Thomas Meyn

In-line coagulation prior to ceramic microfiltration for surface water treatment—minimisation of flocculation pre-treatment

Abstract In-line coagulation/flocculation with subsequent low pressure ceramic membrane filtration has emerged during the last years as a treatment alternative for surface waters with high natural organic matter (NOM) content and low turbidity. In such a hybrid process, the requirements on the flocculation step may significantly differ, if compared to treatment schemes where for example rapid filters are used instead of a membrane. Thus, process performance, expressed as DOC and colour removal, membrane fouling and residual metal concentration, was investigated in dependence on the coagulant dosage, flocculation time and shear, while all other coagulation conditions were kept constant. Minimum flocculation requirements were established. A synthetic surface water (DOC 6.8 mg C l−1, colour 55 mg Pt l−1) was treated by rapid inline coagulation with Polyaluminium chloride (PACl), at Al-dosages of 2.6 and 4.4 mg l−1 and a coagulation pH of 6, followed by inline flocculation at varying conditions (G-values: 4–3...

Field flow fractionation online with ICP-MS as novel approach for the quantification of fine particulate carbon in stream water samples and soil extracts

Reliable and efficient analytical techniques are required for quantitative size-resolved carbon determination of nanoparticles and colloids in complex sample matrices due to the key role of carbon in biological and environmental processes. Field flow fractionation (FFF) online with inductively coupled plasma mass spectrometry (ICP-MS) is a powerful technique for identification and quantification of particle bound metals, but has not been applied for quantitative determination of particulate carbon, yet, due to several challenges. Therefore, our study explores the potential of online particulate carbon detection by ICP-MS to overcome limitations of previously used UV detection or offline total organic carbon measurements. A novel organic carbon detector (OCD) was used as independent sensitive carbon detector to validate the ICP-MS results. Basic validation of organic carbon detection by offline quadrupole and sector-field ICP-MS was performed for fresh water samples using OCD as reference achieving recoveries of 107 ± 16% with Q-ICP-MS and 122 ± 22% with SF-ICP-MS. Limits of detection were 0.6 mg L−1 for Q-ICP-MS, 0.3 mg L−1 for SF-ICP-MS and 0.04 mg L−1 for OCD. The main focus was on comparison of FFF-ICP-MS and FFF-OCD for quantification of particulate carbon in fresh water samples, soil extracts as well as in bovine serum albumin (BSA) as candidate reference standard. Recoveries obtained by FFF-Q-ICP-MS with a flow-injection calibration approach were in a range from 90 to 113% for replicate analyses of fresh water samples compared to FFF-OCD and from 87 to 107% with an alternative post-channel calibration strategy.

Analysis of Membrane and Cake Layer Resistances in Coagulation: Constant Flux Dead-End Microfiltration of NOM

Fouling analysis of tank coagulation (TC)/inline coagulation (IC) followed by dead-end microfiltration (MF) treating natural organic matter (NOM) was assessed using the blocking laws and resistance-in-series models. Different process conditions were found to have no significance on the overall treatment efficiency but did contribute to aspects of membrane operation, that is, membrane fouling. Blocking laws were found to be inadequate in explaining the fouling phenomenon, but may provide insight to the intrinsic membrane resistance behavior. The resistance-in-series model showed that cake compressibility was different in each process configuration tested and may therefore assist in determining the most suitable operating conditions. Floc properties resulting from TC and IC were different, impacting the cake compressibility behavior observed, which further could explain the differences in trans membrane pressure (TMP) increase and reversibility of membrane fouling.

Fractal Dimension Analysis of Flocs in Inline Coagulation-Microfiltration of Natural Organic Matter (NOM)

2D fractal dimension analysis of inline-coagulation (IC) flocs in microfiltration of NOM using power-law relationship and box-counting was done. Different process conditions represented by two types of coagulants (PIX and PAX) at four different hydraulic gradients (G-values of 4, 31, 98, and 300 s−1) were tested. Fractal dimensions of the flocs formed under the varying process conditions were found to be different. Overall NOM removal was found to be similar for all cases; however, the membrane filtration and fouling phenomenon observed were affected by the process conditions. This study has investigated the relationships between fractal dimensions, aggregate properties, and membrane fouling behavior observed. In general, PIX resulted in higher particle concentrations and the more irregular floc shapes resulted in high irreversible fouling, lower specific cake resistance, and a more compressible cake layer. In contrast, PAX resulted in lower particle concentrations and the more regular floc shapes resulted in a more reversible fouling, higher specific cake resistance and a less compressible cake layer. The fractal dimensions properties were found to be complementary for the analysis of membrane and cake resistances and can be useful tools in membrane fouling elucidation and minimization.

Inactivation of marine heterotrophic bacteria in ballast water by an Electrochemical Advanced Oxidation Process

Seawater treatment is increasingly required due to industrial activities that use substantial volumes of seawater in their processes. The shipping industry and the associated management of a ships ballast water are currently considered a global challenge for the seas. Related to that, the suitability of an Electrochemical Advanced Oxidation Process (EAOP) with Boron Doped Diamond (BDD) electrodes has been assessed on a laboratory scale for the disinfection of seawater. This technology can produce both reactive oxygen species and chlorine species (especially in seawater) that are responsible for inactivation. The EAOP was applied in a continuous-flow regime with real seawater. Natural marine heterotrophic bacteria (MHB) were used as an indicator of disinfection efficiency. A biphasic inactivation kinetic model was fitted on experimental points, achieving 4-Log reductions at 0.019 Ah L-1. By assessing regrowth after treatment, results suggest that higher bacterial damages result from the EAOP when it is compared to chlorination. Furthermore, several issues lacking fundamental understanding were investigated such as recolonization capacity or bacterial community dynamics. It was concluded that, despite disinfection processes being effective, there is not only a possibility for regrowth after treatment but also a change on bacterial population diversity produced by the treatment. Finally, energy consumption was estimated and indicated that 0.264 kWh·m-3 are needed for 4.8-Log reductions of MHB; otherwise, with 0.035 kWh·m-3, less disinfection efficiency can be obtained (2.2-Log red). However, with a residual oxidant in the solution, total inactivation can be achieved in three days.