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In this study, zinc oxide nanoparticles immobilized by methylenebisacrylamide were used for anaerobic consortium application and were examined for biomass retention capacity characterized in terms of volatile solids and specific methanogenic activity. The upflow anaerobic sludge blanket reactor was operated at various hydraulic retention times and was fed with palm oil mill effluent as a carbon source. The highest methane production rate of 510 mL CH4·L−1·h−1 with a methane yield of 68.3 L CH4 g−1·CODadded was obtained at palm oil mill effluent concentration of 20 g COD·L-1 and 24 h of hydraulic retention time. The average biogas (4.5 L) showed methane content and chemical oxygen demand reduction of 84.5 and 95.7%, respectively. Rmax was 570 mL L−1·POME·h−1 at 15% of zinc oxide nanoparticles, with butyrate and acetic acid in an effluent contained when operated at a hydraulic retention time of 24 h and a palm oil mill effluent concentration of 20 g COD L−1. A CO2 reduction of 93.6% was obtained at 15% w/v loading of zinc oxide nanoparticle. Experiments demonstrated that with the granule bead size of immobilized zinc oxide nanoparticle of 3.99 mm, production of CH4 and sequester of CO2 were 650 m3·d−1 and 456 m3·d−1, respectively. At 15% zinc oxide nanoparticle, granule leakage was found to be 0.065 mg·L−1. It is significant that this is the first report on immobilized zinc oxide nanoparticle granule biomass for biogas production from wastewater.

The environmental concerns of global warming and energy consumption are among the most severe issues and challenges facing human beings worldwide. Due to the relatively higher predicted temperatures (150–180 °C), the latest research on pavement energy consumption and carbon dioxide (CO2) emission assessment mentioned contributing to higher environmental burdens such as air pollution and global warming. However, warm-mix asphalt (WMA) was introduced by pavement researchers and the road construction industry instead of hot-mix asphalt (HMA) to reduce these environmental problems. This study aims to provide a comparative overview of WMA and HMA from environmental and economic perspectives in order to highlight the challenges, motivations, and research gaps in using WMA technology compared to HMA. It was discovered that the lower production temperature of WMA could significantly reduce the emissions of gases and fumes and thus reduce global warming. The lower production temperature also provides a healthy work environment and reduces exposure to fumes. Replacing HMA with WMA can reduce production costs because of the 20–75% lower energy consumption in WMA production. It was also released that the reduction in energy consumption is dependent on the fuel type, energy source, material heat capacity, moisture content, and production temperature. Other benefits of using WMA are enhanced asphalt mixture workability and compaction because the additives in WMA reduce asphalt binder viscosity. It also allows for the incorporation of more waste materials, such as reclaimed asphalt pavement (RAP). However, future studies are recommended on the possibility of using renewable, environmentally friendly, and cost-effective materials such as biomaterials as an alternative to conventional WMA-additives for more sustainable and green asphalt pavements.

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