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This study investigates the performance of a combined anaerobic-aerobic system in the treatment of leachate within 5 months. Experiments were carried out in a two-stage anaerobic completely stirred tank reactor followed by an aerobic reactor with effective volumes of 10, 30, and 14 L at a constant rate of 2 L/day. The reactors were placed in series so that the output from the first anaerobic reactor was the input for the second one, and the output from the second reactor was connected to the input of the aerobic phase. After an initiation phase, the organic loading rate (OLR) was increased from 0.55 to 2.65 kg COD/m3. day. The optimum OLR was found to be 2.05 kg COD/m3. day at which, the removal efficiency of chemical oxygen demand (COD) in the two-stage anaerobic phase, the aerobic phase, and the treatment system as a whole were 93%, 37.1%, and 95.6%, respectively. The BOD5 removal efficiency of the system was 96.8%. The coefficients of determination between the removed COD and produced biogas were 0.98 and 0.99. Although the two-stage anaerobic phase increased the levels of ammonia nitrogen, alkalinity and turbidity by 31.28%, 15.18%, and 18.7%, the aerobic phase reduced these parameters by 50.30%, 57.23%, and 72.1%, respectively.

This study was conducted to examine the feasibility of recovering ferric coagulant from drinking water treatment sludge (DWTS) for green synthesis of iron nanoparticles (NPs). Black tea extract was utilized for the bio-reduction of ferric chloride. The as-synthesized product was characterized and confirmed as iron NPs, using UV–vis spectrometry, XRD, FT-IR, SEM, and EDX analyses. The synthesized NPs were sphere-like with diameter in the range of 20–40 nm. The performance of the iron NPs as micronutrients supplements in anaerobic digestion of slaughterhouse wastewater was studied at three different concentrations. The results showed that the addition of iron NPs in all concentrations improved the biogas production and shortened the lag phase. The highest biogas yield was obtained from 9 mg L−1 of additive which corresponds to up to 37.6% enhancement over the control reactor. Moreover, iron NPs improved COD reduction efficiency to 42%.

A large number of biogas plants feeding with municipal solid waste (MSW) are installed throughout the world. However, researches are widely conducted with the aim of maximizing the process yield, in order to make it more comparable with fossil fuels. In the present paper, biomethane potential test (BMP) assays (37 °C) were conducted to maximize the biomethane production from anaerobic digestion (AD) of municipal solid waste (MSW) under different mixing ratios with sewage sludge (SS) (50:50, 60:40, 80:20, and 90:10), the total solid (TS) concentrations (5%, 10%, 15%, and 20%), and pretreatment with sodium hydroxide. Increase in SS ratio up to 40% led to a substantial increase in biomethane yield. After 18 days of retention time, 90% of the methane (280 NmL/g VS) was achieved. The results showed that the methane yield in liquid anaerobic digestion (L-AD) (5%-10% TS) was greater than high-solids anaerobic digestion (HS-AD) (15%-20% TS). Biomethane yield was increased up to 18% with sodium hydroxide pretreatment. The findings shows that such optimization framework can generally increase the biomethane yield up to 57%.

Anaerobic degradation of bioplastics is a controversial challenge. Size reduction is a must for degradation while it requires a significant amount of energy, which lowers the overall energy efficiency of the system. On the other hand, inoculum to substrate ratio has interaction effects in the process. The present work aimed to optimize these two parameters for the improvement of energy efficiency through response surface methodology. The central composite design procedure was implied. The levels of the experimental variables were 0.72, 4.3, 7.87 mm for particle size and 2, 3, and 4 for inoculum to substrate ratio. The input variable effects on biomethane yield were estimated, discussed, and then also optimized using the genetic algorithm. Moreover, energy balance analysis was done for the samples. The highest biomethane yield was found at the particle size of 4.3 mm and inoculum to substrate ratio of 4, which corresponds to 23% energy efficiency. Despite the high energy consumption for size reduction to less than 1 mm, more biomethane yield was not observed. Inoculum to substrate ratio showed more effect on biomethane yield than particle size.

Thermochemical technologies used to burn municipal solid waste are one of the relatively new and appropriate methods for waste management. By burning waste, heat and gases have arisen which can be used as the energy source to generate electricity. Due to the high cost, pollution emissions and diversity of such power plants, comprehensive studies are required. Therefore, the purpose of this study is to investigate the thermal methods in the field of waste management and to optimum for the most suitable methods. The selected thermochemical technologies include incineration, gasification, plasma, and pyrolysis. Data gathering was done through a questionnaire completed by experts. The decision-making models based on the Analytical Hierarchical Process (AHP) and the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) methods are proposed to select the best thermochemical technology by the technical, economic, and environmental criteria. Ultimately, the environmental criteria (0.355), economic criteria (0.338) and, technical criteria (0.307) were introduced as the most effective criterion in choosing thermal methods respectively. The results of both AHP and TOPSIS models showed that the plasma method is the optimal thermochemical technology in terms of three existing criteria. Incinerator, gasification, and pyrolysis systems were ranked next.

Anaerobic digestion for biogas production is known as an effective way of organic waste management. However, in countries rich in fossil fuels resources, its application is very limited. The present research aimed to find whether farm biogas plant could be economic in Iran, where low price natural gas and electricity are available in the most of the regions. Capital cost, net income, internal rate of return, and return of investment of a farm biogas plant was calculated assuming three different scenarios for a 400 head dairy farm; 1) Combined heat and power biogas plant by treatment of 4,562 t y−1 manure: power injection to the grid, and heat to be used in farm or be sold to the potential nearby clients, 2) biogas plant only for power generation by treatment of 4,562 t y−1 manure: power injection to the grid, and 3) No power generation: Treatment of 1,200 t.y-1 for substitution of current heating and cooking fuel (liquefied petroleum gas and diesel) by biogas. The technical and economic calculations were based on biomethane potential test (BMP). The economic analysis results showed that the return of investment in all scenarios was less than 4 years. The surplus net income of the farm from digester including energy and bio-fertilizer production from the three scenarios were 32,000, 38,000, and 6,400 US$ per year. Overall, all three scenarios are economically feasible in Iran, if the biogas plant is constructed domestically.

Sugarcane bagasse is one of the major resources of agricultural wastes in the Khuzestan Province of Iran. With the aim of maximum hydrogen production, supercritical water gasification of lignocellulosic feedstock was studied in a batch reactor at the constant pressure of 25 MPa. The effect of catalyst (five different alkali salts, Raney nickel, and activated carbon) and reaction temperature (400–800 °C) on gas yield and composition, gas heating value, carbon gasification efficiency (CGE), and hydrogen gasification efficiency (HGE) was investigated. An increase in reaction temperature led to significant improvement in hydrogen yield. The highest amount of hydrogen (75.6 mol kg −1 ) was achieved at 800 °C with the presence of KOH as catalyst where the complete gasification of bagasse took place. The annual potential of hydrogen production in the Khuzestan Province of Iran was roughly estimated to be 470 millions of Nm 3 and this calculation showed that this figure is capable of substituting the need of 6550 ha of sugarcane farms to chemical fertilizer.