical cost | Payback | Best suited for | |---|---|---|---| | 🐔 Chicken brooding | ~$220 USD | ~4 months | Any poultry farm with digester | | 🌿 Fodder chopping | Low (carburettor swap) | Short | Farms with livestock & fodder need | | ☀️ Food drying | $800–1,100 USD | 1–3 years | Cooperatives, schools, large farms | | 💡 Lighting | Low | Very short | Any household or small enterprise | **The key questions to ask yourself:** 1. Do I have consistent surplus biogas beyond cooking needs? 2. What farm activity currently costs me most — fuel, labour, or lost product quality? 3. Can I offer this as a service to neighbours? 4. Is there a cooperative, school, or institution that could share the investment? ```{raw} html

⚡ Which Productive Use Suits Your Farm?

Select everything that applies to your situation.

🐔 I keep chickens or other poultry 🐄 I have livestock needing fodder 🌾 I grow high-value crops (coffee, maize, veg) 🤝 I'm part of a cooperative or school ⚡ I have surplus gas beyond cooking needs 💰 I want to offer services to neighbours

Tick the options that apply to your farm to see a recommendation.

``` ### Calculate Your Surplus Biogas Most households are surprised to discover how much gas they are already wasting. The interactive **Surplus Biogas Calculator** was built specifically for CREATIVenergie systems — enter your digester size and daily cooking time and it will show you exactly how many hours of surplus gas you have and which productive uses that could support. **Try it now — experiment with different inputs to see what becomes possible:** ```{raw} html

⚡

Surplus Biogas Calculator

Built for CREATIVenergie systems. Enter your digester size and daily cooking use — see your surplus hours and which productive uses are within reach.

Open Calculator →

Opens in a new tab. Try changing the inputs — what happens if you reduce cooking time by 30 minutes? What if you add a second animal?

``` --- ## Environmental and Social Benefits The case for productive use extends well beyond farm economics. | Environmental | Social | |---|---| | **🌳 Less deforestation** — My Passion Farm avoided 480–560 kg of briquettes per brooding cycle. Multiplied across hundreds of farms, the impact on tree cover is significant. | **⏱ Labour reduction** — 40 person-hours per week previously spent making briquettes, eliminated entirely. Time reinvested in farm management and family. | | **🌍 Methane capture** — Methane is 28–36× more potent than CO₂ over 100 years. Burning it productively converts CH₄ to CO₂ and H₂O, and displaces petrol and LPG. | **❤️ Health improvements** — Reduced smoke exposure versus briquettes or charcoal. Cleaner working environments. Lower respiratory illness risk. | | **♻️ Circular economy** — Crops → bio-slurry → animals → waste → biogas → farm operations → back to crops. Multiple loops closed simultaneously. | **🤝 Community services** — One digester can serve many. Brooding and drying services let neighbours benefit without owning their own system. Demonstration effects accelerate adoption. | ```{note} **The opportunity in summary:** - The resource exists — many digesters produce surplus gas that is currently vented. - The technology works — brooding, fodder chopping, and food drying are all proven in field conditions. - The economics are compelling — payback as short as 4 months for brooding. - Service models multiply impact — one investment can serve an entire community. The question is not whether productive use works. The question is: **which application fits your context, and who is your first neighbour to serve?** ``` --- ## Session 6 Quiz ```{raw} html ``` --- ## Summary Surplus biogas is a wasted resource for most smallholder farmers. The three proven productive uses are: - 🐔 **Chicken brooding** — fastest payback (~4 months), minimal investment - 🌿 **Fodder chopping** — closes the farm energy loop at low cost - ☀️ **Food drying** — highest revenue potential for cooperatives and schools Next: **[Session 7: Building the Digester](session7-building)**