Cooling Tower Blowdown Water Research Articles

Evaluation of return cooling water reuse in the wet cooled power plant to minimise the impact of water intake and drainage

The treatment and reuse of industrial water is a matter of great interest, given the severe shortage of water resources. It is widely acknowledged that power plants, particularly wet-cooled power plants, consume a significant amount of water. Therefore, research on the circulating cooling system (CCS) and the treatment of the return cooling water is of utmost importance. This study examined data on CCS inlet (water body), make up, and cooling water parameters, calculated a water balance, and predicted the hydrochemical quality of cooling tower blowdown water (CTBD). The study was conducted for an operating power plant to propose an effective treatment scheme for the return of CTBD to the process cycle. Additionally, it evaluated the possibility of recycling CTBD in the clarifier through laboratory modeling. Therefore, based on the results of this study, an effective treatment scheme is proposed to return CTBD to the technological cycle to ensure environmental sustainability. Recycled water was used as the water supply for the cooling tower, and a lime softening treatment was applied to clean the CTBD. According to the results, it is possible to recover quality indicators from a portion of the return cooling water after lime softening treatment. The novelty of this study lies in the successful demonstration of a lime softening regime that enables the blending of up to 25 % CTBD with make up water, without necessitating an increased CaO dose. This regime maintains TH levels at 2.2 mg-eq/dm³ and ensures that the discharge velocity of 0.7 m/s remains within regulatory standards. Additionally, it maintains standard concentrations of chloride (Cl⁻) and sulfate (SO₄²⁻) in CTBD at 200 mg/dm³ and 250 mg/dm³, respectively.

Performance and economic analysis of the cooling tower blowdown water treatment system in a coal-fired power plant

In recent years, the treatment and reuse of wastewater have been widely of interest due to the severe shortage of water resources. As is well known, a huge amount of water is consumed in coal-fired power plants, especially for the circulation cooling system in a cooling tower. Therefore, research on the circulating cooling system and cooling tower blowdown water (CTBD) treatment is crucial. In this study, a computational model was established to study the treatment of CTBD by reverse osmosis (RO) and direct contact membrane distillation (DCMD). Recycled fresh water was used as a water supply for the cooling tower. The effects of the main operating parameters on the performances of the RO and DCMD with/without waste heat utilization were explored. The water-saving effects, energy consumption amounts, and economics of the three systems were analyzed comparatively. The results showed that better water-saving performance of the DCMD with waste heat utilization was achieved with a water-saving rate of 18.4% and that the energy consumption and cost were slightly lower than those of the RO. The lowest water treatment cost of the DCMD with waste heat utilization was 3.38 Ұ/m3. In addition, the effect of electricity price on the costs was studied. When the electricity price was higher than 0.31 Ұ/kWh, the DCMD with waste heat utilization was more economical.

Application of UF and RO for power plant's wastewater treatment and recycling for environmental sustainability

Abstract Global indicators have warned of freshwater scarcity in Asia. However, the utilization of freshwater resources has skyrocketed for commercial and industrial purposes without any strategy for recycling and reuse. The power plant's wastewater/reject mainly consisted of cooling tower blowdown water and reverse osmosis (RO) plant reject water. Due to the high turbid nature of reject water, pretreatment was carried out to achieve SDI15 <3 by employing multimedia filters (MMF), activated carbon filters (ACF) and ultrafiltration (UF). Operational parameters of RO membranes were optimized (11.5 bar, 29 °C) to achieve maximum water recovery along with higher rejection rates of critical scale forming species such as 81% total dissolved solids (TDS), 73% calcium hardness and 72% silica (Si). After accounting for backwash water and other concentrate rejections, the membrane treatment plant has achieved an appreciable recovery rate of more than 44%. The RO membrane-treated water was then incorporated in the cooling tower and a 16% reduction in freshwater makeup was achieved. Reduction of microbial growth rate as well as corrosion and scaling in the cooling tower was observed due to the reuse of treated water. This is to confirm here that brackish water RO membranes can act as a strong contender for reject water reclamation and effective utilization.

A pilot study on recycling cooling tower blowdown water through ultrafiltration and reverse osmosis

A pilot study on recycling cooling tower blowdown water through ultrafiltration and reverse osmosis

Performance evaluation of resin wafer electrodeionization for cooling tower blowdown water reclamation

The complicated nexus between water resource and energy consumption poses the problems of water scarcity, safety, affordability and carbon emissions. In the industrial and commercial buildings, the cooling tower is an inevitable system and has been considered to contribute water-energy consumption. Therefore, the high energy efficiency of water recovery technology should be practically developed to minimize the freshwater usage with lower energy consumption. In this study, a robust ion-exchange resin-wafer electrodeionization (RW-EDI) technology was used to demonstrate the desalination of cooling tower blowdown wastewater. Immobilizing the conventional ion-exchange resin into porous material between compartment can enhance ion transportation and significantly reduce the service labor for assembling and maintenance. The removal efficiency for blowdown water reclamation using RW-EDI was evaluated along with energy consumption, productivity, and current efficiency by investigating the key operating parameters including applied voltage and superficial velocity. The experimental design was based on the response surface methodology to statistically elucidate the optimal conditions. Results show that the energy consumption was 0.28 kWh m− 3 and productivity 23.4 L h− 1 m− 2 with around 90% removal of hardness to meet the standard of make-up water for blowdown water reclamation.

Advanced oxidation processes for removal of organics from cooling tower blowdown: Efficiencies and evaluation of chlorinated species

One of the major challenges in reusing cooling tower blowdown water (CTBD) utilizing membrane processes is its remaining organic compounds, e.g., humic substances leading to biofouling. Besides, the possible abundance of chloride in CTBD imposes the concern of the formation of chlorinated by-products. To choose a pre-treatment process for the studied CTBD composition, various advanced oxidation processes (AOPs), including electrooxidation (EO), photocatalytic degradation (PCD), heat-activated persulfate oxidation (PS), UVC/vacuum UV (UVC/VUV), and UVC processes, were evaluated and compared based on two main targets: i) highest removal and mineralization of the organics, especially humic substances; and ii) lowest formation of chlorinated by-products including adsorbable organic halides and oxychlorides. All the processes were conducted in the natural condition of the real CTBD, while solution pH was monitored. Based on results of chemical oxygen demand, total organic carbon, dissolved organic carbon, UV254 absorbance, liquid-chromatography–organic carbon detection (LC-OCD), and fluorescence excitation-emission matrices (FEEM), it is concluded that PS leads to complete removal of organic compounds along with the lowest formation of low molecular weight organic acids and organic neutrals. FEEM and LC-OCD data also indicated that EO, PCD, and UVC/VUV processes brought about substantial removal of organic compounds and broke down the humic substances into low molecular weight building blocks and organics. Besides, EO exhibited the highest AOX and oxychlorides formation, while these were limited when using the other AOPs. Summarizing, PS, PCD, and UVC/VUV were efficient processes for the degradation and mineralization of organics without generating significant amounts of chlorinated by-products.

The effects of pretreatment on membrane distillation of cooling tower blowdown water

In the membrane processes, pretreatment of the hardness is an effective way to minimize membrane fouling, and to increase the quality of the permeate. Many pretreatment methods can be applied for hardness removal in way of individual or combined before membrane processes. In this study, effects of pretreatment, pH adjustment, caustic soda (NaOH) softening and soda ash (Na2CO3) + caustic soda softening, on desalination performance of the coal fired power plant cooling tower blowdown water (CTBD) by membrane distillation (MD) was investigated. By the MD system operated with hot feed (60°C) and cold permeate (20°C) sides of membrane, approximately 32 LMH permeate flux and more than 99.8% salt rejection were obtained in all experiments. While it was observed that the recovery rate of raw CTBD was 66.2%, recovery rate of pretreated CTBD with caustic soda was 79.4%. It was also found that pretreatment significantly reduces membrane scaling.

Towards green thermal power plants with blowdown water reuse and simultaneous biogenic nanostructures recovery from waste

In thermal power plants, the cooling tower blowdown (CTBD) water represents a substantial amount of wastewater generated, whose recyclability holds the potential of enormous water savings. However, silica in reactive and colloidal form is a major contaminant, with inefficient removals by existing treatment technologies that prevent CTBD water reuse. The present work illustrates a sustainable approach for simultaneous silica removal and biogenic silica production from CTBD water of a thermal power plant. The 3 L attached biofilm reactor, inoculated with enriched diatom consortium ‘D’ (Navicula vilaplanii and Denticula subtilis) was utilized for treatment. D consortium efficiently removed both reactive (66.76%) and colloidal silica (83.05%) below the make-up water desired limit, and gave high biomass productivity (2.21± 0.17 g m − 2d−1). Also, a reduction of 91.84% total dissolved phosphorous, 69.61% nitrate nitrogen, 48.4% chemical oxygen demand, and 15.38% total dissolved solids were achieved. On downstream processing of D consortium biomass, 52.4% frustules, 19.6% lipid, 11.9% protein, and 8.2% carbohydrates were recovered per diatom cell weight. The extracted frustules were found to be negatively charged, symmetrical pennate-shaped, robust, mesoporous structures composed of SiO2 with wide nanotechnological applications. Projection analysis of the proposed biofilm process for a 500 MW power plant illustrated 1485 million liters of water-saving along with 57 tonnes of frustules, 22 tonnes of lipid, and 13.2 tonnes of protein production annually. This diatom based biofilm technology can provide a paradigm shift in blowdown water management practices and help build a fresh ‘waste to wealth’ industrial perspective.

Treatment of cooling tower blowdown water by using adsorption-electrocatalytic oxidation: Technical performance, toxicity assessment and economic evaluation

An eco-friendly process was adopted to treat cooling tower blowdown water (CTBD) and the toxicity of correspondingly produced water/eluate was evaluated using the transcriptional effect level index (TELI) based on toxicogenomics. The objective of the work is to provide a feasible treatment loop including adsorption to remove organics and phosphorus from CTBD, electrocatalytic oxidation to improve the biodegradability of the eluate after desorption. Results showed that PANI/TiO2 was a promising adsorbent in the removal of organics and phosphorus from CTBD and exhibited a satisfied regeneration ability beyond 30 times of reuse. During the electrocatalytic oxidation process the biodegradability of desorption eluate was gradually increasing and BOD5/COD of the oxidized eluate reached 0.4 after 4.8 h of treatment, indicating that the treated wastewater could be returned to the biological treatment loop for further processing. The analysis of the quantitative toxicogenomics assay revealed that the toxicity of CTBD was mainly caused by oxidizing biocides of trichloroisocyanuric acid (TCCA), leading to a significant membrane stress response of bacteria. And the toxicity level of CTBD decreased after adsorption treatment while the desorption eluate experienced increase and then decrease during the electrocatalytic oxidation, meaning that certain oxidation duration was needed to keep the eluate safe for biological treatment. According to economic analysis, the operation cost of treatment loop was estimated at around 0.6 dollars/m3, ensuring high reuse water quality and safe eluate for further biological treatment.

Recovery of cooling tower blowdown water through reverse osmosis (RO): review of water parameters affecting membrane fouling and pretreatment schemes

Recovery of cooling tower blowdown water through reverse osmosis (RO): review of water parameters affecting membrane fouling and pretreatment schemes

Electrochemical treatment of industrial cooling tower blowdown water using magnesium-rod electrode

Cooling tower blowdown water (CTBW) was treated with simple electrocoagulation (EC) using magnesium-rod electrode. This study examined the effects of the treatment parameters (current density, electrolysis time, electrode distance, initial pH and stirring speed) on the EC ability to remove hardness ions (Ca2+, Mg2+) and dissolved silica from CTBW. Under the optimized condition, magnesium-rod electrode removed 51.80% and 93.70% respectively for total hardness and silica; with an operating cost of 0.88 US$/m3 treated CTBW. EC sludge has been characterized by SVI, SEM-EDX, XRD, and FTIR exploring the ability of sludge to settle, surface morphology, elemental composition, crystalline type, and functional groups. It can be concluded that EC using magnesium-rod electrode can be successfully applied for the treatment of CTBW to facilitate its reuse.

Membrane distillation of power plant cooling tower blowdown water

The objective of this study was to examine the recovery of the power plant cooling tower blowdown water (CTBD) by membrane distillation. The experiments were carried out using a flat plate poly vinylidene fluoride (PVDF) membrane with a pore diameter of 0.22 um by a direct contact membrane distillation unit (DCMD). The effects of operating parameters such as transmembrane temperature difference (delta-T), circulation rate and operating time on permeate flux and membrane fouling have been investigated. The results indicated that permeate flux increased with increasing delta-T and circulation rate. Whereas maximum permeate flux was determined as 47.4 L/m2.h at delta-T of 50 degree Celcius for all short term experiments, minimum permeate flux was determined as 7.7 L/m2.h at delta-T of 20 degree Celcius. While 40 degree Celcius was determined as the optimum delta-T in long term experiments. Inorganic and non-volatile substances caused fouling in the membranes.

Layered Double Hydroxide Sorbents for Removal of Selenium from Power Plant Wastewaters

Selenium is an essential trace element but is increasingly becoming a contaminant of concern in the electric power industry due to the challenges of removing solubilized selenate anions, particularly in the presence of sulfate. In this work, we evaluate granulated layered double hydroxide (LDH) materials as sorbents for selenium removal from wastewaters obtained from a natural gas power plant with the aim to elucidate the effect of competing ions on the sorption capacities for selenium removal. We first present jar test data, followed by small-scale column testing in 0.43 inch (1.1 cm) and 2 inch (5.08 cm) diameter testbed columns for the treatment of as-obtained cooling tower blowdown waters and plant wastewaters. Finally, we present field results from a pilot-scale study evaluating the LDH media for treatment of cooling tower blowdown water. We find that despite the high levels of total dissolved solids and competing sulfate ions, the selenium oxoanions and other regulated metals such as chromium and arsenic are successfully removed using LDH media without needing any pre-treatment or pH adjustment of the wastewater.

Removal of scale forming species from cooling tower blowdown water by electrocoagulation using different electrodes

This work investigates the effect of electrocoagulation (EC) using Al, Fe, and Zn electrodes for removing hardness ions and dissolved silica from cooling tower blowdown (CTB) water. The real samples were collected from urea fertilizer factory (Helwan Fertilizer Company), Cairo, Egypt. The effect of operational parameters, such as current density, electrolysis time, inter-electrode distance and stirring rate were studied and evaluated for the maximum efficiency. At the optimum operational conditions, Al-electrode removed the scale forming species from CTB water more efficiently than Zn and Fe electrodes. Al, Fe, and Zn electrodes removed 55.36% and 99.54%, 36.99% and 98.93% as well as 38.63% and 95.62% for the total hardness and silica ions, respectively. In order to rationalize the removal mechanism, the EC generated sludge was characterized by SEM-EDX, XRD, and FTIR. The present investigation inferred that Al-EC generates amorphous nature crystalline and other anode materials (Fe and Zn) forms definite crystalline particles. EDX showed the presence of Ca2+, Mg2+, and silica ions in the sludge which proved the removal of these scale species from CTB water. As a conclusion, this study revealed that EC process using Al-electrode is a promising technology for the removal of scale forming species from CTB water.

Membrane distillation of industrial cooling tower blowdown water

The potential of membrane distillation for desalination of cooling tower blowdown water (CTBD) is investigated. Technical feasibility is tested on laboratory and pilot scale using real cooling tower blowdown water from Dow Benelux in Terneuzen (Netherlands). Two types of membranes, polytetrafluorethylene and polyethylene showed good performance regarding distillate quality and fouling behavior. Concentrating CTBD by a factor 4.5 while maintaining a flux of around 2l/m2*h was possible with a water recovery of 78% available for reuse. Higher concentration factors lead to severe decrease in flux which was caused by scaling. Membrane distillation could use the thermal energy that would otherwise be discharged of in a cooling tower and function as a heat exchanger. This reduces the need for cooling capacity and could lead to a total reduction of 37% water intake for make-up water, as well as reduced energy and chemicals demands and greenhouse gas emissions.

Recovery of cooling tower blowdown water for reuse: The investigation of different types of pretreatment prior nanofiltration and reverse osmosis

The suitability of two different pretreatment methods, i.e., coagulation-filtration and ultrafiltration (UF), and two final membrane treatment technologies, namely nanofiltration (NF) and reverse osmosis (RO), for desalination of a cooling tower blowdown (CTBD) was investigated. Particular attention was paid to ensuring that the best pretreatment method could enhance the permeate flux and lifespan of the NF and RO membranes and decrease the membranes' fouling characteristics. Furthermore, the difference of NF and RO performances in CTBD treatment was investigated.In order to find the most appropriate type of coagulant, coagulant dosage, pH and co-coagulant dosage, 21 jar tests were performed. The results showed that 50mg/L of Polyaluminium chloride (PACl) in the presence of 0.5ppm co-coagulant in pH of 6.5–7.5 has the best treatment performance. Silt density index (SDI), chemical oxygen demand (COD), turbidity, electrical conductivity, and membrane permeate flux tests were performed for both pretreatment and treatment stages. Both pretreatment methods produced appropriate feed for NF and RO in terms of SDI and turbidity. Using the coagulation–filtration pretreated water instead of raw water as a feed for NF and RO membranes showed about a 25 and 33 percent improvement in permeate flux after 100min in 10 and 15bar applied pressure for NF and RO, respectively.

Carbon Nanotube–Based Electrodes for Detection of Low–ppb Level Hexavalent Chromium Using Amperometry

Carbon nanotube (CNT)-based electrodes, prepared using a printable technique, were investigated for the electrochemical detection of hexavalent chromium (Cr(VI)). CNT pastes were coated onto paper substrates and commercially available screen-printed electrodes and used as amperometric sensors for Cr(VI). The CNT electrodes showed electrochemical current responses as high as 500 nA/ppb Cr(VI) and limit of detection as low as 5 ppb when a large area electrode was used. The CNT-modified, screen-printed electrodes showed good selectivity to Cr(VI) and were effective for quantifying the Cr(VI) levels in cooling tower blowdown water. A selective H2O2 reduction technique was also applied to Cr(VI) detection and integrated into amperometric detection in a flow cell. These studies show that CNT-based electrodes can be promising for field applications and real-time monitoring of low-level Cr(VI) in power plant waters.

Hexavalent Chromium Removal in Industrial Relevant Water Matrices Using Metal Oxide Photocatalysts

Photocatalysis is an attractive treatment method for removing hexavalent chromium, Cr(VI), from water. Thus far, photocatalytic reduction of Cr(VI) has been investigated mostly using TiO2 photocatalysts in acidic water solutions. Here we investigate Cr(VI) removal using zinc oxide (ZnO), tungsten trioxide (WO3), and sodium tantalate (NaTaO3), metal oxides that display good activity for other photocatalytic reactions such as water splitting, as well as the P90 form of TiO2 . The efficiency for Cr(VI) removal using these photocatalysts was investigated in synthetic neutral and alkaline water, as well as in cooling tower blowdown water. A few common industrial additives were examined and the improvement on Cr(VI) removal using NaTaO3 from high to low was: sodium sulfite > ammonium chloride > sodium formate. At neutral pH, citric acid was found to inhibit Cr(VI) reduction with NaTaO3. Sulfite alone could remove Cr(VI) by chemical reduction, but required large quantities in excess. The combination of sulfite and photocatalyst greatly improved the Cr(VI) removal. Cr(VI) removal using photocatalysts was only slightly affected by other constituents in cooling tower blowdown and had similar removal rates as those observed in pH 7 DI water. NaTaO3 was found to display the highest Cr(VI) removal rates on a photon basis at pH = 3 and in the presence of sodium sulfite, while ZnO and TiO2 showed the best performance in pH = 7 and cooling tower blowdown water. Different regeneration protocols were applied to the used photocatalysts. The alkaline treatment was more effective for removing adsorbed Cr(III) compared to nitric acid treatment, but acid treated TiO2 had better subsequent Cr(VI) reduction capabilities due to surface modifications that enhanced Cr(VI) adsorption. Both acid regenerated TiO2 and NaTaO3 demonstrated comparable Cr(VI) reduction rates with the pristine forms, indicating that these photocatalysts could be stable during regeneration and recycled for multiple uses. These results show that large scale wastewater treatment using metal oxide photocatalysts to remove Cr(VI) may be possible.

Hexavalent chromium removal using metal oxide photocatalysts

Photocatalysis is an attractive treatment method for removing hexavalent chromium (Cr(VI)) from water. Thus far, photocatalytic reduction of Cr(VI) has been investigated mostly using TiO2 photocatalysts in acidic water solutions. Here we investigate Cr(VI) removal using zinc oxide (ZnO), tungsten trioxide (WO3), and sodium tantalate (NaTaO3), metal oxides that display good activity for other photocatalytic reactions such as water splitting, as well as titanium oxide (TiO2, Evonik P90). The efficiency for Cr(VI) removal using these photocatalysts was investigated in synthetic neutral and alkaline water, as well as in cooling tower blowdown water. The effect of several additives used in water treatment processes on the Cr(VI) removal rate was also studied. For NaTaO3, citric acid was found to have a detrimental effect to Cr(VI) removal, while sodium formate, ammonium chloride, and sodium sulfite were beneficial. While sulfite alone could chemically reduce Cr(VI), sulfite in combination with a photocatalyst resulted in faster and complete removal of Cr(VI) in 10min using a SO32−/Cr(VI) ratio >35 in pH∼8 solutions. NaTaO3 was found to display the highest Cr(VI) removal rates on a photon basis at pH 3 and in the presence of sodium sulfite, while ZnO and TiO2 showed the best performance in pH 7 and cooling tower blowdown water.

Experimental evaluation on concentrating cooling tower blowdown water by direct contact membrane distillation

Concentration of simulated cooling tower blowdown water (CTBD) by the desalination process of direct contact membrane distillation (DCMD) has been evaluated. A bench-scale DCMD setup was used to test the desalination performance. Both silica-free and silica-containing simulated CTBD water were prepared and concentrated. The concentration process using DCMD produced a permeate flux of about 30L/m2·h and a salt rejection of more than 99.95% under feed side temperature of about 60°C. Membrane scaling was examined for the simulated feeds. It was exhibited that insoluble calcium carbonate scale formed on membrane under concentration factor of about 3.7–4.0 for silica-free simulated CTBD water. Silica, calcium carbonate and sulfate scaling precipitated together under concentration factor of about 3.2–5.0 for silica-containing simulated CTBD water. The scales resulted in the drop of both permeate flux and salt rejection, while the performance was recovered after membrane cleaning. The addition of antiscalant enhanced the concentration factor to about 8.0 and the corresponding water recovery to about 87%. The experimental results indicated that MD is a potential feasible technology for the water recovery of CTBD water.