Removal of abamectin and conventional pollutants in vertical flow constructed wetlands with Fe-modified biochar

Wastewater reuse in agriculture: Prospects and challenges

Sustainable water recycling and wastewater reuse are urgent nowadays considering water scarcity and increased water consumption through human activities. In 2015, United Nations Sustainable Development Goal 6 (UN SDG6) highlighted the necessity of recycling wastewater to guarantee water availability for individuals. Currently, wastewater irrigation (WWI) of crops and agricultural land appears essential. The present work overviews the quality of treated wastewater in terms of soil microbial activities, and discusses challenges and benefits of WWI in line with wastewater reuse in agriculture and aquaculture irrigation. Combined conventional-advanced wastewater treatment processes are specifically deliberated, considering the harmful impacts on human health arising from WWI originating from reuse of contaminated water (salts, organic pollutants, toxic metals, and microbial pathogens i.e., viruses and bacteria). The comprehensive literature survey revealed that, in addition to the increased levels of pathogen and microbial threats to human wellbeing, poorly-treated wastewater results in plant and soil contamination with toxic organic/inorganic chemicals, and microbial pathogens. The impact of long-term emerging pollutants like plastic nanoparticles should also be established in further studies, with the development of standardized analytical techniques for such hazardous chemicals. Likewise, the reliable, long-term and extensive judgment on heavy metals threat to human beings's health should be explored in future investigations.

Responses of bacterial and three sub-microeukaryote communities in the water of white shrimp Penaeus vannamei aquaculture ponds in two polyculture models

Polyculture operations in freshwater aquaculture ponds can disrupt microbial communities. High-throughput sequencing was used to assess the impact of polyculture operations on bacterial and three sub-microeukaryote communities (fungi, zooplankton, and eukaryotic phytoplankton) in Penaeus vannamei aquaculture ponds containing oriental river prawns and giant freshwater prawns, respectively. The results showed that the bacterial community was less sensitive than the microeukaryote communities to both the polyculture activity and environmental variations. The polyculture of giant freshwater prawns rather than oriental river prawns was the primary factor affecting the beta diversity of the three sub-microeukaryote communities. This may be due to the larger biomass of the polyculture varieties of giant freshwater prawns compared with oriental river prawns. The polyculture activity of giant freshwater prawns with a higher density and that of oriental river prawns with a lower density increased the stochasticity of the community assembly of the three sub-microeukaryote communities. It also affected the topological properties of the microbial communities, including greater correlations between ecosystem elements, and reducing the correlations among zooplanktons. The eukaryotic phytoplankton was the only microbial community that could also be explained by nutrient variation (mainly the total nitrogen). This highlights the potential role of the eukaryotic phytoplankton as a suitable indicator of the effects of nutrient input into ecosystems.

Roles of substrates in removing antibiotics and antibiotic resistance genes in constructed wetlands: A review

Antibiotics and corresponding antibiotic resistance genes (ARGs) are emerging pollutants in wastewater that pose a significant threat to the environment and human health. Constructed wetlands (CWs) are a cost-effective technology for eliminating these pollutants through substrates, plants, and microorganisms. Detailed reviews of the roles of CW substrates on antibiotic and ARG removal and recent progress in the field are lacking. This paper reviews the mechanisms influencing antibiotic and ARG (intracellular and extracellular) removal in CWs, and natural, biomass, chemical, modified, industrial, novel, and combined substrates on their removal efficiencies. Generally, substrates remove antibiotics and ARGs mainly through adsorption, biodegradation, chemical oxidation, and filtration. Other mechanisms, such as photolysis, may also contribute to removal. Natural substrates (e.g., gravel, zeolite) are more frequently employed than other types of substrates. The removal performance of antibiotics and intracellular ARGs by zeolite was better than that of gravel through enhanced substrate adsorption, filtration, and biodegradation processes. Moreover, Mn ore showed promising high capability to remove high concentration of antibiotics through various removal pathways. In addition, combined substrates of soil/sand/gravel and other substrates further facilitate antibiotic removal. Future research is suggested to explore the mechanisms of competitive adsorption and redox-controlled biodegradation, investigate the effect of Fe/Mn oxides on the removal of antibiotics and ARGs via chemical oxidation, evaluate the removal of extracellular ARGs by CWs with different substrates, and investigate the effect of substrates on removal of antibiotics and ARGs in full-scale CWs.

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

Pharmaceuticals (PCs) residues are considered an emerging threat to the environment due to their persistency, ecotoxicity and bioaccumulative nature. To study the PC (amoxicillin, AMX; caffeine, CF; ibuprofen, IBU) removal efficiency of vertical flow constructed wetland (VFCW), three setups of VFCWs were configured: SB (substrate matrix + biochar (BC)); SBP (substrate matrix + BC + plant); SP (substrate matrix + plant) and changes in effluent PC load was estimated at 24, 48, 72, 96, 120, 144 and 168 h intervals. SBP with an influent load of 1,000 μg L^-1 showed the maximum removals of 75.51% (AMX), 87.53% (CF), and 79.93% (IBU) significantly higher than that of SB and SP (p < 0.00). Results showed an inverse relationship between removal efficacy and influent PCs loading. The average removal (%) by VFCWS (of all studied setups) was in the order: 66.20 > 47.88 > 39.0 (IBU), 56.56 > 42.12 > 34.36 (AMX), and 74.13 > 64.0 > 52.07 (CF) with 1,000, 5,000 > 10,000 μg L^-1 influent load, respectively. The maximum removal of COD, NH₄⁺-N, and NO₃-N was recorded at 88.8%, 83.1%, and 64.9%, respectively in SBP, and their removal was hardly affected by influent PC concentration. In summary, planted VFCW spiked with BC could be a viable approach for the removal of PCs in wastewater. The impact of PC load on plant toxicity in VFCWs can be taken as a research problem for future work in this series.

Biochar immobilized bacteria enhances nitrogen removal capability of tidal flow constructed wetlands

To improve the nitrogen removal (NR) capability of tidal flow constructed wetlands (TFCWs) for treatment of saline wastewater, biochar, produced from Cyperus alternifolius, was used to adsorb and immobilize a salt tolerant aerobic denitrifying bacteria (Zobellella sp. A63), and then was added as a substrate into the systems. Under low (2:1) or high (6:1) C/N ratio, the removal of NO₃^--N and total nitrogen (TN) in the biochar immobilized bacteria (BIB) dosing system (TFCW3) was significantly higher (q < 0.05) than that in the untreated system (TFCW1) and the biochar dosing system (TFCW2). At low C/N ratio, the removal rates of NO₃^--N, TN and chemical oxygen demand (COD) of TFCW3 were 68.2%, 72.6% and 82.5%, respectively, 15-20% higher than TFCW1 and 5-10% higher than TFCW2. When C/N ratio was further increased to 6, the pollutant removal rate of each system was greatly improved, but the removal rate of TFCW3 for NO₃^--N/TN was still nearly 10% and 5% higher than TFCW1 and TFCW2, respectively. Microbial community analysis showed that aerobic denitrifying bacteria, sulfate reducing bacteria and sulfur-driven denitrifiers (DNSOB) played the most important role of NR in TFCWs. Moreover, biochar bacterial agent significantly increased the abundances of genes involved in NR. The total copy numbers of bacterial 16S rRNA, nirS, nirK, drsA and drsB genes in the TFCW3 were 1.1- to 3.76-fold higher than those in the TFCW1; Especially at low C/N ratio, the copy number of drsA and drsB in the upper layer of TFCW3 were 85.5 and 455 times that of TFCW1, respectively. Thus, BIB provide a more feasible and effective amendment for constructed wetlands to improve the N removal of the saline wastewater by enhancing the microbial NR capacity mainly via aerobic and sulfur autotrophic denitrification.

A Literature Review of Wetland Treatment Systems Used to Treat Runoff Mixtures Containing Antibiotics and Pesticides from Urban and Agricultural Landscapes

Wetland treatment systems are used extensively across the world to mitigate surface runoff. While wetland treatment for nitrogen mitigation has been comprehensively reviewed, the implications of common-use pesticides and antibiotics on nitrogen reduction remain relatively unreviewed. Therefore, this review seeks to comprehensively assess the removal of commonly used pesticides and antibiotics and their implications for nitrogen removal in wetland treatment systems receiving non-point source runoff from urban and agricultural landscapes. A total of 181 primary studies were identified spanning 37 countries. Most of the reviewed publications studied pesticides (n = 153) entering wetlands systems, while antibiotics (n = 29) had fewer publications. Even fewer publications reviewed the impact of influent mixtures on nitrogen removal processes in wetlands (n = 16). Removal efficiencies for antibiotics (35–100%), pesticides (−619–100%), and nitrate-nitrogen (−113–100%) varied widely across the studies, with pesticides and antibiotics impacting microbial communities, the presence and type of vegetation, timing, and hydrology in wetland ecosystems. However, implications for the nitrogen cycle were dependent on the specific emerging contaminant present. A significant knowledge gap remains in how wetland treatment systems are used to treat non-point source mixtures that contain nutrients, pesticides, and antibiotics, resulting in an unknown regarding nitrogen removal efficiency as runoff contaminant mixtures evolve.