Substances for hastening the growth of Ulva pertusa in treated wastewater were studied and the following results were obtained.
1) Cultivation tests were carried out adding treated wastewater to sea water. The quantiative ratio of treated wastewater to culture medium was varied from 0% to 100%. When this ratio was less than 20%, the growth of Ulva pertusa was hastened.
2) The composition of the treated wastewater was inverstigated with sephadex G-15. On doing so, it became clear that humic-like substances were in the treated wastewater.
3) Cultivation tests were carried out adding concentrated humic-like substances to sea water. It was found that concentrated humic-like substances that are obtained by using a concentration under reduced pressure and carrying out ultra-filtration are one of the agents that promotes the growth of Ulva pertusa.