Managing rice straw remains a challenge in Asia where more rice, and hence, more straw, is grown each year to meet rising demand. The widespread burning of rice straw is a major contributor to dangerously high levels of air pollution in South- and Southeast Asia associated with health issues. At the same time, researchers, engineers, and entrepreneurs are developing a range of alternative uses that turn rice straw into a commodity around which sustainable value chains can be built to benefit rural people. The best alternative to burning rice straw in any one location depends on context. However, available information remains scattered in different media and no publication yet exists that helps people learn about, and decide between, rice straw management options. This book provides a synthesis of these options and integrates knowledge on relevant areas: sustainable rice straw management practices, rice straw value chains, and business models. The book is also based on new research and practice data from research organizations and innovators in Vietnam, the Philippines, and Cambodia.

Anaerobic digestion (AD) is a process of degradation of organic matter by microorganisms in an oxygen-free environment, which produces biogas, a vital renewable energy source. Using solely an organic source, such as monosubstrates, it is difficult to optimize the AD process due to nutrient imbalance, lack of appropriate microbial communities, and the effect of operational parameters. This chapter reviews the current studies on biogas production from the anaerobic codigestion process of mixing agricultural byproducts, focusing on rice straw and livestock manure as substrates. Because rice straw is high in cellulose, it needs to be pretreated before feeding into the anaerobic digester. Different rice straw pretreatments are summarized including physical, chemical, and biological methods. Current biogas systems are discussed. The utilization of bioslurry from the anaerobic fermentation process to agricultural cultivation and aquaculture activities is also discussed.

Biomass conversion into various forms of energy, such as heat, power, or biofuels using thermal processes, involves the decomposition of biomass by exposure to heat, typically above 300 °C. Thermal conversion processes include pyrolysis, gasification, and direct combustion. Several factors affect the yields and energy recovery from these processes including temperature, reaction time, heating rate, absence, or presence of oxygen, use of catalysts, and pressure. Due to rice straw’s relatively high carbon and hydrogen contents, it contains a considerable amount of energy that make it a suitable feedstock for thermal conversion. In this chapter, the basic principles and factors affecting the thermal conversion of biomass into energy are discussed. Studies on the use of rice straw as feedstock to produce heat, power, and biofuels via thermal conversion are reviewed. Utilization of thermal conversion byproducts including biochar and ash will are presented. Thermal processes are compared in terms of energy conversion, possible environmental impacts, and technological and commercial maturity.

This study used a simple and efficient dipping method to prepare oleophilic calcium stearate-coated kapok fibers (CaSt₂-KF) with improved hydrophobicity. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) confirmed the deposition of calcium stearate particles on the surface of the kapok fibers. This led to higher surface roughness and improved static water contact angle of 137.4°. The calcium stearate-coated kapok fibers exhibited comparable sorption capacities for kerosene, diesel, and palm oil. However, the highest sorption capacity of 59.69 g/g was observed for motor oil at static conditions. For motor oil in water, the coated fibers exhibited fast initial sorption and a 65% removal efficiency after 30 s. At equilibrium, CaSt₂-KF attained a sorption capacity of 33.9 g/g and 92.5% removal efficiency for motor oil in water. The sorption kinetics of pure motor oil and motor oil in water follows the pseudo-second-order kinetic model, and the Elovich model further described chemisorption. Intraparticle diffusion and liquid film diffusion were both present, with the latter being the predominant diffusion mechanism during motor oil sorption.

Rice is a staple food crop, and its production generates large volumes of agricultural waste, rice straw. Several studies have proven that open-field burning and soil incorporation are unsustainable practices of managing rice straw, but remain as prevalent methods of treating and disposing of rice straw. An alternative solution is to harness the energy from rice straw via a small-scale heat conversion system for paddy drying applications, which can reduce rice grain post-processing costs and improve paddy storage conditions. This study investigated the energy flow, Greenhouse Gas (GHG) emissions, and cost of a small-scale rice-straw-based heat generation (RBHG) system using a downdraft furnace and a dryer simulator setup. The highest input energy and GHG emissions of 92% and 68%, respectively, were from the heat generation stage. The RBHG energy ratio was between 1.4 and 1.7, and the percent net energy was between 39 and 67%. The best case of RBHG offers a possibility of a net GHG avoided (−61 kg CO₂-eq Mg⁻¹), while the worst case (856 kg CO₂-eq Mg⁻¹) has a net GHG emission comparable with soil incorporation. The average total cost of RBHG is 0.096 USD kWh⁻¹. Overall, RBHG technology has the potential to improve energy flow, GHG emissions, and the cost of rice production systems.

Nitrate is considered as a major groundwater pollutant causing serious health and environmental effects. In this study, the removal of nitrate from aqueous solutions using municipal solid waste-derived activated biochar (MSWAB) via adsorption was explored. Initially, municipal solid waste (MSW), another prominent source of environmental pollution, was used as feedstock to produce biochar, which was chemically activated using potassium hydroxide, producing MSWAB. Activation of MSWAB resulted to an increase in surface area from 2.5 to 6.5 m²/g. The effect of initial nitrate concentration (A), pH (B), and adsorbent dosage (C) on nitrate removal were then evaluated using a 2k factorial experimental design. Results show that initial nitrate concentration, pH, and two-way interactions AB and AC have significant effects on % nitrate removal. Nitrate removal was found to increase as the initial nitrate concentration and pH decreases. Using Response Surface Methodology (RSM), the local optimum conditions for maximum nitrate removal of 66.97 % were determined to be at 30 mg/L initial nitrate concentration and pH 2 at 10 mg/mL adsorbent dosage. The appropriate isotherm for nitrate adsorption onto MSWAB was the Freundlich isotherm. Comparison with commercial activated carbon (CAC) in terms of nitrate removal efficiency at local optimum conditions showed that MSWAB is inferior to CAC. However, it is still notable that MSWAB was able to reduce the nitrate concentration from 30 mg/L to 11.27 mg/L which satisfies the 14 mg/L DENR effluent standard for Class C water bodies, showing its potential as an alternative adsorbent for treatment of nitrate-laden wastewaters.