Rice mill wastewater management in the era of circular economy.

Several nations around the world use rice as their primary food staple because of its tremendous nutritional value. India's expanding population has sparked a proliferation of rice mills as a result of the country's growing rice demand. However, small and medium-scale industries lack adequate facilities for processing effluents and other waste generated. Paddy is typically processed by parboiling, which involves soaking it in water, boiling it with steam, and then drying and milling. Around 1-1.5 L of water is necessary to partially cook 1 kg of unhusked rice, with approximately half of this water being discharged as effluent. Disposal of rice mill effluent (RME) in water bodies or on the land causes severe damage to soil and water. An inclusive examination of diverse approaches for the treatment and stabilization of partially cooked rice milling effluents is provided. Moreover, the document provides a concise overview of contemporary and environmentally friendly technologies for treating RME. Adsorption, electrocoagulation, chemical coagulation, and bioremediation using microbes, plants, and microalgae are all included in these methods. This manuscript discusses the concept of a circular economy, which is focused on enhancing environmental sustainability through the recycling and repurposing of generated waste into raw materials for the creation of new products. In addition, this review aims to focus on the impact of RME on soils and water species and the status of sustainable management at the point of circular economy with RME bioenergy production (bioelectricity, biomethane, and bio-hydrogen).

Comparison of GHG emissions from open field burning and anaerobic digestion of rice straw.

Rice straw (RS) has been burned in open fields in many countries, which is a growing environmental concern. Anaerobic digestion (AD) of RS is one of the sustainable alternatives to open burning of RS for converting the biomass into methane, carbon dioxide, and digestate for use as agricultural manure. The present study evaluates the RS generation, use patterns, and greenhouse gas emissions from open field burning and the AD of RS. Results indicate the AD of RS offers greater environmental benefits than that by RS open field burning. As a result of the open burning of RS in India emitted 592032.52 kg of CO2 equivalents/kg per year, whereas AD of RS contributes 122.86 kg of CO2 equivalents/kg per year. If RS were burned in an open field, its Global Warming Potential would be 493,873 times greater than that of AD. By minimizing GHG emissions and creating sustainable energy from waste, sustainable development, and circular economies are achieved.

Greenhouse gas emissions in sludge ultrasonication followed by anaerobic digestion processes.

This paper presents the greenhouse gas (GHG) emissions during ultrasonication of sludge and anaerobic digestion (AD) of the ultrasonicated sludge using mass-energy balance. Computation of the net energy (energy recovered - energy input) revealed that high solids concentration with low sonication specific energy provides positive net energy. Moreover, the GHG emissions can be minimised at low sonication specific energy input and high solids concentration compared to that of the control without sonication. Increase in temperature of sludge during sonication will reduce the energy input required for raising the sludge temperature to AD temperature and thus decreases the GHG emissions. With energy recovery from the methane produced in AD, the total GHG emissions can further be reduced, lower than that without energy recovery from methane.