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Wet flue-gas purification in non-ferrous smelting facilities consumes large volumes of fresh water and generates wastewater rich in sulfate and nitrate. On-site recirculation of this wastewater is currently limited by progressive nitrate accumulation, because no conventional single-step technology can simultaneously remove sulfate and nitrate; the available routes are separate, energy- or reagent-intensive steps that either transfer nitrate into hazardous mixed salts or generate secondary sludge. The raw wastewater investigated here contained 53.3–57.5 g/L nitrate, 10.5–12.5 g/L sulfate, approximately 1.35 g/L TOC, and trace Cr, Cu, and Al. Herein, we report a one-step hydrothermal process in which an organic iron reagent, ferric citrate, simultaneously removes sulfate and nitrate from flue-gas wastewater at a moderate temperature of 120 °C—a temperature attainable with low-grade waste heat that is otherwise unrecovered on site. The advancement of knowledge lies in the underlying chemistry: thermally activated electron transfer from the citrate ligand to Fe³⁺ generates Fe²⁺, which catalytically reduces nitrate (>99% removal), while Fe³⁺ concurrently precipitates sulfate (and co-removes Cr and Al) as schwertmannite, an iron oxyhydroxysulfate that itself becomes a potentially recyclable iron resource. Subsequent neutralization with Ca(OH)₂ further reduced residual sulfate to 4.1 g/L, making the water suitable for return to the flue-gas purification loop after optional polishing. For plant operators and decision-makers, the implication is that the current evaporation-to-hazardous-salt practice can, in principle, be replaced by a closed water cycle driven by the plant’s own waste heat, thereby reducing freshwater withdrawal, avoiding the disposal of a nitrate-bearing mixed salt, and recovering an iron-rich by-product.

Wood waste and residues are increasingly viewed as feedstocks for the circular bioecon-omy, yet their market development remains uneven. This rapid review synthesized 125 studies published between 1967 and 2025 to examine research trends, feedstock characteristics, market constraints, and emerging opportunities through Marketing Mix and Innovation perspectives. Research was concentrated in North America and Europe (68.0%), and quantitative approaches accounted for 75.2% of the studies. Logistics and infrastructure were the most frequently reported constraints (61.6%), followed by competition (38.4%), supply–demand conditions (32.0%), and lack of standardization (14.4%). Energy-related applications remained prominent (87.2%), while 45.6% of studies also addressed material or bioproduct applications, indicating diversification rather than replacement of established uses. The synthesis shows that technological advances alone do not create viable markets. Residue characteristics, transportation, processing capacity, competing uses, pricing and distribution arrangements, institutional coordination, policy, and financing jointly shape utilization pathways. Marketing Mix and Innovation perspectives provide complementary explanations of how these markets are configured and how they change. Wood residues can become valuable feedstocks, but their value is context dependent and relies on alignment between specific residue streams and viable markets.

Natural farming (NF) has emerged as a promising agro-ecological tactic to enhance resource use and reduce dependence on synthetic agricultural inputs. However, comprehensive field-based evidence across diverse agro-climatic regions remains limited. This study assessed the effects of NF on water use, water and crop productivity, economic returns, energy consumption, and soil fertility across four agro-climatic zones of Andhra Pradesh, India, using a paired-field approach during 2023–2025. Compared with conventional farming (CF), NF reduced total water utilization by 16.1–39.0%, resulting in a 15.0–55.5% improvement in water productivity. Although rice yield declined marginally by 4.40–8.40% in the Southern, Krishna, and High-Altitude zones during some seasons, yields remained comparable in the Godavari zone. The cost of cultivation decreased substantially by 20.6–35.1%, while gross returns remained largely comparable between production systems, varying from −7.0% to +5.05%. Consequently, NF increased net returns by 8.8–29.0% and improved the benefit-cost ratio by 23.7–47.8% relative to CF. Irrigation-related energy consumption was reduced by 21.8–57.7%, indicating greater resource-use efficiency under NF. The sustainable yield index values remained high (0.68–0.91), demonstrating stable crop productivity despite reduced external inputs. Natural farming practices also improved soil health by buffering soil pH towards neutrality; soil organic carbon (SOC) enhanced from 0.38–0.73% under CF to 0.57–1.01% under NF. Similarly, available nitrogen, phosphorus, and potassium increased under NF. Overall, these findings demonstrate that natural farming improves water and energy productivity, reduces production costs, and increases farm profitability while maintaining stable rice productivity across diverse agro-climatic conditions. The results highlight the potential of natural farming as a climate-resilient and resource-efficient strategy for sustainable rice production in India.