According to our earlier work, the total phosphorus concentration in the biogas fluid-soaked water hyacinth stalks doubled. To explain why the total phosphorus concentration increased, experiments on phosphorus and suspended solids adsorption by water hyacinth stalks were performed. The results of the present study indicated that soluble phosphorus was not adsorbed by the water hyacinth stalks, neither was Ca3(PO4)2. The experimental results also showed that per 100g the stalks adsorbed about 60g suspended solids which contained 0.71% total phosphorus. So it was concluded that the increase of total phosphorus in the biogas fluid-soaked water hyacinth stalks was mainly induced by suspended solids adsorption.