WWW.WA S .ORG • WORLD AQUACULTURE • JUNE 2022 65 residues (e.g., bamboo, bark, sawdust, pitch pine and shavings), agricultural waste or crop residues (e.g., wheat straw, rice husks, corn cobs, bagasse, coconut waste, stover) and wood waste, animal manure, non-food energy crops, yard trimmings, methane digester residues and grasses (Raul et al. 2021). Biochar Preparation Locally available rawmaterials or organic materials are collected, dried and ground into a fine powder with a pulverizer machine. In pyrolysis, steel or iron containers are filled with the fine powder and then heated at 300-1000 C in the absence of oxygen for 1 hr. The resulting product is cooled to room temperature and sieved through a 40mesh sieve. To make activated biochar, finely sieved biochar is mixed with an acid or alkali solution and stirred for 24 hrs. The resulted mixture is then washed with water to remove chemicals and dried in an oven at 110 C for 24 hr. This dried, activated biochar is ready for further use as a feed additive. Charcoal, biochar and activated biochar are related substances but they have different properties. Charcoal is produced by burning wood-based material while biochar is produced by burning organic material in a controlled environment and activated biochar is prepared by additional alkali or acidic treatment of biochar (Schmidt andWilson 2012). The rising cost of feed has caused feed producers and nutritionists to shift focus to low-cost unconventional plant ingredients for fish feed production. These ingredients may have toxins or antinutritional components, pesticides, herbicides and many other harmful substances that farmers may use during crop production to achieve high yields. Worldwide, approximately 25 percent of animal feeds or feed ingredients are affected annually by mycotoxin contamination. These toxic substances can have negative effects on fish growth and health. Zeolites, bentonites and aluminosilicates are absorbents used as feed additives to protect animals from these toxins, but the use of these chemicals can have negative environmental effects. Biochar can be used as a safe toxin absorber in feed because it is a natural product derived from organic matter (Lao and Mbega 2020). Biochar Biochar is a stable carbonaceous organic material synthesized through pyrolysis of organic materials in the absence of oxygen (EBC 2018). Pyrolysis is the thermal decomposition of materials at elevated temperatures in a control atmosphere. Biochar is a very fine, odorless, tasteless black powder containing more than 70 to 98 percent carbon and small amounts of minerals, including phosphorus, potassium, calcium, magnesium, zinc, iron and manganese. Biochar has a pore size of less than 2 nm and a high surface area of 500-3000 m2/g, making it a universal absorbent. Biochar is produced from a variety of organic materials of plant and animal origin, such as forestry Biochar: An Excellent Fish Feed Additive Chetan Kumar Garg, Manas Kumar Maiti, Manish Jayant, Ravi Kumar Patel and Sinha Jateen ( C O N T I N U E D O N P A G E 6 6 ) Raw material for biochar: (A) bamboo and (B) rice straw; (C) pyrolyzed rice straw and (D) fine biochar powder. Biochar preparation unit: (A) drum for biochar preparation, (B) drum filled with raw material (C) drum with lid, (D) drum placed inside the firebrick kiln for heating and (E) prepared biochar in drum.
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