Structural and metabolic responses of microbial community to sewage-borne chlorpyrifos in constructed wetlands

Resilience of aerobic sludge biomass under chlorpyrifos stress and its recovery potential

Non-agricultural sources of pesticides in urban areas are responsible for their presence in domestic wastewater. Therefore, pesticides are typically found in sewage treatment plants in developed and developing countries as micro-pollutant. The presence of pesticides in the wastewater can impart stress on the aerobic sludge biomass and disrupt the functioning of the plant. However, there exists a knowledge gap regarding the resilience of aerobic sludge biomass towards stress due to the presence of pesticides in the wastewater. This study investigated the impact of chlorpyrifos (CPS) - a widely used pesticide, on sludge biomass and explored its recovery capability when CPS is discontinued in the influent. Four duplicate reactors were operated with different CPS concentrations ranging from 50 to 200 mg/L. Chemical oxygen demand (COD) removal for reactors has ranged within 18-73 % at the steady state of the stressed phase, whereas COD removal for the control reactor was 91 %. CPS stress slightly inhibited filamentous biomass growth. Biomass activity and cell viability have decreased significantly, whereas biochemical contents have varied slightly under CPS stress. The activities of the enzymes dehydrogenase and urease were significantly inhibited when compared to catalase and protease. Amplified ribosomal DNA restriction analysis reflected changes in the microbial community. The discontinuation of CPS has allowed aerobic sludge biomass to recover in its organic degradation capability (COD removal of more than 88 % at steady-state conditions of recovery phase operation), biomass growth, and cell viability. In addition, enzyme activities have retrieved to their original levels, and 78-93 % similarity of microbial community structure has been displayed between CPS-exposed and control reactor biomasses. Overall, the present study has indicated the orderly changes in the quality of aerobic sludge biomass under CPS stress through physico-chemical and biological characteristics. The study also has highlighted the self-recovery of sludge biomass characteristics stressed with different concentrations of CPS.

The Effects of Different Lead Pollution Levels on Soil Microbial Quantities and Metabolic Function with/without Salix integra Thunb. Planting

Background and Objectives: Salix integra Thunb., a fast-growing woody species, has been used in phytoremediation in recent years. It has the potential to accumulate high amounts of lead (Pb) in its growth, however, its effects on soil microbial community structure and function during its phytoextraction processes are not well understood, especially at different pollution levels. Materials and Methods: In our study, we set unplanted and planted Salix integra in areas with four levels of Pb treatments (0, 500, 1000, and 1500 mg/kg). After six months of planting, the rhizospheric soil, bulk soil, and unplanted soil were collected. Soil properties and microbes participating in nitrogen and phosphorus cycling were measured, following standard methods. Microbial metabolic functions were assessed using a Biolog-ECO microplate. Results: The bacteria (nitrogen-fixing bacteria, ammonifying bacteria, inorganic phosphorus-solubilizing bacteria, and nitrosobacteria) all increased in the 500 mg/kg treatment and decreased in the 1500 mg/kg treatment compared with the 0 mg/kg treatment, especially in rhizospheric soil. The microbial metabolisms decreased along with the increase of Pb levels, with the exception of the rhizospheric soil with a 500 mg/kg treatment. The metabolic patterns were relative to the pollution levels. The utilization of carbohydrates was decreased, and of amino acids or fatty acids was increased, in the 500 mg/kg treatment, while the opposite occurred in the 1500 mg/kg treatment. The values of soil properties, microbial quantities, and metabolic activities were higher in rhizospheric than bulk soil, while the differences between bulk and unplanted soil were different among the different Pb treatments. The soil properties had little effect on the microbial quantities and metabolic activities. Conclusions: S. integra planting and Pb levels had an interactive effect on the microbial community. In general, S. integra planting promoted microbial quantities and metabolic activity in rhizospheric soil. Lower Pb pollution increased microbial quantities and promoted the utilization of amino acids or fatty acids, while higher Pb concentrations decreased microbial quantities and metabolic activities, and promoted the utilization of carbohydrates.

Efficiency of pilot-scale horizontal subsurface flow constructed wetlands and microbial community composition operating under tropical conditions

This study assesses the microbial diversity of Thalia geniculate (L.) and Cyperus articulates (L.) in the rhizosphere in planted and unplanted systems with respect to removal efficiency in an experimental horizontal sub-surface constructed wetland pilot plant. The pilot-scale units consisted of six (6) cells of concrete of 0.94 × 0.6 × 0.4 m arranged in a parallel configuration. 29 L d^-1 were distributed to the cells by gravity. The hydraulic retention time was 3 days and influent and effluent measurements of COD and nutrients were monitored with standard methodology. Bacteria samples were isolated from the roots of plants and gravel in selective media and incubated at 37 °C. Isolates were biochemically characterized and genotyped with group-specific primers. Results showed that systems planted with T. geniculata removed greater proportions of COD (82%), NH₄⁺-N (83%) and PO₄²-P (83%) than C. articulatus (85, 74 and 72%, respectively) and unplanted wetland systems (80, 72 and 66%, respectively). Bacterial typing revealed several phyla were most abundant, α-Proteobacteria followed by β-Proteobacteria and there was a significant difference (p < 0.05) in CFU between planted and unplanted treatments. The bacterial community varied with respect to plant species or unplanted and demonstrated significant effects to contaminants removal efficiency.