Conclusions
This study shows that by adjusting pH and separating the solid and liquid fractions of pot ale the following removal of the main pollutants can be achieved: COD 14%, free phosphate 60%, total phosphorus 45%, ammonia 65%, copper >80%. Phosphorus and ammonia are only removed at pH 9, the highest investigated pH value, and this indicates that they are probably removed by precipitation. Copper is removed when pH is higher than 7, and this is also likely due to precipitation. The majority of the removed COD is removed at the original acidic pH of the pot ale, so indicating that
a fraction of the total pot ale COD is bound to the solids. Chitosan shows a good adsorption capacity for COD and phosphorus in pot ale, in line with other experimental studies on different wastewaters or synthetic solutions. However, the overall removal of COD and phosphorus that can be obtained with unmodified chitosan is limited to approximately 10% of COD and 35% of phosphorus. The reason for this is the decrease in adsorption capacity which is observed when pH is higher than approximately 6.3 and the instability of chitosan at pH values of 6.0 or lower. The use of chemically modified or cross-linked chitosan, with better mechanical properties and better resistance to acidic pH values, might offer a more effective treatment method for pot ale and deserves further investigation.