The submarine bottom sediment is improved by electrolyzing seawater to produce magnesium hydroxide near a cathode part 9 from the magnesium ion in the seawater, precipitating/accumulating the produced magnesium hydroxide on the seabottom 6 to alkalinize the submarine bottom sediment, activating and propagating bacteria being fond of alkalinity and promoting that the organic matter contained in submarine slime is decomposed by the propagated bacteria. 海水を電気分解し、陰極部9に海水中のマグネシウムイオンから水酸化マグネシウム11を生成させ、生成した水酸化マグネシウム11を海底6に沈殿・堆積させて海底底質をアルカリ性に移行させ、アルカリ性を好むバクテリアを活性化及び増殖させて、当該バクテリアよる海底ヘドロに含まれる有機物の分解促進を通じて海底底質の改善を図る。 - 特許庁