After studying on the analyzed results in Table3, the treated wastewater quality indicators at the 18.5-km HPDE pipe tip were supposed to decrease by bacterial organic digestion processes but the trends did not follow such concept due to their properties concerning with physically, chemically, and biologically inter-changes as well as the environmental factors inside the mentioned aquatic ecosystems, especially the compounds of nitrogen, phosphorus, sulphur, and carbon (Metcalf and Eddy 1974, Bearman 1957, McColl 1974, and Gorses1989). In reality, the treated wastewater was flown from Khlong Yang collection pond by pumping to the first oxidation pond (sedimentation pond), and passing by oxidation ponds2,3,4,and 5 under gravitational forces until it moved throughout the natural mangrove forest, muddy beach, and seashore of the Gulf of Thailand.