Study on release kinetics of nitrogen and phosphorus from fish feed

Kong, Wenwen, Huang, Suiliang, Shi, Feifei, Yang, Zhenjiang, Feng, Yibei, Khatoon, Zobia, Zhou, Jian Guo ORCID: https://orcid.org/0000-0002-4262-1898 and Xiao, Yao (2020) Study on release kinetics of nitrogen and phosphorus from fish feed. Aquaculture Research, 51 (8). pp. 3216-3229. ISSN 1355-557X

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Abstract

Nitrogen and Phosphorus are the major end products of fish feed loading and affect the water environment as a whole. A magnetic stirrer was used to simulate the intensity of water flow by using different stirring strengths (0, 600, 1,200 rpm), and kinetic experiments on nutrients release from different fish feed (0.2500 and 0.5000 g) were performed. Results have shown that total phosphorus (TP) increase rapidly and become stable in about 96 hr, while orthophosphate ((Formula presented.) ), total nitrogen (TN) and ammonia nitrogen ((Formula presented.) ) increase relatively slowly and gradually reach stable from 200, 300 and 300 hr respectively. Both released contents of unit weight fish feed (i.e. released nutrients contents) and released nutrients concentrations in the condition of stirring were higher than those in the static condition. All of the pseudo-first-order, pseudo-second-order and Elovich kinetic models can be used to describe variations of released TP, (Formula presented.) , TN and (Formula presented.) contents with time, while the pseudo-first-order kinetic and Elovich kinetic models give better results with R2 =.66–.99 and R2 =.57–.99 respectively. Variance analysis showed that both stirring strength and fish feed type have significant effects on released TP, TN and (Formula presented.) contents (p <.05), while fish feed dosage has no significant effects (p >.05). In addition, only the fish feed type does have significant effects on (Formula presented.) contents (p <.05). In sum, the release kinetics and the factors related to the release of nutrients from fish feed are essential in planning strategies of nutrient management and pollution control.