Sun, air, water, geothermal and biomass are the main renewable resources on the planet Earth. Obtaining energy from these sources is almost impossible without expensive equipment. Wind turbines and solar panels cost hundreds of dollars, even for small homes. All generators powered by said resources require constant inspection of moving parts and battery packs.
Biomass energy production is the cheapest. It does not require constant investments and checks of serviceability. Biomass can include: plants, crop residues, manure, food scraps and algae that can be easily harvested.
In most cases, gardeners complain about the constant growth of weeds in their plots. Weeds take nutrients from the earth, so why are we so dismissive of this theft of our bounty?
This instructional article is aimed at the average person. It explains how to make an effective system of biogas production from weeds with your own hands using simple steps.
Step 1: Obtaining energy from plants
Anaerobic digestion (according to the definition) – a set of processes by which microorganisms in the absence of oxygen completely destroy the biomaterial, releasing biogas.
To begin with we fill the biogenerator with shredded weeds. At the same time we will collect information about the amount of biogas emitted as a result of fermentation and the amount of energy.
Step 2: Collect the weeds
The capacity of the digestion tank is 750 liters. We leave 50 liters in reserve. We dilute 2,5 kg of freshly harvested weeds together with enough water to get 20 liters of diluted “biomaterial”. The mixture should ferment for about 35 days. The water after removing the solid biomaterial can be used as fertilizer for plants in the garden. From 4 kg of freshly harvested weeds, after cutting the roots and twigs, you can get about 2.5 kg of material. The untreated material can be kept for up to 3-4 days.
Step 3: Recycle the biomaterial
The red basin in the photo contains about 2.5 kg of weeds ready to be shredded.
Step 4: Shredding the chopped leaves
Simply shredded leaves are not as susceptible to fermentation and give less energy. Therefore, it is better to shred the leaves and grind them with a little water before loading them into the machine. Use the water left over from soaking rice and lentils. Grind the weeds with a chopper. The water left over after washing the crusher can be used to liquefy the shredded weeds.
Caution…do not use chlorinated or soapy water. Use running water without chlorine or any chemical additives.
Step 5: Load the biogenerator
Pour the diluted mixture through a special pipe into the biogenerator. This process must be repeated daily for continuous energy production.
Together with the weeds in the cylinder may accidentally fall into the soil particles, which will remain at the bottom of the container. So, before you release the container with the shredded weeds, make sure there is no soil in the bucket.
Step 6: Calculate the volume of gas to be extracted
Let’s calculate the volume of gas we will get from 2.5 kg of weeds.
The inner diameter of the gas reservoir = 0,8m (radius-0,4m). The gas rises an average of 45 cm(0.45 m). Gas volume: π(3,14) ×(0,4×0,4)×0,45= 0,226 cu. m. The added volume contains impurities – carbon dioxide, nitrogen and hydrogen sulfide.
Another way is to compare the average volume of emitted gas and liquefied petroleum gas (LPG), which is used for domestic purposes.
A full 15-liter gas cylinder is usually enough for 30 days. This means that we use about 0.5 liters of gas per day.
On October 13, 2014, a full cylinder with LPG and biogas was installed (used simultaneously). On November 24, the LPG cylinder was empty.
The cylinder with household gas, which usually only lasts for 30 days, managed to last 41 days using it together with biogas. With the norm of 0.5 liters of LPG per day, we can calculate that 0.5×11= 5.5 liters of household gas was replaced with biogas. In one day in this way we get 5500 grams /41 day = 134 grams of biogas.
So, 0,226 cbm of biogas per day gives 134,15 g for thermal energy.
Step 7: Production waste
How many liters of “weeds” are loaded into the biogenerator, the same amount of products of fermentation and came out through a separate pipe. In this case we get about 20 liters of water, which can be used as fertilizer in the garden.
Step 8: Hydrogen value of the fermentation products
Measured the hydrogen index of the fermentation products using pH tests. According to the test chart that came with the test, the hydrogen value of the fermentation products was 7-8. This means that the ammonia in the weeds contributes to a slight excess of alkalinity in the resulting product. The mixture would work well as a fertilizer for the red soil in our garden, which has a slightly higher acidity.
Step 9: Functionality check
The anaerobic biogenerator does not need a diligent serviceability check.
The anaerobic process produces heat and water vapor, which is also mixed with the biogas. The steam condenses and accumulates in the gas pipe. To prevent this, close the outlet valve after using the gas. This helps the water to settle back into the biogenerator. Once a week, disconnect the gas pipe and dry it of condensed water.
Step 10: Summarize.
Advantages of the system:
- The garden is weeded regularly;
- Weeds go to biofuel;
- Fermentation products go into the fertilizer;
- Biofuel saves a lot of gas;
- Environmentally friendly production.
Some important “do’s” and “don’ts”:
- Need to use the biogas generator regularly;
- No need to exceed the rate. Excess is better left for tomorrow;
- No need to harvest weeds from land treated with pesticides/herbicides;
- No need to use chlorinated water. Clean running water is used for all needs;
- Need to reuse one water in the process if possible;
- No need to use water intended for dishwashing.
The biogas generator consistently provides gas and fertilizer to the house every day. Every 4 months we save on a cylinder of household gas, thanks to almost nothing worth of biogas. Since my biogas generator is also able to withstand higher loads, I plan to increase the weed portion from 2.5 to 3.5 kilograms.