Nutrient recovery from wastewater for hydroponic systems: A comparative analysis of fertilizer demand, recovery products, and supply potential of WWTPs

Nutrient recovery from wastewater treatment plants (WWTPs) for hydroponic cultivation holds promise for closing the nutrient loop and meeting rising food demands. However, most studies focus on solid products for soil-based agriculture, thus raising questions about their suitability for hydroponics. In this study, we address these questions by performing the first in-depth assessment of the extent to which state-of-the-art nutrient recovery processes can generate useful products for hydroponic application. Our results indicate that less than 11.5% of the required nutrients for crops grown hydroponically can currently be recovered. Potassium nitrate (KNO3), calcium nitrate (Ca(NO3)2), and magnesium sulfate (MgSO4), constituting over 75% of the total nutrient demand for hydroponics, cannot be recovered in appropriate form due to their high solubility, hindering their separated recovery from wastewater. To overcome this challenge, we outline a novel nutrient recovery approach that emphasizes the generation of multi-nutrient concentrates specifically designed to meet the requirements of hydroponic cultivation. Based on a theoretical assessment of nutrient and contaminant flows in a typical municipal WWTP, utilizing a steady-state model, we estimated that this novel approach could potentially supply up to 56% of the nutrient requirements of hydroponic systems. Finally, we outline fundamental design requirements for nutrient recovery systems based on this new approach. Achieving these nutrient recovery potentials could be technically feasible through a combination of activated sludge processes for nitrification, membrane-based desalination processes, and selective removal of interfering NaCl. However, given the limited investigation into such treatment trains, further research is essential to explore viable system designs for effective nutrient recovery for hydroponics.

Synchronous Achievement of Advanced Nitrogen Removal and N2O Reduction in the Anoxic Zone in the AOA Process for Low C/N Municipal Wastewater

Continuous flow processes for the in situ determination of N2O emissions during low C/N municipal wastewater treatment have rarely been reported. The anaerobic/aerobic/anoxic (AOA) process has recently shown promising potential in energy savings and advanced nitrogen removal, but it still needs to be comprehensively explored in relation to N2O emissions for its carbon reduction advantages. In this study, a novel gas-collecting continuous flow reactor was designed to comprehensively evaluate the emissions of N2O from the gas and liquid phases of the AOA process. Additionally, the measures of enhancing endogenous denitrification (ED) and self-enriching anaerobic ammonium oxidation (Anammox) were employed to optimize nitrogen removal and achieve N2O reduction in the anoxic zone. The results showed that enhanced ED coupled with Anammox led to an increase in the nitrogen removal efficiency (NRE) from 67.65 to 81.96%, an enhancement of the NO3- removal rate from 1.76 mgN/(L h) to 3.99 mgN/(L h), and the N2O emission factor in the anoxic zone decreased from 0.28 to 0.06%. Impressively, ED eliminated 91.46 ± 2.47% of the dissolved N2O from the upstream aerobic zone, and the dissolved N2O in the effluent was reduced to less than 0.01 mg/L. This study provides valuable strategies for fully evaluating N2O emissions and N2O reduction from the AOA process.

Removal of emerging micropollutants from nanofiltration retentate of municipal wastewater within biological fixed-bed reactors under nitrifying and denitrifying conditions

Municipal water resource recovery facilities are not designed to eliminate micropollutants, leading to many pollutants entering the aquatic environment. Within this study, as part of the project MicroStop, the biological treatment of nanofiltration effluent (retentate) under pure aerobic (without nitrification) as well as nitrifying and denitrifying conditions has been investigated for micropollutant elimination. A potential of further biotransformation under increased hydraulic retention time (HRT) of 14 days was shown. Under both HRT of 7 and 14 days, eliminations below LOQ were achieved in the aerated bioreactor for gabapentin, iomeprol, and metoprolol, reaching > 95%, > 69 to > 92%, and > 72%, respectively. The reduction of diclofenac was positively influenced by longer HRT leading to an elimination of up to 67%. Sulfamethoxazole was reduced under denitrification, but accumulated under aeration, resulting in fluctuating results and an overall elimination of 78% under 14 days HRT. PRACTITIONER POINTS: The micropollutant elimination in fixed-bed bioreactors of highly concentrated nanofiltration retentate was studied. Pure aerobic (without nitrification), nitrifying, and denitrifying conditions were investigated under hydraulic retention times (HRT) of 7 and 14 days. Higher initial pollutant concentrations enhanced the biological degradability in attached growth for substances being moderately degradable in activated sludge systems. 4A potential of further biological micropollutant elimination was shown for gabapentin, iomeprol, metoprolol, and diclofenac.

Embedded Graphite and Carbon Nanofibers in a Polyurethane Matrix Used as Anodes in Microbial Fuel Cells for Wastewater Treatment

Composites of polyurethane and graphite and polyurethane and carbon nanofibers (PU/Graphite 0.5% and PU/CNF 1%) were synthesized and used as anodes in dual-compartment microbial fuel cells (MFCs) for municipal wastewater treatment; electrical energy generation and organic matter removal were assessed. The maximum power density, coulombic efficiency and chemical oxygen demand (COD) removal efficiency in the MFCs packed with the PU/Graphite 0.5% and PU/CNF 1% composites were 232.32 mW/m3 and 90.78 mW/m3, 5.87 and 4.41%, and 51.38 and 68.62%, respectively. In addition, the internal resistance of the MFCs with the best bioelectrochemical performance (PU/Graphite 0.5%) was 1051.11 Ω. The results obtained in this study demonstrate the feasibility of using these types of materials in dual-compartment MFCs for wastewater treatment with electric power generation.

Efficacy of Biogenic Zinc Oxide Nanoparticles in Treating Wastewater for Sustainable Wheat Cultivation

Water scarcity due to overuse and growing water pollution has led to the need for upgrading of conventional methods of wastewater treatment. The biological synthesis of zinc oxide nanoparticles (ZnO-NPs) and their photocatalytic capacity to degrade contaminants offer a promising and environment-friendly approach to municipal wastewater treatment. This technique is advantageous due to its cost-effectiveness, sustainability, and reduction in toxic residual substances. In this study, microbial-synthesized ZnO-NPs were used for the treatment of municipal wastewater. The objective of this study was to evaluate the potential of treated wastewater for wheat crop cultivation. Zinc oxide nanoparticles were synthesized from a pre-isolated bacterial strain, namely Shewanela sp., and characterized using UV-VIS, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) analyses. The results showed that after the treatment of wastewater, the concentration of total dissolve solids (TDS), the chemical oxygen demand (COD), and sulfate and phosphate levels decreased by 76.5%, 57.1%, 81.1%, and 67.4%, respectively. However, the application of treated wastewater increased chlorophyll, carotenoids, and antioxidants by 45%, 40.8%, and 10.5 to 30.6%, respectively. Further, the application of treated wastewater also significantly decreased oxidative stress induced by hydrogen peroxide (H2O2) and malondialdehyde (MDA) by 8.1% and 30.1%, respectively. In conclusion, biosynthesized ZnO-NPs could be an important choice to treat municipal wastewater and to improve wheat productivity.

Forward Osmosis Application for the Removal of Emerging Contaminants from Municipal Wastewater: A Review

Forward osmosis (FO) has attracted special attention in water and wastewater treatment due to its role in addressing the challenges of water scarcity and contamination. The presence of emerging contaminants in water sources raises concerns regarding their environmental and public health impacts. Conventional wastewater treatment methods cannot effectively remove these contaminants; thus, innovative approaches are required. FO membranes offer a promising solution for wastewater treatment and removal of the contaminants in wastewater. Several factors influence the performance of FO processes, including concentration polarization, membrane fouling, draw solute selection, and reverse salt flux. Therefore, understanding and optimizing these factors are crucial aspects for improving the efficiency and sustainability of the FO process. This review stresses the need for research to explore the potential and challenges of FO membranes to meet municipal wastewater treatment requirements, to optimize the process, to reduce energy consumption, and to promote scalability for potential industrial applications. In conclusion, FO shows promising performance for wastewater treatment, dealing with emerging pollutants and contributing to sustainable practices. By improving the FO process and addressing its challenges, we could contribute to improve the availability of water resources amid the global water scarcity concerns, as well as contribute to the circular economy.

Electrochemical degradation of surfactants in domestic wastewater using a DiaClean® cell equipped with a boron-doped diamond electrode

Treating domestic wastewater has become more and more complicated due to the high content of different types of detergents. In this context, advanced electro-oxidation (AEO) has become a powerful tool for complex wastewater remediation. The electrochemical degradation of surfactants present in domestic wastewater was carried out using a DiaClean® cell in a recirculation system equipped with boron-doped diamond (BDD) as the anode and stainless steel as the cathode. The effect of recirculation flow (1.5, 4.0 and 7.0 L min-1) and the applied current density (j = 7, 14, 20, 30, 40, and 50 mA cm-2) was studied. The degradation was followed by the concentration of surfactants, chemical oxygen demand (COD), and turbidity. pH value, conductivity, temperature, sulfates, nitrates, phosphates, and chlorides were also evaluated. Toxicity assays were studied through evaluating Chlorella sp. performance at 0, 3, and 7 h of treatment. Finally, the mineralization was followed by total organic carbon (TOC) under optimal operating conditions. The results showed that applying j = 14 mA cm-2 and a flow rate of 1.5 L min-1 during 7 h of electrolysis were the best conditions for the efficient mineralization of wastewater, achieving the removal of 64.7% of surfactants, 48.7% of COD, 24.9% of turbidity, and 44.9% of mineralization analyzed by the removal of TOC. The toxicity assays showed that Chlorella microalgae were unable to grow in AEO-treated wastewater (cellular density: 0 × 104 cells ml-1 after 3- and 7-h treatments). Finally, the energy consumption was analyzed, and the operating cost of 1.40 USD m-3 was calculated. Therefore, this technology allows for the degradation of complex and stable molecules such as surfactants in real and complex wastewater, if toxicity is not taken into account.

Evaluation of Forward Osmosis and Low-Pressure Reverse Osmosis with a Tubular Membrane for the Concentration of Municipal Wastewater and the Production of Biogas

Currently, freshwater scarcity is one of the main issues that the world population has to face. To address this issue, new wastewater treatment technologies have been developed such as membrane processes. Among them, due to the energy disadvantages of pressure-driven membrane processes, Forward Osmosis (FO) and Low-Pressure Reverse Osmosis (LPRO) have been introduced as promising alternatives. In this study, the behavior of a 2.3 m² tubular membrane TFO-D90 when working with municipal wastewater has been studied. Its performances have been evaluated and compared in two operating modes such as FO and LPRO. Parameters such as fouling, flow rates, water flux, draw solution concentration, organic matter concentration, as well as its recovery have been studied. In addition, the biogas production capacity has been evaluated with the concentrated municipal wastewater obtained from each process. The results of this study indicate that the membrane can work in both processes (FO and LPRO) but, from the energy and productivity point of view, FO is considered more appropriate mainly due to its lower fouling level. This research may offer a new point of view on low-energy and energy recovery wastewater treatment and the applicability of FO and LPRO for wastewater concentration.

Dissolved Organic Phosphorus Removal in Secondary Effluent by Ferrate (VI): Performance and Mechanism

Dissolved organic phosphorus (DOP), which is recalcitrant in municipal wastewater treatment, accounts for 26-81% of dissolved total phosphorus in the effluent. More importantly, the majority of DOP could be bioavailable, potentially threatening the aquatic environment through eutrophication. This study aimed to develop a ferrate (VI)-based advanced treatment to effectively destruct and remove DOP from secondary effluent and use deoxyribonucleic acid (DNA) and adenosine-5'-triphosphate (ATP) as DOP model compounds to explore the relevant mechanisms. The results showed that ferrate (VI) treatment could efficiently destruct and remove 75% of the DOP in secondary effluent from an activated sludge-adopted municipal wastewater treatment plant, under normal operating conditions. Moreover, the coexistence of nitrate, ammonia, and alkalinity barely affected the effectiveness, while the presence of phosphate significantly inhibited DOP removal. The mechanistic study revealed that ferrate (VI)-induced particle adsorption was the dominant way to achieve DOP reduction, rather than oxidating DOP to phosphate and forming precipitation afterward. Meanwhile, DOP molecules could be effectively decomposed into smaller ones by ferrate (VI) oxidation. This study clearly demonstrated that ferrate (VI) treatment could achieve a promising DOP removal from secondary effluent for mitigating the risk of eutrophication in receiving water bodies.

Removal of Antibiotic Resistance Genes, Class 1 Integrase Gene and Escherichia coli Indicator Gene in a Microalgae-Based Wastewater Treatment System

Microalgae-based wastewater treatment systems (AWWTS) have recently shown promise in the mitigation of antibiotic resistance genes (ARGs) from municipal wastewater (MWW). However, due to the large number of ARGs that exist in MWW, the use of indirect conventional water quality parameters to monitor ARGs reduction in wastewater would make the process less burdensome and economically affordable. In order to establish a robust relationship between the ARGs and water quality parameters, the current study employed different microalgae strains in monoculture (CM2, KL10) and multi-species combinations (CK and WW) for the MWW treatment under outdoor environmental conditions. The studied genes were quantified in the MWW influents and effluents using real-time PCR. All the cultures substantially improved the physicochemical qualities of the MWW. Out of the 14 genes analyzed in this study, tetO, tetW, tetX and ermB were decreased beyond detection within the first 4 days of treatment in all the cultures. Other genes, including blaCTX, sul1, cmlA, aadA, int1 and uidA were also decreased beyond a 2 log reduction value (LRV). The mobile genetic element, int1, correlated positively with most of the ARGs, especially sul1 (r ≤ 0.99, p < 0.01) and aadA (r ≤ 0.97, p < 0.01). Similarly, the Escherichia coli indicator gene, uidA, correlated positively with the studied genes, especially with aadA, blaCTX, blaTEM and cmlA (r ≤ 0.99 for each, p < 0.01). Some of the studied genes also correlated positively with total dissolved solids (TDS) (r ≤ 0.98, p < 0.01), and/or negatively with total suspended solids (TSS) (r ≤ −0.98, p < 0.01) and pH (r ≤ −0.98, p < 0.01). Among the tested cultures, both monocultures, i.e., KL10 and CM2 were found to be more consistent in gene suppression than their multi-species counterparts. The findings revealed water quality parameters such as TDS, TSS and E. coli as reliable proxies for ARGs mitigation in AWWTS and further highlight the superiority of monocultures over multi-species cultures in terms of gene suppression from the MWW stream.

Municipal Wastewater Connection for Water Crisis and Jaundice Outbreaks in Shimla City: Present Findings and Future Solutions

The felicitous tourist destination "Hills Queen" and the capital city of Himachal Pradesh, an enticing state in the Himalayan region, are met with water crisis every year and jaundice outbreaks occasionally. In 2016, there was a severe jaundice outbreak in Shimla city. In a contemporaneous investigation, we attempted to trace out the possible reason for these crises in Shimla. Samples were collected month wise from different water-supply sources and their physicochemical and microbial loads were analyzed. The microbiological examination found a totally excessive microbial load (1.064 × 10⁹ cfu/mL on common) throughout the year with a maximum (>1.98 × 10¹⁰ cfu/mL) in the wet season and minimum (>3.00 × 10⁷ cfu/mL) in the winter. Biochemical and morphological evaluation confirmed that most of the water resources reported a high number of coliforms and Gram-negative microorganisms due to sewage-water infiltration. These microorganisms in the water are responsible for the liver infection that ultimately causes jaundice. For safe and potable water, infiltration of municipal wastewater must be prevented at any cost. Scientific disposal of wastewater and purification of uncooked water have to be conducted earlier than consumption or use for different domestic functions, to avoid water crises and fetal ailment outbreaks in the near future.

USAEME-GC/MS Method for Easy and Sensitive Determination of Nine Bisphenol Analogues in Water and Wastewater

A new, simple and sensitive method for isolating nine compounds from the bisphenol group (analogues: A, B, C, E, F, G, Cl₂, Z, AP) based on one-step liquid-liquid microextraction with in situ acylation followed by gas chromatography-mass spectrometry was developed and validated using influent and effluent wastewaters. The chemometric approach based on the Taguchi method was used to optimize the main conditions of simultaneous extraction and derivatization. The recoveries of the proposed procedure ranged from 85 to 122%, and the repeatability expressed by the coefficient of variation did not exceed 8%. The method's limits of detection were in the range of 0.4-64 ng/L, and the method's limits of quantification ranged from 1.3 to 194 ng/L. The developed method was used to determine the presence of the tested compounds in wastewater from a municipal wastewater treatment plant located in northeastern Poland. From this sample, eight analytes were detected. Concentrations of bisphenol A of 400 ng/L in influent and 100 ng/L in effluent were recorded, whereas other bisphenols reached 67 and 50 ng/L for influent and effluent, respectively. The removal efficiency of bisphenol analogues in the tested wastewater treatment plant ranged from 7 to approximately 88%.

Effect of light intensity and wavelength on nitrogen and phosphate removal from municipal wastewater by microalgae under semi-batch cultivation

Domestic, agricultural and industrial water activities lead to organic and inorganic pollution of the environment. Biotreatment of municipal wastewater with the potential production of biomass is a valuable feature of microalgae. In this study we evaluated the effects of wavelength and light intensity on phosphate and ammonium removal on the one hand, and biomass and protein production on the other hand by Spirulina platensis in municipal wastewater treatment under semi batch cultivation. S. platensis was inoculated at 40% in artificial wastewater open pond system. Red, blue and purple light with 3800, 4800 and 5800 lux light intensity under 12 h light and 12 h darkness were investigated. Cultivation was conducted in semi-batch conditions; after four days cultivation, one third of the culture was replaced with fresh medium. The highest biomass and protein concentrations were observed under blue light at 5800 lux light intensity, 5.45 and 3 g/l respectively cumulatively; while the highest amount of phosphate and ammonium removal were about 145 and 218 mg/l under purple light at 5800 lux intensity, respectively. The amounts of biomass and protein produced, as well as phosphate and ammonium removed, are therefore impacted by wavelength, light intensity, results show that light intensity and wavelength can be customized to reach on the one hand the highest biomass and protein production, and on the other hand to maximize the removal of phosphorous and ammonium.

Evaluation of the Removal of Selected Phthalic Acid Esters (PAEs) in Municipal Wastewater Treatment Plants Supported by Constructed Wetlands

Phthalic acid esters (PAEs) have a negative impact on living organisms in the environment, therefore, are among the group of Endocrine Disrupting Compounds (ECDs). Unfortunately, conventional methods used in municipal wastewater treatment plants (MWWTPs) are not designed to eliminate PAEs. For this reason, the development of cheap and simple but very effective techniques for the removal of such residues from wastewater is crucial. The main aim of this study was the evaluation of the removal of six selected PAEs: diethyl phthalate (DEP), di-n-octyl phthalate (DOP), di-n-butyl phthalate (DBP), benzyl butyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP) and dimethyl phthalate (DMP), in real MWWTPs supported by constructed wetlands (MWWTP-CW system). For the first time, the possibility of using three new plants for this purpose, Cyperus papyrus (papyrus), Lysimachia nemorum (yellow pimpernel) and Euonymus europaeus (European spindle), has been presented. For determining the target PAEs in wastewater samples, a method of SPE (Solid-Phase Extraction)-GC-MS(SIM) was developed and validated, and for plant materials, a method of UAE (Ultrasound-Assisted Extraction)-SPE-GC-MS(SIM) was proposed. The obtained data showed that the application of the MWWTP-CW system allows a significant increase in the removal of DEP, DBP, BBP and DEHP from the wastewater stream. Euonymus europaeus was the most effective among the tested plant species for the uptake of analytes (8938 ng × g^-1 dry weight), thus, this plant was found to be optimal for supporting conventional MWWTPs.

Cationic Lignin Polymers as Flocculant for Municipal Wastewater

The radical polymerization of acid-washed and unwashed softwood kraft lignin with [2-(methacryloyloxy) ethyl] trimethylammonium chloride (METAC) was attempted to investigate the production of lignin-based flocculants for simulated wastewater. The incorporation of METAC onto lignin resulted in a cationic charge density (2.3–3.3 meq/g), increased water solubility (89–96% in neutral pH), and increased molecular weight (70,000–210,000 g/mol) of lignin. The lignin–METAC polymers generated from acid-washed lignin had higher molecular weights than those generated from unwashed lignin. The lignin–METAC polymers showed lower resistance to thermal decomposition than unmodified lignin due to the inclusion of PolyMETAC. The unmodified acid-washed lignin samples did not significantly affect the COD of the wastewater, while the unmodified unwashed lignin samples contributed to the COD, implying that unmodified lignin was not suitable for wastewater treatment. The flocculation of wastewater with lignin–METAC led to the chemical oxygen demand (COD) reduction of 17–23% and total organic carbon (TOC) drop of 51–60%. The lignin–METAC polymer with the highest molecular weight (produced from acid-washed lignin) reached the highest COD removal, while lignin–METAC polymer with the highest charge density (produced from unwashed lignin) reached the highest TOC removal. Focused beam reflectance measurement (FBRM) studies revealed that the lignin–METAC polymer produced from acid-washed lignin with a high molecular weight generated larger and more flocs in wastewater than the lignin–METAC polymer produced from unwashed lignin. The comparison of theoretical and experimental dosages required for neutralizing the charges of wastewater demonstrated that charge neutralization was the main flocculation mechanism, although a bridging mechanism was also involved for component removals from wastewater. The use of 1 mg/L of alum along with 65 mg/L lignin–METAC in a dual coagulation–flocculation system led to higher average phosphorous (42%) and COD (44%) removals than the singular flocculation system only using 65 mg/L of lignin–METAC (with phosphorous removals of 3.4% and COD removals of 18.7%). However, lignin–METAC flocculant slightly increased the ammonia–nitrogen content in both singular flocculation and dual coagulation–flocculation systems due to the residual ammonia content of lignin–METAC. The coagulation–flocculation system determined that the use of lignin–METAC (65 mg/L) could reduce the alum dosage significantly while maintaining a similar organic content reduction of 44% for wastewater.

Metagenomic Survey Reveals More Diverse and Abundant Antibiotic Resistance Genes in Municipal Wastewater Than Hospital Wastewater

Alongside antibiotic resistance, co-selection of antibiotics, biocides, and metal resistance is a growing concern. While hospital wastewater is considered a hotspot for antibiotic-resistant bacteria (ARB) and genes (ARGs), the scenario in India, one of the biggest consumers of antibiotics, remains poorly described. In this study, we used metagenomic sequencing to characterize ARGs and biocide/metal resistance genes (BMRGs) in four wastewater treatment plants (WWTPs) in Jaipur City of India. We observed a significantly lower richness and abundance of ARGs in the influent of a WWTP exclusively receiving hospital wastewater when compared to other three WWTPs involving municipal wastewater treatment. Several tetracycline and macrolide-lincosamide-streptogramin resistance genes were enriched in influents of these three municipal wastewater-related treatment plants, whereas hospital wastewater had a higher abundance of genes conferring resistance to disinfectant-related compounds such as synergize and wex-cide-128, reflecting the patterns of antibiotic/disinfectant use. Of note, in the wastewater system with more chemicals, there was a strong correlation between the numbers of ARGs and BMRGs potentially harbored by common hosts. Our study highlights significant influxes of ARGs from non-hospital sources in Jaipur City, and thus more attention should be paid on the emergence of ARGs in general communities.

New Insight on Antibiotic Resistance and Virulence of Escherichia coli from Municipal and Animal Wastewater

Antibiotic resistance of the indicator microorganism Escherichia coli was investigated in isolates from samples collected during the course of one year from two wastewater treatment plants treating municipal and animal wastes in Slovakia, respectively. The genes of antibiotic resistance and virulence factors in selected resistant E. coli isolates were described. A high percentage of the isolates from municipal and animal wastewater were resistant to ampicillin, streptomycin, tetracycline, ceftiofur, ceftriaxone, and enrofloxacin. In the selected E. coli isolates, we detected the following phenotypes: ESBL (20.4% in animal wastewater; 7.7% in municipal wastewater), multidrug-resistant (17% of animal and 32% of municipal isolates), high resistance to quinolones (25% of animal and 48% of municipal samples), and CTX-M (7.9% of animal and 17.3% of municipal isolates). We confirmed an integro-mediated antibiotic resistance in 13 E. coli strains from municipal and animal wastewater samples, of which the Tn3 gene and virulence genes cvaC, iutA, iss, ibeA, kps, and papC were detected in six isolates. One of the strains of pathogenic E. coli from the animal wastewater contained genes ibeA with papC, iss, kpsII, Int1, Tn3, and Cit. In addition, one bla_IMP gene was found in the municipal wastewater sample. This emphasises the importance of using the appropriate treatment methods to reduce the counts of antibiotic-resistant microorganisms in wastewater effluent.

[Effects of Dissolved Oxygen on Nutrient Removal Performance and Microbial Community in Low Carbon/Nitrogen Municipal Wastewater Treatment Process]

To explore the effects of dissolved oxygen (DO) on the treatment of low carbon/nitrogen municipal wastewater, this study examined the characteristics of the microbial community in a low carbon source environment. The treatment process was conducted with the aeration area having DO concentrations of 2-3, 1-2, and lower than 1 mg·L^-1. The results demonstrated that reduced DO concentration in the aeration area increased the efficiency of the nitrogen removal process by 20.23% and 80.54%, for external and internal carbon sources, respectively. Similarly, the efficiency of internal carbon source utilization in the phosphorus removal process increased by 13.89%, thus enhancing the nutrient removal efficiency of the low carbon/nitrogen wastewater treatment system. High-throughput sequencing and RDA analysis showed that reduced oxygen concentration motivated an adjustment in microbial community structure, causing functional microorganisms (i.e., Dechloromonas) to become dominant. In addition, the upregulation of genes associated with energy production and conversion, signal transduction, substrate transport, and metabolism provided favourable nutritional conditions for the proliferation of functional microorganisms in low carbon source conditions. This study provides a theoretical basis for improving the growth of microorganisms involved in the nutrient removal process when treating low carbon/nitrogen municipal wastewater.

Evaluation of Health Risk after Nitrate Exposure in Drinking Water in the Al Duliel Area, Jordan

&lt;b&gt;Background and Objective:&lt;/b&gt; Jordan's drinking water scarcity is desperately needed and it plays a critical role in improving safe drinking water quality, which is critical for nutritious and clean drinking water quality, which is a vital component of good public health. Recognize the potential risk of repeated exposure to high nitrate concentrations in drinking water in the A Duliel area and measure the impact on local communities' human health. &lt;b&gt;Materials and Methods:&lt;/b&gt; In 2016, samples of groundwater were taken. With a mean value of 44.4 mg L&lt;sup&gt;1&lt;/sup&gt;, nitrate concentrations ranged from 10-81.0 mg L&lt;sup&gt;1&lt;/sup&gt;. &lt;b&gt;Results:&lt;/b&gt; The findings showed that human activities, especially the extensive use of chemical fertilizers in agriculture, could be attributed to high NO&lt;sub&gt;3&lt;/sub&gt; concentrations. To assess the possible risk to human health, Chronic Daily Intake (CDI) and Hazard Quotient (HQ) has been assessed. In the classes considered, infants tended to be at a greater risk than children and adults. Furthermore, the findings showed that in most of the groundwater considered, the health of people from nitrate contamination was not adequate and was also at risk from known concentrations of nitrate. &lt;b&gt;Conclusion:&lt;/b&gt; Appropriate steps to improve groundwater protection and to better track and control stable sources of nitrate emissions are also important.

Increasing Phosphorus Uptake Efficiency by Phosphorus-Starved Microalgae for Municipal Wastewater Post-Treatment

Four microalgal species, Chlorella vulgaris, Botryococcus braunii, Ankistrodesmus falcatus, and Tetradesmus obliquus were studied for enhanced phosphorus removal from municipal wastewater after their exposure to phosphorus starvation. Microalgae were exposed to phosphorus starvation conditions for three and five days and then used in a batch experiment to purify an effluent from a small WWTP. After 3-day P-starvation, C. vulgaris biomass growth rate increased by 50% and its PO₄ removal rate reached > 99% within 7 days. B. braunii maintained good biomass growth rate and nutrient removal regardless of the P-starvation. All species showed 2–5 times higher alkaline phosphatase activity increase for P-starved biomass than at the reference conditions, responding to the decline of PO₄ concentration in wastewater and biomass poly-P content. The overall efficiency of biomass P-starvation on enhanced phosphorus uptake was found to be dependent on the species, N/P molar ratio in the wastewater, as well as the biomass P content.

Advanced Phosphorus Recovery from Municipal Wastewater using Anoxic/Aerobic Membrane Bioreactors and Magnesium Carbonate-Based Pellets

Effective recovery of phosphorus from municipal wastewater could be one of the best practical alternatives to protect aquatic environments from eutrophication and save natural phosphorus resources. This paper focuses on validating magnesium carbonate (MgCO₃)-based pellets combined with a bench-scale anoxic/aerobic membrane bioreactor (MBR) system for advanced phosphorus recovery from municipal wastewater. As the flow rate of wastewater into the MgCO₃ column decreased from 10 L/d to 2.5 L/d, the phosphorus recovery rate of the MgCO₃-based pellets increased from 54.3 to 93.5%. However, the column's severe clogging was found after a 13-days operation due to the high removal of total suspended solids (TSS) (~82%) through the MgCO₃ column. The anoxic/aerobic MBR introduction provided efficient removal of TSS, organic matter, and ammonia nitrogen before the MgCO₃ column. The combination of MBR with the MgCO₃ column achieved 73.1% phosphorus recovery from municipal wastewater without physical clogging. The P recovery capacity of the MgCO₃-based pellets was maintained at 0.47 mg ortho-P/g MgCO₃-based pellet during the continuous operation. Physical and chemical properties of MgCO₃-based pellets before and after the experiment were characterized using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) surface area analyzer.

Concentration of Municipal MBBR Effluent by FO for Resource Recovery: Batch Experiments in Side-Stream Configuration

A novel approach for resource recovery includes forward osmosis (FO) as a concentration step in municipal wastewater treatment. The current study investigates different pre-treatment strategies including biological treatment with a moving-bed bioreactor (MBBR) at different loading rates and particle removal by filtration and sedimentation. Membrane performance and recovery potential for energy and nutrients were investigated in laboratory-scale FO experiments in batch mode using pre-treated municipal wastewater as feed and 35 g/L NaCl as a draw solution. Initial water fluxes were in the range of 6.3 to 8.0 L/(m²·h). The baseline fluxes were modelled to account for flux decline due to concentration effects and to enable the prediction of flux decline due to membrane fouling. Fouling-related flux decline varied from 0 to 31%. Both organic fouling and precipitation of CaCO₃ and CaHPO₄ were identified by using SEM–EDS. High-rate flushing resulted in complete flux recovery under most conditions. Scaling could be avoided by lowering the pH. Two operation strategies were tested to achieve this: (1) applying a bioreactor with a low organic loading rate to achieve high nitrification, and (2) adding a strong acid. A low organic loading rate and the use of additional particle removal were efficient measures that reduced organic/particulate fouling. The recovery potentials for COD and phosphorous in FO concentrate were close to 100%.

A Hybrid NF-FO-RO Process for the Supply of Irrigation Water from Treated Wastewater: Simulation Study

Municipal treated wastewater could be considered as a water source for food crop irrigation purposes. Enhancing the quality of treated wastewater to meet irrigation standards has become a necessary practice. Nanofiltration (NF) was used in the first stage to produce permeate at relatively low energy consumption. In the second stage, two membrane combinations were tested for additional water extraction from the brine generated by the NF process. The simulation results showed that using a hybrid forward osmosis (FO)–reverse osmosis (RO) system is more efficient than using the RO process alone for the further extraction of water from the brine generated by the NF process. The total specific energy consumption can be reduced by 27% after using FO as an intermediate process between NF and RO. In addition, the final permeate water quality produced using the hybrid FO-RO system was within the allowable standards for food crops irrigation.

[One-step Preparation of Lanthanum-Magnesium Ferrite and Its Phosphate Adsorption Capacity in Aqueous Solutions]

Due to the shortage of phosphate and the eutrophication caused by phosphorus pollution, it is urgent to recover phosphate from wastewater. Given their high adsorption capacity and convenient separation from water to which a magnetic field is applied, ferrite composites have received increasing attention for phosphate recovery. In this study, Spinel La@MgFe₂O₄ was prepared using a one-step co-precipitation method. La³⁺ loading on grain boundary defects of MgFe₂O₄, and phosphorus absorption capacity were examined using X-ray diffraction (XRD), Fourier-transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The structure of La@MgFe₂O₄ involved La³⁺ loading on grain boundary defects of MgFe₂O₄ in the form of La(OH)₃. The addition of La changed the crystallinity and morphology of MgFe₂O₄, which greatly improved the capacity of MgFe₂O₄ for phosphorus adsorption. Saturation magnetization remained at 14 emu·g^-1, which was easily separated from water using an external magnetic field. The maximum adsorption capacity was 143.156 mg·g^-1 at pH 6 and 10℃, which was comparable to that achieved at 25℃. Kinetic observations showed that a low phosphorus concentration (10 mg·L^-1) could result in extremely low phosphorus adsorption by La@MgFe₂O₄ after 30 min. The adsorption mechanism shows that phosphorus is removed through ligand exchange and the formation of inner spherical complexes. La@MgFe₂O₄ has highly selective adsorption with respect to phosphate, and the adsorbent can be reused many times after desorption. Based on addition of 1 g·L^-1 of La@MgFe₂O₄ in the treatment of low temperature municipal wastewater in Northern China, phosphate concentrations could be reduced to less than 0.5 mg·L^-1 an hour, offering a promising means of phosphate adsorption even in cold regions.

Long-Term Trends in Water Quality Indices in the Lower Danube and Tributaries in Romania (1996-2017)

The Danube River is the second longest in Europe and its water quality is important for the communities relying on it, but also for supporting biodiversity in the Danube Delta Biosphere Reserve, a site with high ecological value. This paper presents a methodology for assessing water quality and long-term trends based on water quality indices (WQI), calculated using the weighted arithmetic method, for 15 monitoring stations in the Lower Danube and Danube tributaries in Romania, based on annual means of 10 parameters for the period 1996–2017. A trend analysis is carried out to see how WQIs evolved during the studied period at each station. Principal component analysis (PCA) is applied on sub-indices to highlight which parameters have the highest contributions to WQI values, and to identify correlations between parameters. Factor analysis is used to highlight differences between locations. The results show that water quality has improved significantly at most stations during the studied period, but pollution is higher in some Romanian tributaries than in the Danube. The parameters with the highest contribution to WQI are ammonium and total phosphorus, suggesting the need to continue improving wastewater treatment in the studied area. The methodology and the results of the study may be very useful instruments for specialists and decision makers in updating river basin management plans and prioritising intervention measures.

Desalination of Municipal Wastewater Using Forward Osmosis

Membrane technology has gained much ground in water and wastewater treatment over the past couple of decades. This is timely, as the world explores smart, eco-friendly, and cheap water and wastewater treatment technologies in its quest to make potable water and sanitation commonplace in all parts of the world. Against this background, this study investigated forward osmosis (FO) in the removal of salts (chlorides, sulphates, and carbonates) and organics (chemical oxygen demand (COD), turbidity, total suspended solids (TSS), and color) from a synthetic municipal wastewater (MWW), mimicking secondary-treated industrial wastewater, at very low feed and draw solution flow rates (0.16 and 0.14 L/min respectively), using 70 g/L NaCl solution as the draw solution. The results obtained showed an average of 97.67% rejection of SO₄²⁻ and CO₃²⁻ while Cl⁻ was found to enrich the feed solution (FS). An average removal of 88.92% was achieved for the organics. A permeation flux of 5.06 L/m².h was obtained. The kinetics of the ions transport was studied, and was found to fit the second-order kinetic model, with Pearson’s R-values of 0.998 and 0.974 for Cl⁻ and CO₃²⁻ respectively. The study proves FO as a potential technology to desalinate saline MWW.

Biogas production by co-digestion of municipal wastewater and food waste: Performance in semi-continuous and continuous operation

Municipal wastewater has recently attracted interest in relation to anaerobic wastewater treatments. Biogas production with co-digestion of mixed substrates has been proposed and has many potential benefits for municipal wastewater. The aim of this research was to assess the performance of biogas production during co-digestion of municipal wastewater and food waste under semi-continuous and continuous operation with various hydraulic retention times (HRTs). A laboratory-scale continuous stirred tank reactor (CSTR) at room temperature operation (27-32°C) was employed in this research. The highest methane yields of 167.41 ± 66.52, 194.35 ± 85.44, and 214.81 ± 85.44 ml/g-Vs were found in semi-continuous mode, respectively, at 30, 10, and 10 days of HRTs with a 10:90 ratio of municipal wastewater to food waste (based on TS). Result finding of optimum condition (10 days of HRTs) presented a methane yield of 485.58 ± 82.35 ml/g with continuous operation. Hence, food waste has practical implications for use as a co-substrate with the optimization condition of HRT and operation mode for biogas production from municipal wastewater. PRACTITIONER POINTS: Food waste has good potential for use as a co-substrate for biogas production from municipal wastewater. HRT reduction from 30 to 10 days in semi-continuous, biogas production from municipal wastewater and food waste increased by 59%. Co-digestion of municipal wastewater and food waste with continuous mode and 10 days of HRT was the effective biogas production.

Microalgae based wastewater treatment: a shifting paradigm for the developing nations

Decreased water quality in freshwater resources due to untreated or partially treated wastewater disposal resulting in eutrophication has led to water scarcity. Hence, the present work was aimed to determine the effectiveness of Chlorella vulgaris for municipal wastewater treatment in terms of various physico-chemical parameters and nutrient removal. Primary treated effluent was collected from a sewage treatment plant as an influent for the study. Parameters analyzed during the lab-scale batch study of 7 hours of detention time were pH, EC, TDS, TSS, TS, COD, phosphate, ammonia, nitrate and DO. Removal efficiency reached 98.32, 97.26 and 84.71% for phosphate, ammonia and COD, respectively, for non-filtered effluents. However, filtered effluent removal efficiency reached 98.53, 98.63 and 89.41% for phosphate, ammonia and COD, respectively. The study revealed that microalgal treatment, if incorporated in conventional wasteater treatment, can be a solution to the limitations of the activated sludge process. It could be a promising technique for low income and developing countries, which could efficiently reduce the effluent concentration to much lesser than the desirable limits in an eco-friendly and cost-effective way. Statement of novelty Municipal wastewater treatment in most developing countries is confined to aerobic secondary treatments, which are costly and are not efficient in removing nutrients from the treated effluents before discharging and leading to the imbalance and eutrophication in the receiving bodies. Hence in this study, an attempt was made to study the effectiveness of Chlorella vulgaris for wastewater treatment at a detention time of 7 hours without any external aeration. The present study revealed that microalgae have efficiently removed organics and nutrients to much lesser than the desirable limit. Thus, if the Chlorella vulgaris is introduced in the wastewater treatment system can reduce the nutrients and organics concentrations without the need for aeration, which can be an energy-saving and cost-effective approach.

Membrane Bioreactor Technology: The Effect of Membrane Filtration on Biogas Potential of the Excess Sludge

Although the membrane bioreactor technology is gaining increasing interest because of high efficiency of wastewater treatment and reuse, data on the anaerobic transformations of retentate are scarce and divergent. The effects of transmembrane pressure (TMP) in microfiltration (MF) and ultrafiltration (UF) on the pollutant rejection, susceptibility of ceramic membrane to fouling, hydraulic parameters of membrane module, and biogas productivity of retentate were determined. Irrespective of the membrane cut-off and TMP (0.2-0.4 MPa), 97.4 ± 0.7% of COD (chemical oxygen demand), 89.0 ± 4.1% of total nitrogen, and 61.4 ± 0.5% of total phosphorus were removed from municipal wastewater and the permeates can be reused for irrigation. Despite smaller pore diameter, UF membrane was more hydraulically efficient. MF membrane had 1.4-4.6 times higher filtration resistances than UF membrane. In MF and UF, an increase in TMP resulted in an increase in permeate flux. Despite complete retention of suspended solids, strong shearing forces in the membrane installation changed the kinetics of biogas production from retentate in comparison to the kinetics obtained when excess sludge from a secondary clarifier was anaerobically processed. MF retentates had 1.15 to 1.28 times lower cumulative biogas production than the excess sludge. Processing of MF and UF retentates resulted in about 60% elongation of period in which 90% of the cumulative biogas production was achieved.

Hydrolysis and Methanogenesis in UASB-AnMBR Treating Municipal Wastewater Under Psychrophilic Conditions: Importance of Reactor Configuration and Inoculum

Three upflow anaerobic sludge blanket (UASB) pilot scale reactors with different configurations and inocula: flocculent biomass (F-UASB), flocculent biomass and membrane solids separation (F-AnMBR) and granular biomass and membrane solids separation (G-AnMBR) were operated to compare start-up, solids hydrolysis and effluent quality. The parallel operation of UASBs with these different configurations at low temperatures (9.7 ± 2.4°C) and the low COD content (sCOD 54.1 ± 10.3 mg/L and pCOD 84.1 ± 48.5 mg/L), was novel and not previously reported. A quick start-up was observed for the three reactors and could be attributed to the previous acclimation of the seed sludge to the settled wastewater and to low temperatures. The results obtained for the first 45 days of operation showed that solids management was critical to reach a high effluent quality. Overall, the F-AnMBR showed higher rates of hydrolysis per solid removed (38%) among the three different UASB configurations tested. Flocculent biomass promoted slightly higher hydrolysis than granular biomass. The effluent quality obtained in the F-AnMBR was 38.0 ± 5.9 mg pCOD/L, 0.4 ± 0.9 mg sCOD/L, 9.9 ± 1.3 mg BOD₅/L and <1 mg TSS/L. The microbial diversity of the biomass was also assessed. Bacteroidales and Clostridiales were the major bacterial fermenter orders detected and a relative high abundance of syntrophic bacteria was also detected. Additionally, an elevated abundance of sulfate reducing bacteria (SRB) was also identified and was attributed to the low COD/SO₄ ^2- ratio of the wastewater (0.5). Also, the coexistence of acetoclastic and hydrogenotrophic methanogenesis was suggested. Overall this study demonstrates the suitability of UASB reactors coupled with membrane can achieve a high effluent quality when treating municipal wastewater under psychrophilic temperatures with F-AnMBR promoting slightly higher hydrolysis rates.

[Competitive Selection of Hydroxylamine on Ammonia Oxidizing Bacteria and Nitrite Oxidizing Bacteria]

The effective inhibition of nitrite oxidizing bacteria (NOB) is the key to realizing satisfactory nitrite accumulation and achieving effective nitritation. In order to explore the selective effect of hydroxylamine (NH₂ OH) on ammonia oxidizing bacteria (AOB) and NOB, a sequencing batch reactor (SBR) with the operation mode of anaerobic/aerobic/anoxia (A/O/A) was used to observe the start-up of nitritation at different concentrations and frequencies of NH₂ OH. The results showed that when 5 mg·L^-1 of NH₂ OH was added once every 2 cycles, the nitrite accumulation rate (NAR) increased from 0.1% to 57.4% in 6 days, and was maintained at (62.0±4.6)% until the end of the trials. In the typical cycle on day 6, the NN₄⁺-N dropped from 26.05 mg·L^-1 to 8.06 mg·L^-1, thus producing 9.02 mg·L^-1 of NO₂^--N and 6.70 mg·L^-1 of NO₃^--N. Meanwhile, the ratio of the maximum activity of AOB (rAOB) to NOB (rNOB) increased from 1.05 on day 1 to 4.22 on day 9. Moreover, qPCR results indicated that the abundance of AOB and NOB decreased to 30.2% and 19.1%, respectively, on day 9 in comparison to the original sample. The results indicate that the selective effect of AOB and NOB based on NH₂ OH is expected to provide a feasible application for the rapid start-up nitritation of municipal wastewater.

Forward osmosis with an algal draw solution to concentrate municipal wastewater and recover resources

This study aimed to concentrate and recover resources from municipal wastewater with a novel forward osmosis (FO) system. The FO system used synthetic seawater as the draw solution (DS) to extract water from the feed solution (FS) (synthetic raw municipal wastewater). Because ammonium passed through the FO membrane from the FS to the DS, we cultivated an algal strain (Chlorella vulgaris) in the DS to remove and recover ammonium. For three consecutive FO cycles, the algal FO system removed 35.4% of the ammonium from the DS, increased the concentrations of COD and PO 4 3 - - P in the FS by 43.0%, and achieved a water flux of 11.59 ± 0.49 L m^-2  hr^-1 . Throughout the FO cycles, the algal biomass concentration of the DS stayed at 606 ± 29 mg COD/L due to simultaneous algal growth and DS dilution. This FO process may be feasible to implement for full-scale applications to concentrate wastewater and recover resources. PRACTITIONER POINTS: A novel forward osmosis (FO) system with an algal draw solution (DS) concentrated municipal wastewater and recovered resources (ammonium). Ammonium but not organic matter or phosphate diffused across the FO membrane from the feed solution (FS) to the DS. The algal FO system increased COD/phosphate concentration in the FS by 43.0% and removed 35.4% of ammonium from the DS. The water fluxes in the algal FO system and the control were 11.59 and 12.02 L m^-2  hr^-1 , respectively. The novel algal FO process has the potential to improve full-scale efficiency by concentrating municipal wastewater and recovering nutrients.

[Advanced Nitrogen Removal Characteristics of Low Carbon Source Municipal Wastewater Treatment via Partial-denitrification Coupled with ANAMMOX]

Partial-denitrification coupled with ANAMMOX is a novel biological nitrogen removal technology, which is expected to significantly reduce the external carbon source dosage for advanced nitrogen removal from municipal wastewater. In this study, ANAMMOX sludge was inoculated to investigate advanced nitrogen removal performance and sludge characteristics in a partial-denitrification/ANAMMOX reactor. The results showed that inoculation of ANAMMOX sludge could quickly start the partial-denitrification/ANAMMOX reactor. The effluent total nitrogen concentrations were (4.82±1.84) mg·L^-1 with a chemical oxygen demand of 2.19±0.08. Sludge particles larger than 0.20 mm accounted for 86.16% in the reactor. This meant that granular sludge was formed, which was conducive to good retention of ANAMMOX bacteria in the reactor. The external carbon source dosage and the oxygen requirement for nitrification can be reduced by applying partial-denitrification coupled with ANAMMOX to advanced nitrogen removal from the effluent of secondary clarifier in municipal wastewater treatment plants.

[Effect of Alkaline Sludge Fermentation Products on the Nitrification Process and Performance]

The aim of the present study was to investigate the effect of alkaline sludge fermentation products as a carbon source on the nitrification process and performance. During the operation of a biological nitrogen removal (BNR) system with sludge fermentation mixture as the carbon source, the activities of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were inhibited at the beginning. After 16 days, the activity of AOB began to recover rapidly, but the activity of NOB was still inhibited. The specific nitrate production rate (SNaPR, N/VSS) decreased from 0.1791 g·(g·d)^-1 to 0.0078 g·(g·d)^-1. At the same time, the nitrite accumulation rate increased from 8.12% to 91.42% and remained stable. The sludge fermentation mixture was separated into sludge fermentation liquid and sludge fermentation sediment. The changes in nitrification activity by adding different types of fermentation products were investigated. The results showed that the activity of NOB decreased in the experimental group fed with the sludge fermentation mixture and the fermentation liquid. The SNaPR decreased from an initial 0.1793 g·(g·d)^-1 to 0.1510 g·(g·d)^-1 and 0.1617 g·(g·d)^-1, respectively. In the experimental group fed with fermentation sediment, the activity of NOB increased. SNaPR rose from 0.1793 g·(g·d)^-1 to 0.1864 g·(g·d)^-1. Therefore, the activity of the NOB can be inhibited when the sludge fermentation mixture and the fermentation liquid are used as a carbon source in the nitrification process. In addition, the short-range nitrification process can be realized, which is beneficial to accelerating the reaction speed and saving investment in this type of carbon source.

Kinetic study of nutrients removal from municipal wastewater by Chlorella vulgaris in photobioreactor supplied with CO2-enriched air

The microalgae Chlorella vulgaris ATCC 13482 was used in the present study for municipal wastewater treatment. Batch experiments were performed in bubble column photobioreactors of 7 L working volume maintained at 25 ± 2°C and 14 h/10 h of photo and dark cycle. The treatment process was enhanced by using CO₂-augmented air (5% CO₂ v/v) supply into the microalgal culture in comparison to the use of normal air (0.03% CO₂ v/v). For a period of 7 days, C. vulgaris effected maximum removals of 74.4% soluble fraction of chemical oxygen demand, 72% ammonia (NH₄-N), 60% nitrate (NO₃-N) and 81.93% orthophosphate (PO₄-P) with use of normal air, whereas 84.6% sCOD, 88% NH₄-N, 72% NO₃-N and 92.8% PO₄-P removals, respectively, with use of 5% CO₂/air supply. Using kinetic study data, the specific rates of ammonia and phosphate uptake (q_ammonia and q_phosphate) by C. vulgaris at 5% CO₂/air supply were found to be 2.41 and 0.85 d^-1, respectively. Using the algal remediation technology, nitrogen-phosphorus-potassium recovery from sewage treatment plant of 37.5 million litres per day wastewater influent capacity was calculated to be ∼298.5, 55.4 and 83.7 kg d^-1, respectively.

Quantification and Multidrug Resistance Profiles of Vancomycin-Resistant Enterococci Isolated from Two Wastewater Treatment Plants in the Same Municipality

Wastewater treatment plants (WWTPs) are points of control for the environmental dissemination of antimicrobial resistant bacteria. Vancomycin-resistant enterococci (VRE) were used as indicators of antimicrobial resistance (AMR) in two WWTPs (biologically aerated filter (BAF) and conventional activated sludge (CAS)) in the same municipality. The removal and abundance of enterococci and VRE as well as the species and antimicrobial resistance profiles of VRE were assessed. Enterococci and VRE from the primary and final effluents were enumerated. Results were assessed from an ecological context. VRE was not selected for by either WWTP but the BAF system outperformed the CAS system for the removal of enterococci/VRE. Enterococcus faecalis (n = 151), E. faecium (n = 94) and E. casseliflavus/E. gallinarum (n = 59) were the dominant VRE species isolated. A decrease in levofloxacin resistance in enterococci was observed in the BAF WWTP. An increase in nitrofurantoin resistant (p < 0.001) and a decrease in quinupristin/dalfopristin (p = 0.003) and streptomycin (p = 0.022) resistant enterococci were observed in the CAS WWTP, corresponding to a shift of VRE from E. faecalis to E. faecium. Wastewater treatment processes can be managed to limit the dissemination of antimicrobial resistance determinants into the surrounding environment.

Performance of horizontal sub-surface flow constructed wetlands with different flow patterns using dual media for low-strength municipal wastewater: a case of pilot scale experiment in a tropical climate region

The work presented in this paper is based on the pilot study that was performed to investigate the role of flow pattern in the constructed wetlands (CWs) on the treatment performance of real low-strength municipal wastewater. Four identical pilot-scale horizontal sub-surface flow constructed wetlands (HSSF-CWs) were installed, out of which three beds were planted with a common macrophyte, whereas one was kept as a control. The distinction in the hydraulic design was baffles, vertical up-down (CW2) and side slits (CW3), and the third bed (CW1) was kept horizontal plain type (without baffles). The filter media used in all the beds was dual type, coarse and fine gravel. Monitoring was carried out to determine BOD₅, COD, TSS, NH₄⁺-N, TN, and TP concentrations at different sampling points. Results show that the baffled beds performed better compared to the non-baffled in the order of CW2 > CW3 > CW1 > Control. The highest removal efficiency was measured in the CW2 with a reduction in BOD₅ (86%), COD (77%), TSS (80%), NH₄⁺-N (59%), TN (66%), and TP (64%). The statistical method used also showed that the flow pattern has an impact on the treatment performances of the CWs.

[Advanced Denitrification of Municipal Wastewater Achieved via Partial ANAMMOX in Anoxic MBBR]

Anoxic MBBR is a process to achieve advanced denitrification from municipal wastewater. Here, anoxic MBBR was applied as a post-denitrification SBR to achieve advanced denitrification by partial anammox (anaerobic ammonium oxidation). During a 250-day operation, denitrification performance gradually improved and the total nitrogen concentration of the effluent was approximately 5 mg·L^-1. The average nitrate, ammonia, and total inorganic nitrogen removal efficiencies were (97.7±2.9)%, (93.3±2.9)%, and (94.3±2.7)%, respectively, between day 211 and 250. The simultaneous removal of ammonia and nitrate was observed in the anoxic reactor. Analysis of the ammonia removal pathway revealed that assimilation and nitrification were poor in the anoxic MBBR. The anammox activity test and the denitrification performance showed that anammox occurred and played a not insignificant role in the anoxic MBBR. The results of real-time quantitative PCR showed that anammox bacteria enriched in anoxic MBBR, especially in the anoxic carrier biofilms, where the abundance of anammox bacteria increased from 4.37×10⁷ copies·g^-1 to 2.28×10¹⁰ copies·g^-1. This study demonstrates that anoxic carrier biofilms may have potential applications in anammox bacterial enrichment to enhance denitrification from municipal wastewater.

A new enzymatic method assessing the impact of wastewater treatment plant effluents on the assimilative capacity of small rivers

Microorganisms play an important role in maintaining a good water quality in rivers by degrading organic material, including toxic substances. In the present study, we analyzed the potential impact of municipal wastewater treatment plant (WWTP) effluents as a major stress factor on the assimilative capacity of small rivers. It was the aim to develop a new bioassay for assessing such impacts in the receiving rivers by measuring the activity of extracellular enzymes (exoenzymes) in bacteria. Therefore, we established a specific in-vitro assay to detect inhibitory effects of solid phase-enriched water samples on β-glucosidase (BGL) activity of the actinobacterium Cellulomonas uda as a proxy for the microbial decomposition of organic substances and thus for the assimilative capacity of surface waters. We found significant reductions of BGL activity in the WWTP effluents and in the receiving waters directly downstream as well as a relative quick recovery over the further course of the water bodies. The new bioassay offers a promising tool for the assessment of the assimilative capacity in surface waters and a potential impact of WWTP effluents on this key ecosystem function. Abbreviations WWTP wastewater treatment plant BGL β-glucosidase EU-WFD European Water Framework Directive FAU Formazin Attenuation Units PE population equivalents REF relative enrichment factor; SPE solid phase extraction MTBE methyl-tert-buthyl-ether DMSO dimethyl-sulfoxide NPG 4-nitrophenol-β-d-glucopyranoside DOC dissolved organic carbon.

Efficiency of nitrogen and phosphorus compounds removal in hydroponic wastewater treatment plant

Wastewater treatment with the use of plants is one of the most promising treatment technologies for municipal, domestic and industrial wastewater. The aim of this study was to evaluate the reduction of biogenic compounds concentrations in municipal wastewater treated with the use of hydroponic technology as a tertiary treatment. Research was conducted to assess the suitability of hydroponic lagoon use for municipal wastewater treatment. Samples of sewage for its quality tests were taken from a wastewater treatment plant (WWTP) located in the south-western part of Poland. Average efficiencies of nutrients removal were calculated. Analyses show that the effectiveness of purification is similar for systems with and without the use of the third stage of purification and reached around 82-83% for total nitrogen and 77-79% for ammonium nitrogen. N-NO₂ and N-NO₃ removal efficiency was very low for both analysed systems where for total phosphorus and phosphates it oscillated around 83-84%.

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.

[Assessing Performance of Pollutant Removal from Municipal Wastewater by Physical and Chemical Methods Based on Membranes]

The removal characteristics of various pollution factors in municipal wastewater by membrane-based physical and chemical treatment, especially the enrichment characteristics of dissolved organic matter, were investigated by high performance liquid chromatography and three-dimensional fluorescence spectroscopy. The results showed that the municipal wastewater had a low COD/TN ratio after the treatment. The micro-flocculation filtration mainly enriched the non-dissolvable organic matter in the raw water and aromatic protein substances with relative molecular mass greater than 30 000. The enrichment degree was up to 60.93%, especially for tyrosine-like and tryptophan-like substances. The dissolved organic matter (DOM) with a molecular weight greater than 30 000 was enriched fully by 0.45 μm and 0.22 μm acetate membranes, but the microfiltration membrane was not selective for the enrichment of organic matter. Thus, NF mainly enriched the fulvic acid and humic acid in urban sewage. The enrichment degree was 52.01% and 53.57%, respectively, and the total enrichment degree of dissolved organic matter was about 42%.

[Operating Characteristics of a DPR-SNED System Treating Low C/N Municipal Wastewater and Nitrate-containing Sewage]

In order to realize the simultaneous treatment of low C/N municipal wastewater and high nitrate wastewater, a sequencing batch reactor (SBR), inoculated with activated sludge, was used to initiate the denitrifying phosphorus removal coupled with simultaneous nitrification and endogenous denitrification (DPR-SNED). The anaerobic/anoxic/hypoxic durations and dissolved oxygen (DO) concentration were appropriately controlled, and the nitrogen and phosphorus removal characteristics were examined. The experimental results demonstrated that, in the anaerobic/hypoxia operation mode, with an anaerobic duration of 3 h and DO concentration of 0.5-1.0 mg·L^-1, the simultaneous nitrification of phosphorus removal (SNEDPR) system successfully began in 60 d. The effluent PO₄^3--P concentration was below 0.5 mg·L^-1, the nutrient and COD removal efficiencies were stably maintained above 90% and 80%, respectively, and the SNED efficiency and COD_ins efficiency reached 70% and 95%, respectively. When the operation mode was anaerobic/anoxic/hypoxic and nitrate-containing sewage was added at the beginning of the anoxic stage, DPR-SNED was achieved with the effluent PO₄^3--P concentration<0.5 mg·L^-1, nutrient and COD removal efficiencies above 88% and 90%, respectively, and SNED efficiency and COD_ins efficiency maintained at 62% and 90%, respectively. After the successful initiation of DPR-SNED, enhanced intracellular carbons storage was achieved by phosphorus-and glycogen-accumulating organisms using the limited carbons in raw municipal wastewater to provide sufficient carbon sources for subsequent nutrient removal. In addition, the endogenous partial denitrification ensured the efficient nitrogen removal performance of the DPR-SNED system at low C/N conditions (average 4).

Effect of COD/N ratio on denitrification from nitrite

The objective of this study was to investigate dynamic specific denitrification rates (SDNRs) from nitrite at various chemical oxygen demand (COD)/nitrogen (N) ratios using municipal wastewater (MWW). A sequencing batch reactor (SBR) continuously fed with primary effluent and nitrite solution was operated at hydraulic retention time of 8.4 hr and solids retention time of 26-30 days for 3 months. Influent MWW characteristics varied significantly during the study, that is, 200-810 mgCOD/L and 6-80 mgN/L. The SDNRs from the SBR were compared with those determined in four batch reactors using acetate. The SDNR was directly related to COD/N until a maximum SDNR (mgNO₂ -N/mgVSS/day) of 0.07 for MWW and 0.4 for acetate occurred at COD/N ratios of 6 and 13, respectively; beyond this COD/N ratio, SDNR decreased. The biomass yield coefficients (mgVSS/mgCOD) were 0.33 for MWW and 0.51 for acetate. The relationships of SDNR with COD/N and F/M ratios were developed. PRACTITIONER POINTS: The optimum carbon dose for denitrification should be determined using acclimatized biomass. Each carbon source should only be dosed at an optimum that maximizes denitrification.

Heavy metal phyto-accumulation in leafy vegetables irrigated with municipal wastewater and human health risk repercussions

In this study, heavy metal phyto-accumulation potential of selected cultivars of two leafy vegetables on irrigation with municipal wastewater and human health risks were investigated. Municipal wastewater chemistry was recorded significantly different from groundwater control and led to the two-fold high enrichment of soil heavy metal contents (Ni, 19.46; Pb, 23.94; Co, 4.68; Cd, 1.4 in mg/kg, respectively). Interactive effects for phyto-accumulation of most heavy metals were also recorded significant at p < 0.001 in four vegetable cultivars. Heatmap revealed higher accumulation of heavy metals (Fe, Zn, Mn, Cu, Pb, Cr, Co) in spinach cultivars than lettuce cultivars creating elevated health risk index (HRI) and hazard index (HI) values for adults and children. Highest HI was recorded for Lahori palak (adults, 1.42; children, 2.58) and lowest for iceberg (adults, 0.04; children, 0.07). The NPK supplementation improved mineral composition of leafy vegetables within safer human health limits in control treatments. However, in municipal wastewater treatments, NPK fertilization decreased heavy metal uptake and phyto-accumulation in S2 (Lahori palak) than remaining vegetable cultivars leading to reduced health risk values. Because of higher heavy metal phyto-accumulation and health risks, cultivation of spinach cultivars must be discouraged in agro-ecologies receiving municipal wastes, whereas lettuce cultivars should be promoted.

Decentralized wastewater treatment using passively aerated biological filter

This study aimed to evaluate the efficiency of a novel pilot-scale passively aerated biological filter (PABF) as a low energy consumption system for the treatment of municipal wastewater. It consists of four similar compartments, each containing 40% of a non-woven polyester fabric as a bio-bed. The PABF was fed with primary treated wastewater under a hydraulic retention time (HRT) of 3.5 hr and a hydraulic loading rate of 5.5 m²/m³/d. The effect of media depth, HRT, dissolved oxygen (DO) and surface area of the media on the removal efficiency of pollutants was investigated. Results indicated that increasing media depth along the axis of the reactor and consequently increasing the HRT and DO resulted in great removal of different pollutants. A significant increase in the DO levels in the final effluent up to 6.7 mg/l resulted in good nitrification processes. Statistical analysis using SPSS showed that the reactor performance has significant removal efficiency (p < .05) for all pollutants. Overall results indicated that PABF is a viable ecological engineering approach that can be optimized and applied to improve water quality with minimal consumption of energy and low sludge production compared with conventional activated sludge and trickling filter systems.

Treatment efficiency of a hybrid constructed wetland system for municipal wastewater and its suitability for crop irrigation

Design and implementation of wastewater treatment is inevitable due to toxic effects of wastewater irrigation on crops, soil and human health. Current investigation is the pioneer attempt on full-scale hybrid constructed wetland system (HCWS) built for municipal wastewater treatment from Pakistan. HCWS was comprised of vertical sub-surface flow constructed wetland (VSSF-CW) and five phyto-treatment ponds connected in series. Higher environmental risk was associated with untreated municipal wastewater usage in irrigation as estimated through discharge of metals to recipient soils. Treatment efficiency percentages recorded for HCWS reclaimed water quality parameters were, i.e., EC (56.68), TDS (56.86), alkalinity (39.67), chloride (39.68), sulfate (46.73), Na (28.80), Mn (65.24), Cr (78.07), Ni (81.02), BOD (68.74), total hardness (19.56), Fe (70.09), phosphate (55.40), Pb (80.48), COD (63.64), Mg (17.24), K (60.05), Co (100), Cu (67.73), Zn (59.97), Cd (100), and Ca (21.47) respectively. Wastewater treatment in HCWS was due to aquatic plants [Phragmites australis Cav. Trin. ex Steud., Canna indica L. Typha latifolia L., and Hydrocotyle umbellata L.], microbial activities and substrate based wetland processes. The HCWS treated water was well under irrigation standards and recommended for safer crop production in water scarce regions.

[Effect of Denitrification and Phosphorus Removal Microorganisms in Activated Sludge Bulking Caused by Filamentous Bacteria]

Activated sludge bulking or foaming caused by filamentous bacteria is a frequent problem in the operation and management of wastewater treatment plants. To clarify the effect of filamentous bacteria sludge bulking on the functional flora in the biological denitrification and phosphorus removal system, morphological identification and Illumina MiSeq sequencing were applied to investigate the distribution of key micro-flora from the non-bulking period, sludge bulking period, and biological foaming period in five municipal wastewater treatment plants. The results showed that the sludge bulking and biological foaming were caused by Microthrix parvicella when the maximum contents were 6% and 38%, respectively. The main bacteria for denitrification and phosphorus removal were Nitrosomonas, Nitrospira, Thauera, and Candidatus Accumulibacter phosphatis. Compared to the non-bulking period, the relative abundance of AOB and PAO was significantly decreased when the maximum contents were 54% and 47%, respectively, during the bulking period. In addition, the relative abundance of denitrifying bacteria was significantly increased when the maximum content was 73%. The fluctuation of micro-flora for denitrification and phosphorus removal was affected by the activated sludge bulking and was related to the treatment process and physiological characteristics of the bacteria.

[Pilot-scale Experiment on Enrichment of Nitrifying Activated Sludge and Its Application in Enhancing a Wastewater Biological Treatment System Against Ammonia Shocking Loads]

Nitrifying activated sludge (NAS) was enriched in a membrane bioreactor (MBR) with pre-treated municipal wastewater and additional ammonium sulfate as the culture medium. The influences of temperature, dissolved oxygen (DO), ammonia nitrogen volumetric load, free ammonia (FA), and free nitrite (FNA) on the enrichment of NAS were investigated, the cost of the process was evaluated, and then NAS's application in enhancing a wastewater biological treatment system against ammonia shocking loads was attempted. The results showed that after 182 days of cultivation in an MBR, NAS had a nitrification activity of 98.41 mg·(L·h)^-1, which was 30-times higher than that of the seeding sludge. The yield of NAS was 14.96 mg·(L·d)^-1, costing 3.52 Yuan for 1 kg. Temperature was found to be a key factor affecting the sludge nitrification activity. The sludge nitrification activity was decreased to 1/3 of the maximum value at temperatures below 15.0℃, while lowering the ammonium volumetric load retarded the decrease in the sludge nitrification activity to some extent. In addition, dissolved oxygen deficiency resulted in nitrite accumulation, and thereby slowed down the NAS enrichment rate. The enriched NAS was then applied to a wastewater biological treatment pilot equipment, which had just been exposed to an ammonium shocking load. The removal rate of ammonia nitrogen in the biological system increased from 29.4% to 88.4% after 2.0% of NAS was inoculated. The enhanced biological system retained ammonia removal rates of as high as 99.0%, even as the temperature dropped to 13.3℃±1.6℃ afterwards. The above pilot-experiment results suggested that enriched nitrifying sludge is suitable for quickly increasing the start-up or recovery rates of the nitrifying function in a biological system.