H.H.M. Rijnaarts

Optimization of salt adsorption rate in membrane capacitive deionization.

Membrane capacitive deionization (MCDI) is a water desalination technique based on applying a cell voltage between two oppositely placed porous electrodes sandwiching a spacer channel that transports the water to be desalinated. In MCDI, ion-exchange membranes are positioned in front of each porous electrode to prevent co-ions from leaving the electrode region during ion adsorption, thereby enhancing the salt adsorption capacity. MCDI can be operated at constant cell voltage (CV), or at a constant electrical current (CC). In this paper, we present both experimental and theoretical results for desalination capacity and rate in MCDI (both in the CV- and the CC-mode) as function of adsorption/desorption time, salt feed concentration, electrical current, and cell voltage. We demonstrate how by varying each parameter individually, it is possible to systematically optimize the parameter settings of a given system to achieve the highest average salt adsorption rate and water recovery.

Time-dependent ion selectivity in capacitive charging of porous electrodes

In a combined experimental and theoretical study, we show that capacitive charging of porous electrodes in multicomponent electrolytes may lead to the phenomenon of time-dependent ion selectivity of the electrical double layers (EDLs) in the electrodes. This effect is found in experiments on capacitive deionization of water containing NaCl/CaCl(2) mixtures, when the concentration of Na(+) ions in the water is five times the Ca(2+)-ion concentration. In this experiment, after applying a voltage difference between two porous carbon electrodes, first the majority monovalent Na(+) cations are preferentially adsorbed in the EDLs, and later, they are gradually replaced by the minority, divalent Ca(2+) cations. In a process where this ion adsorption step is followed by washing the electrode with freshwater under open-circuit conditions, and subsequent release of the ions while the cell is short-circuited, a product stream is obtained which is significantly enriched in divalent ions. Repeating this process three times by taking the product concentrations of one run as the feed concentrations for the next, a final increase in the Ca(2+)/Na(+)-ratio of a factor of 300 is achieved. The phenomenon of time-dependent ion selectivity of EDLs cannot be explained by linear response theory. Therefore, a nonlinear time-dependent analysis of capacitive charging is performed for both porous and flat electrodes. Both models attribute time-dependent ion selectivity to the interplay between the transport resistance for the ions in the aqueous solution outside the EDL, and the voltage-dependent ion adsorption capacity of the EDLs. Exact analytical expressions are presented for the excess ion adsorption in planar EDLs (Gouy-Chapman theory) for mixtures containing both monovalent and divalent cations.

Electrochemical conversion of micropollutants in gray water

Electrochemical conversion of micropollutants in real gray water effluent was studied for the first time. Six compounds that are frequently found in personal care and household products, namely methylparaben, propylparaben, bisphenol A, triclosan, galaxolide, and 4- methylbenzilidene camphor (4-MBC), were analyzed in the effluent of the aerobic gray water treatment system in full operation. The effluent was used for lab-scale experiments with an electrochemical cell operated in batch mode. Three different anodes and five different cathodes have been tested. Among the anodes, Ru/Ir mixed metal oxide showed the best performance. Ag and Pt cathodes worked slightly better than Ti and mixed metal oxide cathodes. The compounds that contain a phenolic ring (parabens, bisphenol A, and triclosan) were completely transformed on this anode at a specific electric charge Q = 0.03 Ah/L. The compounds, which contain a benzene ring and multiple side methyl methyl groups (galaxolide, 4-MBC) required high energy input (Q ≤ 0.6 Ah/L) for transformation. Concentrations of adsorbable organohalogens (AOX) in the gray water effluent increased significantly upon treatment for all electrode combinations tested. Oxidation of gray water on mixed metal oxide anodes could not be recommended as a post-treatment step for gray water treatment according to the results of this study. Possible solutions to overcome disadvantages revealed within this study are proposed.

Mitigation of micropollutants for black water application in agriculture via composting of anaerobic sludge.

The excess sludge from Up-flow anaerobic sludge bed (UASB) reactor operated on source separated toilet wastewater is a potential source of nutrients and organic matter. It can be further stabilized and dried by composting and applied as a soil amendment. Presence of pathogens, heavy metals and micropollutants in the compost derived from anaerobic sludge is thus undesirable. This paper focuses on removal of micropollutants, typically present in domestic wastewater, via composting of UASB sludge with waste wood. Estrone, diclofenac, ibuprofen, metoprolol, carbamazepine, galaxolide and triclosan were spiked to a mixture of UASB sludge and waste wood. Their concentrations were monitored during 92 days of composting at controlled temperature conditions. All studied micropollutants were removed at various rates with overall removal ranging from 99.9% for ibuprofen, diclofenac and estrone to 87.8% for carbamazepine. Accumulation of methyltriclosan as by-product of triclosan degradation was observed. The prospects and limitations of the integration of a composting process into Source Separated Sanitation concepts are discussed.

Fate of pharmaceuticals in full-scale source separated sanitation system

Removal of 14 pharmaceuticals and 3 of their transformation products was studied in a full-scale source separated sanitation system with separate collection and treatment of black water and grey water. Black water is treated in an up-flow anaerobic sludge blanket (UASB) reactor followed by oxygen-limited autotrophic nitrification-denitrification in a rotating biological contactor and struvite precipitation. Grey water is treated in an aerobic activated sludge process. Concentration of 10 pharmaceuticals and 2 transformation products in black water ranged between low μg/l to low mg/l. Additionally, 5 pharmaceuticals were also present in grey water in low μg/l range. Pharmaceutical influent loads were distributed over two streams, i.e. diclofenac was present for 70% in grey water, while the other compounds were predominantly associated to black water. Removal in the UASB reactor fed with black water exceeded 70% for 9 pharmaceuticals out of the 12 detected, with only two pharmaceuticals removed by sorption to sludge. Ibuprofen and the transformation product of naproxen, desmethylnaproxen, were removed in the rotating biological contactor. In contrast, only paracetamol removal exceeded 90% in the grey water treatment system while removal of other 7 pharmaceuticals was below 40% or even negative. The efficiency of pharmaceutical removal in the source separated sanitation system was compared with removal in the conventional sewage treatment plants. Furthermore, effluent concentrations of black water and grey water treatment systems were compared with predicted no-effect concentrations to assess toxicity of the effluent. Concentrations of diclofenac, ibuprofen and oxazepam in both effluents were higher than predicted no-effect concentrations, indicating the necessity of post-treatment. Ciprofloxacin, metoprolol and propranolol were found in UASB sludge in μg/g range, while pharmaceutical concentrations in struvite did not exceed the detection limits.

Fate of personal care and household products in source separated sanitation

Removal of twelve micropollutants, namely biocides, fragrances, ultraviolet (UV)-filters and preservatives in source separated grey and black water treatment systems was studied. All compounds were present in influent grey water in μg/l range. Seven compounds were found in influent black water. Their removal in an aerobic activated sludge system treating grey water ranged from 59% for avobenzone to >99% for hexylcinnamaldehyde. High concentrations of hydrophobic micropollutants in sludge of aerobic activated sludge system indicated the importance of sorption for their removal. Six micropollutants were found in sludge of an Up-flow anaerobic sludge blanket (UASB) reactor treating black water, with four of them being present at significantly higher concentrations after addition of grey water sludge to the reactor. Hence, addition of grey water sludge to the UASB reactor is likely to increase micropollutant content in UASB sludge. This approach should not be followed when excess UASB sludge is designed to be reused as soil amendment.

Micropollutants in source separated wastewater streams and recovered resources of source separated sanitation

ABSTRACT The quality of anaerobic sludge and struvite from black water treatment system, aerobic sludge from grey water treatment system and effluents of both systems was assessed for organic micropollutant content in order to ensure safety when reusing these products. Use of anaerobic black water sludge and struvite as soil amendments is recommended based on the low micropollutant content. Aerobic grey water sludge is recommended for disposal, because of the relatively high micropollutant concentrations, exceeding those in sewage sludge. Effluents of black and grey water treatment systems require post‐treatment prior to reuse, because the measured micropollutant concentrations in the effluents are above ecotoxicological thresholds. HighlightsBlack water contains personal care products, grey water contains pharmaceuticals.High risk quotients are calculated for biocides triclosan and triclocarban.Effluent post‐treatment is required before grey and black water reuse.UASB sludge and struvite can be applied as soil amendments.Soil applications of grey water sludge should be prohibited.

The potential of osmolytes and their precursors to alleviate osmotic stress of anaerobic granular sludge.

Increasing amounts of saline (waste)water with high concentrations of organic pollutants are generated globally. In the anaerobic (waste)water treatment domain, high salt concentrations are repeatedly reported to inhibit methanogenic activity and strategies to overcome this toxicity are needed. Current research focuses on the use of potential osmolyte precursor compounds for osmotic stress alleviation in granular anaerobic sludges upon exposure to hypersalinity shocks. Glutamic acid, aspartic acid, lysine, potassium, gelatine, and tryptone were tested for their potential to alleviate osmotic stress in laboratory grown and full - scale granular sludge. The laboratory grown granular sludge was adapted to 5 (R5) and 20 (R20) g Na+/L. Full-scale granular sludge was obtained from internal circulation reactors treating tannery (waste)water with influent conductivity of 29.2 (Do) and 14.1 (Li) mS/cm. In batch experiments which focused on specific methanogenic activity (SMA), R5 granular sludge was exposed to a hypersalinity shock of 20 g Na+/L. The granular sludge of Do and Li was exposed to a hypersalinity shock of 10 g Na+/L with sodium acetate as the sole carbon source. The effects on R20 granular sludge were studied at the salinity level to which the sludge was already adapted, namely 20 g Na+/L. Dosing of glutamic acid, aspartic acid, gelatine, and tryptone resulted in increased SMA compared to only acetate fed batches. In batches with added glutamic acid, the SMA increased by 115% (Li), 35% (Do) and 9% (R20). With added aspartic acid, SMA increased by 72% (Li), 26% (Do), 12% (R5) and 7% (R20). The addition of tryptone resulted in SMA increases of 36% (R5), 17% (R20), 179% (Li), and 48% (Do), whereas added gelatine increased the SMA by 30% (R5), 14% (R20), 23% (Li), and 13% (Do). The addition of lysine, meanwhile, gave negative effects on SMA of all tested granular sludges. Potassium at sea water Na/K ratio (27.8 w/w) had a slight positive effect on SMA of Do (7.3%) and Li (10.1%), whereas at double the sea water ratio (13.9% w/w) had no pronounced positive effect. R20 granular sludge was also exposed to hyposalinity shock from 20 down to 5 g Na+/L. Glutamate and N-acetyl-β-lysine were excreted by microbial consortium in anaerobic granular sludge adapted to 20 g Na+/L upon this exposure to hyposalinity. A potential consequence when applying these results is that saline streams containing specific and hydrolysable proteins can be anaerobically treated without additional dosing of osmolytes.

Micropollutant removal from black water and grey water sludge in a UASB-GAC reactor

The effect of granular activated carbon (GAC) addition on the removal of diclofenac, ibuprofen, metoprolol, galaxolide and triclosan in a up-flow anaerobic sludge blanket (UASB) reactor was studied. Prior to the reactor studies, batch experiments indicated that addition of activated carbon to UASB sludge can decrease micropollutant concentrations in both liquid phase and sludge. In continuous experiments, two UASB reactors were operated for 260 days at an HRT of 20 days, using a mixture of source separated black water and sludge from aerobic grey water treatment as influent. GAC (5.7 g per liter of reactor volume) was added to one of the reactors on day 138. No significant difference in COD removal and biogas production between reactors with and without GAC addition was observed. In the presence of GAC, fewer micropollutants were washed out with the effluent and a lower accumulation of micropollutants in sludge and particulate organic matter occurred, which is an advantage in micropollutant emission reduction from wastewater. However, the removal of micropollutants by adding GAC to a UASB reactor would require more activated carbon compared to effluent post-treatment. Additional research is needed to estimate the effect of bioregeneration on the lifetime of activated carbon in a UASB-GAC reactor.