Dissolution of minerals during hydrolysis of fish waste solids

Biological degradation of fish waste solids in the anaerobic zones of settling basins can reduce water quality and increase the environmental impact of aquaculture farms. The objectives of this study were to measure the rate of hydrolysis of waste solids from a salmon smolt hatchery and to investigate the concomitant dissolution of phosphorus and nitrogen. Hydrolysis followed first order kinetics with a reaction time constant of about 2 days. The rate of production of volatile fatty acids (VFA) appeared to be limited by the rate of conversion of solids into soluble organic material. The total ammonia-nitrogen concentration increased linearly with VFA concentration. As the pH dropped due to the generation of VFA, the concentrations of dissolved phosphorus and calcium increased, especially once the pH dropped below 6.5. Solids content had little effect on dissolved phosphorus concentration within the range of solids concentrations tested (0.5 wt.%-9.02 wt.%). The effect of pH on the dissolved phosphorus and calcium concentrations is well described by an equilibrium model based on the solubility of dicalcium phosphate dihydrate. (C) 2009 Published by Elsevier B.V.