64 SEPTEMBER 2019 • WORLD AQUACULTURE • WWW.WAS.ORG contamination of groundwater and could be a problem for the safety of drinking water. • Enrichment of Mineral Nutrients. The mineral nutrient concentration of inland saline pond water is not same as brackish water or seawater. A potassium deficiency (minimum 50 percent potassium level of seawater required for) and imbalance in the Ca:Mg ratio (minimum 1:2.25 required in inland saline water for shrimp) can result in muscle deformities in shrimp. Biochar produced from banana peduncle, sugarcane bagasse and other agro-wastes are rich in potassium, calcium and magnesium that can supplement these minerals (Fig. 4, Dahlawi et al. 2018). • Use as a Feed Additive. Research shows the incorporation of biochar as a feed additive increases growth rate in catfishes (Lan et al. 2016). It improves ammonia absorption from fecal matter and, hence, reduces the ammonia toxicity in high-density larval rearing units. • Use as Plant Bed in Aquaponics System. Biochar beads are used as plant substrate in an aquaponics system (Fig. 5). It retains nutrients from wastewater and facilitates symbiotic association of mycorrhizal fungus with plant roots, which helps in mineral and Biochar, which has been extensively used in agriculture for productivity enhancement, can also be used in aquaculture for similar purposes, although there are few examples of practice and research on the use of biochar in aquaculture. Biochar is a finegrained, carbon-rich, porous product produced from agricultural, industrial, urban, and animal waste by pyrolysis at a temperature 350-600 C in the absence of oxygen. The type of biomass and temperature are the deciding factors for physicochemical properties and nutrient content of biochar. It has high potential for use in aquaculture by virtue of its novel physicochemical properties such as high surface area to volume ratio, functional groups, trace elements and absorption properties, among others. Biochar Application in Aquaculture In aquaculture, biochar can be a useful input, with potential uses (Fig. 1) ranging from pH adjustment of soil and water to the reduction in greenhouse gas emissions from the system. Some of the identified potential uses of the biochar are discussed below. • Acid Neutralization. The pH of biochar remains in the alkaline range and contains calcium, magnesium and carbonate ion (identified by FT-IR analysis). Use of biochar can reduce the lime application in aquaculture ponds, by acting as an alternative, owing to its good buffering capacity (Figs. 2 and 3, Schmidt and Wilson 2012). • Reduction in seepage and leaching loss of nutrients. Biochar application in the pond bottom can reduce seepage by enhancing water holding capacity. These can be particularly in the inland saline aquaculture ponds of Haryana, Punjab, and Rajasthan, which are facing high seepage losses, necessitating large withdrawals of saline groundwater for aquaculture. Further, the high anion exchange capacity of biochar can retain nitrate ions produced from nitrification. Leaching of nitrate can lead to Biochar: An Emerging Solution for Sustainable Aquaculture Chittaranjan Raul, Sambit Priyadarshi, Vidya Shree Bharti and Satya Prakash FIGURE 1. Potential uses of biochar in aquaculture. FIGURE 2. Biochar production unit: electrical (left), non electrical (right). FIGURE 3. Biochar produced using an electrical kiln.
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