UV-visible spectrophotometry as a rapid surrogate tool for multi-stage effluent quality monitoring in a campus-scale sewage treatment plant

ABSTRACT Rapid urbanisation and campus expansion in India have increased the need for reliable decentralised wastewater treatment systems that can be monitored rapidly and economically. The main objective of this study is to assess the practical utility of UV-visible spectrophotometry as an expeditious, reagentless surrogate monitoring technique for a campus-scale sewage treatment plant (STP) by stage-wise physicochemical and spectroscopic characterisation of Maharishi Markandeshwar (Deemed to be University) (MM(DU)), Mullana, Haryana, India campus-scale STP. Effluent samples were collected from the primary settling tank outlet (S1), sequencing batch reactor outlet (S2), and chlorine contact tank outlet (S3). Treatment performance was assessed through pH, total dissolved solids (TDS), and UV-visible spectroscopy (190–800 nm). Results showed progressive improvement across treatment stages: pH increased from 6.47 ± 0.06 (S1) to 7.50 ± 0.00 (S3), while TDS decreased from 624.33 ± 22.73 to 463.00 ± 0.00 mg/L, with an overall removal of 25.8%. One-way analysis of variance confirmed that inter-stage differences were statistically significant for both pH (F = 931.0, p < 0.001) and TDS (F = 138.6, p < 0.001); Tukey post hoc comparisons showed that most of the TDS reduction occurred during biological treatment (S1–S2, p < 0.001) rather than during disinfection (S2–S3, p = 0.32). UV-Vis spectra revealed a substantial reduction in organic chromophore absorption, particularly within 200–300 nm, with marked attenuation of the characteristic 254 nm aromatic organic peak in the final effluent. The final pH of 7.50 was within the Bureau of Indian Standards (BIS) and Food and Agriculture Organisation (FAO) guideline ranges for irrigation reuse. The final TDS of 463 mg/L was within the BIS discharge limit and fell within the FAO 450–2,000 mg/L band of water generally suitable for irrigation, depending on crop- and soil-specific sensitivity thresholds, rather than the more permissive <450 mg/L unrestricted-use category. General irrigation suitability depends on additional parameters beyond pH and TDS. The findings demonstrate the utility of UV-Vis spectrophotometry for rapid, qualitative to semi-quantitative, assessment of treatment stage changes in a decentralised institutional STP, but further multi-season sampling and site-specific calibration against directly measured chemical oxygen demand/dissolved organic carbon are needed before it can be established as a quantitative surrogate monitoring tool.