PROBLEM TO BE SOLVED: To provide a compounding agent capable of utilizing effectively iron phosphide isolated from slag, and to provide an algae field structure, a vegetation structure, and a method for producing a compounding agent.SOLUTION: A compounding agent includes a solid solution containing as main components, iron and iron phosphide obtained by being isolated by a sorting mechanism 18 from slag obtained by melting sewage sludge or night soil sludge by a melting facility 14, and is used as a supply source of an iron component and a phosphorus component which are necessary for rooting and growth of algae or aquatic plants, and is installed on an algae field, a revetment wall or the like as an algae field structure or a vegetation structure in which the compounding agent is carried on a structure so that a manuring effect can be controlled.【課題】スラグから分離したリン化鉄を有効に活用できる配合剤、藻場構造物、植生構造物、及び配合剤の製造方法を提供する。【解決手段】下水汚泥またはし尿汚泥を溶融設備１４で溶融処理して得たスラグから選別機構１８で分離して得られる鉄とリン化鉄を主成分とする固溶体を含む配合剤で、藻類または水生植物の根付けまたは育成のために必要な鉄成分及びリン成分の供給源として用いられ、当該配合剤が構造体に肥効調整可能に担持された藻場構造物または植生構造物として、藻場や護岸壁等に設置される。【選択図】図１
