Study on release kinetics of nitrogen and phosphorus from fish feed
Wenwen Kong, Suiliang Huang, Feifei Shi, Zhenjiang Yang, Yibei Feng, Zobia Khatoon, Jian Zhou, Yao Xiao
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 ( ), total nitrogen (TN) and ammonia nitrogen ( ) 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, , TN and 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 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 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.