Silkworm Dung: A Versatile Resource for Agriculture, Industry, and Health

Silkworm manure, the excrement of silkworms after consuming mulberry leaves, is a rich and versatile resource often overlooked. This seemingly simple byproduct holds significant potential for various applications, ranging from agriculture and animal feed to industrial and pharmaceutical uses. This article delves into the composition and multiple uses of silkworm manure.

1. Composition of Silkworm Manure

The dried form of silkworm manure is a complex mixture of organic compounds. The key components include:

Within the crude fat content, pigments, which include valuable compounds like chlorophyll and carotenoids, constitute about 0.8%. This composition makes silkworm manure a potential source of nutrients and other useful substances.

2. Agricultural and Animal Feed Applications

The high organic content of silkworm manure makes it an effective fertilizer. It is considered a complete organic fertilizer suitable for improving soil health and promoting plant growth. Farmers can use it in both crop fields and mulberry gardens. It is estimated that feeding silkworm queens in 1 mu of mulberry garden can yield approximately 150 kg of dried silkworm manure.

Moreover, silkworm manure is suitable for feeding livestock, poultry, and pond fish. Its protein content makes it a valuable addition to animal feed, contributing to their nutritional needs.

3. Extraction of Pigments: Chlorophyll and Carotenoids

One of the most significant industrial applications of silkworm manure is the extraction of valuable pigments, primarily chlorophyll and carotenoids.

Chlorophyll: After softening the dried manure with water, chlorophyll is extracted using an organic solvent like acetone. The solvent is then recovered, leaving behind a dark green pasty substance that is then processed further. Through saponification using sodium hydroxide, the chlorophyll is separated into saponified and unsaponifiable fractions. The saponified portion, rich in chlorophyll derivatives, can be further processed under acidic conditions with copper sulfate to create copper chlorophyllin. This is then converted to water-soluble sodium copper chlorophyllin, which is used in pharmaceuticals due to its antibacterial and cell growth-promoting properties. Products like “Ganbao” for treating chronic hepatitis and “Weiganlu” for treating stomach and duodenal ulcers have their roots in this pigment extraction process. Topical applications for burns and ulcers are also common. Sodium copper chlorophyllin is also used as a coloring agent in food, toothpaste, and soap.

Carotenoids: The unsaponifiable portion of the chlorophyll extraction is further processed to extract carotenoids. Using gasoline as a solvent and activated alumina column adsorption chromatography, carotenoids, including beta-carotene (approximately 20% of the total carotenoids), are separated. Beta-carotene is used as a feed additive to supplement vitamin A intake. The refined gasoline extract, after vacuum distillation, yields vegetable alcohol, a vital raw material for producing vitamin E and K1.

4. Recovery of Plant Growth Regulators

Silkworm manure contains natural plant growth regulators like triacontanol and indole acetic acid. These compounds can be recovered from the waste generated during chlorophyll production. Spraying these extracts on crops such as rice, corn, wheat, and mushrooms, or even on mulberry trees, can enhance growth and increase yields.

5. Extraction of Pectin

Defatted silkworm manure also contains approximately 15% pectin. This polysaccharide, primarily composed of galacturonic acid, can be extracted using hot oxalic acid and ammonium oxalate. The resulting filtrate is concentrated and then precipitated with alcohol to obtain the pectin. Pectin serves as a gelling agent in food production, particularly in jams and soft sweets. Additionally, its ability to inhibit bacteria, lower blood cholesterol, and promote the removal of heavy metals makes it valuable in the pharmaceutical industry.

6. Protein and Carbohydrate Applications

The protein content in silkworm manure can be extracted using dilute lye and then precipitated at a pH of 4.0 after neutralization with hydrochloric acid. This extracted leaf protein, containing eight essential amino acids, can serve as a concentrated feed for animals. The carbohydrates in silkworm manure can be hydrolyzed with dilute sulfuric acid and distilled to produce furfural, a raw material in the production of plastics.

In conclusion, silkworm manure offers a treasure trove of valuable components that can be used in agriculture, animal feed, and industrial processes. Its diverse applications highlight the importance of sustainable resource utilization and the potential of what was once considered a waste product.