Fate of silver nanoparticles in constructed wetlands : a microcosm study

Nano-enabled materials are produced at growing volumes which increases the likelihood of nanoparticles being released into the environment. Constructed wetlands (CWs) are likely to receive wastewater containing nanoparticles leaching from products during usage. Therefore, we investigate the retention of silver nanoparticles (Ag-NPs) in microcosms simulating CWs treating domestic wastewater. The effects of aeration and organic matter content on the Ag-NP removal efficiencies are studied in particular. CWs remove most of the Ag (80-90%) and the largest fraction of Ag is found in/on the biofilm. Detailed electron microscopy analyses suggest that Ag-NPs are transformed into Ag2S in all microcosm experiments. The good correlation between total suspended solids (TSS) and the Ag concentration measured in the effluent indicates that Ag-NPs are bound to the solids in the effluent. Aeration of the microcosms does not affect the release of Ag-NPs from the systems but increasing organic matter leads to increased amounts of Ag passing the CWs, correlating with the increased release of TSS from the CWs. These results suggest that Ag-NPs are retained with the (suspended) solids in CWs and that the removal efficiency of TSS is an important factor determining the discharge of Ag-NPs from CWs

Fate of metallic engineered nanomaterials in constructed wetlands : prospection and future research perspectives

Metallic engineered nanomaterials (ENMs) undergo various transformations in the environment which affect their fate, toxicity and bioavailability. Although constructed wetlands (CWs) are applied as treatment systems for waste streams potentially containing metallic ENMs, little is known about the fate and effects of ENMs in CWs. Hence, literature data from related fields such as activated sludge wastewater treatment and natural wetlands is used to predict the fate and effects of ENMs in CWs and to analyze the risk of nanomaterials being released from CWs into surface waters. The ENMs are likely to reach the CW (partly) transformed and the transformations will continue in the CW. The main transformation processes depend on the type of ENM and the ambient environmental conditions in the CW. In general, ENMs are expected to undergo sorption onto (suspended) organic matter and plant roots. Although the risk of ENMs being released at high concentrations from CWs is estimated low, caution is warranted because of the estimated rise in the production of these materials. As discharge of (transformed) ENMs from CWs during normal operation is predicted to be low, future research should rather focus on the effects of system malfunctions (e.g. short-circuiting). Efficient retention in the CW and increasing production volumes in the future entail increasing concentrations within the CW substrate and further research needs to address possible adverse effects caused

PERFORMANCE OF CONSTRUCTED TREATMENT WETLANDS: MODEL-BASED EVALUATION AND IMPACT OF OPERATION AND MAINTENANCE

‘Constructed wetlands’ (CWs) zijn door de mens aangelegde moerassen waarin het natuurlijke zelfreinigende vermogen van een dergelijk aquatisch ecosysteem door middel van een doordacht ontwerp en een aangepaste bedrijfsvoering geoptimaliseerd wordt. Uit veelvuldig onderzoek sinds de jaren 1970 en vooral ook uit praktijkervaring blijkt dat CWs in veel situaties voor een degelijke zuivering zorgen die evenwel afhankelijk is van factoren zoals temperatuur, organische en hydraulische belasting, ... Wat de mechanismen achter deze waarnemingen zijn, is echter nog grotendeels een vraagteken. En in zoverre bepaalde mechanismen wel opgehelderd zijn, bestaat er nog steeds onduidelijkheid over hun interacties en hun respectievelijk aandeel in de zuivering van afvalwater. Een eerste doelstelling van dit doctoraat was dan ook de ‘black box’ die CWs tot nog toe zijn doorzichtiger te maken, enerzijds door aangepaste metingen, anderzijds door middel van mechanistische dynamische modellen. Allereerst werden hoog-frequente metingen uitgevoerd als aanvulling op een bestaande dataset met wekelijkse metingen van influent en effluentconcentraties van een tweetraps pilootschaal CW. Op die manier werd een optimaal beeld bekomen van trage en snelle processen en hun respectievelijke dynamiek. Verder werd ook een nieuw model van een wortelzone CW ontwikkeld waarin acht verschillende microbiële gemeenschappen, samen met de rietplanten en een aantal fysische processen, interageren en voor zuivering van afvalwater zorgen. De respectievelijke submodellen werden opgebouwd naar analogie met bestaande actief slib modellen en anaërobe vergistingsmodellen. Kalibratie van een dergelijk uitgebreid model is een zeer complexe taak en zou veel meer gegevens vereisen dan wat realistischerwijze kan worden verkregen. Daarom werden van alle gevalideerde submodellen telkens de standaard parameterwaarden gebruikt, waarna het model werd uitgetest op twee datasets van respectievelijk een experimenteel (0,55 m2) en een pilootschaal (55 m2) CW. Met inachtneming van alle onzekerheden bleek het model toch behoorlijk goed in staat om de effluentkwaliteit te voorspellen en liet het vooral toe om de experimentele resultaten beter te verklaren en om nieuwe richtingen voor experimenteel onderzoek aan te geven. Alhoewel een degelijk ontwerp logischerwijze aan de basis ligt van een goede performantie, zijn de daaropvolgende bedrijfsvoering en onderhoud eveneens van cruciaal belang. Praktijkervaring uit Vlaanderen en het Verenigd Koninkrijk toonde evenwel aan dat CWs vaak als ‘build-and-forget’ oplossingen worden beschouwd. Op basis van experimenteel onderzoek kon evenwel duidelijk aangetoond worden dat doeltreffend onderhoud bijdraagt tot een langere levensduur van CWs

Natural pigments from microalgae grown in industrial wastewater

The aim of this study was to investigate the cultivation of Nostoc sp., Arthrospira platensis and Porphyridium purpureum in industrial wastewater to produce phycobiliproteins. Initially, light intensity and growth medium composition were optimized, indicating that light conditions influenced the phycobiliproteins production more than the medium composition. Conditions were then selected, according to biomass growth, nutrients removal and phycobiliproteins production, to cultivate these microalgae in food-industry wastewater. The three species could efficiently remove up to 98%, 94% and 100% of COD, inorganic nitrogen and PO43--P, respectively. Phycocyanin, allophycocyanin and phycoerythrin were successfully extracted from the biomass reaching concentrations up to 103, 57 and 30 mg/g dry weight, respectively. Results highlight the potential use of microalgae for industrial wastewater treatment and related high-value phycobiliproteins recovery

Towards water self-sufficiency : pilot operation of an off-grid water cycle based on rainwater harvesting and low-tech, biological greywater treatment in an inhabited demonstration house in Switzerland (KREIS-Haus)

With the aim to address water scarcity and support the sustainable use and treatment of (waste-) water, this study examines a self-sufficient, off-grid water system in the inhabited demonstration house “KREIS-Haus”. The water system is based on rainwater harvesting and greywater treatment with a low-tech treatment implementing submerged, attached biofilm growth. Treated rainwater is used as drinking water and treated greywater is used for the washing machine and irrigation of the rooftop garden. In an experimental period of 17 weeks, several water quality parameters were analyzed once per week before and after the rainwater and greywater treatment. Comparing the results to Swiss/EU regulation and literature, the treated greywater is suitable for irrigation and laundry. However, the treated rainwater did not always meet the required limit values for turbidity and TOC. The greywater treatment unit achieved removal rates of 92% for COD and 98% for turbidity, and no accumulation of substances was observed in the treated greywater. Water self- sufficiency was at 100% over the whole experimental period, and excess water pumped out of the system met the standard for discharge into a water body. While these first results indicate a promising approach to the water concept, more long-term monitoring and testing with higher occupancy is needed

The effect of primary treatment of wastewater in high rate algal pond systems: biomass and bioenergy recovery

The aim of this study was to assess the effect of primary treatment on the performance of two pilot-scale high rate algal ponds (HRAPs) treating urban wastewater, considering their treatment efficiency, biomass productivity, characteristics and biogas production potential. Results indicated that the primary treatment did not significantly affect the wastewater treatment efficiency (NH4+-N removal of 93 and 91% and COD removal of 62 and 65% in HRAP with and without primary treatment, respectively). The HRAP without primary treatment had higher biodiversity and productivity (20 vs. 15 g VSS/m2d). Biomass from both systems presented good settling capacity. Results of biochemical methane potential test showed that co-digesting microalgae and primary sludge led to higher methane yields (238–258 mL CH4/g VS) compared with microalgae mono-digestion (189–225 mL CH4/g VS). Overall, HRAPs with and without primary treatment seem to be appropriate alternatives for combining wastewater treatment and bioenergy recovery.Peer ReviewedPostprint (author's final draft