酪農場において，搾乳施設で生じる洗浄排水（搾乳関連排水）が日々排出されている．膜分離活性汚泥法など既往の浄化方法は，現在の設計基準では中小経営にとって高価であり普及は見込めない．そこで本論文では，同排水の汚濁度合を下げて浄化施設の設計規模を縮小する一手法として，搾乳機器内に残る生乳（残乳）の同排水への混入を少なくする技術を検討した．現地事例調査では，搾乳パイプラインの傾斜角度が大きいほど排水に混じる残乳は少ない傾向であり，小規模試験装置によるエア回収試験では，配管傾斜角度よりもエア回収時間の長さが残乳量に影響を及ぼすことが示唆された．この結果を受けて，現地事例においてエア回収時間を5分から10分に延長したところ，同排水のBOD負荷量は平均で51％低下した．本検討によって，浄化処理施設の設計規模の縮小が可能となり，建設コストの低減が同排水の浄化システム普及に寄与すると考えられた．Milking centers at dairy farms generate wastewater through the washing of milking units, milk line and bulk cooler. High-performance treatment systems for water purification, such as activated sludge systems, have been used at some large-scale dairy farms but are generally not feasible at almost all dairy farms because of the high costs of construction and maintenance. The aim of this study is reducing the contamination of raw wastewater from milking centers by methods for efficient draining of residual milk in milk lines. Residual milk in the milk lines was drained into the pail after milking by letting it flow down the pipeline naturally or by forcing out the line using compressed air. Removing or reducing residual milk from milk lines as much as possible will be beneficial for low-cost treatment systems for milking center wastewater. Investigation of 7 tie-stall dairy barns (TS) with a pipeline milking system and 10 free-stall dairy barns (FS) with a milking parlor revealed the following. At the TS, the average gradient of the milk lines was 0.34±0.14°, and the average time for capturing residual milk was 14±11 min. At the FS, the average gradient of the milk lines was 0.67±0.19°, and the average time for capturing residual milk was 12±5.2 min. Contamination of milking center wastewater with milk was lower for milking pipelines with a high gradient. On the basis of these results, milking pipeline gradient has more effect on the amount of captured residual milk than the capturing time when capturing residual milk after allowing it to flow naturally down the pipeline. In addition, a laboratory experiment revealed that capturing time has more effect on the amount of captured residual milk than pipeline gradient when removing residual milk with compressed air. Therefore, a high gradient and a long drainage time with compressed air will provide the most effective low-cost treatment system for removing or reducing contaminants in milking center wastewater. On average, 51% of BOD in milking center effluent was reduced when extending the drainage time of residual milk with compressed air to 10 min at 3 dairy farms where 5 min of drainage using compressed air was normally conducted. At dairy farms, therefore, extending the drainage time for residual milk with compressed air might be a feasible means to improve the removal efficiency of residual milk while reducing the contaminants of milking center effluent.
雑誌名
日本畜産学会報
巻
86
号
4
ページ
497 - 504
発行年
2015-11
DOI
10.2508/chikusan.86.497
著者版フラグ
publisher
その他のタイトル
Study on removal efficiency of residual milk from milk line for wastewater purification at milk house
搾乳システムからの残乳回収改善による搾乳関連排水の処理負荷低減
S-2016-079_morita.pdf
(507.94KB)
