In compliance with an international lawabout the ocean dumping of the sludge, the proper sewage treatment process which occurs from the wastewater treatment process has been becoming problem.Generally the sewage and the sludge are controlled from anaerobic conditionwhen the sewage is treated and landfilled, where the methane(CH4) and the nitrous oxide(N2O) from this process are discharged.Because these gases have been knownas one of the responsible gases for global warming, the wastewater treatment processis become known as emission sources of green house gases(GHG). This study is to suggesta new approach of estimate and environmental assessment of greenhouse gas emissions andsludge emissions from wastewater treatment processes. It was carried out by calculating the total amounts of GHG emitted from biological wastewater treatment process and the amount of the sludgegenerated from the processes. Four major biological wastewater treatment processes which are Anaerobic/Anoxic/Oxidation(A2O), Bardenpho, Virginia Initiative Plant(VIP), University of Cape Town(UCT)are used and GPS-X software is used to model four processes. Based on the modeling result of four processes, the amounts of GHG emissions and the sludge produced fromeach process are calculated by Intergovernmental Panel on Climate Change(IPCC) 2006 guideline report. GHG emissions for water as well as sludge treatment processes are calculated for environmental assessment has been done on the scenario of various sludge treatments, such as composting, incineration and reclamation and each scenario is compared by using a unified index of the economic and environmental assessment.It was found that Bardenpho process among these processes shows a best process that can emit minimum amount of GHG with lowest impact on environment andcomposting emits the minimum amount of GHG for sludge treatment.