Impact of electrochemically generated iron on the performance of an anaerobic wastewater treatment process.

Anaerobic treatment of domestic wastewater has the advantages of lower biomass yield, lower energy demand and higher energy recover over the conventional aerobic treatment process. However, the anaerobic process has the inherent issues of excessive phosphate and sulfide in effluent and superfluous H2S and CO2 in biogas. An electrochemical method allowing for in-situ generation of Fe2+ in the anode and hydroxide ion (OH-) and H2 in the cathode was proposed to overcome the challenges simultaneously. The effect of electrochemically generated iron (e­iron) on the performance of anaerobic wastewater treatment process was explored with four different dosages in this work. The results showed that compared to control, the experimental system displayed an increase of 13.4-28.4 % in COD removal efficiency, 12.0-21.3 % in CH4 production rate, 79.8-98.5 % in dissolved sulfide reduction, 26.0-96.0 % in phosphate removal efficiency, depending on the e­iron dosage between 40 and 200 mg Fe/L. Dosing of the e­iron significantly upgraded the quality of produced biogas, showing a much lower CO2 and H2S contents in biogas in experimental reactor than that in control reactor. The results thus demonstrated that e­iron can significantly improve the performance of anaerobic wastewater treatment process, bringing multiple benefits with the increase of its dosage regarding effluent and biogas quality.

Nitrification potential of daily-watered biofiltration designs for high ammonium wastewater treatment.

The vegetated biofiltration systems (VBS), also known as bioretentions or rain gardens, are well-established technology for treatment of urban stormwater and recently greywater, offering multiple benefits to urban environments. However, the impact of high ammonium strength wastewater (60 mg/L) on the nitrification process in these systems is not well understood. Hence, a laboratory-based column study was conducted to uncover dominant nitrification mechanisms, based on the learnings from similar onsite wastewater treatment systems. The experimental columns tested the effect of contact time (filter media depth, 150 mm, 300 mm and 700 mm), media oxygenation (active and passive) and alkalinity/pH (marble chips 5 % weight), as well as optimal operational conditions (inflow loading, concentrations, and dissolved oxygen (DO)). All nitrogen species (NH4+, NO3-, NO2-), chemical oxygen demand (COD) and physical parameters (DO, pH, electrical conductivity) were monitored across seven events over thirteen weeks. The results show that dosing with 30 and 60 mg/L of NH4+ resulted in 700 mm sand column depth to perform almost complete nitrification of NH4+ to NO3- (< 90 %), while 300 mm designs achieved partial nitrification of NH4+ to NO2-, likely due to limited contact time and inefficient nitrite oxidizing bacteria activity. Nitrification potential of all designs further supported that appropriate aerobic contact time is necessary for effective nitrification. Inflow concentration of NH4+ and DO did not significantly impact nitrification performance, while reducing daily volume loading reduced NO3- and NO2- leaching. Active and passive aeration and alkalinity buffering did not positively affect ammonium removal. While there is a potential to apply both nitrification-denitrification and anammox processes to future VBS design, further understanding of aeration and alkalinity on microbially driven nitrification processes is needed.

Electrochemical iron production to enhance anaerobic membrane treatment of wastewater.

Although iron salts such as iron(III) chloride (FeCl3) have widespread application in wastewater treatment, safety concerns limit their use, due to the corrosive nature of concentrated solutions. This study demonstrates that local, electrochemical generation of iron is a viable alternative to the use of iron salts. Three laboratory systems with anaerobic membrane processes were set up to treat real wastewater; two systems used the production of either in-situ or ex-situ electrochemical iron (as Fe2+ and Fe2+(Fe3+)2O4, respectively), while the other system served as a control. These systems were operated for over one year to assess the impact of electrochemically produced iron on system performance. The results showed that dosing of electrochemical iron significantly reduced sulfide concentration in effluent and hydrogen sulfide content in biogas, and mitigated organics-based membrane fouling, all of which are critical issues inherently related to sustainability of anaerobic wastewater treatment. The electrochemical iron strategy can generate multiple benefits for wastewater management including increased removal efficiencies for total and volatile suspended solids, chemical oxygen demand and phosphorus. The rate of methane production also increased with electrochemically produced iron. Economic analysis revealed the viability of electrochemical iron with total cost reduced by one quarter to a third compared with using FeCl3. These benefits indicate that electrochemical iron dosing can greatly enhance the overall operation and performance of anaerobic membrane processes, and this particularly facilitates wastewater management in a decentralized scenario.

Community values on governing urban water nature-based solutions in Sydney, Australia.

Since the needs and expectations of communities towards their urban environments often vary, landscape management strategies can often be prone to fail in the absence of social considerations. It is therefore incumbent on policy-makers to investigate and attempt to reconcile diverse community perceptions toward the natural and built environment for more equitable governance. This is of particular interest when planning and managing nature-based solutions (NBS) for river protection. We considered this challenge in understanding human values, perceptions and behaviour in a multilayered ecosystem that includes waterways, NBS, green open spaces, and a built environment. This paper analyses perceptions and behaviour around a public urban park next to the Georges River in Sydney Australia, utilizing a proxy-based approach and a mixed-method comprising community surveys and behavioural mapping. The results showed that while users perceive the significance of the urban river environment differently, naturalistic (ecological), humanistic (recreational) and utilitarian (well-being) values are dominant. Urban river catchments are highly valued for recreational purposes, with a strong perception of potential flooding hazards. Through exploring the literature, we recognized that the dominancy of leisure-related values around urban river catchments can be generalized to similar cases worldwide. While NBS, as an urban stormwater management solution, address some user values (e.g., naturalistic) around urban river catchments, they may lack further delivery of humanistic and utilitarian values due to the poor integration with recreational and cultural spaces. It was also the case around the Georges River, where low prominence of cultural features was observed. We concluded that NBS development around Georges River and other urban river catchments should incorporate socio-cultural considerations and community values, in particular the ones related to leisure. The gaps between users' beliefs and behaviour do not greatly challenge governance, provided that the decision-makers utilise these gaps for optimising management actions.

Effect of filling ratio and backwash on performance of a continuous-flow SPD reactor packed with PCL as carbon source.

In this study, three up-flow fixed-bed bioreactors, named as A, B, and C, packed with polycaprolactone (PCL) under different filling ratios (31%, 62%, and 93%, respectively), were investigated over a long period (96 days). During the stable period, the mean effluent NO 3 - - N concentrations in reactors A, B, and C were 1.35 ± 0.50, 1.07 ± 0.41, and 1.03 ± 0.27 mg/L, respectively, which showed the removal of NO 3 - - N was not closely related to filling ratio (p > 0.05, one-way ANOVA). However, it was found that biomass in reactor A was 2.13 and 5.55 times in B and C, respectively. Excessively thick biofilm refrained the enzymatic hydrolysis of PCL and biofilm's specific denitrification rate (SDNR). Backwash stimulated organic matter release and enabled biofilm to restore its denitrification activity. The maximum cycle of backwash was 6 days for the lowest filling ratio reactor. Additionally, the utilization rates for denitrification were 83.3%, 86.4%, and 60.5% in reactors A, B, and C, respectively, which was higher after backwash than before backwash. PRACTITIONER POINTS: Excessively thick biofilm refrained the enzymatic hydrolysis of PCL. Backwash stimulated organic matter release and enabled biofilm to restore its denitrification activity. The maximum cycle of backwash was 6 days for the lowest filling ratio reactor. A higher utilization rate of PCL for denitrification was observed after backwash.

The effect of intermittent drying and wetting stormwater cycles on the nutrient removal performances of two vegetated biofiltration designs.

Vegetated biofiltration systems (biofilters) are now a well-established technology for treatment of urban stormwater, typically showing high nutrient uptake. However, the impact of high temporal variability of rainfall events (further exacerbated by climate change) on nitrogen and phosphorus removal processes, within different biofiltration designs, is still unknown. Hence, a laboratory-based study was conducted to uncover mechanisms behind nutrient removal in biofilters across different drying and wetting regimes. Two sets of experimental columns were based on (1) the standard biofiltration design (unsaturated zone only), and (2) combination of unsaturated and saturated (submerged) zone (SZ) with additional carbon source. Columns were watered with synthetic stormwater according to three drying and wetting schemes, exploring 1, 2, 3, 4 and 7-week drying. Hydraulic performance, soil moisture and pollutant removal were monitored. The results show that hydraulic conductivity of SZ design experiences less change over time compared to standard design, due to slower media drying, crack formation and lower plant die-off. Varied drying lengths challenged both designs differently, with 2-week drying resulting in significant drop of performance across most pollutants in standard design (except ammonia), while SZ design was able to retain high performance for up to four weeks of drying, sustaining microbial and plant uptake. Increased oxygenation of SZ columns during short-term drying was beneficial for ammonia and phosphorus removal. While SZ design showed better performance and quicker recovery for nitrogen removal, in regions with inter-rain event shorter than two weeks, the standard design (no saturated zone, no carbon source) can achieve similar if not better results.

Effective treatment of greywater via green wall biofiltration and electrochemical disinfection.

Low energy and cost solutions are needed to combat raising water needs in urbanised areas and produce high quality recycled water. In this study, we investigated key processes that drive a unique greywater treatment train consisting of a passive green wall biofiltration system followed by disinfection using a Boron-doped diamond (BDD) electrode with a solid polymer electrolyte (SPE). In both systems, the treatment was performed without any additional chemicals and pollutants of concern were monitored for process evaluation. The green wall system removed over 90% of turbidity, apparent colour, chemical oxygen demand, total organic carbon, and biological oxygen demand, and 1 log of E. coli and total coliforms, mostly through biological processes. The green wall effluent met several proposed greywater reuse guidelines, except for E. coli and total coliform treatment (below 10 MPN/100 mL). Further disinfection of treated greywater (contained 28 mg/L Cl¯ and electrical conductivity (EC) of 181.3 µS/cm) by electrolysis at current density 25 mA/cm2 inactivated over 3.5 logs of both E. coli and total coliforms, in 10 - 15 min of electrolysis, resulting in recycled water with less than 2 MPN/100 mL. A synergistic effect between electrochemically-generated free chlorines and reactive oxygen species contributed to the inactivation process. Although the treated water contained diluted chloride and had low EC, estimated energy consumption was just 0.63 - 0.83 kWh/m3. This is the first study to show the effectiveness of a low energy and a low cost greywater treatment train that combines green urban infrastructure with BDD electrochemical treatment process with SPE, offering a reliable and an environmentally-friendly method for greywater reuse.

Green wall height and design optimisation for effective greywater pollution treatment and reuse.

Green walls that effectively treat greywater have the potential to become a part of the solution for the issues of water scarcity and pollution control in our cities. To develop reliable and efficient designs of such systems, the following two research questions were addressed: what would be the optimal design of a green wall for greywater treatment, and how tall should the system be to assure adequate treatment. This paper reports on (i) a long-term pollutant removal comparison study of two typical green wall configurations: pot and block designs, and (ii) a short-term profile study exploring pollutant retention at different heights of a three-level green wall, across different plant species. Removal of suspended solids (TSS), nitrogen (TN), phosphorus (TP), chemical oxygen demand (COD) and Escherichia coli was tested, as well as various physical parameters. Pot and block designs were found to exhibit similar pollutant removal performance for standard and high inflow concentrations, while the block design was more resistant to drying. However, due to its multiple practical advantages, pot designs are favoured. The greatest removal was achieved within the top green wall level for all studied pollutants, while subsequent levels facilitated further removal of TSS, COD, and TN. Interestingly, colour, pH, and EC increased after each green wall level, which must be taken into account to determine the maximum height of these systems. The optimal size of the system was found to be dependent on plant species choice. The results were used to create practical recommendations for the effective design of greywater treatment green walls.

Assessing water retention and correlation to climate conditions of five plant species in greywater treating green walls.

Green walls are becoming a popular infrastructure choice in densely built urban environments, due to their multiple benefits. However, high and vastly variable water requirements of these systems are preventing their further widespread. Only a small number of studies have investigated water needs of green walls, even though this can help to design more optimal systems with increased benefits. Additionally, the knowledge on interactions between plant uptake and climate conditions (temperature and humidity) is lacking. The aim of this study was to understand daily water requirements of five plant species (C. appressa, N. obliterata, L. muscari, M. parvifolium and O. japonicus) used in greywater treating green walls, across different seasons, temperature, and humidity conditions of temperate-oceanic climate (common in parts of Australia, US and Europe). The results showed that during summer, dominant water uptake processes were plant uptake and transpiration, resulting in three to four times higher water needs than during winter, when evaporation is a major effect. Top levels of the multi-level green wall exhibited significantly higher plant activity compared to bottom levels, showing four times greater water uptake. Temperature and humidity changes during winter caused the change in water uptake of plants, pointing to different growing and activity patterns of tested plants. During summer only N. obliterata showed temperature and humidity dependence. Annual plant water uptake and other practical recommendations are given based on the results. Even though this study focused on water requirements of greywater treating green walls, its findings can also inform traditional green wall designs.