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18There is growing concern about the accumulation of metals in tropical agricultural 19 soils. Experimental results from batch studies were combined with results from the multi-20 surface models to test whether the multi-surface models (DSG and DNG model) could 21 describe metal binding. The multi-surface models were included soil sorption surfaces, i.e. 22 iron hydroxides (Diffuse Layer Model), organic matter (Stockholm Humic Model and NICA-23 Donnan Model), and phyllosilicate clay (Gaines-Thomas). The dissolution of Cd, Cr(III), Cu, 24 2 Mn, Pb and Zn was investigated. We found that for total dissolved Cd, Cu and Zn the two 24multi-surface models being tested provided very good model fits for all soils, as evidenced by 25 low root-mean square errors between model predictions and observations. The results suggest 26 that organic matter is an important sorbent for many metals in these soils. However, poor fits 27 were obtained for Cr(III), Mn and Pb for all soils. The study also suggests that the pH is the 28 main factor that controls the solubility of metals in tropical Fluvisols and Acrisols subjected to 29 application of biosolids and wastewater, and that advanced multi-surface models can be used 30 to simulate the binding and release of many trace metals. 31

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Biomass, one of the renewable resources, is expected to play an important role in the world’s energy future. In Asia, rice straw is an abundant agricultural surplus because rice is one of the leading staple food crops in the region. Often, rice straw is burned directly in the field via uncontrolled combustion methods that emit large amounts of short-lived air pollutants, greenhouse gases, and other pollutants. In Vietnam, the energy and environment protection sectors are facing great challenges because of rapid urbanisation and industrialisation. A national strategic choice is to exploit renewable energy, including biomass-derived energy, to achieve energy security and CO2 emission reduction. This study investigates the potential of rice straw as an energy source for power plants at a local scale in Vietnam using data derived from satellite Sentinel-1 images. The results show that Vietnam can produce 2,565 MW from rice straw, for which 24 out of 63 provinces have a potential capacity higher than 30 MW, and the Kien Giang province has the highest capacity (245 MW). The study also analyses limitations and obstacles overcoming which can promote the biomass energy sector in the country.

Fixed-film biofilm reactors are considered one of the most effective wastewater treatment processes, however, the cost of their plastic bio-carriers makes them less attractive for application in developing countries. This study evaluated loofah sponges, an eco-friendly renewable agricultural product, as bio-carriers in a pilot-scale integrated fixed-film activated sludge (IFAS) system for the treatment of municipal wastewater. Tests showed that pristine loofah sponges disintegrated within two weeks resulting in a decrease in the treatment efficiencies. Accordingly, loofah sponges were modified by coating them with CaCO3 and polymer. IFAS pilot tests using the modified loofah sponges achieved 83% organic removal and 71% total nitrogen removal and met Vietnam’s wastewater effluent discharge standards. The system achieved considerably high levels of nitrification and it was not limited by the loading rate or dissolved oxygen levels. Cell concentrations in the carriers were twenty to forty times higher than those within the aeration tank. Through 16S-rRNA sequencing, the major micro-organism types identified were Kluyvera cryocrescens, Exiguobacterium indicum, Bacillus tropicus, Aeromonas hydrophila, Enterobacter cloacae, and Pseudomonas turukhanskensis. This study demonstrated that although modified loofah sponges are effective renewable bio-carriers for municipal wastewater treatment, longer-term testing is recommended.

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