The management of domestic wastewater in rural areas has always been challenging due to characteristics such as the wide distribution and dispersion of rural households. There are numerous domestic sewage discharge methods used in rural areas, and it is difficult to treat the sewage. To address this problem, decentralized wastewater treatment systems (DWTSs) have been installed around the globe to reuse and recycle wastewater for non-potable uses such as firefighting, toilet flushing, and landscape irrigation. This study compares the currently implemented treatment processes by investigating them from the point of view of their performance and their advantages and disadvantages to provide new ideas for the development of rural wastewater treatment technologies. According to conventional treatment technologies including activated sludge (OD, A/O, A/A/O, SBR), biofilm (biofilter, MBBR, biological contact oxidation, biofluidized bed) and biogas digesters, natural biological treatment technologies including artificial wetlands (surface flow, vertical flow, horizontal submerged flow artificial wetlands), soil percolation systems (slow, fast, subsurface percolation and surface diffusion) and stabilization pond technology and combined treatment technologies are categorized and further described.

The ecological restoration of submerged plants is one of the most widely used technologies in the remediation of eutrophic water bodies. This technology mainly removes nitrogen, phosphorus, and other nutrients in water through the absorption effects of plant roots, stems, and leaves and the biotransformation of microorganisms attached to their surfaces. Root exudates can directly affect root-attached microorganisms and other aquatic organisms, thus significantly influencing water remediation by submerged plants. At present, there are few reviews on the root exudates of submerged plants and their effects on aquatic organisms. In this study, the composition, collection, and methods of detecting the root exudates of submerged plants are reviewed. Factors affecting the release of root exudates from submerged plants are analyzed, including abiotic (light, temperature, and nutritional status) and biotic factors (rhizosphere microorganisms). The positive or negative effects of root exudates on phytoplankton, zooplankton, and microorganisms are also discussed. The results show that plant species, growth stages, and environmental factors (light, temperature, and nutritional status) are crucial factors affecting root exudates. In addition, submerged plants can significantly influence phytoplankton, zooplankton, and microorganisms by releasing allelochemicals or other root exudates. Based on the results of this study, the influencing mechanisms of root exudates on ecological restoration processes by submerged plants are clarified. This review provides important guiding significance for applying submerged macrophytes in water restoration.

Chlorobenzene (CB), as a typical Volatile Organic Contaminants (VOC), is toxic, highly persistent and easily migrates in water, posing a significant risk to human health and subsurface ecosystems. Therefore, exploring effective approaches to remediate groundwater contaminated by CB is essential. As an enhanced micro-electrolysis system for CB-contaminated groundwater remediation, this study attempted to couple the iron-copper bimetal with biochar. Two series of columns using sands with different grain diameters were used, consisting of iron, copper and biochar fillings as the permeable reactive barriers (PRBs), to simulate the remediation of CB-contaminated groundwater in homogeneous and heterogeneous aquifers. Regardless of the presence of homogeneous or heterogeneous porous media, the CB concentrations in the effluent from the PRB columns were significantly lower than the natural sandy columns, suggesting that the iron and copper powders coupled with biochar particles could have a significant removal effect compared to the natural sand porous media in the first columns. CB was transported relatively quickly in the heterogeneous porous media, likely due to the fact that the contaminant residence time is proportional to the infiltration velocities in the different types of porous media. The average effluent CB concentrations from the heterogeneous porous media were lower than those from homogeneous porous media. The heterogeneity retarded the vertical infiltration of CB, leading to its extended lateral distribution. During the treatment process, benzene and phenol were observed as the products of CB degradation. The ultimate CB removal efficiency was 61.4% and 68.1%, demonstrating that the simulated PRB system with the mixture of iron, copper and biochar was effective at removing CB from homogeneous and heterogeneous aquifers.

Due to its advantages in specific surface area and oxygen-containing functional groups, biochar was often utilized for water pollution control. In this study, biochar was prepared from three types of wetland plants—Lotus Leaf, Arundo donax L., and Canna indica L. through slow pyrolysis. This biochar was utilized to adsorb Cr(VI) from wastewater, and the adsorption performance of the biochar under different pyrolysis temperatures and KOH modification ratios was investigated. The experimental results of biochar preparation demonstrated that under the pyrolysis of 500 °C and the lotus leaf powder/KOH mass ratio of 1:3, the prepared biochar (LBC-500(1:3)) exhibited the optimal adsorption capacity for Cr(VI) at a concentration of 50 mg·L⁻¹, with an adsorption capacity reaching up to 27.88 mg·g⁻¹. The optimal pH for Cr(VI) adsorption by LBC-500(1:3) was 3, with an adsorption capacity of 32.14 mg·g⁻¹ at this pH. When the dosage amounted to 60 mg, LBC-500(1:3) demonstrated its highest adsorption capacity for Cr(VI), achieving a maximum of 19.39 mg·g⁻¹. When the initial concentration peaked at 80 mg·L⁻¹, the adsorption capacity was able to attain a value of 34.80 mg·g⁻¹. Characterization analyses of the biochar prior to and subsequent to adsorption were conducted to elucidate the adsorption mechanisms of biochar for Cr(VI). The results revealed that the primary removal mechanisms of LBC-500(1:3) for Cr(VI) were coordination, electrostatic adsorption, and pore filling. The analysis of adsorption kinetics and isotherms revealed that the biochar predominantly adsorbed the Cr(VI) through monomolecular layer chemisorption. Adsorption thermodynamics results demonstrated that the adsorption process of the biochar was a spontaneous endothermic reaction. This study provides new insights and technical support for water pollution control, which holds significant environmental importance and application value.