Is it really a career booster to do certification six sigma in operations, since i have more than 9 years experience in middle management level at various manufacturing and service industries

If you are in operations six sigma training will be highly useful. Six sigma applied in practice will lead to tremendous benefits and this is a proven fact. Many companies across industries and functions have implemented them, for example BPO, manufacturing, suppply chain and so on. We also observe that companies when looking for hiring people include in their criteria of applicants - applied experience in six sigma. Thus not having the experience could be a handicap for you. Like most certifications, however, merely having a certification will itself not help. They can at best be considered a passport but not a visa. My suggestion is therefore yes go for six sigma training and also apply it in practice.