Calcium Phosphate Scale Research Articles

Solugen raises cash to build green chemical factories

After raising more than $350 million last year , the sustainable chemicals company Solugen has raised another $200 million to start building its next factories and expand into new markets. Solugen, one of C&EN’s 10 start-ups to watch in 2018, hopes to use a combination of enzymatic and catalysis manufacturing processes to make cheap, high-performance chemicals without fossil fuels. Solugen’s first factory has been operating in Houston, Texas, for about a year. It produces more than 10,000 metric tons per year of several different molecules from a corn sugar feedstock. The company’s first products were hydrogen peroxide and gluconic acid, which are used in water treatment to prevent calcium phosphate scaling and metal corrosion. More recently, Solugen started selling glucaric acid –made by oxidizing gluconic acid with hydrogen peroxide. Glucaric acid reduces scaling and increases the cleaning power of automatic dishwasher detergents. CEO Gaurab Chakrabarti says the latest round of

Study on the Corrosion and Scale Inhibition Mechanism of the Thiourea-Modified Polyepoxysuccinic Acid (CNS-PESA)

In this paper, thiourea-modified polyepoxysuccinic acid (CNS-PESA) was synthesized and used as a corrosion and scale inhibitor for the circulating cooling water system of the factory. Polyepoxysuccinic acid (PESA) has been widely used in industrial water treatment due to its good corrosion inhibition and scale inhibition performance. It also acts as a reliable material for dispersion of iron oxide, good biodegradation efficiency, and phosphorus-free content. The scale inhibition performance for calcium carbonate and calcium phosphate scale with corrosion inhibition performance using different inhibitor concentrations, temperatures, pH, and calcium ion concentration on scale inhibition efficiency were studied. The scanning electron microscope (SEM) analysis on the scale and corrosion of carbon steel with two methods as GB/T 18175-2000 “Measurement of inhibitors in water treatment: rotation coupon method” and electrochemical method for CNS-PESA and PESA were utilized. Compared to using CNS-PESA and PESA for calcium carbonate and calcium phosphate, the scale inhibition rates were increased by 6% and 18.7%, and the corrosion inhibition rate increased by 22.4%. The scale inhibition efficiency of CNS-PESA is best when the calcium ion concentration is less than or equal to 350 mg/L. Moreover, the thiourea-modified polyepoxysuccinic acid (CNS-PESA) was phosphorus-free corrosion and scale inhibitor and minimizes environmental pollution problems.

Surface grafting with diverse charged chemical groups mitigates calcium phosphate scaling on reverse osmosis membranes during municipal wastewater desalination

Calcium phosphate scaling on reverse osmosis (RO) membranes during the desalination of municipal wastewater remains a major problem. This study modified RO membranes by graft polymerization using hydrophilic methacrylate monomers to reduce scaling and investigated the effects of surface charge and exposed functional groups on scaling during municipal wastewater desalination. Grafting was performed using negatively charged, neutral, positively charged, and mixed charge monomers. Testing the modified membranes during RO desalination of a solution simulating treated domestic wastewater effluents from the Shafdan wastewater reclamation plant in Israel revealed improved antiscaling performance by grafted membranes compared with the pristine (unmodified) membrane. In particular, membranes grafted using neutral and mixed charge monomers showed the best antiscaling tendencies: 25.6% and 27.6% decrease in flux, respectively, compared with a 59.1% decrease using the pristine membrane. These results, together with physico-chemical characterization, suggested that calcium phosphate precipitation and scaling on the grafted RO membranes are driven mainly by electrostatic and dipole–dipole interactions between charged chemical groups exposed on the membrane surface and ionic species in the test solution; these interactions are minimized in membranes grafted with neutral or mixed charge poly (methacrylate) groups, resulting in enhanced antiscaling performance. This study provides insight into the antiscaling mechanisms of hydrophilic poly (methacrylate) chains grafted on RO membranes, and thus can potentially aid efforts to mitigate calcium phosphate scaling during RO desalination of municipal wastewater. • Diverse charged monomers grafted on RO membrane to mitigate Ca 3 (PO 4 ) 2 scaling. •Grafted membranes exhibit enhanced performance in RO wastewater desalination. •Neutral and mixed-charge grafted polymers show lowest flux decline. •Electrostatic interactions of surface functional groups with ions dominate scaling.

Foulant Identification and Performance Evaluation of Antiscalants in Increasing the Recovery of a Reverse Osmosis System Treating Anaerobic Groundwater.

The objectives of this study are to assess the performance of antiscalants in increasing the recovery (≥85%) of a reverse osmosis (RO) plant treating anaerobic groundwater (GW) in Kamerik (the Netherlands), and to identify scalants/foulant that may limit RO recovery. Five different commercially available antiscalants were compared on the basis of their manufacturer-recommended dose. Their ability to increase the recovery from 80% to a target of 85% was evaluated in pilot-scale measurements with anaerobic GW and in once-through lab-scale RO tests with synthetic (artificial) feedwater. A membrane autopsy was performed on the tail element(s) with decreased permeability. X-ray photoelectron spectroscopy (XPS) analysis indicated that calcium phosphate was the primary scalant causing permeability decline at 85% recovery and limiting RO recovery. The addition of antiscalant had no positive effect on RO operation and scaling prevention, since at 85% recovery, permeability of the last stage decreased with all five antiscalants, while no decrease in permeability was observed without the addition of antiscalant at 80% recovery. In addition, in lab-scale RO tests executed with synthetic feed water containing identical calcium and phosphate concentrations as the anaerobic GW, calcium phosphate scaling occurred both with and without antiscalant at 85% recovery, while at 80% recovery without antiscalant, calcium phosphate did not precipitate in the RO element. In brief, calcium phosphate appeared to be the main scalant limiting RO recovery, and antiscalants were unable to prevent calcium phosphate scaling or to achieve a recovery of 85% or higher.

Calcium phosphate scaling in osmotically driven membrane processes: Limiting flux behavior and its implications for scaling mitigation

Calcium phosphate scaling, a typical inorganic scaling, has been identified as a challenging issue in the operation of osmotically driven membrane processes (ODMPs) especially in pressure-retarded osmosis (PRO) mode where membrane porous substrate faces against the impaired feed solution (FS). During scaling in PRO mode, it has been observed that flux declines to a pseudo-stable level - limiting flux, after which further flux decline is negligible. However, the underlying mechanisms of limiting flux and its potential impact on practical PRO processes is poorly understood and necessitate systematic exploration. Herein, in this study, the behavior of limiting flux was examined during calcium phosphate scaling under various solution conditions and the associated mechanisms were elaborated. Experimental results show that for a given membrane and a given water source (a fixed FS composition), an increase in the concentration of the draw solution (DS) has an insignificant impact on the final limiting flux. In contrast, an increase in the concentration of dominant scaling precursor ions (i.e., Ca2+ and PO43− in this study) in the FS significantly decreases the stabilized limiting flux. Therefore, scaling mitigation via adjusting FS pH and adding chelating agent EDTA was investigated. This was demonstrated to be effective in retarding flux decline by lowering the concentration of dominant scaling precursors, leading to an increase in the stabilized limiting flux. Physical cleaning including osmotic backwash (OBW) and surface flushing after scaling was also conducted and compared. While OBW is generally more effective than surface flushing to restore the water flux, it is less effective for scaling dominated by surface crystallization compared to that by bulk crystallization. Finally, we emphasize the significance of limiting flux for optimizing practical PRO performance and we identify other knowledge gaps that should be investigated to further improve PRO performance.

Effectiveness of antiscalants in preventing calcium phosphate scaling in reverse osmosis applications

Antiscalants are well known to prevent the precipitation of carbonate and sulphate scales of calcium in reverse osmosis (RO) applications, but according to literature their inhibitory ability against calcium phosphate is not clear. The objective of this study was to investigate if antiscalants, without acid addition, can prevent calcium phosphate scaling in RO systems. Eight calcium phosphate antiscalants from different manufacturers spanning a range of concentrations were tested in batch (in glass reactors) experiments to inhibit the formation of calcium phosphate in synthetic concentrate corresponding to 85% recovery (Ca2+ = 765 mg/L, PO43− = 13–15 mg/L and pH = 7.6) of a groundwater RO in the Netherlands. Additionally, once-through lab-scale RO tests were conducted where an RO element was fed with synthetic concentrate and the performance of antiscalants was evaluated from the rate of flux-decline in the RO element. Without antiscalant addition, a substantial flux-decline was observed due to the deposition of amorphous calcium phosphate (ACP) on the RO membrane. The tested antiscalants were unable to inhibit the formation of ACP and were incapable of preventing the deposition of the formed ACP particles, since with each antiscalant, the flux of the RO element decreased at least 15% in a 3-h period. Briefly, the available antiscalants, tested in this study, did not provide acceptable inhibition of calcium phosphate scaling in RO applications.

Fouling behavior of calcium phosphate in direct contact membrane distillation

Abstract Membrane distillation is a potential technology to recover more water from the RO brine concentrate for the purpose of high water recovery and zero liquid discharge. However, since calcium phosphate scaling has been widely reported in RO applications, it could also hinder high feed water recovery in the reclamation of wastewater by membrane distillation. In this study, the calcium phosphate saturated feed was used to mimic the RO concentrate, and the fouling mechanism of calcium phosphate on the membranes in direct contact membrane distillation (DCMD) was investigated. Membrane fouling was quantified by permeate flux decline and membrane wetting monitored by variation of the permeate conductivity. Influence of concentration, stream velocity, temperature and pH on the fouling behavior of the calcium phosphate suspension were presented. It was found that both the elevating temperature and turbulence could enhance the calcium phosphate fouling under the testing conditions, due to the crystallization incurred fouling in combination with the boundary effects. Low pH would suppress membrane as expected, and adjusting the suspension’s pH to as low as 4 could effectively inhibit the membrane fouling in the studied water recovery range. It was found that the calcium phosphate fouling will result flux decline and membrane wetting due to the lowering the membrane hydrophobicity (contact angle). Furthermore, the fouling incurred by the crystallization/precipitation of calcium phosphate has more influence on permeate flux than that incurred by the settlement of the suspended calcium phosphate.

Field validation of multifunctional ion exchange process for reverse osmosis pretreatment and phosphate recovery during impaired water reuse

Conventional reverse osmosis (RO) pretreatment hardly achieves multifunctionality for simultaneous membrane scaling prevention and nutrient recovery during impaired water reuse. To address the challenge, we probed a multifunctional ion exchange pretreatment process achieving pH adjustment, calcium and organic compound removal, and phosphate recovery using real impaired surface water. Three types of ion exchangers were integrated in train including a polystyrene strong base anion exchanger (psSBA), a shallow-shell weak acid cation exchanger (SSWAC), and a hybrid anion exchanger (HAIX). The novelty is that SSWAC, which decreased aqueous pH from neutral to ∼ 5 and removed > 70 % calcium, was regenerated by recovered waste CO2 (> 80 % regeneration efficiency) to avoid strong acid regenerants and achieve CO2 utilization and sequestration. The front-positioned psSBA selectively pre-removed hydrophobic ionizable organic compound (HIOC) such as diclofenac at > 80 % removal to reduce HIOC interference on the latter-positioned HAIX. HAIX doped with ferric oxide nanoparticles (FeOnp) enabled selective phosphate removal from complex real impaired water. Over 70 % removal of phosphate and calcium by HAIX and SSWAC reduced calcium phosphate scaling risk and facilitated phosphate recovery as hydroxyapatite from spent regenerants that enriched with calcium and phosphate. We envision this study to facilitate resource recovery in water-nutrient-carbon nexus via engineered multifunctional ion exchange processes.

Impact of salt accumulation in the bioreactor on the performance of nanofiltration membrane bioreactor (NF-MBR)+Reverse osmosis (RO) process for water reclamation

The impacts of salt accumulation, through adjusting the solid retention time (SRT), in the bioreactor on the bioprocess as well as membrane performance of a high retention nanofiltration membrane bioreactor (NF-MBR) and subsequent reverse osmosis (RO) process for water reclamation are addressed in this study. The build-up of salts (i.e., Ca, Mg, PO4) is a function of SRT, hydraulic retention time (HRT) and membrane rejection. Despite the accumulation of salts, both NF-MBRs at SRT of 30 and 60 days, achieved (i) similar biodegradation efficiency; (ii) excellent organic removal (> 97%); and (iii) excellent ammonia removal (> 98%). Extending the SRT could improve the microbial bio-flocculation capability, but did not influence the microbial activity, viability, and community structure. However, more severe membrane fouling was observed in the NF-MBR with elevated salt levels, which was attributed to the greater formation of calcium phosphate scale and Ca-polysaccharides complex (i.e., irreversible fouling layer) as well as the cake-enhanced-osmotic-pressure (CEOP) effect. Although both NF-MBRs produced comparable quality of permeate, a higher RO membrane fouling rate was observed when the permeate of NF-MBR with SRT at 60 days was fed to the RO system, implying organic compositions in NF-MBR permeate may influence RO performance.

Effect of the membrane exclusion mechanism on phosphate scaling during synthetic effluent desalination

Calcium phosphate scaling is one of the main limitations in effluent desalination using membranes. This may be overcome by tailoring membranes with lower rejection of the scalant ions.In this study, we systematically examined the use of negatively and positively charged membranes, rejecting ions mainly based on Donnan exclusion, as a low-scaling alternative to dielectric-exclusion-dominated polyamide NF membranes for effluent desalination.The two charged membranes exhibited a lower calcium and especially phosphate rejection than the polyamide membrane. Consequently, the calcium phosphate supersaturation and then the propensity to scaling of the charged membranes were much lower than the polyamide membrane. This also allowed filtering at a much higher recovery ratio with the charged membranes. It was also found that, despite the fact that the charged membranes had an opposite fixed charge, their scaling behavior was similar. Apparently, although these membranes showed opposite selectivity towards scalant ions (phosphate and calcium) in single salt solutions, the rejection pattern in mixed salt solutions resulted in similar saturation indices, much lower than for polyamide membrane.The scale formed on all three membranes was identified as amorphous calcium phosphate (ACP), although its saturation index was lower than its solubility factor. This was explained by concentration polarization which increases the saturation index in the solution adjacent to the membrane surface.Tests in absence of permeate flux showed a much slower precipitation that took a few days compared with filtration conditions (few hours). In addition, under these conditions, the effect of the scaling on the membrane permeability was generally reduced and the scale contained crystalline calcium phosphate products, different from ACP.The results indicate that the ion rejection and resulting polarization next to the membrane surface plays a crucial role in scaling. Thus, tuning ion selectivity of NF membranes towards scalant ions presents a promising alternative for scaling mitigation during effluent desalination.

Calcium Phosphate Scale Formation in Power Station Condensers Fed by Cooling Towers: A Case of When Not to Use Scaling Indices

Unexpected fouling in condensers on Central Electricity Generating Board power stations operating on the river Trent in the UK in the 1970s prompted an extensive investigation of the phenomenon. Fouling was caused by deposition of calcium phosphate rich scale on the cooling water side. A fouling test rig was specially constructed to study the performance of different chemical treatments. The rig ran two tubes in parallel, one with undosed water, and the latter’s data sets from over 100 “control” tests were analyzed to determine the mechanism and rate of fouling. The trends could not be explained in terms of conventional scaling indices. Insight into the mechanism was provided by separating precipitation (loss from solution) and deposition (adhesion of some of the precipitated mass to the heated surface): scaling was found to be caused by the deposition of particulates in the recirculating cooling water, driven by the change in pH as the water went through the evaporative cooling stage. Quantitative expressions for fouling were generated from tests on 1.83 m long tubes and were found to give a reasonable prediction of the fouling behavior observed on a full sized (18.3 m long) single condenser tube on an operating condenser. The results indicated that recirculating water systems need to be approached very differently to once-through systems, and the use of scaling indices for such systems is not recommended.

The Influence of Natural and Synthetic Additives in Mitigating Calcium Phosphate Scale in Industrial Water Systems

AbstractThe inhibition of calcium phosphate (Ca/P) precipitation by natural organic polyelectrolytes, bio- and hybrid polymers, homo- and co-polymers of acrylic acid and maleic acid containing different functional groups was examined in aqueous solution. Additionally, commonly used phosphonates were also evaluated as Ca/P inhibitors. It has been found that performance of additive (polymeric and non-polymeric) as Ca/P inhibitor depends upon additive concentration, ionic charge, and molecular weight. Based on the inhibition data, the ranking in terms of decreasing effectivess is: biopolymer > hybrid polymer > natural organic polyelectrolytes. Among synthetic polymers the ranking order is: terpolymer > co-polymer > homopolymer. Results on phosphonates evaluation reveal that compared to synthetic polymers, phosphonates show poor performance as Ca/P inhibitors.

Calcium phosphate scaling during wastewater desalination on oligoamide surfaces mimicking reverse osmosis and nanofiltration membranes

Desalinated domestic wastewater is an indispensable water resource in arid regions; however, its recovery can be limited by calcium phosphate scaling and fouling of the membrane. Here we investigated calcium phosphate mineralization on oligoamide surfaces that mimics reverse osmosis (RO) and nanofiltration (NF) membrane surfaces. We used a solution that simulates desalination of secondary treated domestic wastewater effluents for calcium phosphate mineralization experiments with oligoamide-coated gold surfaces. Attenuated total reflection–Fourier transform infrared spectroscopy and energy dispersive spectrometry showed that calcium phosphate and carbonate precipitated on RO mimetic surfaces. The rate of precipitation on oligoamide sensors was monitored by a quartz crystal microbalance, showing that scaling was more intense on the RO than the NF mimetic surface and that excessive carboxyl functional groups on both surfaces promoted scaling. Filtration experiments of similar solutions with commercial membranes showed that scaling was more intense on the RO membranes than on the NF membranes, which supported the results obtained with the oligoamide model surfaces. The results of this study can be implemented in developing RO and NF membranes to prevent calcium phosphate scaling and consequently lower water-treatment costs of domestic wastewater treatment.

Investigation of Failed Coils from a Steam Boiler

This case study presents results of analysis of failed coil samples from a steam-generating boiler. Scanning electron microscope images suggest that the main cause of failure was overheating. Calcium carbonate and calcium phosphate scaling salts probably derived from the water hardness were identified from the energy-dispersive x-ray (EDX) map. The combination of iron oxide and scales was likely to have created an insulating effect resulting in overheating and eventual tube failure. Calcium carbonate and phosphate scales are easily removed by chemical and mechanical methods. However, approximately 9% of the debris consisted of calcium silicate, as identified from the EDX map. Silicate scales adhere strongly to the surface and are not easily removed by chemical and mechanical methods. From the result of this analysis, it was possible to provide the prior information required for satisfactory repair and maintenance of the failed boiler coils.

Application of poly(aspartic acid-citric acid) copolymer compound inhibitor as an effective and environmental agent against calcium phosphate in cooling water systems

Poly(aspartic acid-citric acid) copolymer (PAC) is a new product of poly(carboxylic acid) scale inhibitor. The study aims to develop a “green” water treatment agent for calcium phosphate scale. The article compares the efficiency of three polymeric antiscalants, poly(aspartic acid-citric acid) copolymer (PAC), polymaleic acid (HPMA) and a compound inhibitor (PAC-HPMA), for calcium phosphate scale prevention under varying experimental conditions. Inhibitor concentration, calcium concentration, system pH, temperature and experimental time were varied to determine their influences on inhibitor performance by the static scale inhibition method. The copolymer (PAC) was characterized by FTIR,1H NMR and 13C NMR. The compound inhibitor was applied in the actual circulating cooling water system. An atomic force microscope (AFM), X-ray powder diffraction (XRD) and a scale formation process analysis were used to explore the scale inhibition mechanism. The results showed that scale inhibition rates of PAC, HPMA and PAC-HPMA against Ca3(PO4)2were, respectively, about 23%, 41.5% and 63% when the dosage was 8 mg/L in the experiment. The compound inhibitor showed the better inhibition performance than the above two kinds of monomers. Under the actual working conditions, the inhibition rate of compound inhibitor was close to 100% and completely met the actual application requirements of scale inhibitor in circulating cooling water systems. The main inhibition mechanism was the decomposition-chelation dispersion effect. The compound inhibitor can be used as an efficient “green” scale inhibitor for calcium phosphate.

Fouling control using critical, threshold and limiting fluxes concepts for cross-flow NF of a complex matrix: Membrane BioReactor effluent

The optimization of permeate flux is a particularly interesting strategy to control fouling and, as a consequence, enhance productivity for nanofiltration (NF) processes. Critical flux, threshold flux and limiting flux theories represent significant advance in this strategy. The aim of this study was to apply these concepts to achieve fouling control during NF of a real complex matrix: hospital wastewater after Membrane BioReactor treatment (MBR permeate). At low pressure (3bar) no flux decline was observed, revealing no fouling conditions. By applying a range of transmembrane pressure and using the square-wave method, the critical flux for irreversibility (70Lh−1m−2) and the corresponding critical pressure (3.4bar) were then determined for the NF process in this complex matrix. Above these critical conditions, irreversible fouling started to occur. The threshold pressure and related flux (transition points between low and high fouling regions) were then searched by critical flux data conversion. Our results suggest, even if an exact value for the threshold pressure could not be determined, that it could be located in the range 3.4–10bar. Operating in this pressure range should lead to acceptable fouling rate and flux decline.During filtrations conducted above the critical flux in the MBR effluent, two stable fluxes behaviours were observed indicating that different fouling stages occur: pseudo stable flux was 67Lh−1m−2 at 5bar, whereas 33Lh−1m−2 at 10–35bar. It can be then confirmed that a limiting flux occurred in this system, the value of which 33Lh−1m−2 is rather lower than that of the critical flux. This flux behaviour was proved to be related to a severe fouling in the pressure range 10–35bar due to a combined effect of colloidal silica and organics fouling and calcium phosphate scaling. The early fouling stage at 5bar was expected to be solely related to colloidal silica and organics accumulation. To characterise this change in fouling behaviour, a method allowing the estimation of the permeability before scaling was proposed. The combination of the permeability before scaling and critical flux has enabled a NF working diagram to be drawn from which the fouling stage for a given transmembrane pressure and corresponding permeate flux was able to be determined.

Effect of reverse solute diffusion on scaling in forward osmosis: A new control strategy by tailoring draw solution chemistry

We explored the specific role of reverse solute diffusion (RSD) on the scaling in osmotically-driven membrane processes (particularly forward osmosis (FO)). Both scaling precursors (e.g., Ca2+ and phosphate) and anti-scaling precursors (e.g., H+ and a chelating agent ethylenediamine tetraacetic acid (EDTA)) were used to investigate the effect of RSD and draw solution chemistry on calcium phosphate scaling. While draw solutions containing Ca2+ tend to promote calcium phosphate scaling, this effect was noticeable only if the specific RSD of Ca2+ (i.e., the ratio of Ca2+ flux to water flux) was greater than the original Ca2+ concentration in the feed water. The RSD of H+ and EDTA effectively suppressed scaling. For the first time, we demonstrated a new scaling control strategy for FO by the inclusion of anti-scaling functions in the draw solution chemistry. Our work has important implications for the design and operation of FO processes.

Biopolymer-induced calcium phosphate scaling in membrane-based water treatment systems: Langmuir model films studies

Biofouling and scaling on reverse osmosis (RO) or nanofiltration (NF) membranes during desalination of secondary and tertiary effluents pose an obstacle that limits the reuse of wastewater. In this study we explored the mineral scaling induced by biopolymers originated from bacterial biofilms: bovine serum albumin (BSA), fibrinogen, lysozyme and alginic acid, as well as an extracts of extracellular polymeric substances (EPS) from bio-fouled RO membranes from wastewater treatment facility. Mineralization studies were performed on Langmuir films of the biopolymers deposited at the interface of a solution simulating RO desalination of secondary-treated wastewater effluents. All studied biopolymers and EPS induced heterogeneous mineralization of mainly calcium phosphate. Using IR spectroscopy coupled with systematic quantitative analysis of the surface pressure versus molecular-area isotherms, we determined the mineralization tendencies of the biopolymers to be in the order of: fibrinogen>lysozyme>BSA>alginic acid. The biopolymers and EPS studied here were found to be accelerators of calcium-phosphate mineralization. This study demonstrates the utilization of Langmuir surface-pressure area isotherms and a model solution in quantitatively assessing the mineralization tendencies of various molecular components of EPS in context of membrane-based water treatment systems.

Acrylic Acid‐Allylpolyethoxy Carboxylate Copolymer as an Effective Inhibitor for Calcium Phosphate and Iron(III) Scales in Cooling Water Systems

A novel type of calcium phosphate and iron(III) scale inhibitor acrylic acid‐allylpolyethoxy carboxylate AA‐APELn (ALn) was synthesized. The observation shows that the adsorption of the ALn copolymer on the crystal surface caused deformation of calcium phosphate crystal morphology. Furthermore, both calcium phosphate and iron(III) inhibition increase with increasing the degree of polymerization of ALn from 5 to 15, and the dosage of ALn plays an important role on calcium phosphate and iron(III) inhibition. Inhibition mechanism is proposed that the interactions between calcium or iron ions and polyethylene glycol (PEG) are the fundamental impetus to restrain the formation of the scale in cooling water systems.

Comprehensive utilization of phosphate in a highly concentrated recirculating cooling water system using secondary-treated municipal wastewater as make-up

A comprehensive utilization process using phosphate was developed for the reuse of high hardness secondary-treated municipal wastewater to a highly concentrated recirculating cooling water system (RCWS). It showed that the soluble phosphate in the wastewater could be directly reused as a corrosion inhibitor to prevent the RCWS from severe corrosion caused by the contaminants in the wastewater. Based on the synergetic corrosion inhibition of PO43- and Zn2+, a chemical program was achieved for recirculating cooling water treatment. It contains 1-hydroxyethylidene-1,1-diphosphonic acid, polyepoxysuccinic acid, zinc sulfate heptahydrate, and a copolymer dispersant of LN-104B. In addition, LN-104B was verified to have excellent inhibition capability to calcium phosphate scale and zinc salts scale in the bench experiments. The pilot-scale experimental results showed that the simulated RCWS operated very well under the condition of high Ca2+ concentration (1,500 mg/L as CaCO3) using the chemical program and automatic pH-controlled technique. The corrosion rate and the adhesion rate of the test tubes are only 0.023 mm/a and 2.32 mcm, respectively, which perfectly meet the requirements of the international standard of ISO 16784-2006. Not only can the process cut down the operating cost of RCWS, but also can reduce the environmental risk caused by excessive emission of phosphate. Moreover, large amounts of fresh water and phosphorus resources are expected to be conserved.