Growth of saltwater algae on press water of champost (spent mushroom waste)

For mushroom production usually a mixture of horse and chicken manure and straw is used. For every kg of mushrooms, 5 kgs of waste is produced, a total of 800.000 tonnes per year in the Netherlands. Processing options are often either costly or complex. As the champost contains high salt concentrations, washing results in a solid (less salty) fraction with better re-use options and a nutrient-rich liquid fraction. On the latter fraction growth of five species of commercially relevant micro algae was tested in small-scale well tests. In addition, the press water was also treated with H2O2/UV to reduce the brown colour of the solution. In the majority of the triplicate well tests, growth of three of the five common saltwater algae species (Nannochloropsis gaditana, Porphyridium purpureum, and Tetraselmis chuii) on press water fractions of spent mushroom waste (champost) was found to be comparable to or better than their growth on control media. Dunaliella salina growth was relatively low. Arthrospira platensis only grew on press water when treated with H2O2. Overall, the results indicate that washing of champost results in a mineral rich solution suitable for growth of several (saltwater) algae.