Search

Remediation of contaminated soil and sediment is important for improving the eco-environmental quality. Electro-kinetic remediation (EKR) is an environmentally friendly technology to migrate and remove pollutants from the soil and sediment matrix. This paper analyses the mechanism and performance of EKR of heavy metals, organic pollutants, and compound pollutants. Moreover, the effect of optimizing individual EKR through soil and sediment pre-treatment (adding acid/oxidant/co-solvent/surfactant, stirring, heating, etc.), electrode optimization (exchange electrode, anode approximation, electrode matrix, etc.), and applying multi-technology combination (electro-kinetic permeable reaction barrier/Fenton/ion, exchange membrane/ultrasonic/electrolyte enhancement, etc.) was evaluated. Factors including incomplete separation of pollutants, variation in physico-chemical properties and microstructure of soil/sediment, and difficulties in in situ practice have restrained the field application of EKR. To solve the above technical challenge, an integrated EKR technology based on pollutant in situ separation, followed by separated contaminant treatment, and subsequent valuable elements recovery is proposed.

This paper reviews the ecological environment protection measures of Chinese rural hydropower development schemes. China’s rapid economic growth is making great energy demands and developing rural hydropower currently provides 30.4 GW annually. There is a conflict of interest between hydropower development and ecological and environmental protection. Potential problems include changes in hydrological condition, eutrophication, downstream nutrient reduction, sediment deposition, aquatic ecosystem alteration, and ecological water demand variation. Since most of the rural hydropower resources are located in ecologically fragile regions, it is significantly more important that ecological environment protection is being considered. As exploitation of rural hydropower has developed in China, ecological environment protection schemes had to adapt to changing boundary conditions. Due to improvements in environmental protection management, various environmental impact assessment methods have been applied including fuzzy analysis hierarchy process, ecological scheduling, pressure-state-response, and ecological environment evaluation index. The latter index can both qualitatively and quantitatively analyze ecological environment impacts and has become the most frequently used tool in the evaluation of rural hydropower exploitation. To rebalance the interests regarding energy generation and environmental protection, countermeasures originating from different aspects such as engineering design optimization, management improvement, and ecological restoration were recommended to promote ecological environment protection. The review concludes that by taking ecological environment protection into consideration in the whole rural hydropower plan, adopting ecological scheduling to guarantee river ecological water demand and implementing ecological restoration in watershed management are the most effective approaches in furthering sustainable development of rural hydropower.

This paper investigates the role of plants and sediment in removing nutrients from wastewater being treated in a representative integrated constructed wetland (ICW). It discusses the role of plants and sediment in removing nutrients from an ICW treating agricultural wastewater for more than 7 years. More nitrogen and phosphorus were stored in wetland soils and sediments than in plants. The first cell had the highest depth of sediment accumulation (45 cm). Over the 7-year operation period, the accretion rate was approximately 6.4 cm/year. With respect to maintenance, desludging of the first wetland cell of the ICW system appears to be necessary in 2011. An average of 10,000 m3 per year of wastewater entered the ICW. Approximately 74% (780 kg) of the phosphorus and 52% (5,175 kg) of the nitrogen that entered the wetland system was stored in the wetland soils and sediments. Plants stored a small fraction of nutrients compared to soils (

The relationships between pH, dissolved oxygen (DO) and chlorophyll a in aquaculture and non-aquaculture waters are assessed in this paper. The research includes the evaluation of field and experimental studies at the Panjiakou Reservoir (between Aug and Oct 2009) and the review of international data covering two decades. The results indicated that typical eutrophic non-aquaculture water had mean concentrations of chlorophyll a of higher than 10 μg L−1, and significant positive correlations were found between pH, DO and chlorophyll a. When the mean concentration of chlorophyll a was less than 10 μg L−1, no correlation was found between DO and chlorophyll a for waters with a high exchange rate or heavily organically polluted natural waters. Diurnal variations were found for both pH and DO. A corresponding significant positive correlation was found between both water quality parameters. In general, when the mean concentration of chlorophyll a was less than 10 μg L−1 within aquaculture waters of low exchange rate, only a weak or no correlation at all was found between pH, DO and chlorophyll a during summer and autumn. On the other hand, a significant positive correlation between pH and chlorophyll a and a significant positive correlation or no correlation between DO and chlorophyll a were found for aquaculture waters with a high exchange rate during summer and autumn. Strong diurnal variations for both pH and DO were identified. A significant positive linear correlation between pH and DO was found for field enclosure experiments.

The Haihe River basin is located in the north of China and has an area of 318,000 km2. The region is politically important and economically advanced. For example, the Haihe River basin sustains a population of more than 120 million and generates a gross domestic production of approximately 2,600 billion Chinese Yuan. The ecological health of plain rivers within the Haihe River basin of China is questionable because of severe water shortages, considerable water, soil and air pollution, and the destruction of the natural river morphologies. It is therefore necessary to establish a generic and theoretical restoration methodology to guide river ecological restoration efforts in the future. Thirteen methodologies and technologies were selected from an existing suit of ecosystem restoration techniques currently applied to the Haihe River catchment. These technologies were further divided into three types: water quantity adjustment, water purification, and habitat improvement. The most suitable ecological restoration techniques were selected as a function of all three types. However, direct methods of addressing water quantity and quality problems were identified as critical for the success of future restoration efforts. Examples of the application of the conceptual ecological restoration model for the representative plain rivers Beiyunhe, Yongding and Wei, all located within the Haihe River Basin, are also assessed. The conceptual model provides practical solutions to pollution problems, is generic in nature, and could therefore be applied to other polluted watercourses in densely populated regions in the developed and developing world.

Representative sediment samples rich in nitrogen and phosphorus (both continuous and intermittently submerged) were used to conduct dynamic water level (WL) regulation experiments with various WL velocity modes (0, 3, and 6 cm/day). The experiments lasted three WL regulating cycles (6 months), and each single cycle included four WL dynamic phases: decline, stable, ascend, and re-stable. During the experiment, a greater nutrient stock caused higher nutrient release fluxes for continuously submerged sediments when compared to corresponding intermittently submerged sediments regardless of WL regulation. Moreover, continuous submerged sediment nutrient release showed a similar “U” pattern to the intermittently submerged sediment, and nutrient concentrations within the water phase generally increased with rising WL and decreased with dropping WL. Rapid WL regulation such as 6 cm/day promoted nitrogen release, and slow WL regulation at 3 cm/day favored phosphorus leaching. When three WL regulation cycles were finished, WL regulation of 6 cm/day resulted in 18 and 25 % decline of sediment mean organic matter (OM) content for continuous and intermittently submerged sediment, respectively. However, increased WL regulation cycles impacted on sediment nitrogen and phosphorus stock in different manners. For example, a WL regulation of 6 cm/day led to a 582 mg/kg decline and 322 mg/kg increase for intermittently submerged sediment in terms of total nitrogen (TN) and total phosphorus (TP) content, respectively. Results indicated that direct WL regulation insignificantly affected sediment nutrient release, but changed the overlying water conditions such as pH and redox potential (redox), and then indirectly changed the nutrient release dynamics.

Suspended sediments can decrease the apparent bio-concentration factor of organic pollutants through adsorption. However, whether this process also weakens the toxicity of organic pollutants to non-target aquatic organisms is not clear. Therefore, natural sediments were chosen as suspended sediment examples in this research applying atrazine as the target pollutant and Brachydanio rerio (more recently, Danio rerio (Zebrafish)) as the target organism to conduct acute toxicity experiments. The concentration of atrazine in aqueous solution was measured as a time series. Results show that without suspended sediments, the 96-h LC50 of atrazine to Brachydanio rerio is 29.06 mg/l at 95 % confidence interval (24.41 to 40.70 mg/l). For suspended sediments of 7500 and 15,000 mg/l, the LC50 (i.e., concentration resulting in 50 % mortality) equates to 30.74 and 39.51 mg/l, respectively, and the corresponding confidence intervals are between 27.17 and 40.91 mg/l and between 30.43 and 126.93 mg/l in that order. Probit analysis, which is a type of regression used to analyze binomial response variables, was applied using the Statistical Package for the Social Sciences. For the series of no suspended solids (SS), 7500 and 15,000 mg/l SS, the so-called no-observed-effective concentrations were 3, 9, and 15 mg/l, correspondingly. The uptake quantity and uptake rate of atrazine by B. rerio according to atrazine concentrations in the aqueous solution were computed. The research indicates that suspended sediments can decrease the absorbed rate of atrazine by B. rerio. Thus, suspended sediments weaken the acute toxicity of atrazine to B. rerio.

Water quality protection has become a key concern in water resources development and management. Uncontrolled nutrient input may challenge the quality of some water bodies. This study uses the relatively steep Kan watershed located in the north-west of Tehran (Iran) as an example case study, where an artificial lake is currently under construction for recreational purposes. Two approaches to predict the total annual phosphorous load were assessed: the soil and water assessment tool (SWAT) and the export coefficient approach. River discharge and sediment transport were simulated prior to modeling of the total phosphorous (TP) load in SWAT to make the model more accurate. In addition, an upstream to downstream calibration method was utilized. Findings reveal that the SWAT-simulated phosphorous load had sound Nash–Sutcliffe efficiency (E NS) values (E NS of 75 % for calibration and E NS of 52 % for validation). The relative error in estimating annual TP load was 7 %. The export coefficient approach assigning coefficients of export for each land use is known as an alternative method that can be used for estimating the TP load. Four sets of export coefficients were selected from the literature to examine their suitability in TP load prediction. The results showed significant errors in TP load prediction, which indicates that export coefficients are likely to be watershed-specific. Likewise, the export coefficients were found to vary through four wet months with errors ranging from 9 % to 33 %. This paper demonstrates that the export coefficient method may estimate the pollution load in the Kan watershed with less data than the advance SWAT model. However, it is associated with a higher level of error.

Rural non-point source (RNPS) water pollution control is problematic in Hubei Province, which is a typical agricultural region with abundant rainfall and a developed natural surface water network. The concept of best management practices (BMP) originating from the USA has already been introduced with the aim to reduce the application of chemical fertilizers and pesticides, and water and soil loss. However, a comprehensive evaluation of rural wastewater and nutrient reutilization to benefit the rural communities and the environment has not been attempted. To fill this gap, this review paper explores the major contributors of RNPS water pollution in Hubei Province, assesses the status of watercourses and discusses the prevalent ecological engineering techniques including vegetated filter strips (VFS), ecological ditches (ED), constructed wetlands (CW), and biogas plants (BP) with respect to aspects such as water purification, energy generation, and nutrient reduction and recirculation. Findings indicate that RNPS water pollution continuously increased for the past 10 years. Chemical fertilizers, poultry and livestock breeding, aquaculture, and rural living are the major sources of elevated chemical oxygen demand, ammonia–nitrogen, total nitrogen, and total phosphorus loads discharged to receiving watercourses. Finally, ecological engineering technologies such as VFS, ED, CW, and BP are proposed for villages and communities to combat RNPS water pollution. BMP are a promising approach to create a sustainable agricultural system, improve the rural energy consumption structure and living conditions, decrease wastewater discharges, and reduce chemical fertilizer application rate.

In theory, biological and physical clogging, induced as a result of potentially excessive formation of biomass from degradation of pollutants and retention of inert suspended fine particles, respectively, should result in a decrease of treatment performance. However, some wetlands are not prone to clogging in practice. The aim of this study was to compare the impact of different design (aggregate size) and operational (contact time, empty time and chemical oxygen demand [COD] loading) variables on the treatment efficiency and clogging processes. Different vertical-flow constructed wetlands were constructed and operated from June 2011 until June 2012. Data from June 2011 (setting-up period) were not used. The filter with the highest COD loading performed the worst in terms of outflow COD concentration (120 mg/l) but best in terms of COD load reduction (61 %). The wetland with the largest aggregate size had the lowest mean nitrate-nitrogen outflow concentration of 1.2 mg/l. However, the results were similar regardless of aggregate size (10 versus 20 mm) and resting time (24 versus 48 h) for most water quality variables. However, different COD inflow concentrations (COD of 146 mg/l versus COD of 312 mg/l) had a significant (p