Boudewijn Meesschaert

Flocculation of Chlorella vulgaris induced by high pH: Role of magnesium and calcium and practical implications

Microalgae hold great potential as a feedstock for biofuels or bulk protein or treatment of wastewater or flue gas. Realising these applications will require the development of a cost-efficient harvesting technology. Here, we explore the potential of flocculation induced by high pH for harvesting Chlorella vulgaris. Our results demonstrate that flocculation can be induced by increasing medium pH to 11. Although both calcium and magnesium precipitated when pH was increased, only magnesium (≥0.15 mM) proved to be essential to induce flocculation. The costs of four different bases (sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and sodium carbonate) were calculated and evaluated and the use of lime appeared to be the most cost-efficient. Flocculation induced by high pH is therefore a potentially useful method to preconcentrate freshwater microalgal biomass during harvesting.

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.

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.

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.

Presence of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine in fermentations of Penicillium chrysogenum.

Cultures of Penicillium chrysogenum, growth with [35S]sulfate or labeled amino acids, were examined by ion-exchange chromatography for possible peptidic precursors of penicillin. A sulfur-containing compound, present in both the mycelial extracts and the culture filtrates, was eluted at the location of the synthetic lld-tripeptide δ-(l-α-aminoadipyl)-l-cysteinyl-d-valine. Since this compound was also labeled when the cultures were incubated with dl-[6-14C]α-aminoadipic acid, l-[3,3′-3H]cystine, or dl-[1-14C]valine, its identity with the synthetic lld-tripeptide can be accepted. No δ-(l-α-aminoadipyl)-l-cysteine or lll-tripeptide were detected. The implications of these findings for tripeptide and penicillin biosynthesis are discussed.

Strategic selection of an optimal sorbent mixture for in-situ remediation of heavy metal contaminated sediments: Framework and case study

Aquatic sediments contaminated with heavy metals originating from mining and metallurgical activities pose significant risk to the environment and human health. These sediments not only act as a sink for heavy metals, but can also constitute a secondary source of heavy metal contamination. A variety of sorbent materials has demonstrated the potential to immobilize heavy metals. However, the complexity of multi-element contamination makes choosing the appropriate sorbent mixture and application dosage highly challenging. In this paper, a strategic framework is designed to systematically address the development of an in-situ sediment remediation solution through Assessment, Feasibility and Performance studies. The decision making tools and the experimental procedures needed to identify optimum sorbent mixtures are detailed. Particular emphasis is given to the utilization and combination of commercially available and waste-derived sorbents to enhance the sustainability of the solution. A specific case study for a contaminated sediment site in Northern Belgium with high levels of As, Cd, Pb and Zn originating from historical non-ferrous smelting is presented. The proposed framework is utilized to achieve the required remediation targets and to meet the imposed regulations on material application in natural environments.

Stability of Steviol Glycosides in Several Food Matrices

As steviol glycosides are now allowed as a food additive in the European market, it is important to assess the stability of these steviol glycosides after they have been added to different food matrices. We analyzed and tested the stability of steviol glycosides in semiskimmed milk, soy drink, fermented milk drink, ice cream, full-fat and skimmed set yogurt, dry biscuits, and jam. The fat was removed by centrifugation from the dairy and soy drink samples. Proteins were precipitated by the addition of acetonitrile and also removed by centrifugation. Samples of jam were extracted with water. Dry biscuits were extracted with ethanol. The resulting samples were concentrated with solid-phase extraction and analyzed by high-performance liquid chromatography on a C18 stationary phase and a gradient of acetonitrile/aqueous 25 mM phosphoric acid. The accuracy was checked using a standard addition on some samples. For assessing the stability of the steviol glycosides, samples were stored in conditions relevant to each food matrix and analyzed periodically. The results indicate that steviol glycosides can be analyzed with good precision and accuracy in these food categories. The recovery was between 96 and 103%. The method was also validated by standard addition, which showed excellent agreement with the external calibration curve. No sign of decomposition of steviol glycosides was found in any of the samples.

Incorporation of double-labeled L-cystine and DL-valine in penicillin.

l-[3,3′-3H]cystine was incorporated into penicillin with retention of one tritium. This result can be explained by β-lactam formation through ring closure between C3 of cysteine and NH of valine. No radioactivity of dl-[2,3-3H]valine was incorporated into penicillin. The loss of isotope at C2 occurs during the inversion of configuration. The loss of label at C3 is discussed in terms of possible intermediates for the formation of the thiazolidine ring of penicillin.