Outlining Metabolic Versatility of a Commercial Waste Composting Consortium in Fish Waste Management

Abstract

Effective and sustainable management of fish waste produced in markets and processing industries, is a major challenge faced by the coastal communities. Composting is an environment friendly method for fish waste disposal, and for the production of organic fertilizers. However, quality of compost depends on the use of proficient microbial consortia to mediate the bioconversion processes. Accordingly, as a first step in developing a competent fish waste composting strategy, suitability of a commercial organic waste composting consortium was assessed. For this, various selective media were used for outlining the metabolic activities required for waste degradation such as production of hydrolytic enzymes viz., chitinase, lipase and protease (both in standard media and fish waste component embedded media), ammonia oxidization, organic and inorganic phosphate solubilisation, nitrite oxidization and sulphur oxidization. There were potential producers for all organic waste degrading enzymes with highest enzymatic index (EI) as 1.8, 2.9 and 1.5 for protease, lipase and chitinase respectively. Among these, 10 microbial consortia were able to degrade fish waste components with the highest EI as 1, 2.4 and 0.2 for protein, chitin and oil respectively; indicating that efficacy of fish oil degraders in the evaluated consortia was very less. Four isolates were found efficient for denitrification. Highest organic and inorganic phosphate solubilisation efficiency was 1.9 and 7 respectively. Despite the presence of some AOB (ammonia oxidizing bacteria), NOB (nitrite oxidizing bacteria) and SOB (sulphur oxidizing bacteria), their efficacy was less. Potential isolates were characterized as Lysinibacillus xylanilyticus, Halotalea sp, Bacillus oryzaecorticis, Cronobacter condiment and Bacillus megaterium. As fish waste is rich in nitrogen and sulphur, inclusion of efficient AOB, NOB and SOB can improve the quality of final compost. Similarly, exclusion of denitrifiers can avoid the loss of nitrogen during composting. Consequently, while there were efficient organic matter degrading enzyme producers including fish protein and chitin, absence of efficient AOB, NOB, fish oil degraders and presence of denitrifiers recommends an improvisation of the evaluated consortium before application in fish waste composting.