Limited information is available on arsenic (As) release from As-loaded algae precipitated from As contaminated water and its subsequently appropriate disposal. In this study, selected M. aeruginosa as algal model, changes of As concentrations and its speciation were thus investigated in the in-situ treated algae water by optimal coagulation. Meanwhile, after ex-situ disposal, As release kinetics were also examined from its precipitated algae with living and heat-treated conditions. Results showed that in the in-situ treated water, total dissolved As slowly decreased for 6 days, but arsenite increased largely after 3 days partly caused by its reduction status. While being disposed ex-situ, As release from precipitated algae depended not only on intracellular As content but also on the living or heat-treated status of algae. Additionally, potential risks arised from As release in short-term duration (24 h) from both the precipitated algae at 1.0 μM As(V) pre-exposure with the living and heat-treated conditions due to their higher release. Furthermore, As release in long-term (6 d) duration from heat-treated algae at 10.0 μM As(V) pre-exposure also resulted in potential risks. Accordingly, this study offers insights into the appropriate methods at a proper time of disposing precipitated algae with As-contamination.