Greywater reuse as a key enabler for improving urban wastewater management

Electrochemical oxidation of surfactants as an essential step to enable greywater reuse

The practical application of electrochemical oxidation technology for the removal of surfactants from greywater was evaluated using sodium dodecyl sulfate (SDS) as a model surfactant. Careful selection of electrocatalysts and optimization of operational parameters demonstrated effective SDS removal in treating a complex greywater matrix with energy consumption below 1 kWh g-1 COD (Chemical Oxygen Demand), paving the way for a more sustainable approach to achieving surfactant removal in greywater treatment when aiming for decentralized water reuse. Chromatographic techniques identified carboxylic acids as key byproducts prior to complete mineralization. These innovative approaches represent a novel pathway for harnessing electrochemical technologies within decentralized compact devices, offering a promising avenue for further advancements in this field.

Occurrence and fate of CECs (OMPs, ARGs and pathogens) during decentralised treatment of black water and grey water

Decentralised wastewater treatment is becoming a suitable strategy to reduce cost and environmental impact. In this research, the performance of two technologies treating black water (BW) and grey water (GW) fractions of urban sewage is carried out in a decentralised treatment of the wastewater produced in three office buildings. An Anaerobic Membrane Bioreactor (AnMBR) treating BW and a Hybrid preanoxic Membrane Bioreactor (H-MBR) containing small plastic carrier elements, treating GW were operated at pilot scale. Their potential on reducing the release of contaminants of emerging concern (CECs) such as Organic Micropollutants (OMPs), Antibiotic Resistance Genes (ARGs) and pathogens was studied. After 226 d of operation, a stable operation was achieved in both systems: the AnMBR removed 92.4 ± 2.5 % of influent COD, and H-MBR removed 89.7 ± 3.5 %. Regarding OMPs, the profile of compounds differed between BW and GW, being BW the matrix with more compounds detected at higher concentrations (up to μg L-1). For example, in the case of ibuprofen the concentrations in BW were 23.63 ± 3.97 μg L-1, 3 orders of magnitude higher than those detected in GW. The most abundant ARGs were sulfonamide resistant genes (sul1) and integron class 1 (intl1) in both BW and GW. Pathogenic bacteria counts were reduced between 1 and 3 log units in the AnMBR. Bacterial loads in GW were much lower than in BW, being no bacterial re-growth observed for the GW effluents after treatment in the H-MBR. None of the selected enteric viruses was detected in GW treatment line.

Use of ornamental plants in floating treatment wetlands for greywater treatment in urban areas

Floating treatment wetlands are considered a promising and low-cost technology for the treatment of polluted water and wastewater. However, their functionality and efficiency in different types of wastewater are not fully understood. In this study, several ornamental plant species (monocultures: Canna sp., Iris sp., polyculture: Iris orientalis, Cyperus sp., Acorus gramineus) were tested in two different types of floating mats, including a media supported floating mat (MSFM) or a simple plastic grid, and evaluated for optimal removal of the studied pollutants. The results regarding pollutant removal revealed that planted systems grown in MSFM achieved significantly higher removal rates (up to 90 %) compared to the plastic grid (up to 80 %). Statistically significant higher removal rates were obtained for the planted systems compared to the unplanted systems either grown in MSFM (for turbidity (planted: 82-90 %; unplanted: 44 %), COD (planted: 74-84 %; unplanted: 32 %) and BOD5 (planted: 76-85 %; unplanted: 51 %), respectively) or grown in the plastic grid (for turbidity (planted: 64-78 %; unplanted: 44 %) and COD (planted: 43-75 %; unplanted: 32 %), respectively). During the experimental period (7 months), all plants managed to survive and withstand the weather variations. The plants in polyculture followed by Iris sp. plants in plastic grid floating mats were better adapted, as indicated by maximum quantum efficiency of PSII values and chlorophyll content index, while all the plants were considered well adapted in the MSFM. Overall, the implementation of floating treatment wetlands with ornamental vegetation for greywater treatment in urban areas seems to be a sustainable and efficient approach.

Adsorption of common greywater pollutants and nutrients by various biochars as potential amendments for nature-based systems: Laboratory tests and molecular dynamics

Spruce wood and Typha (wetland plant) derived biochars pyrolyzed at 350 °C and 600 °C were tested for their sorption affinity for organic pollutants (diclofenac, methylparaben, benzotriazole and sodium 1-decanesulfonate) and nutrients (nitrate, ammonium, phosphate and boron) commonly found in greywater. Batch and column studies combined with molecular dynamics modelling determined the sorption capacity, kinetics, and described the underlying mechanisms. The spruce biochar (600 °C) exhibited the highest sorption capacity mainly for the tested organics. The dynamic test performed for spruce biochar (600 °C) showed that the magnitude of desorption was low, and the desorbed amount ranged between 3 and 11 %. Molecular dynamics modelling (a computational tool for elucidating molecular-level interactions) indicated that the increased sorption of nitrate and boron on spruce biochar (600 °C) could be attributed to hydrophobic interactions. The molecular dynamics shows that predominant adsorption of organic pollutants was governed by π-π stacking, with a minor role of hydrogen-bonding on the biochar surface. In summary, higher pyrolysis temperature biochar yielded greater adsorption capacity greywater borne contaminants and the reaction temperature (10-34 °C) and presence of anionic surfactant had a limited effect on the adsorption of organic pollutants, suggesting efficacious application of biochar in general for greywater treatment in nature-based systems.

Production of polyhydroxyalkanoates using sewage and cheese whey

Recently, polyhydroxyalkanoates (PHAs) have been produced using raw sewage in our laboratory; however, the production concentrations are low. Therefore, this study aimed to enhance PHA production by applying different strategies. PHA production was higher in sewage-containing medium than in mineral salt medium and was enhanced 22-fold after glucose supplementation. A relatively high degree of glucose consumption (83.6 ± 1.59 %) was also achieved. Bacteria incubated with cheese whey diluted with sewage showed higher PHA production than bacteria incubated with cheese whey diluted with distilled water did. The expression of the PHA synthase gene (phaC) was evaluated via real-time polymerase chain reaction using low- and high-carbon-containing sewage. Relatively higher phaC expression levels were observed in high-carbon-containing sewage but at lower nitrogen concentrations. The characteristics of the produced PHA were comparable to those of standard PHA. Therefore, this study revealed that the bacterium Bacillus sp. CYR1 can produce PHA from low- or high-carbon-containing wastewater.

Use of zero-valent iron-modified sand filters for greywater treatment: performance evaluation and modelling using response surface methodology

The conventional sand filter when used alone for on-site treatment of greywater fails to meet different reuse standards, and hence there is a need to improve the potential of sand filters to remove different contaminants from greywater. Performance of zero-valent iron-modified (ZVI) sand filters is investigated in the present study for the treatment of real greywater. The experiments were conducted using three filters: an unmodified filter (SF) and two iron-modified filters, MSF-2 (with 2 kg of ZVI) and MSF-4 (with 4 kg of ZVI). The study evaluated the performance of these filters under different conditions: daily feed volumes of 10 L (72 L/m2/day), 20 L (144 L/m2/day), and 30 L (217 L/m2/day), as well as pause periods of 12, 24, and 36 h. The results showed that the ZVI-modified filters outperformed the unmodified filter significantly. Specifically, MSF-4 showed higher pollutant removal compared to MSF-2. The filter MSF-4 achieved 58% COD removal, 59% BOD removal, 56% NH4-N removal, 82% PO4-P removal, and a significant 1.96 log reduction in fecal coliforms. To optimize the filter operation, three key parameters, amount of ZVI, feed volume, and pause period were considered. The Box-Behnken design (BBD) with response surface methodology was employed to achieve optimization. The results of the optimization study indicated that the optimal conditions for the filters were 2.67 kg of ZVI quantity, a feed volume of 30 L (217 L/m2/day), and a pause period of 32.1 h.