Case Study on Technical Performance Evaluation of 60 MLD Municipal STP at Kapurai, Vadodara Using SBR Technology

Rapid urbanisation and industrial growth have increased municipal wastewater generation, necessitating the adoption of advanced sewage treatment technologies to protect the environment and support sustainable water management. The present study evaluates the performance of the 60 MLD Sewage Treatment Plant (STP) located at Kapurai, Vadodara, Gujarat based on Sequencing Batch Reactor (SBR) technology. The plant receives sewage from the Ajawa, Waghodia, VUDA, and Kapurai regions and treats it through biological treatment and chlorination..Performance assessment was conducted under chlorine dosing at 5.0 ppm and 6.0 ppm for two consecutive days. Wastewater samples were analysed for physico-chemical, microbial, and organic parameters, including pH, Total Suspended Solids (TSS), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Coliforms, Faecal Coliforms, Total Organic Carbon (TOC), Dissolved Organic Carbon (DOC), and Trihalomethanes (THMs)..The analytical results demonstrated efficient removal of organic pollutants and microbial contaminants. The treated effluent showed low BOD and COD concentrations, indicating stable biological treatment performance of the SBR system. A significant reduction in microbial counts confirmed effective chlorination. THM compounds such as chloroform, bromodichloromethane, dibromochloromethane, and bromoform were not detected in treated effluent samples, indicating that disinfection practices were environmentally safe..The study highlights that SBR technology is highly effective for large-scale municipal wastewater treatment and supports sustainable wastewater reuse and environmental protection..BackgroundRapid urbanisation, industrialisation, and population growth have significantly increased municipal wastewater generation across urban regions of India, resulting in severe environmental concerns, including water pollution and the degradation of aquatic ecosystems (Metcalf & Eddy, 2014)..To address these environmental challenges, several sewage treatment plants (STPs) employing advanced and emerging wastewater treatment technologies were established across various regions of Gujarat during the period 2016–2022. These treatment facilities have become essential for reducing pollution loads in rivers and promoting environmentally sustainable wastewater management practices (CPCB, 2021)..Among advanced wastewater treatment technologies, the Sequencing Batch Reactor (SBR) has emerged as one of the most efficient and reliable biological treatment systems for municipal and industrial wastewater (EPA, 1999). SBR technology is particularly suitable for areas characterised by fluctuating or varying flow patterns due to its operational flexibility and compact design. The process is based on the activated sludge principle in which biological oxidation, aeration, clarification, and sludge stabilisation occur sequentially within a single reactor basin (Irvine & Busch, 1979)..The SBR process utilises filamentous bacteria and microbial biomass enriched under activated sludge conditions to degrade and stabilise biodegradable organic matter in wastewater (Metcalf & Eddy, 2014). Compared to conventional activated sludge treatment systems, SBR technology requires comparatively less land area and produces high-quality treated effluent with superior pollutant removal efficiency (Mace & Mata-Alvarez, 2002)..Furthermore, the process is highly effective in reducing Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), suspended solids, phosphorus, and nitrogen compounds from wastewater. Under stable operational conditions, SBR systems can achieve approximately 90–95% nitrogen removal efficiency (EPA, 1999)..The performance evaluation of the sewage treatment plant using SBR technology was conducted under peak operating conditions with varying chlorine dosing levels. Wastewater samples were collected from the inlet to the chlorine contact tanks before chlorination and from final discharge points after chlorination under chlorine dosing at 5.0 ppm and 6.0 ppm for two consecutive days. .The collected samples were analyzed for various physio-chemical and microbial parameters including pH, Total Suspended Solids (TSS), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Ammoniacal Nitrogen, Nitrate-Nitrogen, Total Kjeldahl Nitrogen (TKN), Total Coliforms, Faecal Coliforms, Total Organic Carbon (TOC), Dissolved Organic Carbon (DOC), Trihalomethanes (THMs), and THM components such as chloroform, bromodichloromethane, dibromochloromethane, and bromoform (APHA, 2017)..Trihalomethanes (THMs) are formed during chlorination when chlorine reacts with dissolved organic matter and bromide ions naturally present in wastewater (Richardson et al., 2007). When chlorine, typically present as hypochlorous acid (HOCl), is added for disinfection, it initiates oxidation and halogen substitution reactions in organic compounds, yielding intermediate organochlorine compounds. In the presence of bromide ions, chlorine oxidizes bromide into hypobromous acid (HOBr), which further promotes formation of brominated THM compounds. Continued oxidation and cleavage reactions result in the formation of characteristic THM structures containing halogenated carbon atoms (WHO, 2017)..About the STPThe 60 MLD Sewage Treatment Plant (STP) located at Kapurai, Vadodara, Gujarat is situated at geographical coordinates 22°16’11” N and 73°15’37” E. The plant was commissioned in the year 2021 under Gujarat Urban Development Company Limited (GUDC) for the treatment of municipal sewage generated from Ajawa, Waghodia, VUDA, and Kapurai regions of Vadodara city (CPCB, 2021). Sewage generated in these regions is conveyed to the treatment plant via underground sewer pipelines connected to major pumping stations at their respective locations..The overall treatment process adopted at the Kapurai STP consists of the following sequential treatment units:Inlet Chamber → Screen Bar → Grit Chamber → Distribution Chamber → SBR Basins (02 Nos.) involving Filling, Aeration, Settling and Decantation → Chlorine Contact Tanks (02 Nos.) → Final Discharge Channel.Initially, raw sewage enters the inlet chamber, where the incoming flow is regulated before passing through screen bar units to remove floating materials such as plastics, rags, and debris. Subsequently, wastewater enters the grit chamber where heavy inorganic particles, including sand and grit, are removed to prevent abrasion and operational damage to downstream mechanical equipment (Tchobanoglous et al., 2014)..The wastewater is then conveyed to the distribution chamber, from where it is uniformly distributed into two SBR basins. The SBR treatment cycle consists of sequential operational stages, including filling, aeration, settling, and decantation. During the aeration phase, activated sludge microorganisms biologically oxidise biodegradable organic matter, resulting in a substantial reduction of BOD, COD, nitrogen compounds, and suspended solids from wastewater (Irvine & Busch, 1979). The settling phase facilitates efficient biomass separation, while the decantation phase enables withdrawal of clarified treated effluent..Following biological treatment, the treated wastewater is transferred to two chlorine contact tanks for final disinfection and microbial reduction. The final treated effluent is discharged through an open channel into the Jambuwa River, a tributary of the Vishwamitri River. Treated effluents from several STPs located in Vadodara eventually merge into nearby drains and rivers before joining the Arabian Sea..The sludge generated during wastewater treatment operations is further processed through four centrifuge units for sludge dewatering and stabilisation. Approximately 40–60 tons of sludge are generated every month at the Kapurai STP. The stabilised sludge is subsequently supplied to farmers and utilised as agricultural manure, thereby supporting sustainable sludge management and resource recovery practices (FAO, 2018)..The plant's chlorination system consists of two chlorine storage tanks, each with a capacity of 900 kg. Both tanks are equipped with separate flow meters, and one chlorine cylinder remains operational while the other is kept as a standby for uninterrupted disinfection. During the performance monitoring study, flow measurements recorded on the first day for the first and second sampling slots were 2615 m³/day and 2427 m³/day, respectively, under chlorine dosing conditions of 5.0 ppm and 6.0 ppm..Similarly, flow measurements recorded during the second day were 240.6 m³/day and 289.5 m³/day under 5.0 ppm and 6.0 ppm chlorine dosing conditions, respectively. Under routine operational conditions, chlorine dosing is typically set at approximately 0.5 kg/hr to ensure effective microbial disinfection and maintain residual chlorine levels (WHO, 2017)..The operation and maintenance activities of the Kapurai STP are managed by Vadodara Municipal Corporation (VMC). VMC has entered into an agreement with Gujarat Refinery for the utilisation of approximately 40 MLD treated wastewater, while the remaining treated wastewater is proposed to be utilised by Reliance Petrochemicals, Vadodara (formerly IPCL Vadodara). Gujarat Refinery, located at Koyali, Vadodara, presently utilises approximately 20 MLD treated wastewater supplied through specially laid underground pipelines..The treated wastewater undergoes further treatment at the refinery and is subsequently utilised for industrial process and utility applications, including Process Water, Service Water, Cooling Tower Make-Up, Fire Water Network, and feed water for Demineralisation systems (UNESCO, 2020). The underground pipeline infrastructure for the supply of treated wastewater to Reliance Petrochemicals is currently under construction..Note:For physico-chemicals & microbial parameters-Except pH &T. Coli & F. Coli, all other results are expressed in mg/L. T. Coli & F. Coliis expressed in MPN/100ml. Residual chlorine measured at STP sites.Detection limit: Chloroform: < 0.025mg/L, Dibromochloromethane: < 0.05mg/L, Bromodichloromethane: < 0.03mg/L, Bromoform: < 0.05mg/L..Discussion(i) Physico-Chemical and Microbial ParametersThe performance evaluation of the Kapurai STP using SBR technology was conducted under peak operating conditions with chlorine dosing at 5.0 ppm and 6.0 ppm for two consecutive days. Wastewater samples were collected before chlorination from the inlet to chlorine contact tanks and after chlorination from the final outlet of the STP. The collected samples were analysed for pH, Total Suspended Solids (TSS), Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), Ammoniacal Nitrogen (NH₃-N), Total Kjeldahl Nitrogen (TKN), Nitrate Nitrogen (NO₃-N), Total Coliforms, Faecal Coliforms, and Residual Chlorine concentrations (APHA, 2017)..The analytical results indicate efficient biological treatment and microbial reduction performance of the SBR system under varying chlorination conditions. The pH of the treated effluent remained within the neutral range (7.28–7.83), which is suitable for biological treatment efficiency and final discharge standards (CPCB, 2021). The BOD concentration after treatment ranged from 1.4 mg/L to 6.2 mg/L, indicating effective biodegradation of organic matter in the SBR basins. Similarly, COD concentrations remained below 30 mg/L during all sampling conditions, confirming efficient oxidation and stabilisation of biodegradable organic pollutants (Metcalf & Eddy, 2014)..The Total Coliform and Faecal Coliform counts showed significant reduction after chlorination, demonstrating effective microbial disinfection by chlorine dosing systems. Residual chlorine concentrations recorded during 6.0 ppm dosing conditions were 0.21 mg/L and 0.44 mg/L respectively, while residual chlorine under 5.0 ppm dosing remained below detectable limits (BDL). The results confirm that the chlorination process effectively reduced microbial contamination and maintained adequate disinfection efficiency (WHO, 2017)..(ii) TOC, DOC, THM and its CompoundsThe treated wastewater samples were also analysed for Total Organic Carbon (TOC), Dissolved Organic Carbon (DOC), and Trihalomethane (THM) compounds including chloroform, bromodichloromethane, dibromochloromethane, and bromoform. THMs are important disinfection by-products formed by the reaction between chlorine and dissolved organic matter during wastewater chlorination (Richardson et al., 2007)..The analytical observations revealed that all THM compounds remained below detectable limits during both 5.0 ppm and 6.0 ppm chlorine dosing conditions for two consecutive days. The absence of detectable THM concentrations indicates that the chlorination process adopted at the Kapurai STP was environmentally safe and did not result in significant formation of harmful halogenated by-products. The observed TOC and DOC concentrations indicate comparatively low concentrations of dissolved organic precursors responsible for THM formation (WHO, 2017)..Graphical Presentation:.ConclusionThe present study demonstrated the effective performance of the 60 MLD Sewage Treatment Plant (STP) at Kapurai, Vadodara based on Sequencing Batch Reactor (SBR) technology for treatment of municipal wastewater. The plant exhibited efficient removal of organic pollutants, suspended solids, nutrients, and microbial contaminants under chlorine dosing at 5.0 ppm and 6.0 ppm. The observed reduction in Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Coliforms, and Faecal Coliforms confirmed the high treatment efficiency and operational stability of the SBR system..The treated effluent quality remained within acceptable environmental standards, demonstrating the capability of SBR technology to produce high-quality treated wastewater suitable for discharge and industrial reuse. The pH values remained within neutral range throughout the treatment process, indicating favourable biological treatment conditions. Significant microbial reduction following chlorination confirmed the disinfection system's effectiveness in controlling pathogenic contamination..The study further revealed that Trihalomethane (THM) compounds, including chloroform, bromodichloromethane, dibromochloromethane, and bromoform, were not detected in the treated effluent under both chlorine dosing conditions. This indicates that the chlorination process adopted at the Kapurai STP is environmentally safe and does not result in significant formation of harmful disinfection by-products..The reuse of treated wastewater by Gujarat Refinery and the proposed utilisation by Reliance Petrochemicals highlight the importance of treated sewage reuse in sustainable industrial water management. Such practices significantly reduce freshwater demand and support circular economy principles. Additionally, sludge generated from the treatment process is successfully stabilised through centrifuge systems and utilised as agricultural manure, promoting sustainable sludge management and resource recovery..Overall, the Kapurai STP serves as an important example of advanced wastewater treatment infrastructure that addresses urban sewage management challenges while ensuring environmental protection, water conservation, and sustainable resource utilisation. The successful implementation of SBR technology at the plant demonstrates its suitability for large-scale municipal wastewater treatment applications in rapidly urbanising regions of India..Future RecommendationsTo further enhance the operational efficiency, sustainability, and environmental performance of the 60 MLD Kapurai Sewage Treatment Plant (STP), several technical and management-based improvements can be considered in future wastewater treatment strategies..Implementation of Supervisory Control and Data Acquisition (SCADA) systems is recommended for real-time monitoring and automated control of critical operational parameters, including dissolved oxygen, pH, flow rate, residual chlorine, aeration cycles, and sludge characteristics. Automation can significantly improve operational reliability, treatment efficiency, and energy optimisation (Metcalf & Eddy, 2014)..Integration of renewable energy systems such as solar photovoltaic panels may help reduce operational energy consumption and minimise the carbon footprint associated with STP operations. Since aeration systems contribute significantly to overall power consumption in SBR-based treatment plants, adoption of energy-efficient blowers and smart aeration control systems is also recommended (EPA, 1999)..The expansion of treated wastewater reuse applications should be encouraged for industrial processes, landscaping, construction activities, groundwater recharge, and non-potable urban uses. This would reduce dependence on freshwater resources and promote sustainable water resource management practices (UNESCO, 2020)..Advanced nutrient recovery systems may also be incorporated in future upgrades to recover nitrogen and phosphorus from wastewater streams. Nutrient recovery can support circular economy principles by converting wastewater contaminants into valuable agricultural resources (FAO, 2018)..Although Trihalomethane (THM) compounds were not detected during the present study, continuous monitoring of disinfection by-products is recommended to ensure long-term environmental safety and compliance with wastewater discharge standards. Adoption of advanced tertiary treatment and disinfection technologies such as ultraviolet (UV) irradiation or ozonation may further reduce dependency on chlorine-based disinfection systems and minimize formation of halogenated by-products (WHO, 2017)..Regular monitoring of emerging contaminants, including pharmaceutical residues, personal care products, heavy metals, and microplastics, is also recommended in future wastewater quality assessments. Such studies would provide a better understanding of the long-term environmental impacts of treated wastewater discharge and reuse..In addition, public awareness and policy support for wastewater reuse and sludge utilisation should be strengthened to encourage sustainable urban wastewater management practices. Continuous research, technological upgradation, and proper maintenance of treatment infrastructure will further improve the efficiency and environmental sustainability of SBR-based sewage treatment systems.