Groundwater under threat from diffuse contaminants: improving on-site sanitation, agriculture and water supply practices

Acclimatization of a sequencing batch vertical oxidation pond with simulated agricultural wastewater using duckweed as vegetation: analysis of efficiency, Biomass, and Soil properties

Vertical oxidation pond operated in sequencing batch mode (HRT: 1.25 day) with duckweed as the vegetation was used to acclimatize with simulated agricultural wastewater. The maximum removal rate of urea [371 g/(m3.d)] and COD [222.4 g/(m3.d)] were observed at moderate concentrations of urea (500 mg/L), N-P-K (60 mg/L), and pesticide (20 mg/L). Inhibition and toxicity posed by higher concentrations, decreased the removals of urea (83% to 61%), COD (81% to 51%), and TDS (76% to 50%) at the end of the acclimatization. Steady removal (> 99%) of PO43--P was observed during acclimatization. Effluent pH increased due to the generation of NH4+-N (maximum 370 ± 5 mg/L) from the assimilation of urea. Oxidation of ammonia led to the maximum generation of NO2--N and NO3--N of 10 mg/L and 9 mg/L, respectively. Particles less than 300 μm increased, and both specific gravity (from 2.62 to 2.42) and maximum dry density (from 1.73 to 1.30 g/cm3) of the base soil decreased with an increase in urea, N-P-K, and pesticide. Reactor biomass increased (1.42 to 1.90 g/L) up to initial concentrations of urea (500 mg/L), N-P-K (60 mg/L), and pesticide (20 mg/L), then decreased (1.68 g/L) with an increase in concentration.

Performance and microbial community of a novel combined anaerobic bioreactor integrating anaerobic baffling and anaerobic filtration process for low-strength rural wastewater treatment

A novel combined bioreactor integrating anaerobic baffling and anaerobic filtration process was developed and operated for 210 days to treat low-strength rural wastewater. The effects of hydraulic residence time (HRT) and organic loading rate (OLR) on chemical oxygen demand (COD) removal and methane (CH₄) production of the combined bioreactor were investigated. The combined bioreactor can start up successfully in 25 days and achieve enhanced performance. The COD removal rate and CH₄ yield were influenced significantly by HRT and OLR. The influent COD was removed effectively through the synergistic effects of the anaerobic baffling and anaerobic filtration. The baffle zone played the main role in the degradation of the pollutants, and the filter zone mainly contributed to improve the resistance to shock loading. High-throughput sequencing technology was used to analyze the bacterial and archaeal community structure and diversity. Clostridium_sensu_stricto, Longilinea, Acetoanaerobium, Arcobacter, and Acinetobacter were found to be the dominant bacteria. While Methanothrix and Methanoregula were the dominant archaea, which were responsible for methane generation. This study not only highlights the good energy recovery and resource utilization potential of the combined bioreactor but also presents significant guidance for the application of the combined anaerobic process for low-strength rural wastewater treatment.