Acidogenic gas (H₂ and CO₂) from acidogenic reactors is often ignored in two-stage anaerobic digestion due to its high CO₂ content. While biogas recirculation improves methane production and substrate utilization, the underlying metabolic mechanisms remain unclear. This study explores these mechanisms using metagenomics in a novel two-stage system utilizing acidogenic gas. Biogas recirculation in the methanogenic stage increased average methane yield from 554 to 608 mL/g VS as the flow rate rose from 0 to 0.4 L/min, with a peak of 696 mL/g VS at 0.4 L/min. However, the methane yield decreased to 586 mL/g VS at 0.8 L/min. Recirculation enriched fermentative bacteria, boosting soluble metabolite production but slightly reducing organic matter removal. Although dominant microbial communities were significantly unaltered, syntrophic bacteria such as norank_f__norank_o__MBA03 (8.8–12.2%) were enriched, strengthening microbial networks. Different methanogenic genera emerged, enabling rapid metabolite consumption via hydrogenotrophic, acetoclastic, and methylotrophic pathways. Metagenomic analysis revealed that recirculation upregulated key functions like signal transduction, cell motility, aromatic degradation, methanogenesis, and possible methane oxidation. This promoted carbon substrate availability and methane production while highlighting potential for valuable biochemical recovery from volatile fatty acids, supporting the circular economy and enhancing the cost-effectiveness of biogas systems.

This study integrates land‐use/land cover (LULC) dynamics with assessments of irrigation water, soil, and groundwater quality in reclaimed lands west of Mallawi, El Minya Governorate, Egypt. Sixteen groundwater and 16 water‐saturated soil samples were analyzed for physicochemical properties, including electrical conductivity (EC), major ions, and salinity–sodicity indices. LULC changes from 2016 to 2025 were evaluated using remote sensing and modeling, while multivariate analyses explored relationships among quality indicators. Groundwater was generally suitable for irrigation, with an average irrigation water quality index (IWQI) of 3.0, EC of 1817 µS/cm, and total salts of 219 ppm—all within FAO limits. However, soil quality showed marked deterioration: EC averaged 8754 µS/cm (maximum 32 400 µS/cm), sodium reached 1132 ppm, and salinity indices were elevated (sodium adsorption ratio [SAR] = 15.1; residual sodium bicarbonate [RSBC] = 9.6; potential salinity [PS] = 21.2 meq/L). Principal component analysis identified EC, Na ⁺ , Cl ⁻ , Ca ²⁺ , and Mg ²⁺ as dominant salinization factors, explaining 82% and 69.7% of total variance in water and soil, respectively. Multiple linear regression models accurately predicted IWQI ( R ² ≈ 1), with EC, Ca, Mg, and Na as key predictors. The mean soil IWQI (3.7) reflected cumulative degradation compared to groundwater. LULC analysis indicated agricultural expansion and agroforestry growth consistent with reclamation policies, alongside urban encroachment and fallow persistence. Without intervention, salinization risks may intensify. The study emphasizes integrated land–water management, including gypsum application, improved drainage, leaching, and salt‐tolerant crops, to sustain productivity in reclaimed areas.

Groundwater contamination by ammonia is an emerging environmental and public health concern in arid regions that depend heavily on groundwater. This study evaluates groundwater quality in the Northwestern Gulf of Suez, examining chemical characteristics, governing geochemical processes, and noncarcinogenic health risks associated with ammonia. Groundwater was sampled from 12 industrially influenced locations. The water showed near‐neutral pH (7.0–7.9), high electrical conductivity (5310–10 300 µS/cm), and elevated total dissolved solids (3690–6130 ppm), indicating substantial mineralization. Urea concentrations were low (0.12–1.6 ppm), whereas chemical oxygen demand (COD) ranged from 25 to 161 ppm, reflecting variable organic loads. Ammonia reached 277 mg/L in areas adjacent to industrial discharge, far exceeding permissible limits. Principal component analysis revealed that groundwater chemistry is shaped by both natural geochemical processes and anthropogenic inputs, including fertilizer leaching and saline intrusion. Noncarcinogenic health risks from ammonia were assessed for adults, children, and infants across inhalation, dermal, and oral exposure pathways. Hazard quotient values were highest for the oral route, reaching 46.54 for children and 101.19 for infants; dermal exposure also posed significant risk, whereas inhalation was minimal. Most samples—particularly Sample 3—exceeded the safe Hazard Index (HI) threshold (HI > 1), with newborns exhibiting HI values above 100. Overall, groundwater in the study area shows marked chemical deterioration and presents substantial health risks, especially to vulnerable populations. The findings underscore the need for effective mitigation measures, including pollution control, water treatment, and sustained monitoring, to support safe and sustainable groundwater management in ammonia‐affected regions.