Uncovering the reasons behind high-performing primary sedimentation tanks for municipal wastewater treatment: An in-depth analysis of key factors

The paper presents a long-term and extensive pilot-scale study on the primary settlement of municipal sewage to produce an in-depth understanding relating sedimentation efficiency to surface load, hydraulic retention time (HRT), sludge withdrawal time (SWT), temperature (T), and influent solid mass (TSSmass). Besides, primary sludge (PS) was subject to qualitative and quantitative analysis, intending to explore its potential utilization in various applications. These applications encompass enhanced energy and heat generation through conventional anaerobic digesters and the elevated production of volatile fatty acids (VFAs) in hydrolysis reactors, particularly within the context of biorefineries. TSSmass, T, and SWT were shown to be more important in controlling the removal of solids by primary sedimentation tank (PST) than other factors considered. This study introduces a mathematical model that can predict the PS volume based on factors like TSSmass, T, and SWT as a synthesis of the two disparate facets of the study. This model can immensely help maximize PS production quantitively and qualitatively, which can help elevate energy and VFAs production from PS via anaerobic digesters and hydrolysis reactors in conventional municipal WWTP and biorefineries, respectively. Therefore, this model can confidently be applied for calculating the required hopper volume in PST and ascertaining the optimal volume specifications for anaerobic digesters and hydrolysis reactors. Consequently, it leads to cost savings associated with eliminating under or over-designing. The results showed that by improving PST performance for TSS removal, more chemical oxygen demand (COD) would be available for biogas production in conventional municipal WWTPs (from 42 to 59 g (cap. d)−1). By shifting toward biorefineries, the potential to produce more biogas and VFAs, altering from around 40–50 g (cap. d)−1 and 6–12 gVFAs (cap. d)−1, respectively, will also be indicated. [Display omitted] •In-depth analysis of the critical factors affecting the settling process in the primary sedimentation tank (PST).•Proposing a model for predicting primary sludge (PS) production by integrating the most important critical factors.•Stratification of PS to understand nutrient and carbon source variation in each layer.•Proposing reasonable sludge withdrawal time (SWT) for better running of PST and more biogas production.•Assessing improved biogas and volatile fatty acids (VFAs) production through better des