Landfill leachate enhances fermentative hydrogen production from glucose and sugarcane processing derivatives

Fermentation can use renewable raw materials as substrate, which makes it a sustainable method to obtain H₂. This study evaluates H₂ production by a mixed culture from substrates such as glucose and derivatives from sugarcane processing (sucrose, molasses, and vinasse) combined with landfill leachate. The leachate alone was not a suitable substrate for biohydrogen production. However, leachate blended with glucose, sucrose, molasses, or vinasse increased the H₂ production rate by 2.0-, 2.8-, 4.6-, and 0.5-fold, respectively, as compared with the substrates without the leachate. Determination of metals (Cu, Cd, Pb, Hg, Ni, and Fe) at the beginning and at the end of the fermentative assays showed how they were consumed during the fermentation and demonstrated improved H₂ production. During fermentation, Cu, Fe, and Cd were the most consumed leachate metals. The best substrate combination to produce H₂ was molasses and leachate, which gave high volumetric productivity—469 ml H₂/l h. However, addition of the leachate to the substrates stimulated lactic acid formation pathways, which lowered the H₂ yield. The use of leachate combined with sugarcane processing derivatives as substrates could add value to the leachate and reduce its polluting power, generating a clean energy source from renewable raw materials.     

Selection of palm oil mill effluent treatment for biogas generation or compost production using an analytic hierarchy process

Palm oil mill effluent (POME) is the liquid waste from palm oil mills, and is generally treated using open lagoon technology. However, open lagoons can also be combined with more environmentally friendly technologies. In this study, the analytic hierarchy process (AHP) was used to determine the best combination open lagoon of technology (COLT) for POME treatment. The selected criteria were benefit, opportunity, risk, and cost, with sub-criteria further determined based on these criteria. The sub-criteria were revenue, greenhouse gas reduction, employment absorption, corporate social responsibility, co-processing, environmental risk, marketing risk, technology reliability, investment cost, operation and maintenance cost, and opportunity cost. The alternatives were COLT-composting for fertilizer purpose and COLT-biogas for energy generation purpose. Calculation and analysis was performed on questionnaire data using Expert Choice^®. COLT-composting proved to be the superior COLT using tentative performance of alternative in this research, with advantages in benefit, opportunity, and risk. The priority weight for COLT-composting was 0.636. Sensitivity analysis was performed by changing criteria priorities. For COLT-biogas to be considered better than COLT-composting, the cost would need to be weighted more than 0.954.     

Production of natural and recycled aggregates: the environmental impacts of energy consumption and CO<Subscript>2</Subscript> emissions

Natural aggregates (NA) are crushed and processed in crushing plants after the extraction stage in quarries. In the present study, the aggregates are divided into three scenarios, depending on the production methods. The first scenario considers the production of NA, the second scenario deals with the production of recycled aggregates (RA) with respect to construction and demolition waste, and the third scenario, which is a hybrid scenario, handles the combination of NA and RA by assuming a 50% mixing percentage. In this research, we assess the environmental impacts on the production of aggregates via each scenario, using life cycle assessment; in addition, energy consumption and CO₂ emissions are considered as the environmental variables. We conclude that Iran’s current policy with an annual energy consumption of 1.48 million tons of oil equivalent (toe) can have a footprint of 2.88 million tons of CO₂ eq emissions per year (the first scenario). Achieving 30 and 36% reduction in annual energy consumption and CO₂ emissions, respectively, by the third scenario compared to the first scenario indicates the destructive effect of the first scenario from the environmental outlook.     

Gasification characteristics of biomass for tar removal by secondary oxidant injection

Gasification experiments for sawdust were conducted using a fixed bed reactor at 900 °C by varying the secondary oxidant injection ratio to determine the optimal conditions for tar removal along with the enhancement of gasification efficiency. Secondary oxidant was injected as an oxidant at the top zone of the gasifier in varying ratios of 10–30% of the total amount of oxidant. This method was based on the primary method of tar removal and gasification efficiency improvement by thermal cracking of tar. Various gasification performance parameters were evaluated and tar content was estimated by measuring the fluctuation of weight of the activated carbon filter. The results showed that the concentration of tar in the producer gas decreased by injecting the secondary oxidant, even though syngas yield decreased. The recycling potential of the char produced in the gasification experiments was also assessed with the purpose of utilizing char as an adsorbent by determining its surface area and pore volume. The results demonstrated that the char produced from the gasification experiment had similar quality to that of the activated carbon used in this experiment.     

Balancing the energy demand by a resource circulation project in Daejeon,Korea

Demand for sustainable renewable energy is on an increase worldwide, whereas the supply is limited. This paper analyses the feasibility of generating electricity and supplying the surplus steam to Daeduk Industrial Complex, by incinerating the combustible municipal waste generated in Daejeon Metropolitan City. The economic feasibility of surplus biogas generated from the anaerobic digestion of food waste and food waste leachate has been analysed. This study estimated resource circulation facility to supply 23,200 m³/day of biogas generated to Daejeon Combined Heat and Power plant. By 2023, it is expected to supply 25.7 tons of steam per hour all year round. The additional steam demand in Daeduk Industrial Complex is estimated as 101,537 tons/year. Surplus biogas will be supplied through an additional 960-m new installation. The cost of biogas is estimated at 30% of the unit biogas production cost. Daejeon Combined Heat and Power plant expects to make 60% additional profit, and Daeduk Industrial Complex and the communities nearby expect to achieve 10% cost savings. It also reduces the dependence of energy on fossil fuels, contributes to national environmental energy policy in reduction in greenhouse gases, creates competitiveness in local business and reduces corporate tax and generates revenue.     

Catalytic upgrading pyrolysis of pine sawdust for bio-oil with metal oxides

The catalytic upgrading pyrolysis of pine sawdust was performed at 500 °C with various metal oxides to improve the quality of the bio-oil. The aim of this study was to investigate the potential of the metal oxides instead of traditional zeolites for catalytic upgrading pyrolysis with the analysis of Gas Chromatograph/Mass Spectrometer. In this study, the used catalysts were Calcium-oxide, Magnesium oxide, Titanium dioxide, and Zeolite (Si/Al?=?80). The influence of catalysts on products yields and compositions were investigated. Most metal oxides can enhance the bio-gas with the bio-oil yields decreased. The metal oxides led to a decrease of Acids, Aldehydes, Ketones and an increase of Furfural, Cresols, Catechols in Furans and Phenolics. Among the catalysts, the MgO catalysts was the most effective to convert the high molecular into lights ones (6.65% Cresols) with yield of 20.48% for Furfural. The deoxygenation reaction in bio-oil was suggested to convert oxygenated compounds into the low molecular weight of the materials (6.39% Guaiacols). Thus, the used metal oxides can improve the quality of bio-oil by decreasing undesirable compounds as well as increasing the desirable compounds with low oxygen contents via deoxygenation reaction.     

Absorption characteristics of potassium carbonate-based solutions with rate promoters and corrosion inhibitors

In this research, absorbents for CO₂ capture were prepared by blending 30 wt% potassium carbonate, 3 wt% of a rate promoter, and 1 wt% of a corrosion inhibitor. Pipecolic acid, sarcosine, and diethanolamine were chosen as rate promoter candidates. Based on a rate promoter screening test for CO₂ loading capacity and absorption rate, pipecolic acid and sarcosine were selected to be used as rate promoters. 1,2,3-benzotriazole and ammonium thiocyanate were chosen as corrosion inhibitors, and they were mixed with a 30 wt% potassium carbonate-based absorbent mixture containing one of the rate promoters. The absorption rates for four absorbent solutions (30 wt% potassium carbonate?+?3 wt% pipecolic acid?+?1 wt% 1,2,3-benzotriazole, 30 wt% potassium carbonate?+?3 wt% pipecolic acid?+?1 wt% ammonium thiocyanate, 30 wt% potassium carbonate?+?3 wt% sarcosine?+?1 wt% 1,2,3-benzotriazole, and 30 wt% potassium carbonate?+?3 wt% sarcosine?+?1 wt% ammonium thiocyanate) were measured, tabulated, and graphically displayed. These types of absorbents can be used for capturing CO₂ under high temperature and pressure conditions, such as those found in coal-fired power plants.     

Physical separation,mechanical enrichment and recycling-oriented characterization of spent NiMH batteries

Nickel–metal hydride (NiMH) batteries contain high amount of industrial metals, especially iron, nickel, cobalt and rare earth elements. Although the battery waste is a considerable secondary source for metal and chemical industries, a recycling process requires a suitable pretreatment method before proceeding with recovery step to reclaim all valuable elements. In this study, AA- and AAA-type spent NiMH batteries were ground and then sieved for size measurement and classification. Chemical composition of the ground battery black mass and sorted six different size fractions were determined by an analytical technique. Crystal structures of the samples were analyzed by X-ray diffraction. Results show that after mechanical treatment, almost 87 wt% of the spent NiMH batteries are suitable for further recycling steps. Size classification by sieving enriched the iron content of the samples in the coarse fraction which is bigger than 0.25 mm. On the other hand, the amounts of nickel and rare earth elements increased by decreasing sample size, and concentrated in the finer fractions. Anode and cathode active materials that are hydrogen storage alloy and nickel hydroxide were mainly collected in finer size fraction of the battery black mass.     

Production of Curdlan Grown on Cassava Starch Waste Hydrolysates

Cassava starch waste hydrolysates (CSWHs) with different degrees of polymerisation, i.e., CSWHs-1, CSWHs-2 and CSWHs-3, were prepared through the hydrolysis of cassava starch waste with thermostable a-amylase from Thermococcus sp. HJ21. The prepared CSWHs were then used as a carbon source for curdlan production with Alcaligenes faecalis ATCC 31749. The amount of curdlan produced and the glucosyltransferase activity during curdlan synthesis increased more obviously when CSWHs-2 was used as the carbon source than when glucose was used. Using both carbon sources, the maximum curdlan production was observed at day 5, and the maximum glucosyltransferase activity was observed at day 4. Glucosyltransferase activity decreased thereafter, and biomass continued to increase until the end of the experiment (day 6). Results indicated that the enhanced curdlan production with CSWHs as the carbon source was highly correlated with glucosyltransferase activity.     

Effects of Compounded Curing Agents on Properties and Performance of Urea Formaldehyde Resin

The effects of three compounded curing agents on the properties and performance of the urea-formaldehyde (UF) resin were investigated in this study. The compounded curing agents were prepared by mixing ammonium chloride with hexamethylenetetramine, citric acid, and oxalic acid respectively at a ratio of 1:1, named N-H, N–CA, and N–OA, respectively. The curing process, crystallinity, and physical properties were measured, and the three-ply plywood was fabricated to measure its prepress strength, wet shear strength, and formaldehyde emission. Results showed that the compounded curing agents N–CA and N–OA enhanced the initial viscosity, crosslinking density and thermal stability of UF resin. Additionally, the prepress strength of the plywood bonded by UF resin with N–CA and N–OA increased by 82 and 111% respectively compared to the UF resin with NH₄Cl, and the wet shear strength increased by 14 and 16%, the formaldehyde emission decreased by 19 and 42% respectively. However, owing to the short pot-life of these curing agent limited their storage time, the curing agents N–CA and N–OA should be applied to fabricate plywood in winter for obtaining a better bond strength and a lower formaldehyde emission. While the UF resin with N–HT showed a suitable pot-life, so it could be applied to fabricate plywood in summer for long time storage and avoiding procuring problem.