The situation of waste management in Tehran was a typical example of it in developing countries. The amount of municipal solid waste has been increasing and the city has depended on landfill for municipal solid waste management. However, in recent years, various measures have been taken by the city, such as collecting recyclables at the source and increasing the capacity of wasteprocessing facilities. As a result, significant changes in the waste stream are starting to occur. This study investigated the nature of, and reasons for, the marked changes in the waste stream from 2008 to 2012 by analysing the municipal solid waste statistics published by the Tehran Waste Management Organization in 2013 and survey data on the physical composition of the municipal solid waste. The following trends were identified: Although the generation of municipal solid waste increased by 10% during the 5-year period, the amount of waste directly disposed of to landfill halved and resource recovery almost doubled. An increase in the capacity of a waste-processing facility contributed significantly to these changes. The biodegradable fraction going to landfill was estimated by using the quantity and the composition of each input to the landfill. The estimated result in 2012 decreased to 49% of its value in 2008.

Landfilling of organic waste is still the predominant waste management method in Canada. Data collection and analysis of the waste were done for the case study city of Montréal in Canada. A life cycle assessment was carried out for the current and proposed waste management system using the IWM-2 software. Using life cycle assessment results, a non-dominated sorting genetic algorithm was used to optimize the waste flows. The optimization showed that the current recovery ratio of organic waste of 23% in 2017 could be increased to 100% recovery of food waste. Also, recycling could be doubled, and landfilling halved. The objective functions were minimizing the total energy consumption and CO2eq emissions as well as the total cost in the waste management system. By using a three-objective optimization algorithm, the optimized waste flow for Montréal results in 2% of waste (14.7 kt) to anaerobic digestion (AD), 7% (66.3 kt) to compost, 32% (295 kt) to recycling, 1% (8.5 kt) to incineration, and 58% (543 kt) to landfill.

Landfills will likely remain an essential part of integrated solid waste management systems in many developed and developing countries for the foreseeable future. Further improvements are required to model the generated gas from landfills. The literature has not addressed detailed waste characterization in landfill gas (LFG) modeling by a first-order decay model such as LandGEM while using a genetic algorithm. Additionally, little has been done in the literature regarding H2S generation modeling. This paper uses a genetic algorithm to independently fit parameters to a CH4 and H2S generation model based on a modified first-order decay model. In the case of CH4 generation modeling, biodegradable organic waste (OW) was segregated into food waste, yard waste, paper, and wood. In addition to optimizing the OW fractions, key modeling parameters of OW, such as CH4 generation potential ($${L}_{0}$$ L 0 ) and CH4 decay rate ($${k}_{C{H}_{4}}$$ k C H 4 ), were determined independently for different periods in the landfill’s life. Similarly, in the case of H2S generation modeling, the construction and demolition waste (CD) was classified into fines (FCD) and bulky materials (BCD), and H2S generation potential ($${S}_{0}$$ S 0 ) and H2S decay rate ($${k}_{{H}_{2}S}$$ k H 2 S ) of FCD and BCD were determined. LFG collection data from a landfill site in the province of Quebec, Canada, was used to validate the LFG generation model. A range of scenarios was analyzed using the validated model, including fourteen scenarios (two benchmark and twelve optimizing) for CH4 and two for H2S modeling. The results showed that the differentiation of more waste types improves the modeling accuracy for CH4. Moreover, within the decade-long lifetime of a landfill, the waste management strategies change, requiring different assumptions for the modeling. Also, the work showed the importance of considering how different landfill sectors are filled over time. Finally, scenario twelve of optimizing scenarios, which assumed four waste types, constant three periodic waste fractions, and six sectors, had the lowest residual sum of squares (RSS) value. For H2S generation modeling, both scenarios, with or without separate fits of $${S}_{0}$$ S 0 and $${k}_{{H}_{2}S}$$ k H 2 S for FCD and BCD, predicted the generated H2S well and had a very similar RSS value. Further data could improve H2S generation modeling.

In wet climates, leachate formation is inevitable and continues over a long period. However, in arid climates, evaporation considerably exceeds precipitation so that the source of leachate is mainly limited to the water derived from the waste in the landfill. This also implies that leachate generation will eventually cease, and that the waste inside the landfill will gradually dry out. However, to date, this has not been shown quantitatively. In this study, a simple water balance model was created and applied to estimate the time period for which leachate was generated using meteorological data obtained in an arid climate. Several meteorological stations located in arid climates were selected according to the Köppen-Geiger climate classification (in Iran, USA, and Australia), and their climate data from 2000-2013 were used in the model. The configuration of a small trench that exists in landfills in Iran was taken as the landfill form in each location. The results showed that leachate was generated only for the period in which municipal solid waste (MSW) was disposed of because most of the source of leachate was formed by the moisture derived from the waste, and the greater part of the precipitation was consumed by evaporation. Almost no leachate was generated after the end of the disposal operation. This scenario applied for all of the modeled regions. The quantity of water inside the landfill was also calculated. The results from all locations indicated that the quantity of water in the landfill started to decrease after the completion of the waste disposal operation, which implies that the waste inside the landfill will subsequently dry out.