Removal of microfiber in vertical flow constructed wetlands treating greywater.

Nature-based solutions such as constructed wetlands (CW) are considered as a sustainable, green technology for greywater treatment. However, their efficiency to remove microplastics is not well-known even though greywater is considered as a significant source of microfiber pollution. In this study, the removal of fiber microplastics from greywater using a vertical flow constructed wetland (VFCW) was investigated. For the purposes of this study, an experimental wetland was constructed, planted with the flowering plant Zantedeschia aethiopica and filled with a substrate made of sand/gravel of several sizes. The system's performance was monitored for five months during which it received real laundry wastewater. Promising results were obtained showing the significant removal of microfibers from the influent (> 95 %). Moreover, the ability of the system to remove microfibers from laundry wastewater was not significantly affected from the hydraulic loading rate (HLR) applied. The average microfibers concentration decreased from 71 ± 25 microparticles/L in the influent to 1 ± 1 microparticles/L in the effluent of VFCW when an HLR of 63.7 mm/d was applied. High removal efficiencies were also observed for COD and turbidity (93 % and 94 %, respectively). Thus, the results indicate a significant improvement in the overall quality of laundry wastewater due to the use of the VFCW.

Use of green roofs for greywater treatment: Role of substrate, depth, plants, and recirculation.

This work focuses on the use of green roof as a modified shallow vertical flow constructed wetland for greywater treatment in buildings. Different design parameters such as substrate (perlite or vermiculite), substrate depth (15 cm or 25 cm), and plant species (Geranium zonale, Polygala myrtifolia or Atriplex halimus) were tested to determine optimum selection. In addition, the application of a 40% recirculation rate was applied during last month of the experiment to quantify the efficiency of pollutants removal. The experiment was conducted for a period of 12 months under typical Mediterranean climatic conditions in Lesvos island, Greece. Results showed that green roofs planted with Atriplex halimus and filled with 20 cm of vermiculite had the best COD (91%), BOD (91%), TSS (93%) and turbidity (93%) average removal efficiencies. In contrast, significant lower removals were observed when the substrate depth was decreased to 10 cm (60-75%). Green roof vegetation had significant impact on TN removal as the average TN concentration decreased from 6.5 ± 1.8 mg/L in the effluent of unplanted systems to 4.9 ± 2.7 mg/L in the effluent of green roofs planted with Atriplex halimus. The recirculation of a portion of the effluent in the influent had as a result a significant improvement of turbidity, organic matter and (especially) nitrogen removal. For example, BOD removal in green roofs planted with Atriplex halimus and filled with 20 cm of perlite increased from 76% to 92%, while TN removal in green roofs planted with the same plants and filled with 20 cm of vermiculite increased from 56% to 87%. Overall, the operation of green roofs as modified vertical unsaturated constructed wetlands seems a sustainable nature-based solution for greywater treatment and reuse in urban areas.

Effects of treated wastewater irrigation on the establishment of young grapevines.

Irrigation with treated wastewater could produce excessive accumulations within the plant and soil, negatively affecting the yield and production quality. In addition, the presence of biological and chemical contaminants could harm the agricultural environment, as well as the health of farmers and consumers. During this work, the suitability of secondary and tertiary treated wastewater for use in young grapevines was evaluated by studying the effect of the wastewater irrigation on the soil-plant system, crop yield, fruit quality and the presence of inorganic chemical contamination (salts, elements and heavy metals), organic chemical contamination (polycyclic aromatic hydrocarbons) and microbial contamination (E. coli, total coliforms). The results show that tertiary treated wastewater had positive impact on plant growth and yield while secondary treated wastewater had negative impact on fruit safety in comparison with tap water. Sodium levels in soils irrigated with treated wastewater increased at the end of the irrigation period while decreased during the wet season. The total polycyclic aromatic hydrocarbon concentrations in the soils ranged from 363 µg/kg to 374 µg/kg at the end of the experiment for all irrigation treatments applied. The use of tertiary treated wastewater was recommended for the irrigation of young grapevines as an alternative water source secured protection of environment, plant health and fruit quality.

Single house on-site grey water treatment using a submerged membrane bioreactor for toilet flushing.

Wastewater recycling has been and continues to be practiced all over the world for a variety of reasons including: increasing water availability, combating water shortages and drought, and supporting environmental and public health protection. Nowadays, one of the most interesting issues for wastewater recycling is the on-site treatment and reuse of grey water. During this study the efficiency of a compact Submerged Membrane Bioreactor (SMBR) system to treat real grey water in a single house in Crete, Greece, was examined. In the study, grey water was collected from a bathtub, shower and washing machine containing significant amounts of organic matter and pathogens. Chemical oxygen demand (COD) removal in the system was approximately 87%. Total suspended solids (TSS) were reduced from 95mgL(-1) in the influent to 8mgL(-1) in the effluent. The efficiency of the system to reduce anionic surfactants was about 80%. Fecal and total coliforms decreased significantly using the SMBR system due to rejection, by the membrane, used in the study. Overall, the SMBR treatment produces average effluent values that would satisfy international guidelines for indoor reuse applications such as toilet flushing.

Co-digestion of sewage sludge with glycerol to boost biogas production.

The feasibility of adding crude glycerol from the biodiesel industry to the anaerobic digesters treating sewage sludge in wastewater treatment plants was studied in both batch and continuous experiments at 35 degrees C. Glycerol addition can boost biogas yields, if it does not exceed a limiting 1% (v/v) concentration in the feed. Any further increase of glycerol causes a high imbalance in the anaerobic digestion process. The reactor treating the sewage sludge produced 1106+/-36 ml CH(4)/d before the addition of glycerol and 2353+/-94 ml CH(4)/d after the addition of glycerol (1% v/v in the feed). The extra glycerol-COD added to the feed did not have a negative effect on reactor performance, but seemed to increase the active biomass (volatile solids) concentration in the system. Batch kinetic experiments showed that the maximum specific utilization rate (mu(max)) and the saturation constant (K(S)) of glycerol were 0.149+/-0.015 h(-1) and 0.276+/-0.095 g/l, respectively. Comparing the estimated values with the kinetics constants for propionate reported in the literature, it can be concluded that glycerol uptake is not the rate-limiting step during the process.