Treatment of wastewater from milk rooms with ferric sulphate.
Närvänen, Aaro; Jansson, Håkan; Yli-Halla, Markku
Wastewaters from the milk rooms of dairy farms are rich in phosphorus (P) and in some parts of Finland, particularly in the rural north, they may locally account for a large proportion of the P load on watercourses. In this study, we tested the treatment of milk room wastewaters with ferric sulphate liquid (trade name Kemwater PIX-115) in batch experiments and on a practical scale at two farms. The concentration of dissolved reactive P (DRP) could be decreased by >90% with relatively small amounts of the chemical (40 l/kg of reduced DRP); other P forms required higher doses. In the farm scale experiments, the chemical was dosed with an automatic pump, and the precipitate was separated 1) with straw/sandbed filtration on a farm with 35 cows, and 2) by sedimentaton on a farm with 70 cows. The systems were not very expensive to construct (6200 or 2500 € per farm and 177 or 36 € per cow, respectively). In this study, separation by sedimentation was more effective in reducing total phosphorus from the wastewater than filtering.