The rate of NHEJ in e.coli is low therefore you must use a HR template. There is a paper however where they expressed NHEJ enzymes from other bacteria to make this kind of edit possible (ref:https://www.nature.com/articles/srep37895)

If you're just going to trying to knock out a gene I would recommend using lambda red, recET recombination, recombineering or possibly allelic exchange. If you're working with a K12 strain you can also just order a deletion mutant from the Keio collection. A lot of people gravitate towards Cas9 editing of E. coli because of how well it works in mammalian cells but the efficiency of it in most bacteria is low, as Hanna Alalam mentioned, and often just results in a point mutation that stops Cas9 targeting. It can be combined with other methods and make them more efficient but honestly I think it just adds an extra layer of complexity to the procedure in an organism like E. coli, where older established methods tend to be pretty efficient already.

thans for all your answers.