Water Circulation Rate Research Articles

Wastewater reuse and recycling of the steel industry in China: history, current situation, and future perspectives

Abstract China is the largest steel producer in the world. Effective methods to alleviate the contradiction between water supply and water demand of the iron and steel industry in China are to implement the recycling of wastewater from the iron and steel industry and develop unconventional water resources. This paper reviews the development of wastewater recycling in the iron and steel industry in China in the past 40 years (1980–2020). During this period, steel output has increased from 36 to 1,053 million tons, freshwater consumption per ton of steel has decreased from 35.9 to 2.45 tons, and water resources reuse has soared from 61.2 to 98.02%. Four typical cases, including the Anyang Steel Group, the Tangshan Steel Group, the Tianjin Steel Group, and the Taihang Steel Group, were analyzed. In addition, a water efficiency research project of iron and steel enterprises in China was carried out in 2019. Statistical analyses on wastewater recycling rate, reuse rate, direct cooling water circulation rate, and other indicators were performed. The recycling of wastewater in the iron and steel industry would be continuously improved by policy drivers, economic drivers, and technical drivers.

Effects of disinfectants, sponge densities, water circulation rates, and vibration frequency on the artificial incubation of redclaw crayfish embryos

Artificial incubation of embryos is helpful to large-scale production of redclaw crayfish. In this study, we applied a recirculating mechanical pulling device to incubate redclaw embryos, and evaluated the effects of eco-friendly disinfectants, sponge densities, water circulation rates, and vibration frequencies on hatching % and survival % of embryos. Each factor was tested separately from the others. (1) Of the five solutions tested, a disinfectant solution comprising an essential oil base solution (1 mg/L), Zn-superoxide dismutase (SOD) 10,000 U/mg, trehalose (30 mmol/L), bovine serum protein (200 mmol/L), and astaxanthin (30 mmol/L) (solution 4) resulted in the significantly highest hatching 89.54% and survival 62.22%, which were not significantly different from the formaldehyde-treated group, but significantly higher than other treatments. It could be used as an eco-friendly, effective disinfectant for the artificial incubation of redclaw embryos instead of using traditional formaldehyde. (2) Medium density sponges with a length of 4.5 cm helped improve the survival %, it was hypothesized that the low and high density sponges were not conducive to the attachment of the newly hatched juveniles, and 5.5 cm long sponge would cause hypoxia death of juveniles. (3) Hatching 94.83%, 94.08%, and 92.58%, and survival 65.66%, 66.33%, and 67.08%, at water circulation rates of 7.1, 4.8, and 2.1 cycles/h, respectively. There was no significant difference in hatching % and survival % among groups. (4) Hatching 94.08%, 89.17%, and 91.92%, and survival 73.92%, 61.75%, and 60.50%, at vibration frequencies of 11, 16, and 26 vibrations/min, respectively. The survival % of the group exposed to 11 vibrations/min was significantly higher than at the other two frequencies. The results may have application on a large scale to improve production.

Remarkable Thermal Performance Enhancement of Micro Heat Pipes with Graphene-Nanoplatelet Nano-Wicks

The ultrafast water permeation property of graphene nanoplatelets (GNPs) synergically enhances the evaporation and water circulation processes in a micro heat pipe (MHP). An MHP is a promising phase-change heat-transfer device capable of transferring large amounts of heat energy efficiently. The hydrophobic, atomically smooth carbon walls of GNPs nanostructures provide a network of nanocapillaries that allows water molecules to intercalate frictionlessly among the graphene layers. Together with the attraction force of the oxygenated functional groups, a series of hydrophobic and hydrophilic surfaces are formed that significantly improve the water circulation rate. The intercalation of water molecules encourages the formation of water-thin film for film-wise evaporation. The effect of nano-wick thickness on the thermal performance of the MHP is investigated. A thinner GNP nano-wick is more favorable to film-wise evaporation while a thicker nano-wick promotes a higher water circulation rate from the condenser to the evaporator, leading to the existence of an optimal thickness. By benchmarking with the uncoated MHP, the thermal conductance of an MHP with a 46.9-µm GNP nano-wick manifests a maximum enhancement of 128%. This study provides insights on the feasible implementation of GNP nano-wicks into a highly efficient micro-scale electronics cooling device for environmental sustainability.

Insights into the streamwater age in the headwater catchments covered by glaciers and permafrost, Central Tibetan Plateau

Improving our understanding of streamwater age knowledge is critical for revealing the complex hydrological processes in alpine cryosphere catchments. However, few studies on water age have been conducted in alpine cryosphere catchments due to the complicated and inclement environment. In this study, the Buqu catchment, a typical alpine catchment covered by glaciers and permafrost on the central Tibetan Plateau (TP), was selected as the study area. Using the sine-wave approach and a gamma model based on the seasonal cycle of stable isotopes in water, the young water fraction (Fyw) and mean transit time (MTT) of the Buqu catchment outlet and 23 sub-catchments was estimated to comprehensively reveal the potential driving mechanism of water age variability. The streamwater MTT for the entire catchment was 107 days, and 15.1 % of the streamwater was younger than 41 days on average. The estimated water age showed significant spatial heterogeneity with shorter water ages in high-elevation and glacier catchments and longer water ages in low-elevation and non-glacier catchments. Precipitation was the primary driver for spatial variations in water age, while the thickness of the permafrost active layer may function as an intermediate hub to drive water age variability. Mechanically, the thickness of the permafrost active layer controls the water ages by modifying the flow direction and length of water flow path. Spatially, this control mechanism is indirectly driven by the elevation gradient. The TDS concentration in streamwater is significantly related to water age, thus revealing a close link between water quality and hydrology. Our findings suggest that cryosphere retreats likely alter water age, thereby slowing water circulation rates and affecting water quality security under global warming. This study provides insights into the evolution of water ages, thereby deepening our understanding of the hydrological processes and guiding the protection of water resources in alpine headwater catchments.

Continuous performance improvement of aquatic centres: A Taguchi-based optimization approach towards sustainability

Aquatic centres are important for enhancing the quality of life and human health benefits in cold regions. These useful facilities face serious performance-related challenges, such as imperfect indoor environmental flows, higher water and energy demands, and higher costs, consequently, struggling to achieve sustainability. Improving the performance of aquatic centres at minimum cost is not possible without optimizing the operational factors. This study developed a Taguchi-based optimization approach for improving performance with minimal economic stress. This study used an orthogonal array L27 consisting of twelve control factors (pH, temperature, total organic content, free chlorine, humidity level, lifeguard-to-bather ratio, number of working hours, daily average user, dosing rate, water circulation rate, air change hour, and ventilation rate) with three levels (low, medium, and high). Signal to noise (S/N) ratio and analysis of variance were generated to identify optimal conditions of the control factors. The proposed approach was validated with a confirmation test by predicting the S/N ratio at optimum conditions. The results showed that all the control factors were optimum at their second level, i.e., medium level except for total organic content and lifeguards-to-bather ratio. Additionally, at optimal factors levels, the performance-to-cost (P/C) ratio of an aquatic centre significantly improved from 26 to 37.89 dB. The number of working hours, air change hours, and free chlorine were found to be the most significant factors for the P/C ratio. The application of the approach demonstrated its practicability for performance optimization of aquatic centres in British Columbia (Canada) and elsewhere to achieve long-term sustainability.

Development and Experimental Study of Smart Solar Assisted Yogurt Processing Unit for Decentralized Dairy Value Chain

Yogurt production at the farm level is important for adding value to milk. In this study, a solar-assisted yogurt processing unit capable of performing the three processes of heating, fermentation, and cooling in a single unit was developed. It consisted of a circular chamber surrounded by a coil for heating by a solar vacuum tube collector and a pillow plate for cooling by a solar PV-powered chiller unit. Experiments were performed using 50, 40 and 30 L of raw milk under a constant water circulation rate of 50 L per minute for heating followed by a cooling process under 36, 18 and 6 rpm of stirrer speeds. The heat absorption rates of the milk were 5.48–0.31, 4.75–0.16 and 4.14–0.24 kW, and the heat removal rates from water ranged from 6.28–0.49, 5.58–0.49 and 4.88–0.69 kW for 50, 40 and 30 L of milk volume, respectively. The overall heat transfer efficiency was above 80% during the heating process. A stirring speed of 18 rpm was found to be optimal in terms of cooling speed and consistency of the yogurt. The total energy consumed was calculated to be 6.732, 5.559 and 4.207 kWh for a 50, 40 and 30 L batch capacity, respectively. The study offers a sustainable energy solution for the decentralized processing of raw milk, particularly in remote areas of the developing countries where access to electricity is limited.

Swimming Pool Regulations in the COVID-19 Era: Assessing Acceptability and Compliance in Greek Hotels in Two Consecutive Summer Touristic Periods

The COVID-19 pandemic has urged many countries to issue new regulations to assure safety in pool environments. Greece enforced stricter requirements in 2020 and 2021 for hotel pools. However, even though regulations are important, they can only be effective when accepted by the pool managers and users. The aim of this study was to (a) assess the acceptability of the regulations by hotel managers; (b) assess compliance during the summer touristic periods in 2020 and 2021; and (c) identify challenges during the implementation of the regulations that need to be addressed. Several non-compliances from the regulations were identified. Continuous chlorination with an automatic chlorinator was not a regular practice and suggested water circulation rates were poorly met. The microbiological and chemical testing frequency of the pool water and keeping the number of bathers allowed per surface area in the pool were reported as the most difficult requirements to meet. Most pool managers agreed that new measures contribute to the pool users’ safety; however, they reported increased cost as the main impediment for their implementation. The modernization of regulations governing swimming pools’ function, in terms of risk assessment orientation, will contribute to the adoption of an integrated compliance strategy on emerging health issues, such as COVID-19.

Evaluation of Water Circulation by Modeling: An Example of Nonpoint Source Management in the Yeongsan River Watershed

Owing to urbanization, impervious areas within watersheds have continuously increased, distorting healthy water circulation systems by reducing soil infiltration and base flow; moreover, increases in surface runoff deteriorate water quality by increasing the inflow of nonpoint sources. In this study, we constructed a Hydrological Simulation Program—Fortran (HSPF) watershed model that applies the impervious area and can set medium- and long-term water circulation management goals for watershed sub-areas. The model was tested using a case study from the Yeongsan River watershed, Korea. The results show that impervious land-cover accounts for 18.47% of the upstream reach in which Gwangju City is located; approximately twice the average for the whole watershed. Depending on the impervious area reduction scenario, direct runoff and nonpoint source load could be reduced by up to 56% and 35%, respectively; the water circulation rate could be improved by up to 16%. Selecting management goals requires the consideration of both policy objectives and budget. For urban areas with large impervious cover, the designation of nonpoint source management areas is required. For new cities, it is necessary to introduce water circulation systems (e.g., low impact development techniques) to improve rainwater penetration and recharge and activate preemptive water circulation.

Well-scale demonstration of distributed pressure sensing using fiber-optic DAS and DTS

In this study, we used data from optical fiber-based Distributed Acoustic Sensor (DAS) and Distributed Temperature Sensor (DTS) to estimate pressure along the fiber. A machine learning workflow was developed and demonstrated using experimental datasets from gas–water flow tests conducted in a 5163-ft deep well instrumented with DAS, DTS, and four downhole pressure gauges. The workflow is successfully demonstrated on two experimental datasets, corresponding to different gas injection volumes, backpressure, injection methods, and water circulation rates. The workflow utilizes the random forest algorithm and involves a two-step process for distributed pressure prediction. In the first step, single-depth predictive modeling is performed to explore the underlying relationship between the DAS (in seven different frequency bands), DTS, and the gauge pressures at the four downhole locations. The single-depth analysis showed that the low-frequency components (< 2 Hz) of the DAS data, when combined with DTS, consistently demonstrate a superior capability in predicting pressure as compared to the higher frequency bands for both the datasets achieving an average coefficient of determination (or R2) of 0.96. This can be explained by the unique characteristic of low-frequency DAS which is sensitive to both the strain and temperature perturbations. In the second step, the DTS and the low-frequency DAS data from two gauge locations were used to predict pressures at different depths. The distributed pressure modeling achieved an average R2 of 0.95 and an average root mean squared error (RMSE) of 24 psi for the two datasets across the depths analyzed, demonstrating the distributed pressure measurement capability using the proposed workflow. A majority of the current DAS applications rely on the higher frequency components. This study presents a novel application of the low-frequency DAS combined with DTS for distributed pressure measurement.

How Carbon Footprint Responds to Water Circulation Rates and Availability at Different Timescales in a Subtropical Forest Ecosystem

In the subtropics, the influence of water on the net ecosystem carbon exchange (NEE) is critical, subsequently determining net primary productivity (NPP). Water also contributes the majority of int...

A novel technology with precise oxygen-input control: Application of the partial nitritation-anammox process

Reliable and accurate oxygen-input control, which is critical to maintaining efficient nitrogen removal performance for partial nitritation-anammox (PN-A) process, remains one of the main operational difficulties. In this study, a novel, yet simple system (a simple process for autotrophic nitrogen-removal, SPAN) with precise oxygen-input control was developed to treat ammonium-rich wastewater via PN-A process. SPAN brings oxygen to biomass by circulating water and creating water spray (shower) at the water-air interface, and effectively balances the activities of core functional microorganisms through precise oxygen-input control. The oxygen-input rate is decided by the water circulation rate and shower rate and is measurable and predictable. Therefore, the required amount of oxygen for ammonium oxidation can be precisely delivered to the biomass by adjusting the circulation rate and shower rate. The results of two parallel SPAN reactors demonstrated that during long-term operation, the required oxygen input was precisely and reliably controlled. More than 99% of NH4+-N and 81% - 85% of total nitrogen were stably removed, with anammox bacteria contributing to more than 96% of total nitrogen removal. Anammox bacteria were efficiently enriched to the highest level among the key nitrogen-converting microbial groups, both in terms of abundance (8.17%) and nitrogen-conversion capacity, while ammonium oxidizing bacteria were well controlled to provide sufficient ammonium-oxidizing capacity. Nitrite oxidizing bacteria were maintained stable (relative abundance of 1.08%-1.88%) and their activity was effectively suppressed. This study provided a novel technology, SPAN, to precisely control oxygen input in PN-A system, and proved that SPAN was effective and reliable in achieving long-term high-efficiency nitrogen removal.

Theoretical modeling of a glass-cooled solar still incorporating PCM and coupled to flat plate solar collector

Abstract The performance of a modified solar still was investigated considering the following cases: solar still with glass cooling (SC), SC connected to an external collector (SCC), and SCC with phase change material (SCCP). Three different PCMs were used; sodium acetate trihydrate, sodium thiosulfate pentahydrate, and paraffin wax. The effect of various parameters; controllable (hot water circulation rate, PCM mass, and cooling water flowrate) and uncontrollable parameters (solar irradiation, ambient temperature, and wind speed) were investigated. Increasing the solar irradiation from 200 to 700 W/m2 increased the productivity from 0.9 to 3.4, 2.35 to 10, and 3 to 11.9 ml/min for the SC, SCC, and SCCP (with SAT as PCM) systems, respectively. The addition of external collector and PCM increased the productivity 2.4 times. Increasing the coolant mass flow rate from 0 to 10 kg/s, increased the productivity from 1 to 2.14, 1 to 6.65, and 1 to 7.5 ml/min for the SC, SCC, and SCCP systems, respectively. Additionally, increasing the hot water circulation rate of external collector from 0 to 0.1 kg/s increased the productivity from 2.4 to 6 and from 4 to 7.4 ml/min for SCC and SCCP system, respectively. The optimum mass ratio of basin water: PCM was found to be 2:1, while the best PCM type was found to be the one with the highest melting point and latent heat of fusion. The 24-h operation for a typical May month weather data in Jordan, revealed that the productivity improved 1.8 times for SCC and 2.3 times for SCCP-SAT compared with SC system.

Predicting the effect of impervious area change on water circulation rate in the Geum River watershed using HSPF modeling

Predicting the effect of impervious area change on water circulation rate in the Geum River watershed using HSPF modeling

Assessing the efficiency of a pilot-scale GDE/BDD electrochemical system in removing phenol from high salinity waters

Enhanced mineralization of phenol in brines with high chloride content was investigated by employing an electrochemical advanced oxidation treatment that couples anodic oxidation, electrochlorination and electro-Fenton in a single process. Experimental work was carried out in a pilot scale unit with an undivided plate-and-frame cell equipped with a boron-doped diamond anode and a carbon-PTFE gas diffusion electrode as cathode, in batch recirculation mode. The effects of operating conditions on phenol degradation, including current density, air flow rate, water feed flow rate, Fe2+ dosage and pH as well as of the water matrix, were evaluated. Applied current exhibited the greatest effect on phenol degradation/mineralization efficiency. Complete degradation of phenol (of initial concentration 50 mg L−1) was achieved under the near-optimum operating conditions (40 mA cm−2, pH 7, 0.4 m3 h−1 water circulation rate) within 30 min. Both air flow rate and Fe2+ dosage did not show a measurable impact on phenol removal. However, increasing the chloride content of water significantly improved the efficiency of treatment due to the enhanced indirect oxidation by the electrogenerated chlorine. Several trihalomethane intermediates (chloroform, bromodichloromethane) and chlorinated/brominated phenol byproducts forming during treatment, were eliminated after 60 min of processing time.

Electricity generation from a three-horizontal-well enhanced geothermal system in the Qiabuqia geothermal field, China: Slickwater fracturing treatments for different reservoir scenarios

Hot dry rock (HDR), as a clean renewable energy source, can help fulfill future energy needs and reduce the greenhouse effect. This energy source in the Qiabuqia geothermal field of Northwest China is expected to generate electricity. In this study, we used the lab parameters and the GR1 well data from the Qiabuqia site to numerically investigate the reservoir stimulation and electricity generation from a three-horizontal-well EGS system created in the granitic reservoir at depth 3500–3700 m, and at an average temperature of 218 °C. Slickwater fracturing and the resulting reservoir scenarios for different expected conditions in the region were analyzed in order to find suitable fracturing strategies. We then proposed three optimized EGS scenarios and evaluated their economic and environmental benefits. Results indicate that EGS power generation significantly depends on the reservoir stimulation results. The potential 2.61–4.90 MW installed capacity and 433.72–913.05 GWh total power generation are expected to be realized if the well spacing of 300–500 m and the hot water circulation rate of 20–40 kg/s in a 20-year period are achieved via the slickwater fracturing treatment. The final production temperature can be maintained at approximately 200 °C, and the corresponding temperature drops less than 10%. Such a case of geothermal engineering is expected to result in a reduction in greenhouse gas (GHG) emissions of 0.15–1.1 Mt, and its levelized cost of energy (LCOE) is estimated at 0.047–0.066 $/kWh.

Study of Cycling Air-Cooling System with a Cold Accumulator for Micro Gas-Turbine Installations

Using the cycling air-cooling systems of the CTIC type (Combustion Turbine Inlet Cooling) with a cold accumulator in a micro gas-turbine installation (micro-GTI) to preserve its capacity under the seasonal temperature rise of outside air is described. Water ice is used as the body-storage in the accumulators, and ice water (water at 0.5–1.0°C) is used as the body that cools air. The ice water circulates between the accumulator and the air-water heat exchanger. The cold accumulator model with renewable ice resources is considered. The model contains the heat-exchanging tube lattice-evaporator covered with ice. The lattice is cross-flowed with water. The criterion heat exchange equation that describes the process in the cold accumulator under consideration is presented. The calculations of duration of its active operation were performed. The dependence of cold accumulator service life on water circulation rate was evaluated. The adequacy of the design model was confirmed experimentally in the mock-up of the cold accumulator with a refrigerating machine periodically creating a 200 kg ice reserve in the reservoir-storage. The design model makes it possible to determine the weight of ice reserve of the discharged cold accumulator for cooling the cycle air in the operation of a C-30 type micro- GTI produced by the Capstone Company or micro-GTIs of other capacities. Recommendations for increasing the working capacity of cold accumulators of CTIC-systems of a micro-GTI were made.

Siting enhanced geothermal systems (EGS): Heat benefits versus induced seismicity risks from an investor and societal perspective

Enhanced geothermal systems (EGS) harness thermal energy from the deep underground to produce renewable and low-carbon electricity and heat. Siting EGS in rural versus urban areas involves trading off benefits of sold heat and avoided CO2 emissions and induced seismicity (IS) risk. In remote areas, IS risk is minimal, but EGS heat cannot be purposefully used for residential district heating. In urban areas, the heat can be sold, but EGS poses higher IS risk. We quantify this trade-off using cost-benefit analysis (CBA) from both private and social perspectives. We model 12 hypothetical EGS scenarios, with EGS of differing size (water circulation rate of 50–150 l/s) and siting (0–100′000 residents nearby). We bound uncertainties using Monte Carlo and sensitivity analyses. Assuming a price of electricity that would make EGS investment in half of our scenarios worthwhile to investors, we show that large EGS (150 l/s) near a large population (10′000 or 100′000 residents), enabling high heat sales, are most profitable. The CBA from the social perspective shows that medium- or large-sized EGS (100 or 150 l/s) near some residents (1′000 or 10′000) are most beneficial, based on reasonable heat sales while limiting potential IS damage. Siting EGS in remote areas is less favorable, even if expected IS damage is zero.

Water quality in simulated eutrophic shallow lakes in the presence of periphyton under different flow conditions.

Although the effects of periphyton on water quality and its relationship with flow conditions have been studied by researchers, our understanding about their combined action in eutrophic shallow lakes is poor. In this research, four aquatic model ecosystems with different water circulation rates and hydraulic conditions were constructed to investigate the effect of periphyton and flow condition on water quality. The concentrations of NH4+, TP, and chlorophyll-a and flow conditions were determined. The results show that, as a result of the rising nutrient level at the early stage and the decline in the lower limit, the presence of periphyton can make the ecosystem adaptable to a wider range of nutrients concentration. In terms of the flow condition, the circulation rate and hydraulic condition are influential factors for aquatic ecosystem. Higher circulation rate in the ecosystem, on one hand, facilitates the metabolism by accelerating nutrient cycling which is beneficial to water quality; on the other hand, high circulation rate leads to the nutrient lower limit rising which is harmful to water quality improvement. At low velocities, slight differences in hydraulic conditions, vertical velocity gradient and turbulence intensity gradient could affect the quantity of phytoplankton. Our study suggests that, considering environmental effect of periphyton, flow conditions and their combined action is essential for water quality improvement and ecological restoration in eutrophic shallow lakes.

Performance optimization of CO2 heat pump water heater

A preliminary analysis was conducted to analyze the performance of a heat pump water heater (HPWH) that uses CO2 as the refrigerant. A model to predict the performance was developed and calibrated based on the experimental data for an existing HPWH using a CO2 refrigerant. The calibrated model was then used to run a parametric analysis in which factors such as water supply temperature, water circulation rate, tank stratification, and condenser configuration were considered. The performance of a commercial CO2 system was compared with that of a similar system using R-134a as the refrigerant. It was found that CO2 HPWH performance was comparable to that of an R-134a HPWH, more so for a separated gas cooler configuration. For comparable performance, the compressor size and the tube-in-tube heat exchanger (condenser/gas cooler) size were compared for CO2- and R-134a-based systems. The impact of the water circulation rate on the water temperature stratification in the tank, an essential requirement for higher performance for CO2 HPWH systems was also investigated.

Hot Particles and Radionuclide Transport in Water Media

The characteristics of hot particles in the ambient environment are presented: activity, propagation, size, and density as well as contribution to the total activity of contaminants, distribution factor, leach rate, and deposition rate. The differences of suspensions, bottom deposits, and hot particles are shown. The equations governing the transport of radionuclides are formulated for systems, consisting of hot particles and suspensions, in water and bottom deposits. The coefficients in the equations are determined and the possibility of radionuclides being removed from bays by tides is taken into account. Solutions are obtained for the transport equations and the average sizes of the activity spots owing to hot particles and ordinary suspensions are determined. The possibility of transport of hot particles over large distances in a river floodplain is examined. The water circulation rate at which hot particles are carried out of flooded objects is determined.