Luc Pinoy

Evaluation of electro-coagulation-flocculation for harvesting marine and freshwater microalgae.

Although microalgae are considered as a promising feedstock for biofuels, the energy efficiency of the production process needs to be significantly improved. Due to their small size and low concentration in the culture medium, cost‐efficient harvesting of microalgae is a major challenge. In this study, the use of electro‐coagulation–flocculation (ECF) as a method for harvesting a freshwater (Chlorella vulgaris) and a marine (Phaeodactylum tricornutum) microalgal species is evaluated. ECF was shown to be more efficient using an aluminum anode than using an iron anode. Furthermore, it could be concluded that the efficiency of the ECF process can be substantially improved by reducing the initial pH and by increasing the turbulence in the microalgal suspension. Although higher current densities resulted in a more rapid flocculation of the microalgal suspension, power consumption, expressed per kg of microalgae harvested, and release of aluminum were lower when a lower current density was used. The aluminum content of the harvested microalgal biomass was less than 1% while the aluminum concentration in the process water was below 2 mg L−1. Under optimal conditions, power consumption of the ECF process was around 2 kWh kg−1 of microalgal biomass harvested for Chlorella vulgaris and ca. 0.3 kWh kg−1 for Phaeodactylum tricornutum. Compared to centrifugation, ECF is thus more energy efficient. Because of the lower power consumption of ECF in seawater, ECF is a particularly attractive method for harvesting marine microalgae. Biotechnol. Bioeng. 2011;108: 2320–2329.

Global Phosphorus Scarcity and Full-Scale P-Recovery Techniques: A Review

Phosphorus (P) is an essential element for all life on earth. However, natural P resources (phosphate rock) are depleting. The authors describe the current situation and a forecast for future phosphate production and reserves. The current depletion of phosphate reserves and the increasingly stringent discharge regulations have led to the development of various P-recovery techniques from wastewater. Existing full-scale P-recovery techniques from the liquid phase, sludge phase, and sludge ash are reviewed. Although the full-scale P-recovery techniques have been shown to be technologically feasible, the economical feasibility, legislation and national policies are the major reasons why these techniques are not yet operational worldwide.

Electrochemical degradation of surfactants by intermediates of water discharge at carbon-based electrodes

The electrochemical oxidation of anionic (sodium dodecylbenzenesulfonate) and cationic (hexadecyltrimethyl ammonium chloride) aqueous dilute surfactant solutions at a BDD (boron-doped diamond) electrode has been studied by batch electrolysis experiments and potentiodynamic measurements. In the potential region of water decomposition (E>2.3 V vs. SHE), surfactants could be deactivated and oxidised with total organic carbon (TOC) removals up to 82% by the action of intermediates of water discharge (e.g. hydroxyl radicals). Of the investigated process parameters, the initial electrolyte pH had the highest impact on surfactant oxidation. An initial pH of 10 significantly enhanced the electrochemical oxidation of both surfactants. The process was not diffusion-controlled and instantaneous current efficiencies (ICE) for TOC removal were in all cases low, varying from 5 to 12% on average. The surfactant deactivation and oxidation potential of the BDD electrode was compared with other carbon-based electrodes. Applying an equal electrode surface, the BDD electrode showed much higher surfactant removals compared to plane graphite. Graphite granules and carbon felt suffered from abrasion, leading to additional carbon loading of the surfactant solutions. Based on the current electrolysis configuration, the specific energy requirement with the BDD electrode for the electrochemical oxidation of surfactants was estimated at 10–20 kW h m−3 effective wastewater.

Phosphate Separation and Recovery from Wastewater by Novel Electrodialysis

Stimulated by the depletion of phosphate resources, phosphate recovery systems have been studied in recent years. The use of struvite reactors has proven to be an effective phosphate recovery process. However, the struvite reactor effluent still consists of an excessive amount of phosphate that cannot be recovered nor can be directly discharged. In this study, selectrodialysis (SED) was used to improve the efficiency of phosphate recovery from a struvite reactor: SED was implemented in such a way that phosphate from the effluent of an USAB (upflow anaerobic sludge blanket) reactor was transferred to the recycled effluent of a struvite reactor. Prior to the experiments, synthetic water with chloride and phosphate was used to characterize the efficiency of SED for phosphate separation. Results indicate that SED was successful in concentrating phosphate from the feed stream. The initial current efficiency reached 72%, with a satisfying (9 mmol L(-1)) phosphate concentration. In the experiments with the anaerobic effluent as the phosphate source for enrichment of the effluent of the struvite reactor, the phosphate flux was 16 mmol m(-2) h(-1). A cost evaluation shows that 1 kWh electricity can produce 60 g of phosphate by using a full scale stack, with a desalination rate of 95% on the feed wastewater. Finally, a struvite precipitation experiment shows that 93% of phosphate can be recovered. Thus, an integrated SED-struvite reactor process can be used to improve phosphate recovery from wastewater.

A Natural Driven Membrane Process for Brackish and Wastewater Treatment: Photovoltaic Powered ED and FO Hybrid System

In isolated locations, remote areas, or islands, potable water is precious because of the lack of drinking water treatment facilities and energy supply. Thus, a robust and reliable water treatment system based on natural energy is needed to reuse wastewater or to desalinate groundwater/seawater for provision of drinking water. In this work, a hybrid membrane system combining electrodialysis (ED) and forward osmosis (FO), driven by renewable energy (solar energy), denoted as EDFORD (ED-FO Renewable energy Desalination), is proposed to produce high-quality water (potable) from secondary wastewater effluent or brackish water. In this hybrid membrane system, feedwater (secondary wastewater effluent or synthetic brackish water) was drawn to the FO draw solution while the organic and inorganic substances (ions, compounds, colloids and particles) were rejected. The diluted draw solution was then pumped to the solar energy driven ED. In the ED unit, the diluted draw solution was desalted and high-quality water was produced; the concentrate was recycled to the FO unit and reused as the draw solution. Results show that the water produced from this system contains a low concentration of total organic carbon (TOC), carbonate, and cations derived from the feedwater; had a low conductivity; and meets potable water standards. The water production cost considering the investment for membranes and solar panel is 3.32 to 4.92 EUR m(-3) (for 300 days of production per year) for a small size potable water production system.

RO concentrate minimization by electrodialysis: techno-economic analysis and environmental concerns.

This paper presents a systematic techno-economical analysis and an environmental impact evaluation of a reverse osmosis (RO) concentrate treatment process using electrodialysis (ED) in view of environmental management of brine discharges. The concentrate originates from a secondary effluent treated by RO. Without any treatment, the concentrate would have to be discharged; this is compared in this study to the costs and benefits of an effective treatment method in a pilot scale ED plant. A technical analysis was done both on lab scale and pilot scale for the determination of operational and maintenance costs for the ED installation at the required conditions of process performance and safety. Subsequently, an economical analysis was done to calculate the cost of the different parts of the ED system. It was shown that an operational cost of 0.19 EUR m(-3) can be achieved, assuming that the ED concentrate is to decarbonated at pH 6.0 to prevent membrane scaling. Finally, environmental impact issues were calculated and discussed for the overall system. Results imply that if renewable energy is applied for the ED power source, CO(2) emission from membrane processes can be much less than from the conventional treatment methods.

Equilibrium Studies of Nickel(II), Copper(II), and Cobalt(II) Extraction with Aloxime 800, D2EHPA, and Cyanex Reagents

Abstract A study has been made of the extraction equilibrium of nickel(II), cobalt(II) and copper(II) from chloride solutions with 5‐dodecylsalicylaldoxime (Aloxime 800), di(2‐ethylhexyl)phosphoric acid (D2EHPA), bis (2,4,4‐trimethylpentyl)phosphinic acid (Cyanex 272) and its sulphur substituted analogs, called respectively Cyanex 302 and Cyanex 301, dissolved in hexane. The configuration of the metal complexes has been determined by the method of continuous variation. With D2EHPA, Cyanex 272 and Aloxime 800, NiL2, and CuL2 complexes were found. To obtain the octahedral coordination in the case of nickel(II), water molecules are required to occupy the axial positions. Similar results were found for cobalt, although in the case of Aloxime 800, the oxidation of cobalt(II) towards cobalt(III) was suggested. In the presence of Cyanex 301 and 302, NiL2(HL)2 species were formed, whereas for cobalt, the coordination of neutral extractant molecules was only observed with Cyanex 302. The coordination of copper(II) with Cyanex 301 and Cyanex 302 was less pronounced based on Jobs method. Furthermore, equilibrium constants and distribution coefficients were calculated for the different metal ions principally assuming that only monomeric ligands are involved.

Desalination feasibility study of an industrial NaCl stream by bipolar membrane electrodialysis.

The industrial implementation of alternative technologies in the processing of saline effluent streams is a topic of growing importance. In this technical feasibility study, the desalination of an industrial saline stream containing about 75 g L(-1) NaCl contaminated with some organic matter using bipolar membrane electrodialysis (EDBM) was investigated on lab-scale. Bipolar membranes of two different manufacturers (PCA - PolymerChemie Altmeier GmbH and FuMA-Tech GmbH) were tested and compared in terms of electrical resistance, current efficiency and purity of the produced acid and base stream. In both cases, almost complete desalination (>99%) was achieved and simultaneously HCl and NaOH were produced with a concentration between 1.5 and 2 M with a relatively good purity. The Fumasep bipolar membranes scored slightly better for electrical resistance and current efficiency. On the other hand, slightly higher current densities were achieved with PCA bipolar membranes. Simultaneously, some information was obtained on the transport behavior of the organic matter present in the saline stream. It was observed that a transport competition occurred between the organic matter and the accompanying chlorides. From this lab-scale study it was concluded that EDBM is a promising and attractive technology in the area of saline effluent reclamation and reuse.

Experimental and kinetic modelling study of DeNOx on an industrial V2O5-WO3/TiO2 catalyst

Abstract The selective catalytic reduction of nitric oxide with ammonia has been studied over an industrial V 2 O 5 -WO 3 /TiO 2 catalyst. A suitable rate equation is presented, based on mechanistic considerations, including interactions of reacting species with the active catalytic sites and rate aspects of the catalyst reoxidation. The kinetic parameters have been estimated on the basis of an extensive experimental program, whereby the process parameters, ammonia over nitric oxide ratio, oxygen level, nitric oxide level, space time and temperature, have been varied over a wide range. The proposed kinetic expression is able to predict adequately the influence of these process parameters on the DeNOx reaction.

Pellet reactor pretreatment: a feasible method to reduce scaling in bipolar membrane electrodialysis.

This study aims to evaluate the feasibility of a pellet reactor in reducing the scaling potential in electrodialysis with bipolar membranes for water containing a high concentration of calcium by adding sodium carbonate to precipitate carbonate as calcium carbonate on granular seed material. The optimized operating condition obtained at pH 11.1, and a ratio of [CO3(2-)]:[Ca(2+)]=1.2:1 enabled to obtain 90% efficiency of calcium removal from real water. The efficiency of scaling potential removal was validated by comparing the scaling level on the membrane surface of two electrodialysis batches of a washing water, with and without pretreatment. For the latter, scalants were found at both sides of the cation exchange membrane (FKB), diluate and base sides, identified as calcium and magnesium precipitates. Furthermore, there was also a severe scaling effect at the base side of the bipolar membrane (FBM). However, a different observation was found for the pretreated water. SEM and elemental analysis for both FKB and FBM membranes demonstrated less scaling on both membrane surfaces.