This study aims to evaluate the performance of the Sewage Treatment Plant (STP) at PT PLN Nusantara Power Unit Pembangkitan Gresik in reducing pollutant loads from domestic wastewater. The evaluation involves analyzing water quality parameters including pH, BOD, COD, TSS, oil and grease, total ammonia, and total coliform at both inlet and outlet of the STP. Additionally, the actual daily discharge was observed and compared to the design capacity to assess operational efficiency. The method used was descriptive qualitative, involving field observation, documentation, and laboratory test data analysis during the January–March 2025 period. The results show that all outlet parameters met the effluent standards set by Regulation No. 68/2016 of the Ministry of Environment and Forestry. However, the actual flow rate, which is only 1.6–3.3% of the design capacity, indicates potential inefficiencies in energy use and biological processes. Therefore, operational adjustments and optimization of STP capacity utilization are necessary for more efficient and sustainable system performance.

Using a descriptive method with a triangulation approach including observation, document analysis, and interviews this study ensures data reliability. Daily monitoring is conducted on wastewater flow and pH levels, while monthly laboratory analysis covers eight key parameters: Total Suspended Solids (TSS), iron (Fe), copper (Cu), zinc (Zn), total chromium (Cr), phosphate (PO³), oil and grease, and pH to evaluate the perfomance of the treatment system. The treatment process begins with the inflow of 960 m³ of wastewater per day into the storage pond, where aeration is applied to ensure homogenization before being transferred to the neutralization unit. pH adjustment is carried out by adding NaOH or HCl before the wastewater undergoes coagulation and flocculation stages. The study’s findings indicate that the WWTP meets the environmental quality standards established in accordance with the Decree of the Head of the Investment Coordinating Board of the Republic of Indonesia (2020), Number SK.214/1/KLHK/2020 concerning the Permit for Wastewater Disposal into the Sea on Behalf of PT Pembangkit Jawa Bali Unit Pembangkitan Gresik. This study emphasizes the importance of systematic monitoring and treatment in wastewater management.

PT X is one of the industries located in East Java that produces liquid waste. The industrial sector is indeed a large producer of liquid waste. One of the liquid wastes produced is domestic liquid waste. The industry has the responsibility to manage domestic liquid waste in accordance with Government Regulation Number 22 of 2021 which requires industries to carry out domestic wastewater management before being discharged into water bodies. One of the efforts made by the industry to manage the domestic wastewater produced is to use a Domestic Wastewater Treatment Plant. The quality of the treated water has met the domestic wastewater quality standards to be discharged into river and does not pollute the environment.

Currently, the government is increasingly building PLTMG to fulfill the electricity needs of the society. Beside for fulfill the electricity needs of the Indonesian people, PLTMG also has a negative impact on the society, especially for the community around the PLTMG in the city of Batam. So companies need to conduct studies on environmental impacts, one of which is the impact of the air produced on the surrounding area. The PLTMG industry does not use air pollution control devices, but uses a leanox combustion control system on each gas engine with a chimney outlet that emits SO2 and particulate emissions. The model simulation was carried out using Aermod view software with meteorological data from the affected locations. The results of AERMOD modeling show that the PLTMG industry will have an impact on particulate emissions in the ambient air around the activity location which will spread to the northwest, north, south and east of the activity location. The Aermod Model also shows that current conditions have resulted in dispersion with concentrations below the maximum limit stated in the 2021 Government Regulation. The addition of an emission monitoring system such as CEMS can be used to help monitor the concentration of dispersed emissions. Apart from that, emission control devices such as incinerators or combustion can also be used to reduce the concentration of the emissions used.