Removal of pharmaceuticals by vertical flow constructed wetland with different configurations: Effect of inlet load and biochar addition in the substrate

Improved remediation of amoxicillin-contaminated water by floating treatment wetlands intensified with biochar, nutrients, aeration, and antibiotic-degrading bacteria

Residual antibiotics have become emerging contaminants of concern for their adverse impact on the ecosystem. Additionally, their accumulation in the environment is increasing antibiotic resistance among pathogens. This study assessed the impact of intensification of biochar, nutrients, aeration, and bacteria (BNAB) on the remediation potential of floating treatment wetlands (FTWs) to treat amoxicillin (AMX)-contaminated water. The FTWs were developed with saplings of Vetiveria zizanioides and intensified with biochar (1.5%), nutrients (25 mgL-1 N, 25 mgL-1 P, 20 mg L1 K), aeration (7 mg L-1), and AMX-degrading bacteria. The results showed that all the amendments enhanced the AMX degradation, while the maximum reduction in COD (89%), BOD (88%), TOC (87%), and AMX (97%) was shown by the combined application of all the amendments. The combined application also enhanced plant growth and persistence of the inoculated bacteria in the water, roots, and shoots. This approach can be employed for the low-cost, environment-friendly treatment, and recycling of antibiotic-contaminated wastewater, where BNAB intensification can further improve the bioremediation efficiency of FTWs in the case of heavily polluted waters.

Enhancement of energy recovery from caffeine wastewater in constructed wetland-microbial fuel cell through operating conditions

The enhancement of up-flow constructed wetland-microbial fuel cell (UFCW-MFC) performance in energy retrieval from caffeine containing wastewater has been explored via various operating conditions (hydraulic retention time (HRT), multianode (MA), multicathode current collector (MC), external resistance). The anaerobic decaffeination and COD removal improved by 37 and 12% as the HRT extended from 1 to 5 d. The increment in contact time between the microbes and organic substrates promoted the degradation and contributed to higher power output (3.4-fold), CE (eightfold), and NER (14-16-fold). The MA and MC connections facilitated the electron transfer rate and the degradation rate of organic substrates in the multiple anodic zones, which enhanced the removal efficiency in the anaerobic compartment (Caffeine: 4.2%; COD: 7.4%) and led to higher electricity generation (Power: 4.7-fold) and energy recovery (CE: 1.4-fold; NER: 2.3-2.5-fold) compared to SA. The lower external resistance favored the growth of electrogens and induced higher electron flux, where the best treatment performance and electricity production was obtained when the external resistance approached the internal resistance. Overall, it was noteworthy that the optimum operating conditions were achieved with 5 d HRT, MA, and MC connection along with external resistance of 200 Ω, which significantly outperformed the initial conditions (1 d HRT, SA connection, and 1000 Ω) by 43.7 and 29.8% of caffeine and COD removal in the anaerobic compartment, respectively as well as 14-fold of power generation.

Removal of chloramphenicol and resistance gene changes in electric-integrated vertical flow constructed wetlands

The performance of an electric-integrated vertical flow constructed wetland (E-VFCW) for chloramphenicol (CAP) removal, changes in microbial community structure, and the fate of antibiotic resistance genes (ARGs) were evaluated. CAP removal in the E-VFCW system was 92.73% ± 0.78% (planted) and 90.80% ± 0.61% (unplanted), both were higher than the control system which was 68.17% ± 1.27%. The contribution of anaerobic cathodic chambers in CAP removal was higher than the aerobic anodic chambers. Plant physiochemical indicators in the reactor revealed electrical stimulation increased oxidase activity. Electrical stimulation enhanced the enrichment of ARGs in the electrode layer of the E-VFCW system (except floR). Plant ARGs and intI1 levels were higher in the E-VFCW than in the control system, suggesting electrical stimulation induces plants to absorb ARGs, reducing ARGs in the wetland. The distribution of intI1 and sul1 genes in plants suggests that horizontal transfer may be the main mechanism dispersing ARGs in plants. High throughput sequencing analysis revealed electrical stimulation selectively enriched CAP degrading functional bacteria (Geobacter and Trichlorobacter). Quantitative correlation analysis between bacterial communities and ARGs confirmed the abundance of ARGs relates to the distribution of potential hosts and mobile genetic elements (intI1). E-VFCW is effective in treating antibiotic wastewater, however ARGs potentially accumulate.

Synthesizing biochar-based slow-releasing fertilizers using vermicompost leachate, cow dung, and plant weed biomass

Biochar-based slow-releasing fertilizers (BSRF) have been recommended widely for efficient soil nutrient management and crop production. In this study, we examined the N, P, and K release behaviour of pyrolysed (at 350 °C) cow dung (CDB), vermicompost (VCB), and Lantana (LB) weed and impregnated LB (LBVW) and CDB (CDBVW) with vermicompost leachate (1:1 v/v) under a lab-scale trial. BSRFs (CDB, VCB, LBVW and VCBVW) characterization (FT-IR, SEM-EDX and surface area analysis) was done and then tested for its suitability for soil-plant applications. Soil incubation study indicated the slow-releasing behaviour of BSRFs and overall P, N, and K release was found to be in the ranges of 72.3-84.5%, 73.1-79.0%, and 43.1-85.3%, respectively in different BSRFs setups. Furthermore, lab trials suggested the highest P (64.5%), N (75.3%), and K (86.8%) uptakes by the plant (Vigna radiata) in CDBVW and LBVW setups. Moreover, pot trails with moong bean (Vigna radiata) suggested a high growth in shoot and root and plant yield as well in seedlings cultivated with BSRFs. This study indicates that animal manure, vermicompost and terrestrial weed Lantana biochar can be used effectively to prepare BSRFs for efficient soil-plant nutrient management with multiple environmental benefits.

Application of a new baffled horizontal flow constructed wetland-filter unit (BHFCW-FU) for treatment and reuse of petrochemical industry wastewater

The shortage of water resources and generation of large quantum of wastewater has posed a significant concern to the environment and public health. Recent research on wastewater treatment has started to focus on reusing wastewater for different activities to reduce the stress on natural water resources. Constructed wetland (CWs) is a low-cost wastewater treatment option. However, some drawbacks include large areal requirements and the need for tertiary treatment units for reusable effluent. In this study, a novel composite baffled horizontal flow CW filter unit (BHFCW-FU) was developed to overcome the drawbacks of the conventional CW. The BHFCW-FU planted with Chrysopogon zizanioides provided a nine times longer flow path, and the adjoined variable depth dual media filter reduced the total area requirement and served as a polishing unit. On average, the BHFCW-FU with horizontal sub-surface flow regime could efficiently remove around 93.93%, 87.20%, and 66.25% of turbidity, phenol, and COD, respectively, from real petrochemical wastewater (initial turbidity: 29.6 NTU, phenol: 4.52 mg/L, and COD: 381 mg/L) and rendered the effluent quality reusable for irrigation, industrial, and other environmental purposes. In synthetic wastewater (initial turbidity: 754 NTU, phenol: 10.87 mg/L, and COD: 1691 mg/L), the removal efficiency of turbidity, phenol, and COD were 99.50%, 93.73%, and 87.05%, respectively. In-depth substrate characterization was done to study the removal mechanism. The developed BHFCW-FU required less space and maintenance, provided reusable effluent, and overcame the drawbacks of conventional CWs. Hence, it may show immense potential as an effective wastewater treatment.