BIOTECHNOLOGY - V. H. Gerasymenko - 2006

Part II. Special Biotechnologies

Chapter 22. BIOTECHNOLOGIES FOR THE UTILIZATION AND BIORECYCLING OF AGRO-INDUSTRIAL WASTES

22.3. NON-TRADITIONAL METHODS. BIOTECHNOLOGY OF BIOGAS PRODUCTION VIA ANAEROBIC DIGESTION OF WASTE

22.3.4. Fractions formed during biomethanogenesis

22.3.4.2. Sludge: composition and application

The solid manure fraction, or sludge generated during biogas production, contains significant amounts of nutrients and can be utilized as a valuable, sanitized organic fertilizer or feed additive. It is free from any specific odor.

Anaerobic Fermentation of manure biomass reduces the dry organic matter content in the sludge by nearly 50% compared to raw manure. This reduction occurs because 10–15% of the substrate carbon is incorporated into microbial biomass, while the remainder is converted into biogas components such as methane and carbon dioxide.

The COMPOSITION OF THE sludge depends on The chemical composition of the initial feedstock and the operational parameters of biomethanogenesis. The organic fraction of the sludge consists of Three types of substances:

1) substances originally present in the raw material that are protected from microbial degradation by Lignin and cutin;

2) novel bacterial Cells;

3) trace amounts of volatile Fatty acids.

Sludge serves as a valuable organic, nitrogenous, and mineral fertilizer, in which nutrients are present in a more accessible form. Anaerobic Digestion preserves essential plant nutrients (N, P, K), whereas composting can result in nutrient losses of up to 40%.

The primary advantage of anaerobic digestion over aerobic Treatment is the conservation of almost all the nitrogen originally present in the manure biomass in organic or ammonium form. For instance, out of 37 kg of nitrogen contained in manure, only 12–15 kg is returned to the soil after aerobic treatment, whereas anaerobic fermentation returns 36 kg (Alekseev V.V., Lyamin M.Ya., 1985). The ratio of organic to ammoniacal nitrogen in the sludge depends on their ratio in the fermented biomass. To minimize losses of ammoniacal nitrogen, sludge is stored in deep pits or reservoirs with a minimal surface area to prevent ammonia volatilization. Nitrogen retention is maximized when the sludge is applied to the soil a few days prior to sowing or cultivation. If the sludge is spread on the soil surface and no precipitation occurs for an extended period, nearly all the ammoniacal nitrogen is lost to the atmosphere.

In many cases, the sludge is dried, which facilitates its transportation over considerable distances.

Sludge is utilized as a protein and vitamin (vitamin B₁₂) feed Supplement. This practice is widespread in the United States, both for on-farm use and for commercial distribution. For example, the US company Thermotenix produces feed additives from sludge with a protein content of up to 12%, with future projections ranging from 26 to 28%.

At a 10,000-HEAD cattle feedlot operated by Kaplan Industries in Florida, USA, waste Processing into biogas via anaerobic digestion yields a feed protein byproduct that surpasses cottonseed meal—a widely used feed supplement—in nutritional value.

An Analysis of the sludge for pathogenic microflora demonstrates that enteric microorganisms are destroyed at a digestion Temperature of

37 ^oC (i.e., under mesophilic conditions). The risk of crop contamination by pathogens can be entirely eliminated by pasteurizing the sludge.

Additionally, sludge can be utilized directly as a substrate for earthworms without prior preparation (fermentation).