First, you have to know wich kind of sludge you have. Is it Copper hydroxyde?Which pH do you have? If it is Copper hydroxyde, may be you can try (not sure) chelation first. (EDTA,...?)

You have almost certainly precipitated Cu(OH)2. Monoethanolamine will not help.

I suspect the precipitation is Cu(OH)2.The pH is about 12. I have repeat the experiment by adding some monoethanolamine first before adding the BC, and no precipitation was found. 

I would like to seek for advice, beside monoethanolamine, is there any compound that able to replace monoethanolamine?

You can try a polyaminopolycarboxylic acid such as EDTA or DTPA in combination with a synergist, preferably oxalate or monocarboxylic acid anion such as salicylate. The pH should be about 12. 

Thanks Zaidi!