Assessing the potential suitability of dynamic membrane system for post-treatment of effluents from municipal wastewater plants in Saudi Arabia using MCDM approaches

Abstract

This study aimed to assess the potential of Dynamic Membrane (DM) technology as a feasible alternative to conventional tertiary filtration options for upgrading secondary effluents from wastewater treatment in Saudi Arabia. Initially, An initial trial was conducted to investigate whether this could be achieved by looking at DM system design based on calculation methods used for conventional treatment systems and parameter values for DM performance extracted from literature data. The research shifted to comparing three tertiary treatment alternatives viz Rapid Sand Filtration (RSF), Microfiltration and ultrafiltration (MF/UF), and DM to investigate the optimal choice for Saudi conditions. RSF technology is a tertiary treatment option with relatively low maintenance and operational expenses. However, it has limitations, such as head loss build-up and significant chemical pre-treatment requirements. MF/UF technology is gaining popularity for upgrading the sewage treatment plants (STP) in Saudi Arabia due to stricter regulations and water reuse initiatives. However, membrane fouling, and operational cleaning costs are challenges to using these systems in tertiary wastewater treatment, especially in remote areas. DM is a novel approach to wastewater treatment that relies on a layer of the deposited material to act as a self-generated barrier to filter wastewater particles. multi-criteria decision-making (MCDM) approaches were used to provide a structured and logical method when comparing the proposed tertiary options. The research required the engagement of participants as decision-makers who followed a structured survey incorporating three parts, i.e., RSF performance, choosing by advantage (CBA), and the analytical hierarchy process (AHP). It involved interviews with 20 individuals from different cities in the Al-Qassim and Riyadh provinces. These individuals had an average of 12 years of experience in wastewater treatment, particularly in operation and maintenance. Their job responsibilities included the regular operation of Saudi STP with a daily flow range of 75 to 400000 m3/day. A comparison of proposed options was conducted along three dimensions i.e. environmental, economic, and technical, each with its own set of factors. In total, 16 factors were identified for assessing the option, including removal rates for total suspended solids (TSS), microplastics (MPs), chemical oxygen demand (COD), Escherichia Coli (E. Coli), Fecal Coliforms (FC), Total Dissolved Solids (TDS), total nitrogen (TN), and total phosphorus (TP) within the environmental dimension. Within the economic dimension, factors included energy consumption, area required, chemicals-filtration, and chemicals-cleaning. The technical dimension encompasses factors of small cleaning interval (SCI), small cleaning time (SCT), major cleaning interval (MCI), and major cleaning time (MCT). The task of comparing these three options is unusually challenging because some of them are familiar and widely used while others are novel, and this is the first time a set of factors for comparison of them in the current application has been identified. The overall outcomes revealed that the RSF earned the greatest choice from the participants' views, followed by DM and MF/UF. The work developed and tested a modified version of the CBA approach using an option of dummy technology (DT) to preserve data on participants' preferences. This may be particularly suitable for situations where there are only a small number of alternatives. Although easier to use, conventional CBA may be less favourable to low-tech, low-cost applications. The research concluded that modified CBA and AHP were suitable for comparing options with widely different levels of familiarity and technical sophistication. Participants' responses were collected individually, enabling analysis of factors that influenced them. No major differences were found between responses from participants at large and small STP.