Biological treatment of wastewater was studied with a purpose to remove TOC by the reduction of water hardness. The optimal conditions of coagulant were determined by reaction time and amount of coagulant. Experimental results indicate that the biological treatment after physico-chemical treatment was found to provide very efficient removal efficiency in the process to treat the textile wastewater, including the carbon dioxide treatment. The combined process of carbonization in the physico-chemical treatment respectively was increased the removal efficiencies of $30.0\%$ in biological treatment in comparison with exclusive biological treatment. As a result, the treatment of hardness after carbonization had the best removal efficiency of approximately $60.0\%$. The removal efficiencies in the exclusive biological treatment using Bacillus subtilis and after carbonization were increased by $38.9\%;and;69.0\%$ respectively. The combined Bacillus subtilis-assisted biological treatment was determined to be the most effective method to treat the textile wastewater in an economic point of view, the water quality in the wastewater treatment plays an important role.