Evaluating the potential use of a dairy industry residue to induce denitrification in polluted water bodies: a flow-through experiment.

No abstract

Microbial contamination remains a major challenge in drinking water supplies in developing regions, despite the continuous advances being made in water purification processes. The spread and transmission of pathogens due to consuming unsafe water culminate in waterborne diseases and increased number of deaths worldwide. Recently, the application of nanotechnology for water purification, and in particular the use of antibacterial nanoparticles (NPs) to control microbial contaminations, has received considerable interest. In this study, antibacterial chitosan−silver nanoparticles (CS/AgNPs) were enzymatically grafted on cork matrixes to design a water purification point-of-use device. The antibacterial efficiency of the constructed filtering system was further evaluated against water severely contaminated with Escherichia coli (∼10 7 CFU/mL). The system was tested in two operating filtration modes with varied water residence times. The antibacterial nanocomposite decreased the water bacterial contamination by 4 and 5 log CFU/mL when performing a series of continuous short disinfection cycles of 15 min residence time (experiment I). Nevertheless, complete bacteria removal was achieved only after increasing the water residence time in the filters up to 8 h (experiment II). Durability of the system was demonstrated via performing five disinfection cycles after which the hybrid CS/AgNPs remained on the cork surface. Importantly, the antibacterial nanocomposite prevented bacteria attachment and proliferation during all cycles of the disinfection process.

A surface flow constructed wetland (CW) was set in the Lerma gully to decrease nitrate (NO3 -) pollution from agricultural runoff water. The water flow rate and NO3concentration were monitored at the inlet and the outlet, and sampling campaigns were performed which consisted of collecting six water samples along the CW flow line. After two years of operation, the NO3attenuation was limited at a flow rate of ~2.5 L/s and became negligible at ~5.5 L/s. The present work aimed to assess the feasibility of using rural waste products (wheat hay, corn stubble, and animal compost) to induce denitrification in the CW, to assess the effect of temperature on this process, and to trace the efficiency of the treatment by using isotopic tools. In the first stage, microcosm experiments were performed. Afterwards, the selected waste material was applied in the CW, and the treatment efficiency was evaluated by means of a chemical and isotopic characterization and using the isotopic fractionation (ε) values calculated from laboratory experiments to avoid field-scale interference. The microcosms results showed that the stubble was the most appropriate material for application in the CW, but the denitrification rate was found to decrease with temperature. In the CW, biostimulation in autumn-winter promoted NO3attenuation between two weeks and one month (a reduction in NO3between 1.2 and 1.5 mM was achieved). After the biostimulation in spring-summer, the attenuation was maintained for approximately three months (NO3reduction between 0.1 and 1.5 mM). The ε 15 NNO3/N2 and ε 18 ONO3/N2 values obtained from the laboratory experiments allowed to estimate the induced denitrification percentage. At an approximate average flow rate of 16 L/s, at least 60 % of NO3attenuation was achieved in the CW. The field samples exhibited a slope of 1.0 for δ 18 O-NO3versus δ 15 N-NO3 -, similar to those of the laboratory experiments (0.9-1.2). Plant uptake seemed to play a minor role in NO3attenuation in the CW. Hence, the application of stubble in the CW allowed the removal of large amounts of NO3from the Lerma gully, especially when applied during the warm months, but its efficacy was limited to a short time period (up to three months).