Hamadan University of Medical Sciences Avicenna Journal of Environmental Health Engineering 2423-4583 12 1 2025 06 29 Modifying the Activated Sludge Process by Constructing a Thermo-biological Method in the Returned Sludge to Remove Nutrient Substances from Wastewater 69 78 10.34172/ajehe.5481 EN Naeim Banisaeid https://orcid.org/0009-0006-5289-0545 Afshin Takdastan https://orcid.org/0000-0002-0419-1698 Mahboobeh Cheraghi https://orcid.org/0009-0000-2193-5997 Ali Afrous https://orcid.org/0000-0002-5019-286X Reza Jalilzadeh Yengejeh https://orcid.org/0000-0002-8360-5739 Journal Article 10.34172/ajehe.5481 2024 10 25 2025 01 07 One of the problems of wastewater disposal is the release of nitrogen and phosphorus in addition to organic and microbial substances into receiving waters, and the removal of nutrients from wastewater has become one of the main global problems because the compounds of nitrogen and phosphorus in natural aquatic environments cause eutrophication. This quantitative, sectional, and analytical research explored the use of thermo-biological methods in the return sludge line to reduce the pollution and address excessive sludge production. The research also investigated the impacts of temperature changes in the anoxic tank and the return sludge line. Results showed that the existing conventional bioreactor, with a temperature change in the return sludge to 40 °C, significantly improved total nitrogen (TN) and total phosphorus (TP) removal efficiency. Although the change in the temperature of the returned sludge increased the TN and TP removal efficiency, the removal rate was not significant, and this is despite the fact that this efficiency also decreased with increasing temperature. The study revealed a reduction in biomass production coefficient at higher return sludge temperatures, it also highlighted the negative impact on effluent quality and sludge settling capability.