Understanding Biogas and Biomass: Which Statement is Incorrect?

The question asks us to identify the statement that is NOT correct regarding biomass and biogas.

Let's examine each statement:

• Statement 1: Biomass is a renewable source of energy.
• Statement 2: Gobar gas is produced when cow-dung, crop residues, vegetable waste and sewage are allowed to decompose in the absence of oxygen.
• Statement 3: Biogas generation reduces soil and water pollution.
• Statement 4: Heating capacity of biogas is very low.

Analyzing Each Statement about Biogas and Biomass Energy

Let's break down each statement to determine its accuracy:

Statement 1: Biomass as a Renewable Energy Source

Biomass refers to organic matter from plants and animals. This includes wood, crops, waste products, and even manure. As plants can be regrown and waste is continuously produced, biomass is considered a renewable source of energy because it can be replenished relatively quickly. This statement is correct.

Statement 2: Gobar Gas Production via Anaerobic Digestion

Gobar gas is another name for biogas, especially when produced from cow dung. Biogas is indeed produced through a process called anaerobic digestion. This process involves the breakdown of organic materials (like cow dung, crop waste, vegetable scraps, and sewage) by microorganisms in the absence of oxygen. This biological process yields biogas, which is primarily methane and carbon dioxide, and a nutrient-rich residue called digestate. This statement accurately describes biogas production and is correct.

Statement 3: Biogas Generation and Pollution Reduction

One of the significant benefits of generating biogas is its positive impact on the environment. By processing organic waste in a controlled biogas plant, harmful greenhouse gases like methane that would otherwise be released into the atmosphere during natural decomposition are captured and used as fuel. Furthermore, the controlled digestion process prevents the untreated waste from polluting soil and water bodies. The digestate produced is a better fertilizer than raw manure, reducing the need for chemical fertilizers. Therefore, biogas generation helps in reducing soil and water pollution. This statement is correct.

Statement 4: Heating Capacity of Biogas

The heating capacity, or calorific value, of a fuel indicates the amount of heat energy released when it is burned completely. Biogas primarily consists of methane (\(\text{CH}_4\)), which is a combustible gas. Pure methane has a high calorific value. Biogas, typically containing 50-75% methane, has a calorific value ranging from about \(\text{20 to 25 MJ/m}^3\) (or approximately \(\text{4,700 to 5,900 kcal/m}^3\)). While its heating value per cubic meter is lower than that of natural gas (which is almost pure methane), it is still substantial enough to be used effectively for cooking, heating, and electricity generation. Saying the heating capacity is "very low" is an inaccurate description of its potential as a fuel. Compared to fuels like wood or dried manure burned directly, biogas often provides a cleaner and more efficient burn. This statement is NOT correct.

Based on the analysis, the incorrect statement is that the heating capacity of biogas is very low.

Summary of Statements

Therefore, the statement that is NOT correct is "Heating capacity of biogas is very low".