Comparing the performance of microbial electrochemical assisted and aerated treatment wetlands in pilot-scale: Removal of major pollutants and organic micropollutants.

The combination of treatment wetlands (TWs) with microbial electrochemical technologies (MET) is often studied in the lab to improve the performance and decrease the footprint of TWs. In this article we evaluated the long-term performance of four pilot-scale vertical sub-surface flow TWs for major pollutants' and organic micropollutants' removal from domestic wastewater. Three of them were filled with electroconductive material and operated under saturated (MET SAT), unsaturated (MET UNSAT) and unsaturated-saturated (MET HYBRID) conditions while the fourth one was a saturated intensified aerated system (AEW) filled with gravel. The MET-TWs achieved significant removals of COD (>78 %) with no clogging issues at the maximum applied OLR (249 g COD m-3 d-1) while under these loading conditions TSS removal exceeded 84 %. Among all electroactive TWs, UNSAT could remove 25 g NH4-N m-3 d-1 through nitrification when peak ammonium loading rate was applied; however this removal was significantly lower than AEW (35 g NH4-N m-3d-1). No important removal of P was observed in all systems with the exception of MET-SAT were precipitation reactions of P with iron occurred when anaerobic pretreated wastewater was used. The removal of the sum of studied organic micropollutants ranged between 70 ± 18 % (MET UNSAT) to 91 ± 4 % (AEW) and improved with feeding pulses increase. Moderate to high removal of specific microcontaminants was observed depending on the target compound, the studied system and the operational conditions. AEW and MET HYBRID systems complied with the limits set by EU for wastewater discharge to non-sensitive water bodies and for Class B water reuse. Scale-up calculations for a settlement of 500 PE showed that these systems require much less area per PE (0.51 m2 PE-1) comparing to conventional TWs while the operational cost was calculated to 0.07 € m-3 for the AEW and 0.02 € m-3 for the MET HYBRID.

Investigating upflow anaerobic sludge blanket process to treat forward osmosis effluents of concentrated municipal wastewater under psychrophilic temperature.

This work investigated the stability of the Upflow Anaerobic Sludge Blanket (UASB) reactor under psychrophilic temperatures with varying feed streams, simulating typical and concentrated sewage. In Phase I, treating municipal wastewater, chemical oxygen demand (COD) removal dropped from 77 ± 6 % to 41 ± 2 % as hydraulic retention time decreased from 24 to 12 h and organic loading rate (OLR) increased from 0.6 to 1.3 gCOD/(L∙d). In Phase II, at a similar OLR (≈1.2 gCOD/(L∙d)), the UASB treated organic-rich effluents (from 1.0 to 2.1 ± 0.1 gCOD/L) resulting from the pre-treatment of the forward osmosis (FO) process. The UASB performance improved significantly, achieving 87 ± 3 % COD removal and 63 ± 4 % methane recovery, with microbial analysis confirming methanogen growth. The COD mass balance showed up to 30 % more electrical energy recovery from sewage compared to conventional wastewater treatment plants (WWTPs), indicating that the FO-UASB combination is a promising approach to achieve energy-neutral operation in WWTPs.

Development of an integrated fixed-film activated sludge (IFAS) reactor treating landfill leachate for the biological nitrogen removal through nitritation-denitritation.

The current work investigated the performance of an Integrated Fixed-Film Activated Sludge Sequencing Batch Reactor (IFAS-SBR) for Biological Nitrogen Removal (BNR) from mature landfill leachate through the nitritation-denitritation process. During the experimental period two IFAS-SBR configurations were examined using two different biocarrier types with the same filling ratio (50%). The dissolved oxygen (DO) concentration ranged between 2 and 3 mg/L and 4-6 mg/L in the first (baseline-IFAS) and the second (S8-IFAS) setup, respectively. Baseline-IFAS operated for 542 days and demonstrated a high and stable BNR performance maintaining a removal efficiency above 90% under a Nitrogen Loading Rate (NLR) up to 0.45 kg N/m3-d, while S8-IFAS, which operated for 230 days, was characterized by a limited and unstable BNR performance being unable to operate sufficiently under an NLR higher than 0.20 kg N/m3-d. It also experienced a severe inhibition period, when the BNR process was fully deteriorated. Moreover, S8-IFAS suffered from extensive biocarrier stagnant zones and a particularly poor sludge settleability. The attached biomass cultivated in both IFAS configurations had a negligible content of nitrifying bacteria, probably attributed to the insufficient DO diffusion through the biofilm, caused by the low DO concentration in the liquid in the baseline case and the extensive stagnant zones in the S8-IFAS case. As a result of the high biocarrier filling ratio, the S8-IFAS was unstable and low. This was probably attributed to the mass transfer limitations caused by the biocarrier stagnant zones, which hinder substrate and oxygen diffusion, thus reducing the biomass activity and increasing its vulnerability to inhibitory and toxic factors. Hence, the biocarrier filling fraction is a crucial parameter for the efficient operation of the IFAS-SBR and should be carefully selected taking into consideration both the media type and the overall reactor configuration.

Short-term effect of reclaimed water irrigation on soil health, plant growth and the composition of soil microbial communities.

The scarcity of freshwater poses significant challenges to agriculture, often necessitating the use of alternative water sources such as reclaimed water. While reclaimed water offers a viable solution by providing water and nutrients to crops, its potential impacts on soil microbial communities remain a subject of investigation. In this investigation, we conducted a field experiment cultivating Maize (Zea mays) and Lavender (Lavandula angustifolia), employing irrigation with reclaimed water originating from domestic wastewater, while control samples were irrigated using freshwater. Utilizing high-throughput sequencing, we assessed the effect of reclaimed water on soil bacteria and fungi. Plant biomass exhibited a significant response to treated wastewater. Alpha diversity metrics of soil microbial communities did not reveal significant changes in soils irrigated with reclaimed water compared to control samples. Reclaimed water, however, demonstrated a selective influence on microorganisms associated with nutrient cycling. Co-occurrence network analysis unveiled that reclaimed water may alter soil microbial community structure and stability. Although our work presents overall positive outcomes, further investigation into the long-term implications of reclaimed water irrigation is warranted.

Evaluating an integrated nano zero-valent iron column system for emerging contaminants removal from different wastewater matrices - Identification of transformation products.

The presence of micropollutants in water bodies has become a growing concern due to their persistence, bioaccumulation and potential toxicological effects on aquatic life and humans. In this study, the performance of a column system consisting of zero-valent iron nanoparticles (nZVI) incorporated into a cationic resin and synthesized from green tea extract with the addition of persulfate for the elimination of selected pharmaceuticals and endocrine disruptors from wastewater is evaluated. Ibuprofen, naproxen, diclofenac and ketoprofen were the target pharmaceuticals from non-steroidal anti-inflammatory drugs group, while bisphenol A was the target endocrine disruptor. In this context, different real wastewater effluent matrices were investigated: anaerobic membrane bioreactor (AnMBR), upflow anaerobic sludge blanket reactor (UASB) after microfiltration, tertiary treated by conventional activated sludge system and saturated vertical constructed wetland followed by a sand filtration unit effluent (hybrid). The transformation products of diclofenac and bisphenol A were also identified. The experimental results indicated that the performance of the R-nFe/PS system towards the removal efficiency of the target compounds was enhanced in the order of effluents: tertiary > AnMBR ≈ hybrid > UASB. More than 70% removal was obtained for almost all target compounds when conventional tertiary effluent was used, while the maximum removal efficiency was about 50% in the case of filtered UASB. As far as we know, this is the first time that nZVI has been assessed in combination with persulfate for the removal of micropollutants in a continuous flow system receiving various types of real wastewater with different matrix characteristics.

Integrated selection of PHA-storing biomass and nitrogen removal via nitrite from sludge reject water: a mathematical model.

One of the most recent innovations to promote a circular economy during wastewater treatment is the production of biopolymers. It has recently been demonstrated that it is possible to integrate the production of biopolymers in the form of polyhydroxyalkanoates (PHA) with nitrogen removal via nitrite during the treatment of sludge reject water. In the present study, simulation of a new process for bioresource recovery was conducted by an appropriate modification of the Activated Sludge Model 3. The process consists of the integrated nitrogen removal via nitrite from sludge reject water and the selection of PHA-storing biomass by inducing a feast and famine regime under aerobic and anoxic conditions. According to the results, it is anticipated that simulation data matched very satisfactorily with the experimental data and confirmed the main experimental observation, showing that during the famine period the PHA depletion was almost complete due to the availability of nitrite as the electron acceptor. Simulation results indicate that the selection of the volumetric organic loading rate and of the relative duration of the aerobic feast/anoxic famine duration is critical in order to allow for the effective denitritation of the internally stored PHA during the famine phase.

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review.

Currently, there is growing scientific interest in the development of more economic, efficient and environmentally friendly municipal wastewater treatment technologies. Laboratory and pilot-scale surveys have revealed that the anaerobic membrane bioreactor (AnMBR) is a promising alternative for municipal wastewater treatment. Anaerobic membrane bioreactor technology combines the advantages of anaerobic processes and membrane technology. Membranes retain colloidal and suspended solids and provide complete solid-liquid separation. The slow-growing anaerobic microorganisms in the bioreactor degrade the soluble organic matter, producing biogas. The low amount of produced sludge and the production of biogas makes AnMBRs favorable over conventional biological treatment technologies. However, the AnMBR is not yet fully mature and challenging issues remain. This work focuses on fundamental aspects of AnMBRs in the treatment of municipal wastewater. The important parameters for AnMBR operation, such as pH, temperature, alkalinity, volatile fatty acids, organic loading rate, hydraulic retention time and solids retention time, are discussed. Moreover, through a comprehensive literature survey of recent applications from 2009 to 2021, the current state of AnMBR technology is assessed and its limitations are highlighted. Finally, the need for further laboratory, pilot- and full-scale research is addressed.

Inhibition of free nitrous acid and free ammonia on polyphosphate accumulating organisms: Evidence of insufficient phosphorus removal through nitritation-denitritation.

The purpose of this study is to investigate the effect of Free Nitrous Acid (FNA) and Free Ammonia (FA) on enhanced biological phosphorus removal (EBPR) and in particular on the aerobic phosphorus uptake rate (PUR). To this end, a PAO-enriched biomass was developed at a lab-scale reactor in order to fuel a series of ex-situ batch experiments to test the effect of various nitrite or ammonium concentrations on the phosphorus uptake rate at different pH values. FNA was found to be a strong inhibitor of EBPR, in agreement with other studies with PUR being inhibited by 50 % under 1.5 µg HNO2-N L-1 and 100 % at 13 µg HNO2-N L-1. FA was also found to inhibit EBPR with PUR being inhibited by 50 % under 6.4 mg NH3-N L-1. The results of this study suggest that EBPR under high nitrogen loading alongside nitritation-denitritation may not be a viable option.

Operation of a modified anaerobic baffled reactor coupled with a membrane bioreactor for the treatment of municipal wastewater in Taiwan.

A modified anaerobic baffled reactor (ABR) combined with a submerged membrane bioreactor (MBR) was applied to treat municipal wastewater. The performance of this process was examined in terms of the removal of organic matter, suspended solids, turbidity and nitrogen. The raw wastewater was fed to the 105 L ABR and then the treated effluent was driven to a 58 L MBR equipped with a submerged hollow fibre ultrafiltration membrane module. The integrated modified ABR-MBR process resulted in the complete removal of total suspended solids (TSS) and in very high chemical oxygen demand (COD) removal (93.3 ± 3.8%). Furthermore, the recycling of mixed liquor from the MBR to the modified ABR resulted in some denitrification occurring in the first compartment of the ABR, resulting in 53 ± 6% removal of nitrogen by the integrated process. The membrane flux was stable and above 20 L/m2h. Membrane examination at the nanoscale indicated the deposition of small particles on the surface of the membranes.

Surface water filtration using granular media and membranes: A review.

Significant growth of the human population is expected in the future. Hence, the pressure on the already scarce natural water resources is continuously increasing. This work is an overview of membrane and filtration methods for the removal of pollutants such as bacteria, viruses and heavy metals from surface water. Microfiltration/Ultrafiltration (MF/UF) can be highly effective in eliminating bacteria and/or act as pre-treatment before Nanofiltration/Reverse Osmosis (NF/RO) to reduce the possibility of fouling. However, MF/UF membranes are produced through relatively intensive procedures. Moreover, they can be modified with chemical additives to improve their performance. Therefore, MF/UF applicability in less developed countries can be limited. NF shows high removal capability of certain contaminants (e.g. pharmaceutically active compounds and ionic compounds). RO is necessary for desalination purposes in areas where sea water is used for drinking/sanitation. Nevertheless, NF/RO systems require pre-treatment of the influent, increased electrical supply and high level of technical expertise. Thus, they are often a highly costly addition for countries under development. Slow Sand Filtration (SSF) is a simple and easy-to-operate process for the retention of solids, microorganisms and heavy metals; land use is a limiting factor, though. Rapid Sand Filtration (RSF) is an alternative responding to the need for optimized land use. However, it requires prior and post treatment stages to prevent fouling. Especially after coating with metal-based additives, sand filtration can constitute an efficient and sustainable treatment option for developing countries. Granular activated carbon (GAC) adsorbs organic compounds that were not filtered in previous treatment stages. It can be used in conjunction with other methods (e.g. MF and SSF) to face pollution that results from potentially outdated water network (especially in less developed areas) and, hence, produce water of acceptable drinking quality. Future research can focus on the potential of GAC production from alternative sources (e.g. municipal waste). Given the high production/operation/maintenance cost of the NF/RO systems, more cost-effective but equally effective alternatives can be implemented: e.g. (electro)coagulation/flocculation followed by MF/UF, SSF before/after MF/UF, MF/UF before GAC.

A review on nitrous oxide (N2O) emissions during biological nutrient removal from municipal wastewater and sludge reject water.

Nitrous oxide (N2O) is an important pollutant which is emitted during the biological nutrient removal (BNR) processes of wastewater treatment. Since it has a greenhouse effect which is 265 times higher than carbon dioxide, even relatively small amounts can result in a significant carbon footprint. Biological nitrogen (N) removal conventionally occurs with nitrification/denitrification, yet also through advanced processes such as nitritation/denitritation and completely autotrophic N-removal. The microbial pathways leading to the N2O emission include hydroxylamine oxidation and nitrifier denitrification, both activated by ammonia oxidizing bacteria, and heterotrophic denitrification. In this work, a critical review of the existing literature on N2O emissions during BNR is presented focusing on the most contributing parameters. Various factors increasing the N2O emissions either per se or combined are identified: low dissolved oxygen, high nitrite accumulation, low chemical oxygen demand to nitrogen ratio, slow growth of denitrifying bacteria, uncontrolled pH and temperature. However, there is no common pattern in reporting the N2O generation amongst the cited studies, a fact that complicates its evaluation. When simulating N2O emissions, all microbial pathways along with the potential contribution of abiotic N2O production during wastewater treatment at different dissolved oxygen/nitrite levels should be considered. The undeniable validation of the robustness of such models calls for reliable quantification techniques which simultaneously describe dissolved and gaseous N2O dynamics. Thus, the choice of the N-removal process, the optimal selection of operational parameters and the establishment of validated dynamic models combining multiple N2O pathways are essential for studying the emissions mitigation.

Technical and environmental evaluation of an integrated scheme for the co-treatment of wastewater and domestic organic waste in small communities.

A technical and environmental evaluation of an innovative scheme for the co-treatment of domestic wastewater and domestic organic waste (DOW) was undertaken by coupling an upflow anaerobic sludge blanket (UASB), a sequencing batch reactor (SBR) and a fermentation reactor. Alternative treatment configurations were evaluated with different waste collection practices as well as various schemes for nitrogen and phosphorus removal. All treatment systems fulfilled the required quality of the treated effluent in terms of chemical oxygen demand (COD) and total suspended solids (TSS) concentrations. However, only the configurations performing the short-cut nitrification/denitrification with biological phosphorus removal met the specifications for water reuse. The environmental assessment included the analysis of impacts on climate change (CC), freshwater eutrophication (FE) and marine eutrophication (ME). A functional unit (FU) of 2000 people receiving treatment services was considered. The most relevant sources of environmental impacts were associated to the concentration of dissolved methane in the UASB effluent that is emitted to the atmosphere in the SBR process (accounting for 41% of impacts in CC), electricity consumption, mainly for aeration in the SBR (representing 14% of the impacts produced in CC), and the discharge of the treated effluent in receiving waters (contributing 98% and 57% of impacts in FE and ME, respectively). The scheme of separate waste collection together with biological nitrogen removal and phosphorus uptake via nitrite was identified as the best configuration, with good treated effluent quality and environmental impacts lower than those of the other examined configurations.

Decentralised schemes for integrated management of wastewater and domestic organic waste: the case of a small community.

This study assesses from an environmental perspective two different configurations for the combined treatment of wastewater and domestic organic waste (DOW) in a small and decentralised community having a population of 2000. The applied schemes consist of an upflow anaerobic blanket (UASB) as core treatment process. Scheme A integrates membranes with the anaerobic treatment; while in Scheme B biological removal of nutrients in a sequencing batch reactor (SBR) is applied as a post treatment to UASB effluent. In energy-related categories, the main contributor is electricity consumption (producing 18-50% of the impacts); whereas in terms of eutrophication-related categories, the discharge of the treated effluent arises as a major hotspot (with 57-99% of the impacts). Scheme B consumes 25% more electricity and produces 40% extra sludge than Scheme A, resulting in worse environmental results for those energy categories. However, the environmental impact due to the discharge of the treated effluent is 75% lower in eutrophication categories due to the removal of nutrients. In addition, the quality of the final effluent in Scheme B would allow its use for irrigation (9.6 mg N/L and 2 mg P/L) if proper tertiary treatment and disinfection are provided, expanding its potential adoption at a wider scale. Direct emissions due to the dissolved methane in the UASB effluent have a significant environmental impact in climate change (23-26%). Additionally, the study shows the environmental feasibility of the use of food waste disposers for DOW collection in different integration rates.

Development of a Novel Process Integrating the Treatment of Sludge Reject Water and the Production of Polyhydroxyalkanoates (PHAs).

Polyhydroxyalkanoates (PHAs) from activated sludge and renewable organic material can become an alternative product to traditional plastics since they are biodegradable and are produced from renewable sources. In this work, the selection of PHA storing bacteria was integrated with the side stream treatment of nitrogen removal via nitrite from sewage sludge reject water. A novel process was developed and applied where the alternation of aerobic-feast and anoxic-famine conditions accomplished the selection of PHA storing biomass and nitrogen removal via nitrite. Two configurations were examined: in configuration 1 the ammonium conversion to nitrite occurred in the same reactor in which the PHA selection process occurred, while in configuration 2 two separate reactors were used. The results showed that the selection of PHA storing biomass was successful in both configurations, while the nitrogen removal efficiency was much higher (almost 90%) in configuration 2. The PHA selection degree was evaluated by the volatile fatty acid (VFA) uptake rate (-qVFAs) and the PHA production rate (qPHA), which were 239 ± 74 and 89 ± 7 mg of COD per gram of active biomass (Xa) per hour, respectively. The characterization of the biopolymer recovered after the accumulation step, showed that it was composed of 3-hydroxybutyrate (3HB) (60%) and 3-hydroxyvalerate (3HV) (40%). The properties associated with the produced PHA suggest that they are suitable for thermoplastic processing.

Use of external carbon sources derived from biowaste for short-cut nutrient removal from anaerobic effluents.

This work evaluated the use of different external carbon sources to promote the via-nitrite nutrient removal from anaerobic effluents. The carbon sources consisted of fermentation liquid produced from the organic fraction of municipal solid waste (OFMSW FL), drainage liquid produced from OFMSW, fermentation liquid produced from vegetable and fruit waste (VFW FL) and acetic acid. Denitritation and phosphorus uptake via nitrite were evaluated in two sequencing batch reactors, one treating the anaerobic supernatant produced from the co-digestion of OFMSW and activated sludge (highly nitrogenous anaerobic effluent - HNAE), and the other one treating the weakly nitrogenous anaerobic effluent (WNAE) from an upflow anaerobic sludge blanket reactor. The use of OFMSW FL to treat HNAE resulted in high nitrite (27 mgN/(gVSS·h) (VSS - volatile suspended solids) and phosphate uptake (15 mgP/gVSS·h). In the WNAE, nutrient kinetics were much slower. The use of acetic acid and VFW FL performed poorly, while the use of OFMSW FL, which was rich in butyric acid and propionic acid, resulted in significant nutrient removal (7 mgN/gVSS·h and 6 mgP/gVSS·h). The economic evaluation showed that the use of OFMSW FL is a less expensive option than the acetic acid use.

Inhibition of biomass activity in the via nitrite nitrogen removal processes by veterinary pharmaceuticals.

The inhibitory effect of two veterinary pharmaceuticals was studied for different types of biomass involved in via nitrite nitrogen removal processes. Batch tests were conducted to determine the inhibition level of acetaminophen (PAR) and doxycycline (DOX) on the activity of short-cut nitrifying, denitrifying and anoxic ammonium oxidation (anammox) biomass and phosphorus accumulating organisms (PAOs). All biomass types were affected by PAR and DOX, with anammox being the most sensitive bacteria. DOX inhibited more the biomass treating high strength nitrogenous effluents (HSNE) than low strength nitrogenous effluents (LSNE). The phosphorus uptake inhibition under anoxic conditions was lower than 25% in the presence of PAR up to 400 mg L(-1). The same DOX concentration inhibited anoxic phosphorus uptake more than 65% for biomass treating LSNE and HSNE. Heterotrophic denitrifying bacteria seem to be more robust at high DOX and PAR concentrations than anammox. Both veterinary products inactivated ammonium oxidizing, Accumulibacter phosphatis and denitrifying bacteria.

Investigation of the inhibitory effects of heavy metals on heterotrophic biomass activity and their mitigation through the use of natural minerals.

This study examined the inhibitory effects of lead, copper, nickel and zinc on heterotrophic biomass and their potential mitigation through the use of low-cost, natural minerals. Activated sludge was placed in batch reactors and specific heavy metal concentrations were added. Subsequently, the biomass specific oxygen uptake rate (sOUR) was determined to assess the level of biomass inhibition. Biomass inhibition by heavy metals followed the order Cu(2+)>Pb(2+)>Zn(2+)>Ni(2+), with copper being the most toxic metal, causing high inhibition of heterotrophic biomass even at relatively low concentrations (i.e. 10 mg·L(-1)). Zn had very small toxic effect at 10 mg·L(-1), while at 40 mg·L(-1) the level of biomass inhibition reached 80%. Nickel stimulated activated sludge activity at concentrations of the order of 10 mg·L(-1). The addition of 10 g·L(-1) bentonite and zeolite in activated sludge resulted in the decrease of the inhibitory effect of heavy metals on biomass respiratory activity. In some cases, mineral addition was very favorable as inhibition was reduced from 69-90% to less than 55% and even up to 12%. The beneficial action of minerals is attributed both to the adsorption of heavy metals on the mineral and on the potential aggregation between mineral and sludge particles.

Assessment of metal removal, biomass activity and RO concentrate treatment in an MBR-RO system.

This work investigated the removal of metals from wastewater using a combined Membrane Bioreactor-Reverse Osmosis (MBR-RO) system. The concentrate produced by the RO system was treated by a fixed bed column packed with zeolite. The average metal removal accomplished by the MBR treating municipal wastewater was Cu(90%), Fe(85%), Mn(82%), Cr(80%), Zn(75%), Pb(73%), Ni(67%), Mg(61%), Ca(57%), Na(30%) and K(21%), with trivalent and divalent metals being more effectively removed than monovalent ones. The metal removal achieved by the MBR system treating wastewater spiked with Cu, Pb, Ni and Zn (4-12 mg L(-1) of each metal) was Pb(96%)>Cu(85%)>Zn(78%)>Ni(48%). The combined MBR-RO system enhanced metal removal from municipal wastewater to the levels of >90.9->99.8%, while for wastewater spiked with heavy metals the removal efficiencies were >98.4%. Fixed bed column packed with zeolite was effective for the removal of Cu, Pb and Zn from the RO concentrate, while Ni removal was satisfactory only at the initial stages of column operation. The presence of heavy metals increased inorganic fouling.