Hydrophilic spongy biochar crosslinked with starch and polyvinyl alcohol biocarrier for nitrate, phosphorus, and cadmium removal in low carbon wastewater: Enhanced performance mechanism and detoxification

Biochar coupled with multiple technologies for the removal of nitrogen and phosphorus from water: A review

Water eutrophication caused by nitrogen (N) and phosphorus (P) has become a global environmental issue. Biochar is a competent adsorbent for removing N and P from wastewater. However, compared with commercial activated carbon, biochar has relatively limited adsorption capacity. To broaden the field scale application of biochar, biochar coupled with multiple technologies (BC-MTs) (such as microorganisms, electrochemistry, biofilm, phytoremediation, etc.) have been extensively developed for environmental remediation. Nevertheless, due to the fluctuations and differences in biochar types, coupling methods, and wastewater types, various techniques show different removal mechanisms and performance, hindering the promotion and application of BC-MTs. A systematic review of the research progress of BC-MTs is highly necessary to gain a better understanding of the current research status and progress, as well as to promote the application of these techniques. In this paper, the application of pristine and modified biochar in adsorbing N and P in wastewater is critically reviewed. Then the removal performance, influencing factors, mechanisms, and the environmental applications of BC-MTs in wastewater are systematically summarized. In addition, the cost analysis and risk assessment of BC-MTs in environmental applications are conducted. Finally, suggestions and prospects for future research and practical application are put forward.

Enhanced denitrification and p-nitrophenol removal performance via hydrophilic sponge carriers fixed with dual-bacterial: Optimization, performance, and enhancement mechanism

Effective treatment of industrial wastewater containing complex pollutants, such as nitrate (NO3--N) and organic pollutants, remains a significant challenge to date. Here, a strain Nocardioides sp. ZS2 with denitrification and degradation of p-nitrophenol (PNP) was isolated and its culture conditions were optimized by kinetic analysis. Hydrophilic sponge carriers were prepared using polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and chitosan (CS) to construct bioreactors. Furthermore, to further enhance the PNP degradation and denitrification performance of bioreactors, Pseudomonas stutzeri GF2 with denitrification capability was introduced. The results revealed that the removal efficiencies of PNP and NO3--N reached 97.9 % and 91.9 %, respectively, when hydraulic retention time (HRT) of 6 h, C/N of 2.0, and pH of 6.5. The bioreactor exhibited stable denitrification performance even with fluctuations in the influent PNP concentration. The potential functional prediction results revealed that the abundance of amino acids, fatty acids, and carbohydrates increased as the influent C/N decreased, reflecting a tendency of the microbial community to adjust carbon source utilization to maintain cell growth, metabolic balance, and resist adverse C/N environments. This research provides new insights into the effective removal of organic pollutants and NO3--N in wastewater treatment.

Influence of microplastics and environmentally persistent free radicals on the ability of biochar components to promote degradation of antibiotics by activated peroxymonosulfate

Microplastics (MPs) in sludge can affect the ability of biochar-activated peroxymonosulfate (PMS) to degrade antibiotics. In this work, biochar was prepared by mixing sludge and polystyrene (PS) through hydrothermal carbonization (HTC) and high-temperature pyrolysis processes. The resulting biochar was used to activate PMS to degrade ofloxacin (OFX), levofloxacin (LEV), and pefloxacin (PFX). The addition of PS significantly enhanced the ability of biochar/PMS to degrade antibiotics and the levels of environmentally persistent free radicals (EPFRs, 4.59 × 1020 spin/g) due to the decomposition of PS. The addition of PS resulted in a slight decrease in the specific surface area of biochar (2-3 m2/g on average), but a significant increase in the concentration of EPFRs increased the removal efficiency. The activation of PMS by biochar is dominated by free radicals, accounting for about 70%, in which SO4•- and •OH contribute the most and O2•- the least. However, 1O2 contributes 15-20% to the degradation of antibiotics in non-free radical processes. Overall, the process of biochar/PMS degradation of antibiotics is mainly dominated by free radicals, and the effect of non-free radicals is not obvious. Both hydrochar and pyrocarbon samples showed good hydrophilicity, and this property should improve the ability of active sites on biochar to degrade antibiotics. In the HTC process, PS can decompose during hydrochar preparation, with a maximum reduction value of 40.09%. The three-dimension excitation emission matrix fluorescence spectroscopy (3D-EEM) and total organic carbon (TOC) results show that the protein content in sludge plays a major role in reducing PS, with little effect of polysaccharide and SiO2. There are six to seven degradation intermediates of quinolone antibiotics, which are eventually degraded into CO2, H2O, and inorganic substances. The regeneration experiment showed good reusability of hydrochar and pyrocarbon, further demonstrating the suitability of biochar for the degradation of antibiotics.

Transport and transformations of cadmium in water-biofilm-sediment phases as affected by hydrodynamic conditions

Hydrodynamic conditions play a crucial role in governing the fate, transport, and risks of metal elements. However, the contribution of hydrodynamic conditions to the fate and transport of heavy metals among water, sediment, and biofilm phases is poorly understood. In our study, we conducted experiments in controlled hydrodynamic conditions using a total of 6 two-phase and 9 three-phase mesocosms consisting of water, biofilm, and sediment. We also measured Cd (cadmium) specification in different phases to assess how hydrodynamic forces control Cd bioavailability. We found that turbulent flow destroyed the surface morphology of the biofilm and significantly decreased the content of extracellular polymeric substances (p < 0.05). This led to a decrease in the biofilm's adsorption capacity for Cd, with the maximum adsorption capacity (0.124 mg/g) being one-tenth of that under static conditions (1.256 mg/g). The Cd chemical forms in the biofilm and sediment were significantly different, with the highest amount of Cd in the biofilm being acid-exchangeable, accounting for up to 95.1% of the total Cd content. Cd was more easily released in the biofilm due to its weak binding state, while Cd in the sediment existed in more stable chemical forms. Hydrodynamic conditions altered the migration behavior and distribution characteristics of Cd in the system by changing the adsorption capacity of the biofilm and sediment for Cd. Cd mobility increased in laminar flow but decreased in turbulent flow. These results enhance our understanding of the underlying mechanisms that control the mobility and bioavailability of metals in aquatic environments with varying hydrodynamic conditions.

The performance, mechanism and greenhouse gas emission potential of nitrogen removal technology for low carbon source wastewater

Excessive nitrogen can lead to eutrophication of water bodies. However, the removal of nitrogen from low carbon source wastewater has always been challenging due to the limited availability of carbon sources as electron donors. Biological nitrogen removal technology can be classified into three categories: heterotrophic biological technology (HBT) that utilizes organic matter as electron donors, autotrophic biological technology (ABT) that relies on inorganic electrons as electron donors, and heterotrophic-autotrophic coupling technology (CBT) that combines multiple electron donors. This work reviews the research progress, microbial mechanism, greenhouse gas emission potential, and challenges of the three technologies. In summary, compared to HBT and ABT, CBT shows greater application potential, although pilot-scale implementation is yet to be achieved. The composition of nitrogen removal microorganisms is different, mainly driven by electron donors. ABT and CBT exhibit the lowest potential for greenhouse gas emissions compared to HBT. N2O, CH4, and CO2 emissions can be controlled by optimizing conditions and adding constructed wetlands. Furthermore, these technologies need further improvement to meet increasingly stringent emission standards and address emerging pollutants. Common measures include bioaugmentation in HBT, the development of novel materials to promote mass transfer efficiency of ABT, and the construction of BES-enhanced multi-electron donor systems to achieve pollutant prevention and removal. This work serves as a valuable reference for the development of clean and sustainable low carbon source wastewater treatment technology, as well as for addressing the challenges posed by global warming.

Effect of magnetic fields on simultaneous nitrification and denitrification microbial systems

Magnetic fields positively influence the nitrogen removal efficiency in activated sludge systems. However, the structural succession pattern of microorganisms by magnetic fields still remains further explored. In this paper, a magnetic simultaneous nitrification and denitrification (MSND) reactor was constructed, and the influence of optimized magnetic field intensity (0, 10, 20 and 30 mT) on the nitrogen removal efficiency was investigated at HRT 6 h, 28.0-30.0 °C, and pH 7.0-8.0. Molecular biology was used to investigate the succession process of the dominant microbial flora and the functional gene structure of MSND systems. The results showed that the denitrification effects of the MSND system were significantly enhanced, which contributed to the lower concentration of total nitrogen in the effluent of the magnetic reactor than that of the nonmagnetic group reactor. The magnetic fields induced the succession of microbial community structure and improved the stability of microbial communities, thereby the relative abundances of nitrifying and denitrifying bacteria, and the functional genes were improved. In particular, the abundance of functional genes related to gene proliferation and transmembrane transport was increased. Therefore, the efficient nitrogen removal was achieved, which gives inspiration in the enhanced wastewater treatment by magnetic fields.

Simultaneous immobilization of ammonia and phosphorous by thermally treated sediment co-modified with hydrophilic organic matter and zeolite

The use of calcined sediments (CS) for thin-layer capping is an environment-friendly technology for controlling nitrogen (N) or phosphorus (P) release. However, the effects of CS derived materials and efficiency in controlling the sedimentary N/P ratio have not been thoroughly investigated. While zeolite-based materials have been proven efficient to remove ammonia, it is limited by the low adsorption capacity of PO₄^3-. Herein, CS co-modified with zeolite and hydrophilic organic matter (HIM) was synthesized to simultaneously immobilize ammonium-N (NH₄⁺-N) and remove P, due to the superior ecological security of natural HIM. Studies on the influences of calcination temperature and composition ratio indicated that 600 °C and 40% zeolite were the optimal parameters leading to the highest adsorption capacity and lowest equilibrium concentration. Compared with doping with polyaluminum chloride, doping with HIM not only enhanced P removal but also achieved higher NH₄⁺-N immobilization efficacy. The efficiency of zeolite/CS/HIM capping and amendment in prohibiting the discharge of N/P from sediments was assessed via simulation experiments, and the relevant control mechanism was studied at the molecular level. The results indicated that zeolite/CS/HIM can reduce 49.98% and 72.27% of the N flux and 32.10% and 76.47% of the P flux in slightly and highly polluted sediments, respectively. Capping and incubation with zeolite/CS/HIM simultaneously resulted in substantial reductions in NH₄⁺-N and dissolved total P in overlying water and pore water. Chemical state analysis indicated that HIM enhanced the NH₄⁺-N adsorption ability of CS owing to its abundant carbonyl groups and indirectly increased P adsorption by protonating mineral surface groups. This research provides a novel strategy to control sedimentary nutrient release by adopting an efficient and ecologically secure remediation method to rehabilitate eutrophic lake systems.