A system dynamics model and analytical hierarchy process: an integrated approach for achieving sustainable solid waste management system.

Waste management in low-income countries faces challenges with an average cost of $35/ton approximately 51% collection efficiency. Despite investments in treatment, processing, and recycling, the system remains unsustainable owing to poor planning and policies. The current analysis of Lahore's solid waste management (SWM) system, selected as a major city of a low-income country as a case study, focuses on collection efficiency and waste generation. However, it neglects the complex and dynamic nature of SWM systems. To capture the complexities and dynamic nature of the SWM system, system dynamic (SD) modeling is proposed for its effectiveness in modeling complex and dynamic systems. Unlike previous attempts at SD modeling that mostly consider only some components of the SWM system with varying success, this study attempts to use a holistic approach by considering all aspects of an integrated SWM system. In addition, this study explores different financial and management policies, highlighting the weaknesses of the system through a quantitative comparison of three scenarios: (1) business-as-usual (BAU) which considers the current trends in waste generation and practices of collection and disposal to landfill, (2) waste treatment system (WTS) in which various waste treatment systems are included to reduce burden on landfill, and (3) introduction of user fee with awareness campaigns (UFAC) which encourages community participation towards reduction in waste generation and financially supports the SWM. All three scenarios use four indices: waste generation, waste ending up in landfill, uncollected waste, and annual budget deficit as performance indices. These scenarios were simulated over a 25-year period using an SD model, covering all six components of the SWM system. The BAU scenario shows a 16% increase in waste generation, a 173% increase in landfill waste, an 11% reduction in uncollected waste, and a 64% increase in the budget deficit over the simulation period, indicating an unsustainable SWM system. The WTS scenario exhibits a 16% increase in waste generation, a 155% increase in landfill waste, an 11% reduction in uncollected waste, and a 61% increase in the budget deficit, showing a significant reduction in landfill waste and a slight reduction in deficit but it remains unsustainable. The UFAC scenario, however, results in a 40% reduction in waste generation, a 67% decrease in uncollected waste, an 8% decrease in landfill waste, and a 59% decrease in the budget deficit. These results demonstrate that instituting user fees for SWM services and incentivizing community participation towards waste reduction and segregation can make the SWM system of Lahore sustainable. This SD model provides insights for policymakers, aiding what-if analyses and long/short-term waste management plans for metropolitan cities in low-income countries. To validate the sustainability judgments based on performance indices, the analytical hierarchy process (AHP), a multi-criteria decision analysis (MCDA) tool commonly used for ranking policy decisions based on competing criteria, was employed. It considered the same four criteria as in the SD model. The results of the AHP analysis aligned with those of the SD model, ranking the UFAC scenario as the most sustainable option.

Effect of cycle run time of backwash and relaxation on membrane fouling removal in submerged membrane bioreactor treating sewage at higher flux.

Intermittent backwashing and relaxation are mandatory in the membrane bioreactor (MBR) for its effective operation. The objective of the current study was to evaluate the effects of run-relaxation and run-backwash cycle time on fouling rates. Furthermore, comparison of the effects of backwashing and relaxation on the fouling behavior of membrane in high rate submerged MBR. The study was carried out on a laboratory scale MBR at high flux (30 L/m2·h), treating sewage. The MBR was operated at three relaxation operational scenarios by keeping the run time to relaxation time ratio constant. Similarly, the MBR was operated at three backwashing operational scenarios by keeping the run time to backwashing time ratio constant. The results revealed that the provision of relaxation or backwashing at small intervals prolonged the MBR operation by reducing fouling rates. The cake and pores fouling rates in backwashing scenarios were far less as compared to the relaxation scenarios, which proved backwashing a better option as compared to relaxation. The operation time of backwashing scenario (lowest cycle time) was 64.6% and 21.1% more as compared to continuous scenario and relaxation scenario (lowest cycle time), respectively. Increase in cycle time increased removal efficiencies insignificantly, in both scenarios of relaxation and backwashing.