Discharge Water Quality Research Articles

Environmental impact assessment of renewables and conventional fuels for different end use purposes

In this study, we present a comparative environmental impact assessment of renewables and conventional fossil fuels for electricity and hydrogen generation. The conventional fossil fuels investigated in this study are coal, oil, and natural gas. Renewables considered in this study are geothermal, hydropower, ocean, solar, and wind energies. Furthermore, nuclear and biomass energies are taken into consideration while assessing environmental impact and performances. Environmental impact criteria considered in this study are CO2, NOx, and SO2 emissions, land use, water consumption, water quality of discharge, solid waste and ground contamination, and biodiversity. For comparison purposes, all collected data are normalised and ranked between 0 and 3 while 0 giving highest negative environmental impact and 3 giving lowest negative environmental impact. Our results showed that overall, in terms of both electricity and hydrogen production, oceans give the highest rankings (2.71 for electricity and 2.73 for hydrogen). Coal has the lowest rankings in terms of environmental impact (0.26 for electricity and 0.30 for hydrogen).

Environmental impact assessment of renewables and conventional fuels for different end use purposes

In this study, we present a comparative environmental impact assessment of renewables and conventional fossil fuels for electricity and hydrogen generation. The conventional fossil fuels investigated in this study are coal, oil, and natural gas. Renewables considered in this study are geothermal, hydropower, ocean, solar, and wind energies. Furthermore, nuclear and biomass energies are taken into consideration while assessing environmental impact and performances. Environmental impact criteria considered in this study are CO2, NOx, and SO2 emissions, land use, water consumption, water quality of discharge, solid waste and ground contamination, and biodiversity. For comparison purposes, all collected data are normalised and ranked between 0 and 3 while 0 giving highest negative environmental impact and 3 giving lowest negative environmental impact. Our results showed that overall, in terms of both electricity and hydrogen production, oceans give the highest rankings (2.71 for electricity and 2.73 for hydrogen). Coal has the lowest rankings in terms of environmental impact (0.26 for electricity and 0.30 for hydrogen).

Characterization and Modeling of Urban Water Quality in the City of Calgary, Canada

Non-point source pollution (NPS) besides point source pollution (PS) has contributed to pollutant loading into natural receiving water bodies. Due to the nature of NPS, the quantification of pollutant loading from NPS is very challenging but crucial to riverine water quality management, especially for the river reach flowing through urban areas. The water quality in the river reach of the Bow River flowing through the City of Calgary in Alberta, Canada, is affected by both PS and NPS. Thus, understanding and characterizing water quality of discharges (affected by NPS) into the river reach is necessary for better managing riverine water quality and preventing water quality degradation. In the paper, monitored event mean concentrations (EMCs) of stormwater runoff and mean concentrations of snowmelt and baseflow of seven common pollutants from sub-catchments, which are categorized into four land use types including commercial, industrial, residential and on-going development land uses, were used to investigate the linkage between land use and water quality. Statistical analysis techniques were adopted to identify differences or similarities in water quality among different flow types, different land use types, and among/between catchments of same land use. The results indicated that EMCs of many water quality parameters vary among different land use types and among/between catchments of same land use. The results also showed median EMCs of pollutants of snowmelt and baseflow are, in general, lower than those of stormwater runoff. In addition, Stormwater Management Model was employed to investigate the physical process that would affect water quality response to storm events for two typical land uses, industrial and residential land uses. The modeling results supported that wash-off of particulate matters might primarily affect water quality response of catchments between different land uses. All the results shed the light on the necessity of quantifying pollutant loading considering the characteristics of land uses.

Do salt and low temperature impair metal treatment in stormwater bioretention cells with or without a submerged zone?

Although seasonal temperature changes and (road) salt in winter and/or coastal stormwater runoff might interfere with the metal treatment performance of stormwater bioretention cells, no previous study has evaluated the effect of these factors and their interactions under controlled conditions. In this 18week long study 24 well established pilot-scale bioretention columns were employed to evaluate the individual and combined effect(s) of low/high temperature, salt and presence of a submerged zone with an embedded carbon source on metal removal using a three factor, two-level full factorial experimental design. In most instances, the three factors significantly influenced the metal outflow concentrations and thus the treatment performance; the effect of temperature depended on the metal in question, salt had an overall negative effect and the submerged zone with carbon source had an overall positive effect. Despite these statistically significant effects, the discharge water quality was generally markedly improved. However, leaching of dissolved Cu and Pb did occur, mainly from bioretention cells dosed with salt-containing stormwater. The highest concentrations of metals were captured in the top layer of the filter material and were not significantly affected by the three factors studied. Overall, the results confirmed that bioretention provides a functioning stormwater treatment option in areas experiencing winter conditions (road salt, low temperatures) or coastal regions (salt-laden stormwater). However, validation of these results in the field is recommended, especially focusing on dissolved metal removal, which may be critically affected under certain conditions.

Cumulative Effects of Nutrient Enrichment and Elevated Temperature Compromise the Early Life History Stages of the Coral Acropora tenuis.

Inshore coral reefs are experiencing the combined pressures of excess nutrient availability associated with coastal activities and warming seawater temperatures. Both pressures are known to have detrimental effects on the early life history stages of hard corals, but studies of their combined effects on early demographic stages are lacking. We conducted a series of experiments to test the combined effects of nutrient enrichment (three levels) and elevated seawater temperature (up to five levels) on early life history stages of the inshore coral Acropora tenuis, a common species in the Indo-Pacific and Red Sea. Gamete fertilization, larval survivorship and larval settlement were all significantly reduced as temperature increased, but only fertilization was further affected by simultaneous nutrient enrichment. Combined high temperatures and nutrient enrichment affected fertilization in an additive manner, whereas embryo abnormalities increased synergistically. Higher than normal temperatures (32°C) increased coral juvenile growth rates 1.6-fold, but mortality also increased by 50%. The co-occurrence of nutrient enrichment with high temperatures reduced juvenile mortality to 36%, ameliorating temperature stress (antagonistic interaction). Overall, the types of effect (additive vs synergistic or antagonistic) and their magnitude varied among life stages. Gamete and embryo stages were more affected by temperature stress and, in some cases, also by nutrient enrichment than juveniles. The data suggest that coastal runoff events might exacerbate the impacts of warming temperatures on fertilization if these events co-occur during corals spawning. The cumulative impacts of simultaneous exposure to nutrient enrichment and elevated temperatures over all early life history stages increases the likelihood for failure of larval supply and recruitment for this coral species. Our results suggest that improving the water quality of river discharges into coastal areas might help to enhance the thermal tolerances of early life history stages in this common coral species.

Enhancement of phosphorus removal with near-neutral pH utilizing steel and ferronickel slags for application of constructed wetlands

The objective of this study was to enhance phosphorus (P) removal while achieving near-neutral pH in aqueous solution utilizing steel slags (Blast furnace slag, BFS; Basic oxygen furnace slag-air cooling, BOFS-A; Basic oxygen furnace slag-rapid cooling, BOFS-R) and ferronickel slag (FNS) for application to constructed wetlands (CWs). The maximum P adsorption capacities (mgkg−1) of the slags were in the order BOFS-R (3233)>BOFS-A (2320)≫BFS (607)>FNS (260) based on the Langmuir adsorption isotherm. The pH of the slags were in the following order: BOFS-R (11.9)>BOFS-A (9.0)≫BFS (8.9)>FNS (7.5). The basic oxygen furnace slags had the highest P adsorption capacity, while the ferronickel slag had the lowest pH among the tested slags. To achieve high P removal efficiency with near-neutral pH, the BOF slags and ferronickel slag (BOFS-A+FNS and BOFS-R+FNS) were mixed in batch experiments. To achieve effective P removal with near-neutral pH utilizing steel and ferronickel slags, the optimum conditions were found to be the ratio of BOFS-R:FNS of 7:3. Therefore, when mixed slags at the BOFS-R:FNS ratio of 7:3 were applied to CWs, they could achieve high P removal efficiency and near-neutral pH for meeting the acceptable drinking water quality discharge standard.

Spatial variation in soil properties and diffuse losses between and within grassland fields with similar short-term management.

SummaryOne of the major challenges for agriculture is to understand the effects of agricultural practices on soil properties and diffuse pollution, to support practical farm‐scale land management. Three conventionally managed grassland fields with similar short‐term management, but different ploughing histories, were studied on a long‐term research platform: the North Wyke Farm Platform. The aims were to (i) quantify the between‐field and within‐field spatial variation in soil properties by geostatistical analysis, (ii) understand the effects of soil condition (in terms of nitrogen, phosphorus and carbon contents) on the quality of discharge water and (iii) establish robust baseline data before the implementation of various grassland management scenarios. Although the fields sampled had experienced the same land use and similar management for at least 6 years, there were differences in their mean soil properties. They showed different patterns of soil spatial variation and different rates of diffuse nutrient losses to water. The oldest permanent pasture field had the largest soil macronutrient concentrations and the greatest diffuse nutrient losses. We show that management histories affect soil properties and diffuse losses. Potential gains in herbage yield or benefits in water quality might be achieved by characterizing every field or by area‐specific management within fields (a form of precision agriculture for grasslands). Permanent pasture per se cannot be considered a mitigation measure for diffuse pollution. The between‐ and within‐field soil spatial variation emphasizes the importance of baseline characterization and will enable the reliable identification of any effects of future management change on the Farm Platform.Highlights Quantification of soil and water quality in grassland fields with contrasting management histories.Considerable spatial variation in soil properties and diffuse losses between and within fields.Contrasting management histories within and between fields strongly affected soil and water quality.Careful pasture management needed: the oldest pasture transferred the most nutrients from soil to water.

Hydrologic Evaluation of River Basin Scale Tillage Effects on Non‐Point Source Loads from Upland Crop Areas†

AbstractThis study used the Hydrological Simulation Program—Fortran (HSPF) model to evaluate the river basin scale effects of nonpoint source (NPS) pollution loads caused by tillage and no‐tillage applications to upland crop areas. The study site was the Byulmi‐cheon river basin (1.21 km2) of South Korea. Hourly rainfall, discharge and stream water quality data for 2 years (2012–2013) were collected at the river basin outlet. The HSPF model under tillage conditions was calibrated using 23 rainfall events with an average Nash–Sutcliffe model efficiency value for runoff of 0.61 and determination coefficients for sediment, total nitrogen (T‐N) and total phosphorus (T–P) of 0.58, 0.61 and 0.62 respectively. The field experiment results from the no‐tillage plots with slopes of 3 and 8% under radish and sesame cultivation showed decreases in the runoff ratio, sediment, T‐N and T–P of 10.8, 81.7, 11.9 and 17.1% respectively. The HSPF model parameters soil bulk density (BD) and soil infiltration capacity (INFILT) were controlled for the upland crop areas during the evaluation of the no‐tillage effects. By increasing the parameter values from 1.33 Mg m−3 BD and 4.1 mm h−1 INFILT for the tillage condition to 1.90 Mg m−3 BD and 8.9 mm h−1 INFILT for the no‐tillage condition, the river basin runoff ratio and sediment, T‐N and T–P values were reduced by 10.3, 56.7, 18.3 and 35.9% respectively. Copyright © 2016 John Wiley & Sons, Ltd.

Water Quality Impact from the Discharge of Coal Mine Wastes to Receiving Streams: Comparison of Impacts from an Active Mine with a Closed Mine

This study examined two underground coal mines in the Sydney basin and investigated the water chemistry impact from their wastewater discharges to surface receiving waters. One mine closed 17 years prior to the study, and the other was still active. The geology of both mine locations shared many similarities and some important differences that influenced their wastewater chemistry and its subsequent impact on receiving waterways. Water quality of wastewater discharges from the two mines and their receiving waterways was investigated over a 6-month period. Both mine discharges caused comprehensive modification to receiving water chemistry. The closed mine increased electrical conductivity (EC) 3.3 times from upstream (33 μS/cm) compared to downstream (108 μS/cm). In comparison, the active mine increased EC by 9.4 times (173 μS/cm) upstream to 1628 μS/cm downstream. Both coal mine wastes increased the concentration of different contaminants to levels that are potentially hazardous for receiving water ecosystems. The active mine increased bicarbonate concentration in the receiving water by more than 60 times to 743 mg/L. The closed mine increased zinc and nickel concentrations in its receiving stream by 70 and 20 times to 318 and 360 μg/L. The active coal mine discharge was dominated by sodium and bicarbonate ions compared to magnesium and sulphate ions in the closed mine drainage. Although both receiving waters were sodium and chloride dominated upstream of the mine waste, their ionic composition was strongly modified due to the inflow of coal mine wastes. Results from this study are a reminder that water pollution from coal mines is important for both active mines and for closed mines decades after mining activity ceases.

The Effect of Rice Straw Mulching and No-Tillage Practice in Upland Crop Areas on Nonpoint-Source Pollution Loads Based on HSPF

This study evaluates the watershed-scale effects of non-point-source (NPS) pollution loads caused by rice straw mulching and no-tillage applications in upland crop areas using the Hydrological Simulation Program–Fortran (HSPF) model. The study area is the Byulmi-cheon watershed (1.21 km²) of South Korea. Hourly rainfall, discharge and stream water quality data were collected for three years (2011–2013) at the watershed outlet. The HSPF model under conventional (no rice straw mulching or tillage) conditions was calibrated and validated using 20 rainfall events for runoff and 14 rainfall events for stream water quality (sediment, T-N and T-P). The average Nash–Sutcliffe model efficiency value for runoff was 0.61, and determination coefficients for runoff, sediment, total nitrogen (T-N) and total phosphorus (T-P) were 0.70, 0.56, 0.58 and 0.61, respectively. The results of field experiments with slopes of 3% and 8% for radish and sesame cultivation showed decreases in the runoff ratio, sediment, T-N and T-P of 9.0%, 95.9%, 32.6% and 43.5% for rice straw mulching plots and 22.5%, 82.5%, 67.8 and 70.6% for no-tillage plots. The HSPF model parameters soil infiltration capacity (INFILT), soil bulk density (BD), wilting point (WP) and field capacity (FC) were controlled for the upland crop areas during the evaluation of the rice straw mulching and no-tillage effects. The HSPF evaluation using the application of Best Management Practices (BMPs) showed that the watershed runoff ratio, sediment, T-N and T-P values were reduced by 10.4%, 68.7%, 31.6% and 41.3% using rice straw mulching and 21.5%, 83.4%, 51.9% and 60.2% under no-tillage conditions compared with conventional conditions. The land use change scenarios for the baseline (upland crop areas 5%), Scenario 1 (upland crop areas 10%) and Scenario 2 (upland crop areas 30%) were applied in the model. The results of the evaluation show that the proportion of NPS pollution loads increased by a ratio approximately equal to that of the increasing upland crop area.

Ecological assessment of a transitioned stormwater infiltration basin

Infiltration basins are stormwater control measures (SCMs) widely employed for urban stormwater management. A transitioned infiltration basin is a failed infiltration basin that has gradually transformed into a wetland- or wetpond-like practice. The transitioned basin was found to effectively control the storm runoff flows and volumes, and improve the discharge water quality, thereby reducing the downstream hydrologic and pollutant loads on most occasions. Qualitative assessment of the site showed presence of wetland and non-wetland vegetation, small animals, and some potential for cultural benefit. The ecological evaluation demonstrated that runoff management and habitat provision in a sub-urban setting enhance the overall functionality of this new type of SCM ecosystem. A functionality assessment guide was developed for assessing infiltration basins considered to have failed. The Level-1 assessment includes visual criteria such as hydrophytic vegetation, hydric soils, hydrologic regime modification, and design check. The rapid assessment plans developed in this study can be applied to determine the ecological and stormwater management functions and benefits of failed/transitioning/transitioned basins, and may be adapted for other similar SCMs.

Zooplankton of Mokraya Sura River

Structural and functional characteristics of zooplankton as well as the results of biotesting were researched to indicate the ecological status of Mokraya Sura river sites. Zooplankton sampling was performed at the sites of Mokraya Sura river in autumn 2014 and in spring 2015. Species composition and abundance of zooplankton showed that zooplankton is most depressed at the upper sites of the river due to joint effect of slime accumulation eutrophication and industrial sewage. Biotesting results estimated water quality of the site near aeration plant sewage emergency discharge as most polluted of the river sites where large abundance and biomass of zooplankton were created mostly by planktonic rotifers. Large figures of filter-seeding crustaceans as well as low saprobity index indicate improvement in water quality at the sites 3 km and 2 km upstream from the river mouth.

Zooplankton of Mokraya Sura River

Structural and functional characteristics of zooplankton as well as the results of biotesting were researched to indicate the ecological status of Mokraya Sura river sites. Zooplankton sampling was performed at the sites of Mokraya Sura river in autumn 2014 and in spring 2015. Species composition and abundance of zooplankton showed that zooplankton is most depressed at the upper sites of the river due to joint effect of slime accumulation eutrophication and industrial sewage. Biotesting results estimated water quality of the site near aeration plant sewage emergency discharge as most polluted of the river sites where large abundance and biomass of zooplankton were created mostly by planktonic rotifers. Large figures of filter-seeding crustaceans as well as low saprobity index indicate improvement in water quality at the sites 3 km and 2 km upstream from the river mouth.

Sources and spatial variability of groundwater-delivered nutrients in Maunalua Bay, Oʻahu, Hawai‘i

Study regionMaunalua Bay, Oʻahu, Hawai’i. Study focusWe examined submarine groundwater discharge (SGD), terrestrial groundwater, and nearshore marine water quality in two adjacent aquifers (Waialae East and Waialae West) with differing land-use and hydrogeologic characteristics to better understand the sources and spatial variability of SGD-conveyed nutrients. Nutrient concentrations and NO3− stable isotope ratios were measured and integrated with SGD flux, land-use, and recharge data to examine SGD nutrient loads and potential sources in each aquifer. New hydrological insights for the regionRegionally elevated NO3- concentrations (166–171μM) and δ15N–NO3− values (10.4–10.9‰) were apparent in SGD in the Waialae West Aquifer, an area with high on-site disposal system density (e.g., cesspools). Coastal sites sampled in the neighboring Waialae East Aquifer exhibited significantly lower values for these parameters, with δ15N–NO3− values ranging from 5.7–5.9‰ and NO3− concentrations from 43–69μM. The isotopic composition of NO3− in SGD originating from the Waialae West Aquifer was consistent with wastewater. Modeled recharge data corroborated the NO3− stable isotope source designation. SGD emanating from Waialae West Aquifer was primarily influenced by two-component mixing of a wastewater source with low nutrient groundwater as wastewater effluent accounted for more than 4% of total recharge and 54–95% of total N and P loads in the aquifer.

Enhancement of nitrate removal in constructed wetlands utilizing a combined autotrophic and heterotrophic denitrification technology for treating hydroponic wastewater containing high nitrate and low organic carbon concentrations

To enhance the nitrate removal in constructed wetlands (CWs) for treating hydroponic wastewater discharged from greenhouses, the effectiveness of HF (horizontal flow)-HF hybrid CWs utilizing a combined sulfur-based autotrophic (based on the optimum conditions from batch experiment) and heterotrophic denitrification was evaluated for treating hydroponic wastewater containing high nitrate and low organic carbon concentrations. The optimum ratio of sulfur: limestone:immobilized bead with Thiobacillus denitrificans (T. denitrificans) was found to be 3:1:4; the optimum initial cell density was above 1×106cells; the optimum temperature was 25–35°C; and the optimum sulfur sources were thiosulfate and elemental sulfur to effectively treat hydroponic wastewater utilizing autotrophic denitrification with T. denitrificans in batch experiments. In the HF–HF CWs utilizing the combined autotrophic and heterotrophic denitrification, the average removal efficiencies of nitrate were higher in the order of T2 (71.5%, thiosulfate treatment—combination of heterotrophic and autotrophic denitrification) >T3 (66.6%, element sulfur treatment—combination of heterotrophic and autotrophic denitrification) ≫T1 (43.0%, control—heterotrophic denitrification only). In the HF–HF CWs, the maximum nitrate removal efficiency by the thiosulfate treatment was slightly greater than that by the treatment with elemental sulfur, whereas the sulfate production influence on autotrophic denitrification by elemental sulfur (SO42−: 89.1mgL−1) was lower as compared to thiosulfate (SO42−: 38.3mgL−1). Because the sulfate production is an important factor to meet acceptable drinking water quality discharge standard (Sulfate concentration in the effluent was below 250 in US EPA, and 200mgL−1 in South Korea), elemental sulfur was a more suitable sulfur source in HF–HF hybrid CWs. Overall, a combined process of using E/L/B (element sulfur/limestone/immobilized bead with T. denitrificans) column in HF–HF hybrid CWs would promote autotrophic and heterotrophic denitrification. Therefore, a combined autotrophic and heterotrophic denitrification process in HF–HF CWs would be more suitable than the heterotrophic denitrification alone (conventional technology in CWs) for treating nitrate in hydroponic wastewater since hydroponic wastewater contains little organic carbon.

생물전기화학기술을 이용한 하수처리장 방류수 수질개선 가능성

The study on the improvement of discharge water quality from domestic wastewater treatment plant (DWTP) was performed in a filter type bioelectrochemical system. The COD removal efficiency for a synthetic discharge water was about 88%, and the effluent COD was less than 5mg/L. The nitrification efficiency of the bioelectrochemical system was over 97%, but a considerable amount of the nitrogen was remained as nitrate form in the effluent. The total nitrogen removal efficiency was only around 30%. There are no significant differences in the removal of COD and nitrogen at 0.6 and 0.8V of the applied voltages between anode and cathode. The removal of COD and nitrogen in the system were quite stable when the HRT ranged from 60 to 15 minutes, and at 10 minutes of HRT, the nitrification efficiency was slightly decreased. The performance of the bioelectrochemical system has quickly recovered from the shocks in the influent due to high concentration of COD and nitrogen. For the effluent that discharged from the DWTP, the removal efficiencies of COD and total nitrogen from the bioelectrochemical system were 50 and 30%, respectively. Thus the bioelectrochemical system was a feasible process for further polishing the effluent quality from DWTP.

Effectiveness of ammonia removal by recirculating sand filters

This study examines the ability of in-service domestic wastewater treatment facilities, as opposed to controllable laboratory experiments, to remove ammonia utilising recirculating sand filters (RSFs). Permitted facilities in Missouri, USA, are required to regularly sample, analyse and report discharged water quality. The Missouri Department of Natural Resources stores the results in a central database, which was queried and analysed to assess the performance of these facilities in both the summer and winter seasons and to determine if a correlation exists between ammonia removal and flow capacity. The RSFs were found to discharge ammonia under 44 mg/l 95% of the time in winter and under 30 mg/l in summer. No correlation between performance and flow was found. The results of the study suggest that RSF technology is presently unable to treat ammonia in domestic wastewater to meet acceptable water quality standards for surface discharge.

Relationships between pollutant discharge and water quality in the rivers from “better” to “worse” water quality

The long-term relationship between pollutant discharge and river water quality of biological/biochemical oxygen demand (BOD) in the Yamato-gawa River, Japan, has been found to be similar to perturbation or dynamic equilibrium change of alternative stable states in the ecosystem fields with a linear relationship as a usual condition. Similar relationships have been observed in short-terms for single precipitation events both in the Richmond River, Australia, and in a mountainous watershed in Japan. On the contrary, nutrient concentrations have not changed in a long-term besides nutrient discharge increases in the Richmond River. In this paper, long-term chronological relationships of annual pollutant discharges and water quality in the Brisbane River, Australia, were investigated based on pollutant discharge estimations and water quality monitoring data as a case study in the “better” water quality river. Effects of precipitation variation were taken into account in the pollutant discharge estimations by introducing precipitation variance coefficient (PVC). Total nitrogen (TN) and total phosphorus (TP) concentrations in the river were found to be improved with fluctuations in the lower Brisbane River Catchment during 1975–2012. Long-term dynamic equilibrium alterations of pollutant discharge and water quality were found for TN and TP at the first time in the Brisbane River. The investigated term was found to be divided into two phases, 1975–2001 and 2001–2012 for TN, and 1975–2007 and 2005–2012 for TP. Both pollutant discharges and pollutant concentrations in the river were smaller in Phase 2 than Phase 1. Based on the relationships in the three rivers, a hypothesis on pollutant discharge and water quality from “better” to “worse” river water environment was presented that rapid and/or excess pollutant discharge increases cause perturbation or dynamic equilibrium alterations with the basal relationships as the linear relationships.

Fenton-Anoxic–Oxic/MBR process as a promising process for avermectin fermentation wastewater reclamation

Avermectin fermentation wastewater (AFW) is a highly toxic effluent generated in the pharmaceutical industry and is typically treated by using of an upflow anaerobic sludge blanket (UASB) reactor. This study aims to further optimize the overall treatment process to meet discharge standards and water quality for reuse. After the UASB reactor, the pretreated AFW undergoes Fenton oxidation, which improves the biodegradability of the UASB effluent and the removal of COD and ammonia in subsequent biotreatment processes. Optimal operating conditions for Fenton oxidation (pH=3.5, H2O2=4ml/l, FeSO4⋅7H2O=1.1g/l) and anoxic–oxic–membrane bioreactor (AO–MBR) system (HRT=72h, reflux ratio=300%) show an average removal rate of 84.3%, 79.4%, and 72.3% for COD, ammonia, and TN, respectively, which could be further treated by nanofiltration or reverse osmosis (NF/RO). Toxicity of the effluent was also significantly reduced. For a high-flux MBR system, HCl+NaClO was found to provide the best treatment for increasing the acceptable transmembrane pressure (TMP) caused by cake layer accumulation and fouling by inorganic metal ions. Study results demonstrate the potential of Fenton-AO/MBR process as a post-UASB reactor treatment and a pre-treatment of NF/RO, improving biodegradability, pollutant removal, and toxicity reduction of AFW.

Minimization of Bauxite Residue Neutralization Products Using Nanofiltered Seawater

Currently, open circuit Bayer refineries pump seawater directly into their operations to neutralize the caustic fraction of the Bayer residue. The resulting supernatant has a reduced pH and is pumped back to the marine environment. This investigation has assessed modified seawater sources generated from nanofiltration processes to compare their relative capacities to neutralize bauxite residues. An assessment of the chemical stability of the neutralization products, neutralization efficiency, discharge water quality, bauxite residue composition, and associated economic benefits has been considered to determine the most preferable seawater filtration process based on implementation costs, savings to operations and environmental benefits. The mechanism of neutralization for each technology was determined to be predominately due to the formation of Bayer hydrotalcite and calcium carbonate; however, variations in neutralization capacity and efficiencies have been observed. The neutralization efficiency of each feed source has been found to be dependent on the concentration of magnesium, aluminum, calcium, and carbonate. Nanofiltered seawater, with approximately double the amount of magnesium and calcium required half the volume of seawater to achieve the same degree of neutralization. These studies have revealed that multiple neutralization steps occur throughout the process using characterization techniques such as X-ray diffraction (XRD), infrared (IR) spectroscopy, and inductively coupled plasma optical emission spectroscopy (ICP-OES).