*Biogas Production and Process Control Improvements DOI: http://dx.doi.org/10.5772/intechopen.113061*


#### **Table 2.**

*Methane content and gas yield for different biomass [37, 101].*

As can be seen in **Table 2**, there is a wide range in both the quantity and quality of biogas produced from various forms of biodegradable biomass feedstocks. According to **Table 2**, biogas can be produced from a variety of sources, including algae, cow manure, pig manure, agricultural solid wastes, and grass. Among the many potential sources of biogas, algae have the highest output, followed by sugar beets, elephant grass, sewage sludge, clover, elephant grass, and maize straw. There is not much potential for biogas production from materials like reed, sugarcane bagasse, rice seed coat, or rice seed straw. Therefore, a farmer must carefully select his biomass feedstock, or the plants and animals he raises, to achieve maximum biogas output [100].

#### **3.6 Estimation of biogas potential**

According to [100, 123], biogas can be used to generate heat, the cost of which can be roughly calculated using Eq. (4) as shown:

$$E\_{p^i} = E\_{m}^{\circ d} \ast \eta\_i \tag{4}$$

where:

*Epi* – Production of the energy (heat only, electricity only or heat and electricity in co-generation), [GWh/year].

η*<sup>i</sup>* –efficiency of energy conversion process.

*cd Em* – Possible production of total biogas energy.

Total biogas energy potential from livestock dung can be determined using the following relation in Eq. (5):

$$E\_m = \sum (N\_{i.u} \ast M\_{i.u} \ast o \text{DM}\_{i.u} \ast CH\_{4i.n}) \ast NCV \ast 365 \ast 10^{-6} \tag{5}$$

where:

*E*m - Expected production from livestock manure available in the region, [GWh/ year].

*Ni.n***--**Animals of the same category (cattle, pigs, poultry etc.) in the region, [number of animals].

*Mi.n* - Manure outcome of each category of animals, [kg of manure/animal/day].

*oDM*i.n -Organic dry matter content in the manure for each category of animals, [%].

*CH*4i.n **-**Methane outcome, [Nm3 CH4/kg organic dry weight of the animal manure].

*NCV* – Net Calorific Value [kWh/Nm3 ].

#### **3.7 Biogas production and fertilizer application**

The composition of the feedstock and the stability of the biogas plant's operations are two factors that influence the biogas yield, biogas quality, status of digestate, and stability of plant operations [124], and the quality of the sludge from anaerobic digestion, that can be used as an organic fertilizer [22], to improve soil quality, boost crop yields, and aid in the advancement of sustainable agriculture [61]. Biodigester slurry can boost agricultural output by 10–20% by enhancing soil fertility and productivity. It is advised that 5 tons of the digestate be applied per hectare on farms that do not use irrigation, and that 10 tons be applied per hectare on farms that do use irrigation [125].

The chemical and nutrient composition of the biodigester substrate and digestate is determined by the efficacy of the process and the feedstock composition. Very little preparation is needed before spraying the farm with the substrate or digestate or utilizing it as bedding for the animals [34]. Digester slurry is a 25% more effective fertilizer than just putting manure on the farm. This suggests that increasing agricultural yield by employing digestate in this way. In comparison to applying manure directly, biogas slurry makes it easier for plants to absorb the nutrients they need [61].

Slurry from a biodigester can be used as a fertilizer because of its high nutritional content and low environmental impact compared to synthetic alternatives. The digestate can be used as a foliar fertilizer on the farm if it is mixed with water and sprayed on the right leaves. Slurry is collected from the digester via a ditch as gas pressure increases after the biogas plant is refueled with fresh feedstock. Overflow and back pressure can be avoided in a biodigester system with regular ditch emptying by the operator [126].

Digestate consists of water and any unreacted feedstock or co-substrates. Digestate management is necessary for monitoring and controlling biogas production. A farm can either use the digestate as fertilizer or store it in a lagoon or storage tank. The wastewater from a biogas plant that has not been filtered for coarse fiber reduces bio digestion rates and gas production. Bedding and compost can be made from the screened-out material. After fibers have been extracted, the liquid organic residue is known as filtrate. Dry matter nitrogen, phosphorous, and potassium levels in manure

filtration concentrate range from 3 to 4.5%. The crops can be sprayed with nutrientrich sewage water.

The filtrate can be refined into a liquid concentrate and a solid product known as filter cake. This is especially important when bringing garbage from off-site locations into the digester's sphere of impact. Plants' basic nutrients, nitrogen, phosphorous, and potassium, may be found in abundance in these wastes. Thus, it is important to think about how this would affect the final disposal site's overall nutrient management strategy. Technology for recovering nutrients to control digestate nutrient levels [127].

As a result, biogas generation can be a more economical alternative to costly chemical fertilizers by boosting agricultural output and yields while saving money for farmers and contributing to long-term energy security. Farmers can earn revenue by selling the digestate or filtrate [30, 60, 65, 66].
