Andrea R. Guastalli

NOM characterization by LC-OCD in a SWRO desalination line

Abstract The quantification and characterization of natural organic matter (NOM) in seawater reverse osmosis desalination (SWRO) is of great importance to improve our understanding of NOM role and to evaluate the performance of the different units involved in desalination facilities. In this study, we compared the effectiveness of two pre-treatment methods, operated in a pilot facility fed with Mediterranean seawater, in terms of determining NOM composition and NOM removal using liquid chromatography coupled with organic carbon detection (LC-OCD). LC-OCD was also used to assess the SWRO operation. Conventional pre-treatment using a flotation unit followed by dual-media filtration achieved 12% of dissolved organic carbon (DOC) removal. The same level of DOC removal was achieved by coupling flotation and ultrafiltration. In both pre-treatment methods, low-molecular-weight (LMW) neutrals and biopolymers were reduced by 33–40% and 18–19%, respectively. Reverse osmosis (RO) membranes acted as almost a complete...

Improvement of the analysis of the biochemical oxygen demand (BOD) of Mediterranean seawater by seeding control.

Biochemical oxygen demand (BOD) is a useful parameter for assessing the biodegradability of dissolved organic matter in water. At the same time, this parameter is used to evaluate the efficiency with which certain processes remove biodegradable natural organic matter (NOM). However, the values of BOD in seawater are very low (around 2 mgO(2)L(-1)) and the methods used for its analysis are poorly developed. The increasing attention given to seawater desalination in the Mediterranean environment, and related phenomena such as reverse osmosis membrane biofouling, have stimulated interest in seawater BOD close to the Spanish coast. In this study the BOD analysis protocol was refined by introduction of a new step in which a critical quantity of autochthonous microorganisms, measured as adenosine triphosphate, is added. For the samples analyzed, this improvement allowed us to obtain reliable and replicable BOD measurements, standardized with solutions of glucose-glutamic acid and acetate. After 7 days of analysis duration, more than 80% of ultimate BOD is achieved, which in the case of easily biodegradable compounds represents nearly a 60% of the theoretical oxygen demand. BOD(7) obtained from the Mediterranean Sea found to be 2.0±0.3 mgO(2)L(-1) but this value decreased with seawater storage time due to the rapid consumption of labile compounds. No significant differences were found between two samples points located on the Spanish coast, since their organic matter content was similar. Finally, the determination of seawater BOD without the use of inoculum may lead to an underestimation of BOD.

Disinfection of Seawater: Application of UV and Ozone

Ozone and ultraviolet technologies are proposed as potential disinfecting agents for seawater. Ozone doses were applied in the range 0.38 to 4.89 mg O3 L−1. They permit to observe a complete disinfection as well as UV doses superior to 320 J L−1. Impacts of both processes on organic matter were also studied. UV absorbances were reduced in both cases but in higher proportion using ozone (up to 50% removal). Total organic carbon was slightly reduced by UV radiation, and ozonation achieves up to 10% mineralization. Ozone reaction proceeds with biochemical oxygen demand increase. Seawater ozonation, in addition, leads to the formation of residual oxidants that show an inhibitory effect on autochthonous microorganisms.

Ozonation of Municipal Secondary Effluent; Removal of Hazardous Micropollutants and Related Changes of Organic Matter Composition

Abstract The major part of the regulated priority substances and family of compounds defined in the European Water Framework Directive and some other organic micropollutants were tracked in a municipal biotreated secondary effluent. Micropollutants detected in the effluent were subjected to different ozone doses related to different oxidation extents. Ozone confirmed its efficiency in terms of micropollutant reduction when applied to a municipal biotreated effluent. Accordingly, it achieved reductions exceeding 70% for 91% of the pollutants detected at high ozone dose. Organic matter transformation was also investigated by both controlling evolution of surrogates - including chemical oxygen demand, dissolved organic carbon, UV254 absorbance, etc. - and the fate dissolved organic fractions by means of size exclusion chromatography followed by organic carbon detection. At ozone dose lower than the initial ozone demand of the effluent, ozone first attacked the hydrophobic aromatic compounds. At ozone dose higher than 50 mg/L, ozone probably solubilized suspended particles and principally oxidized high molecular weight molecules (> 1,000 Da) to convert them into more hydrophilic compounds. Therefore, most reactions of ozone with the micropollutants take place in competition with fast reactions of ozone with the hydrophobic fraction of the dissolved organic matter.

The Effect of Surfactants on the Stability of Sodium Hypochlorite Preparations

INTRODUCTION The purpose of the present study was to assess the effect of the presence of surfactants over time on free available chlorine (FAC), pH, viscosity, and surface tension of sodium hypochlorite (NaOCl) preparations. METHODS Three preparations containing surfactant (Chlor-XTRA 6% [Vista Dental Products, Racine, WI], Hypocelle 4% Forte [Dentalife, Ringwood, Australia], and White King Lemon [Pental, Shepparton, Australia]) and 2 without, Vista 6% (Vista Dental Products) and Hypocelle 4% Forte plain (Dentalife), were tested. The solutions were stored in closed plastic bottles and protected from light at a constant 20°C for 213 days. FAC was measured using iodometric titration, whereas pH, surface tension, and viscosity were measured using a pH meter, pendant drop method, and rheometer, respectively. The influence of the type of solution and the presence of surfactant over time on FAC was compared with the aid of linear regression models. Two-way analysis of variance was used to evaluate the effect of passage of time and the type of solution on surface tension and the effect of the presence or absence of surfactant on the solutions. The Bonferroni test was used for multiple comparisons (post hoc) and to evaluate the effect of the presence of surfactant between solutions from the same manufacturer (α = 0.05). RESULTS Degradation of available chlorine was faster in the presence of surfactant when comparing solutions from the same manufacturer [Chlor-XTRA versus Vista (P < .001) and for Hypocelle 4% Forte versus Hypocelle 4% Forte plain (P = .024)]. There was a gradual decline in pH over time, but viscosity remained stable. The surface tension of all products decreased over time (P = .025, F). CONCLUSIONS The presence of surfactant hastened the degradation of FAC in all affected NaOCl solutions. The observed changes in pH and viscosity were minor, whereas their surface tension showed a significant decrease.

Influence of High Salinity on the Degradation of Humic Acid by UV254 and H2O2/UV254

Humic substances constitute an important part of persistent organic matter in natural waters. This study focuses on standard humic acid (HA) degradation by UV irradiation alone and combined with H2O2. At high concentration, chloride is known to be a radical scavenger that could affect humic acid degradation by photochemical processes. The influences of pH, NaCl presence and H2O2 concentration are discussed here. UV irradiation shows a slight HA degradation but addition of H2O2 greatly improved aromatics removal. Higher the pH and higher the H2O2 dose, more HA is degraded. In chloride ion presence, HA degradation is reduced that confirms chloride scavenging effect. Also, high ionic strength impacts on HA molecular configuration limiting its degradation.