A knitwear factory uses water for its production. The wastewater of its production is hazardous for surface water. So this water needs to be treated. In this book a simple biological effluent treatment plant is designed for BOD and TSS removal for a knitwear industry. The characteristics of the effluent were tested in the lab and then the target was set according to the guideline of the DoE (Bangladesh). The design was done according to the suspended growth biological treatment process. According to the calculation after treating the amount of dissolved oxygen in water increases in an allowable scale that it was ready to release in the surface water body. Then computer aided software was created to simplify the calculation process. The initial inputs like BOD, COD and TSS and others was given in the software and the result was came out according the process as this design was followed by.