Cyclic Technology–Based Sequencing Batch Reactors (SBR ) Treating Municipal Wastewater: Full-Scale Experience

Abstract

Cyclic technology–based sequencing batch reactors (SBR) treating municipal wastewater were audited for their performance under full hydraulic load design conditions. The performance data showed that the WWTPs produced an effluent having a very low concentration of chemical oxygen demand (COD, 10 mg/L), biochemical oxygen demand (BOD, <10 mg/L), and SS (<10 mg/L). Total nitrogen and total phosphorus concentrations were reduced significantly, i.e., <5 mg/L and <0.5 mg/L, respectively, which is very impressive in biological nutrient removal (BNR) systems. It was found that more than two log removal of fecal coliforms takes place in the SBR reactor itself. Also, 2–3 mg/L chlorine dosage in the chlorination tank was found sufficient to reduce the fecal coliform numbers well below the WHO standard (1000 MPN/100 mL) set for the reuse of the effluent for unrestricted irrigation. The dewatered sludge has high nitrogen, phosphorus, and potassium (NPK) value; hence, it can be used very effectively as an organic fertilizer after drying/composting. Furthermore, the bio-aerosols concentration in ambient air near the SBR was observed safe for plant workers concerning the health risks derived from exposure to bio-aerosols. All the WWTPs were found to be efficient in producing the excellent effluent quality that not only completely fulfills the Indian effluent discharge standards but also almost fulfills US Environmental Protection Agency (EPA) requirement for non-potable reuse standards. Merely increasing the chlorine dosage can satisfy the US EPA requirement for non-potable reuse such as recreational impoundments, cooling water, horticulture, and toilet flushing.

Graphical Abstract