What to do in case of builder's construction creating nuisance

I would like to let you know that i have purchased a flat in residential complex and residing since last 1.5 years. Builder has constructed a sewage treatment plant(STP) just adjacent to my building which is functional since beginning. Last year they have broken down the RCC cover from top to get permission from government authorities.Now since the STP is open bad unbearable smell keep on coming from the STP on everyday basis.Due to this bad smell neither i can open the door of my balcony nor the windows.It has created a very unhealthy environment to stay in the flat.I have repetitively communicated to the builder about this issue of bad smell but till date nothing concrete is done from their side apart from putting temporary cover at top which has not helped much. It's being a serious health concern for my family.