Phosphorus Removal Efficiency Research Articles

Removal of phosphorus by modified bentonite:polyvinylidene fluoride membrane-study of adsorption performance and mechanism.

Enhanced phosphorus management, geared towards sustainability, is imperative due to its indispensability for all life forms and its close association with water bodies' eutrophication, primarily stemming from anthropogenic activities. In response to this concern, innovative technologies rooted in the circular economy are emerging, to remove and recover this vital nutrient to global food production. This research undertakes an evaluation of the dead-end filtration performance of a mixed matrix membrane composed of modified bentonite (MB) and polyvinylidene fluoride (PVDF) for efficient phosphorus removal from water media. The MB:PVDF membrane exhibited higher permeability and surface roughness compared to the pristine membrane, showcasing an adsorption capacity (Q) of 23.2 mgP·m-2. Increasing the adsorbent concentration resulted in a higher removal capacity (from 16.9 to 23.2 mgP·m-2) and increased solution flux (from 0.5 to 16.5 L·m-2·h-1) through the membrane. The initial phosphorus concentration demonstrates a positive correlation with the adsorption capacity of the material, while the system pressure positively influences the observed flux. Conversely, the presence of humic acid exerts an adverse impact on both factors. Additionally, the primary mechanism involved in the adsorption process is identified as the formation of inner-sphere complexes.

Performance of a Double-Filter-Medium Tandem Membrane Bioreactor with Low Operating Costs in Domestic Wastewater Treatment

To reduce the operating costs of conventional membrane bioreactors (MBRs) and improve the stability and quality of the dynamic membrane bioreactor (DMBR) effluent, a homemade inexpensive filter cloth assembly was connected to an up-flow ultra-lightweight-medium filter (UUF) in lieu of expensive membrane modules to form a double-filter-medium tandem (DT)-MBR. DT-MBR was used to treat domestic wastewater, and its removal efficiencies for chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus were similar to those of aerobic MBR, with average removal rates of 91.1%, 98.4%, 15.1%, and 50.7%, respectively. The average suspended solid (SS) of the final effluent was 5.6 mg∙L−1, and the filter cloth assembly played a leading role in SS removal, with an average removal rate of 86.0% and a relatively stable removal effect with little impact via backwashing. The activated sludge zeta potential, flocculation and sedimentation properties, particle size distribution, microbial compositions, extracellular polymeric substances (EPS), and filtration resistance of the cake layer were analyzed; it was found that the cake layer, which can also be called the dynamic membrane (DM), had an excellent filtration performance. However, the DM theory could not reasonably explain why the effluent quality of the filter cloth assembly maintained good stability even after backwashing. The real reason must be related to the sieving of cloth pores. Therefore, the concept of an in situ autogenous static membrane (ISASM) was proposed. With low operating costs and good and stable effluent quality, DT-MBR is a desirable alternative to the traditional MBR.

Intensified nitrogen and phosphorus removal and mechanism revelation in constructed wetlands amended with iron-carbon based substrate towards low C/N ratio wastewater

Constructed wetlands (CWs) show a promising capability of nutrient removal from the low C/N ratio characterized wastewater with the help of functional substrates, yet the mechanism remains unclear. In this study, sponge iron mixed with biochar was adopted as substrates to construct bench-scale CWs (CW-FeC) treating simulated urban tail water (C/N = 2). Over the experiment, it achieved a prominent performance with total nitrogen (TN) and total phosphorus (TP) removal efficiency of 89.8 and 92.1 %, respectively. Meanwhile, greenhouse gas emissions such as CO2 and N2O were extensively depressed. Mechanism analysis revealed that the deposition of ferrous ions on biochar would enlarge the micro-electrolysis interfaces and amplify the binding sites between P and Fe compared to CW systems with other substrates (gravel, biochar, and gravel mixed with sponge iron remarked as CW-G, CW-C, and CW-FeG). A significant difference regarding the mechanism of N removal was proposed based on the bacterial community analysis. The released ferrous (due to electrolysis and high abundance of iron-reduced bacteria) as electron donors could be easily captured by iron-based autotrophic denitrification bacteria as evidenced by 1.98 times higher the relative abundance of denitrifying bacteria and upregulated related genes expression. In contrast, the iron-oxidized bacteria have to be acclimatized in the CW-FeG to supply electrons for denitrification via interspecies extracellular electron transfer. The positive correlation between iron-redox bacteria and denitrification bacteria further demonstrated the integrity of the iron cycle in CWs for better nitrogen removal. These findings provide an elaborated insight into the nutrient transformation and removal processes interacting with substrates in CWs.

Comparison of the Work of Wastewater Treatment Plant “Ravda” in Summer and Winter Influenced by the Seasonal Mass Tourism Industry and COVID-19

Mass tourism puts enormous pressure on wastewater treatment plants due to its expansive growth during the summer months. To adapt to the fluctuations, the Ravda wastewater treatment plant (WWTP) uses innovative methods and technologies, allowing for “shrinking” and “expanding” of the facilities according to the season. This has been built in stages over the years, with two separate biological treatment lines adapting to different numbers of tourists and to the quantity of influent wastewater. The aim of this study is to make a comparative assessment of the work of WWTP Ravda in the summer and winter seasons and its effectiveness, as well as to compare them. In addition, it examines the years of the COVID-19 pandemic, when a much higher consumption of water per person was noted. Data were analyzed for the period of 2018–2022 inclusive, comparing influent and effluent BOD5 and COD in the summer and winter. Nitrogen and phosphorus removal efficiencies were also tracked. The study shows that municipal wastewater treatment is effective, but much higher values, close to the maximum permissible discharge values, are observed during the tourist season. With the continued growth of the tourism sector, the Ravda wastewater treatment plant would not be able to cope with the discharge standards set by the Ministry of Environment and Water, so measures need to be taken promptly.

A novel γ-Fe3O4-N-BC combined membrane bioreactor for wastewater treatment: Performance and mechanism

In this study, a new type of iron–nitrogen doped biochar (γ- Fe3O4-N-BC) was developed to improve nutrient removal efficiency and mitigate membrane fouling in combination with MBR. The characteristion of γ-Fe3O4-N-BC, N-BC, and BC revealed that the BET surface area (SBET) of γ-Fe3O4-N-BC, which was 1320.86 m2/g, was greater than that of N-BC (702.75 m2/g) and BC (1033.63 m2/g). The excellent SBET exhibited by γ-Fe3O4-N-BC compared to that of the other biochars is attributed to hydrogen bonding and electrostatic interactions. Compared to the addition of N-BC or BC or the absence of biochar, the addition of γ-Fe3O4-N-BC in the membrane bioreactor (MBR) resulted in superior wastewater treatment performance, for which the average removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and total phosphorus (TP) were 94.65 %, 82.56 %, and 65.90 %, respectively. Moreover, after inoculation with γ-Fe3O4-N-BC, the TMP increase rate and time required to reach 42.37 kPa were 2.35 kPa/d and 18 d, respectively. The investigation of the effect of the γ-Fe3O4-N-BC concentration on MBR performance showed that the nutrient removal efficiency in the 500-MBR greater than that in the 350-MBR, 650-MBR, and 800-MBR, and that the membrane fouling was more ameliorative. A mechanistic investigation demonstrated that the 500-MBR had a beneficial influence on sludge biomass growth and helped to improve the nutrient removal capacity of the MBR. The 500-MBR improved the flocculability and stability of the sludge flocs in the MBR by increasing particle size and zeta potential. Changes in the extracellular polymeric substance (EPS) concentration and the smaller protein (PN) / polysaccharide (PS) ratio in 500-MBR also had significant impacts on alleviating the adhesion and accumulation of fouling layers on the improved membrane surface. Consequently, this study provides a new method for nutrient removal and membrane fouling mitigation in the MBR process.

Co-pelletization of fungi and microalgae for efficient tetracycline and nutrient removal

The potential harm to environmental and human health caused by antibiotic abuse has attracted widespread concern. In this study, the effects of the initial biomass ratio of Chlorella vulgaris and Ganoderma lucidum on the basic properties (sphericity, diameter, and color), growth, and photosynthetic performance of microalgae-fungi symbionts were analyzed. The effect and mechanism of tetracycline hydrochloride (TC) removal were investigated. Optimal removal was obtained at a 10:1 ratio (microalgae/fungi) with a 5 mm diameter symbiont. Under these conditions, the chlorophyll a concentration was 186.49 ± 17.81 μg L−1, and maximum removal efficiencies for total phosphorus, total nitrogen, chemical oxygen demand, and TC in wastewater were 84.68% ± 8.13%, 82.96% ± 8.12%, 81.77% ± 7.68%, and 94.57% ± 5.14%, respectively. These results provide important theoretical guidance for treatment applications for antibiotic-containing wastewater.

Novel Fe/Ca oxide co-embedded coconut shell biochar for phosphorus recovery from agricultural return flows.

Efficient elimination and recovery of phosphorus from agricultural return flows are crucial for effective eutrophication management and phosphorus reuse. In this study, a neutral Fe/Ca oxide co-embedded biochar (FCBC) was synthesized using calcium peroxide and ferrous chloride as precursors for phosphate recovery from agricultural return flows. FCBC possesses a highly intricate pore structure and an abundance of surface-active groups. Fe/Ca oxides were loaded onto the biochar in the form of Ca2Fe2O5, Fe2O3, and CaCO3. FCBC demonstrated a broad pH tolerance range (pH = 6-12) in the aquatic environment. The maximum saturation adsorption capacity was 53.31 mg g-1. Phosphorus removal is influenced by Ca3(PO4)2 generation, intra-particle diffusion, and electrostatic attraction. The produced FCBC showed exceptional phosphorus removal efficiency in the presence of various anions, except for wastewater with high concentrations of SO4 2-, CO3 2-, HCO3 -, and F- (>500 mg L-1). FCBC can effectively remove phosphorus from agricultural return flows and reduce the risk of the water environment. Returning it to the field can also mitigate the depletion of phosphorus resources, effectively reduce carbon emissions from farmland, improve soil fertility, and realize multiple benefits.

Optimization of phosphorus adsorption on honeycomb briquette ash by application of response surface methodology

Honeycomb coal ash was selected as phosphorus adsorbent to explore the influence of different factors on phosphorus adsorption performance for phosphorus containing wastewater. The structural, physical and chemical properties of coal ash were determined by SEM, BET and XRF analysis methods. The response surface methodology (RSM) was applied for experimental design of phosphorus adsorbent. The effect of five independent variables including initial concentration of phosphorus, coal ash dosage, coal ash particle size, adsorption time and pH on the phosphorus removal efficiency (R (%)) was studied in the ranges of 5–7 mg/L, 6–10 g, 180–220 mesh, 20–30 min and 6.12–6.92 respectively. 46 runs of experiments were designed by the Design-Expert software. The optimum conditions for initial concentration of phosphorus, coal ash dosage, coal ash particle size, adsorption time and pH were found as 6.34 mg/L, 8.17 g, 207.97 mesh, 23.33 min and 6.64, respectively. At these conditions, removal efficiency and desirability function were found to be 96% and 1.000, respectively. The results of kinetic model reveals that the adsorption process conforms to Pseudo-first-order kinetics Equation (R2 =0.9991). The briquette ash has a good application prospect for the actual treatment of phosphorus containing wastewater, which provides a certain treatment strategy for the restoration of damaged water environment.

Optimizing the formation of aerobic granular sludge and enhanced pollutant removal efficiency in a constant current variable voltage electric field

Aerobic granular sludge (AGS) disintegration occurs during long-term operation, decreasing particle settling performance and deteriorating the pollutant removal effect. Therefore, this experiment proposes an electric field synergistic AGS construction to improve the strength of particles and the efficiency of nitrogen and phosphorus removal. The study revealed that under the influence of an electric field, iron ions dissolved from the iron electrode and phosphate formed mineral nuclei inside the particles, which effectively increased the average size of the particles and increased the protein content of extracellular polymeric substances (EPS). The experimental results demonstrated that including Fe–C electrodes in the electric field group increased the TN removal rate to 86.65%, surpassing the rates observed in the blank without an electric field and C–C electrode electric field groups by factors of 1.13 and 1.11, respectively. Under the electric field, AGS enriched some functional microorganisms for denitrogenation, thus improving total nitrogen removal efficiency. Furthermore, the phosphorus removal efficiency in the electric field group featuring Fe–C electrodes exhibited a notable enhancement, reaching 90.16%. This improvement was 1.71 and 1.62 times that of blank without an electric field and C–C electrode electric field groups, respectively. The phosphorus removal efficacy of electrode-released iron is distinct from that of exogenous ferrous sulfate, with the former demonstrating superior activity and pronounced phosphorus removal capabilities. Therefore, this study comprehensively revealed AGS construction mechanism and pollutant removal efficacy under the electric field's synergistic effect.

Harnessing diurnal dynamics: Deciphering the interplay of light cycles on algal-bacterial membrane bioreactors

Light profoundly modulates the algal-bacterial membrane bioreactor (algal-bacterial MBR) performance. Yet, its outdoor deployment grapples with the inherent diurnal cycle of sunlight, engendering suboptimal light conditions. The adaptability of such systems to these fluctuating light conditions and their implications for practical outdoor applications remained an under-explored frontier. In response, this study meticulously scrutinized two laboratory-scale algal-bacterial MBRs under varying light regimes: a 24-h continuous and a 12-h cyclic illumination. Over 70 days, continuous illumination was observed to yield superior biomass production and total nitrogen and total phosphorus removal efficiencies compared to its cyclic counterpart. Contrarily, when focusing on membrane fouling, the 12-h cyclic illumination exhibited lower membrane fouling. The spectral analyses coupled with adhesion ability evaluation, traced the enhanced membrane fouling under continuous illumination to the elevated organics and heightened adhesive properties of the flocs. Given the tangible benefits of reduced membrane fouling and the potential harnessing of solar radiation, the 12-h cyclic illumination emerges as an economically astute operational paradigm for algal-bacterial MBRs. The significance of this study is to promote the application of algal-bacterial MBR in sewage treatment and provide robust support for the development of green technology in the future.

Developing upflow filters operated in a cascade sequence to compare two green sorption media for phosphorus removal

Finding solutions to treat stormwater runoff and wastewater effluent that contain phosphorus is an important effort due to the potential harmful algal bloom impacts on both human health and the environment, such as red tide in coastal regions, eutrophication of waterbodies, and fish kills. However, many of the remaining phosphorus reserves are becoming depleted. Finding low-cost, energy-efficient, and low-maintenance solutions that incorporate green sorption media (GSM) mixed with natural and recycled materials to treat nutrient-laden water, with potential for recovery, is of critical importance for sustainable material development. Biochar and zero-valent iron (ZVI) have received significant attention as low-cost, low-impact adsorbents for the removal of heavy metals, pathogens, and nutrients due to their ability to aid in structural support and reasonable removal efficiencies in GSM. In this study, phosphorus removal efficiencies were studied using two new recipes of GSM within a unique passive cascade upflow filtration system. The two new GSM include zero-valent iron and perlite green environmental media (ZIPGEM) composed of 85% sand, 5% clay, 5% ZVI, and 5% perlite by volume, and biochar zero-valent iron and perlite green environmental media (BIPGEM) containing 80% sand, 5% biochar, 5% clay, 5% perlite, and 5% ZVI by volume. Results indicate that the ZIPGEM-based filtration system achieved an average removal of 78.9% to 97.9% in the initial 60-min to 300-min range, whereas BIPGEM exhibited an average 67.1% to 86.9% removal during this same time interval. At the time of shutdown as a system, BIPGEM showed an average 52.8% removal at the 5480-min mark, and ZIPGEM exhibited an average 69.1% removal at the 11,180-min mark. After examining three isotherm models, the dose-response model estimated the adsorption capacity of ZIPGEM as 6.5 mg·g−1. Further comparison of the material structures and compositions of both raw and spent media samples using X-ray diffraction, X-ray fluorescence spectrometry, and a scanning electron microscope helped confirm part of the removal mechanisms.

Sustainable Lutein Production from Chlorella sorokiniana NIES-2168 by Using Aquaculture Wastewater with Two-Stage Cultivation Strategies

Unnecessary discharge of nutrient-rich aquaculture wastewater is a significant threat to the environment, exacerbating massive resource wasting worldwide. Microalgae-based circular economy strategies utilize atmospheric CO2 and aquaculture wastewater nutrients and convert them into valuable compounds. Lutein, a natural pigment, is a nutritional supplement for eye protection, anti-cancer and anti-inflammatory effects, and other health benefits. It is widely utilized in the food and pharmaceutical industries. The primary purpose of this study is to reuse aquaculture wastewater to grow microalgae and optimize conditions to achieve a high yield of lutein as well as the removal of nutrients from wastewater. When cultured in 1.0× BG11 nutrient-added aquaculture wastewater and aerated using 2% CO2, the biomass concentration and lutein content of Chlorella sorokiniana NIES-2168 increased to 1.78 g L−1 and 7.43 mg g−1, respectively. A two-stage culture strategy further increased the lutein content and yield of microalgae. The highest lutein content of 13.95 mg g−1 and lutein productivity of 3.63 mg L−1 d−1 in the second stage aligned with other phototrophic microalgae currently used for lutein production. C. sorokiniana NIES-2168 also showed exceptional nitrogen and phosphorus removal efficiency, with nitrate and phosphate removal rates reaching 96.07% and 96.75% during the two-stage culture process.

Simultaneous nitrogen and phosphorus removal through an integrated partial-denitrification/anammox process in a single UAFB system

With the aim of obtaining enhanced nitrogen removal and phosphate recovery in mainstream sewage, we examined an integrated partial-denitrification/anaerobic ammonia oxidation (PD/A) process over a period of 189 days to accomplish this goal. An up-flow anaerobic fixed-bed reactor (UAFB) used in the integrated PD/A process was started up with anammox sludge inoculated and the influent composition controlled. Results showed that the system achieved a phosphorus removal efficiency of 82% when the influent concentration reached 12.0 mg/L. Batch tests demonstrated that stable and efficient removal of chemical oxygen demand (COD), nitrogen, and phosphorus was achieved at a COD/NO3−-N ratio of 3.5. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis indicated that hydroxyapatite was the main crystal in the biofilm. Furthermore, substrate variation along the axial length of UAFB indicated that partial denitrification and anammox primarily took place near the reactor's bottom. According to a microbiological examination, 0.4% of the PD/A process's microorganisms were anaerobic ammonia oxidizing bacteria (AnAOB). Ca. Brocadia, Ca. Kuenenia, and Ca. Jettenia served as the principal AnAOB generals in the system. Thauera, Candidatus Accumulibacter, Pseudomonas, and Acinetobacter, which together accounted for 27% of the denitrifying and phosphorus-accumulating bacteria, were helpful in advanced nutrient removal. Therefore, the combined PD/A process can be a different option in the future for sewage treatment to achieve contemporaneous nutrient removal.

Copper oxide nanoparticles influence on the performance of sequencing batch reactor and the transfer of antibiotic resistance genes by regulating bacterial quorum sensing system

The environmental pollution caused by copper oxide nanoparticles (CuO NPs) has attracted widespread attention. In this study, microbial community, key metabolic pathways and quorum sensing (QS) were investigated to reveal the impact of copper oxide nanoparticles (CuO NPs) on the performance of sequencing batch reactor (SBR) and the transfer of antibiotic resistance genes (ARGs). Results showed that under CuO NPs impact, the removal efficiency of COD, ammonium nitrogen (NH4+-N) and total nitrogen (TN) was stable at around 90%, 96% and 60%, respectively. However, removal efficiency of total phosphorus (TP) was reduced to below 60% under 0.1 mg/L and 1 mg/L CuO NPs exposure. Microbial community analysis showed CuO NPs was advantageous to the growth of key functional bacterial phyla Bacteroidetes, Proteobacteria and Patescibacteria. The relative abundance of Candidatus Accumulibacter genus and ppX gene were decreased, which then lower the TP removal efficiency. Besides, CuO NPs might trigger QS system, affecting Candidatus Accumulibacter, Aeromonas genus and ppX gene, and then regulated the removal of TP in the SBR system. The co-occurrence network analysis revealed a correlation among core ARGs, signaling molecule, QS-related microbial community and ARGs’ hosts, suggesting that the spread of ARGs might be driven by QS system under selective pressure of CuO NP. These findings could reveal the effect of CuO NPs on the performance of activated sludge system and provides new ideas for ARGs control through regulating the QS system.

Enhanced removal efficiency of nitrogen and phosphorus from swine wastewater using MgO modified pig manure biochar

Pig manure and swine wastewater from livestock and poultry contain high levels of nitrogen and phosphorus, which can seriously threaten ecosystems. In this study, biochar derived from pig manure (PMBC) was modified by various magnesium salts to obtain pig manure biochar modified with MgO (MgO-PMBC), Mg(OH)2 (Mg(OH)2-PMBC) and MgCl2 (MgCl2-PMBC), and their capacities of simultaneous adsorption of NH4+-N and PO43--P were investigated. Results showed that the adsorption quantities for NH4+-N and PO43--P decreased in the order: MgO-PMBC >Mg(OH)2-PMBC > MgCl2-PMBC > PMBC. When the optimal dosage for MgO-PMBC was determined to be 0.6 g/L and the initial solution pH was set to the ideal value of 7, the maximum adsorption quantities for NH4+-N and PO43--P by MgO-PMBC reached 122.01 mg/g and 206.85 mg/g, respectively, which were 49.8 and 85.5 times of those of the PMBC. The specific surface area and total pore volume of MgO-PMBC were 9.4 times and 4.1 times of the PMBC. Removal rate of PO43--P from swine wastewater was 97.57%, and the concentration of PO43--P from treated swine wastewater was lower than 0.5 mg/L, the primary discharge standard of China’s Comprehensive Wastewater Discharge Standard. The enhanced simultaneous adsorption of NH4+-N and PO43--P by modified PMBC (MgO-PMBC) was ascribed to its greater specific surface area and total pore volume, and the reaction of crystallisation of struvite. Our results demonstrated that pig manure biochar modified by MgO can be used to treat swine wastewater effectively.

Experimental Investigation of Lanthanum-Modified Reinforced Composite Material for Phosphorus Removal

Adsorption stands as an economically viable, efficient, recyclable, operationally straightforward, cost-effective, and low-sludge method extensively employed for phosphorus removal. In an effort to enhance the adsorption capabilities of the adsorbent, this study employs the rare-earth metal lanthanum in conjunction with the group’s previously researched high-efficiency composite industrial residue phosphorus removal materials (EPRC) for modification, thereby generating lanthanum-modified reinforced composite phosphorus removal materials (La-EPRC). Subsequently, the novel material undergoes static modification, followed by experimental investigations into static and dynamic adsorption for phosphorus removal. Static adsorption experiments reveal optimal phosphorus removal efficiency when the initial phosphorus solution concentration is 20 mgP/L, with a La-EPRC particle dosage of 3 g/250 mL and a temperature of 25 °C. The removal efficiency of phosphorus particles is above 90% within the pH range of 4 to 10. Common coexisting anions in water, including Cl−, SO42−, HCO3−, and CO32−, demonstrate minimal impact on the efficacy of phosphorus removal. La-EPRC demonstrates a robust adsorption stability in both water and hot water environments. In a 2.5 mol/L NaOH solution, effective desorption of La-EPRC particles is observed, facilitating material regeneration. The raw materials for La-EPRC are easily accessible and cost-effective, imparting significant potential for widespread applications.

High-efficient nutrient removal in a single-stage electrolysis-integrated sequencing batch biofilm reactor (E-SBBR) for low C/N sanitary sewage treatment

To efficiently remove nutrients from low C/N sanitary sewage by conventional biological process is challenging due to the lack of sufficient electron donors. A novel electrolysis-integrated sequencing batch biofilm reactor (E-SBBR) was established to promote nitrogen and phosphorus removal for sanitary sewage with low C/N ratios (3.5–1.5). Highly efficient removal of nitrogen (>79%) and phosphorus (>97%) was achieved in the E-SBBR operating under alternating anoxic/electrolysis-anoxic/aerobic conditions. The coexistence of autotrophic nitrifiers, electron transfer-related bacteria, and heterotrophic and autohydrogenotrophic denitrifiers indicated synergistic nitrogen removal via multiple nitrogen-removing pathways. Electrolysis application induced microbial anoxic ammonia oxidation, autohydrogenotrophic denitrification and electrocoagulation processes. Deinococcus enriched on the electrodes were likely to mediate the electricity-driven ammonia oxidation which promoted ammonia removal. PICRUSt2 indicated that the relative abundances of key genes (hyaA and hyaB) associated with hydrogen oxidation significantly increased with the decreasing C/N ratios. The high autohydrogenotrophic denitrification rates during the electrolysis-anoxic period could compensate for the decreased heterotrophic rates resulting from insufficient carbon sources and nitrate removal was dramatically enhanced. Electrocoagulation with iron anode was responsible for phosphorus removal. This study provides insights into mechanisms by which electrochemically assisted biological systems enhance nutrient removal for low C/N sanitary sewage.

Optimizing sludge retention time for sustainable photo-enhanced biological phosphorus removal systems: Insights into nutrient fate, microbial community, and bacterial phototolerance

Photo-enhanced Biological Phosphorus Removal (PEBPR) systems, promising wastewater treatment technology, offer efficient phosphorus removal without external oxygen. However, comprehending the impact of sludge retention time (SRT) on the system is crucial for successful implementation. This study investigated the SRT effect on nutrient fate, microbial community, and bacterial phototolerance in PEBPR systems. PEBPR systems exhibited good bacterial phototolerance at SRT of 10, 15, and 20 d, with optimal phosphorus-accumulation metabolism observed at SRT of 10 and 15d. However, at SRT of 5d, increased light sensitivity and glycogen-accumulating organisms (GAOs) growth resulted in poor P removal (71.9%). Accumulibacter-IIC were the dominant P accumulating organisms (PAOs) at SRT of 10, 15, and 20 d. Accumulibacter-I, IIC and IIF were the major PAOs at SRT of 5 d. The decrease in SRT promoted the microalgal population diversity, and Dictyosphaerium and Chlorella were the major microalgal species in this study. Flow cytometry results revealed high light intensity triggered intracellular Fe2+ efflux, limiting translation activity and metabolism. Moreover, PAOs had lower phototolerance than GAOs due to Poly-P bound intracellular Mg2+ affecting enzyme activity. This study provides an in-depth understanding of PEBPR systems operation strategy toward environmentally sustainable wastewater treatment.

New insight into the granule formation in the reactor for enhanced biological phosphorus removal.

While granulated activated sludge exhibits high productivity, the processes of granule formation are incompletely studied. The processes of granule formation and succession of communities were investigated in a laboratory sequencing batch reactor (SBR) under conditions for enhanced biological phosphorus removal (EBPR) using microbiological and molecular techniques. Active consumption of acetate, primarily by the phosphate-accumulating organisms (PAO), commenced at day 150 of cultivation. This was indicated by the high ratio of molar P-released/acetate uptake (0.73-0.77 P-mol/C-mol), characteristic of PAO. During this period, two types of granule-like aggregates formed spontaneously out of the activated sludge flocs. The aggregates differed in morphology and microbial taxonomic composition. While both aggregate types contained phosphorus-enriched bacterial cells, PAO prevailed in those of morphotype I, and glycogen-accumulating organisms (GAOs) were predominant in the aggregates of morphotype II. After 250 days, the elimination of the morphotype II aggregates from the reactor was observed. The subsequent selection of the community was associated with the development of the morphotype I aggregates, in which the relative abundance of PAO increased significantly, resulting in higher efficiency of phosphorus removal. Metagenomic analysis revealed a predominance of the organisms closely related to Candidatus Accumulibacter IС and IIС and of Ca. Accumulibacter IIB among the PAO. Based on the content of the genes of the key metabolic pathways, the genomes of potential PAO belonging to the genera Amaricoccus, Azonexus, Thauera, Zoogloea, Pinisolibacter, and Siculibacillus were selected. The patterns of physicochemical processes and the microbiome structure associated with granule formation and succession of the microbial communities were revealed.

Nutrient removal performance from agricultural drainage by strengthening ecological ditches in hilly areas

Agricultural drainage from catchment greatly impacts water quality in the hilly area due to high nitrogen concentrations in the central basin of Sichuan Province, China. The original ecological ditches have proven effective in removing associated nutrient loads, but their nitrogen removal efficiency is limited by the elevated nitrogen levels of overland flow and subsurface flow. Field experiments were conducted to optimize the drainage network to enhance the performance of ecological ditches and enhance nitrogen removal efficiency in hilly regions. The results suggested that ecologically permeable dam ditches exhibited superior total nitrogen (TN) and total phosphorus (TP) removal efficiencies compared to single dams, multiple dams, and ecological intercept dams. Specifically, in single, multiple, and ecological intercept dams, TN removal was 20.2 %, 12.7 %, and 2.5 % higher, respectively, while TP removal was 18.2 %, 10.3 %, and 3.7 % higher, respectively. The TN removal efficiency by the Hydrocotyle verticillate and Iris pseudacorus L. ditch was 15.8 % and 2.3 % higher than that of the Myriophyllum verticillatum L. and Hydrocotyle verticillata and Hydrocotyle verticillata and Thalia dealbata Fraser, respectively. The TP removal efficiency in Hydrocotyle verticillata and Thalia dealbata Fraser ditch was 11.4 % and 3.5 % higher than that in Myriophyllum verticillatum L. and Hydrocotyle verticillata and Hydrocotyle verticillate and Iris pseudacorus L., respectively. The soil bed ditch demonstrated superior TN and TP removal efficiencies, with rates of 15.2 % and 11.3 %, respectively, compared to the pebble bed and mudstone bed (2.9 % and 3.4 %, respectively). Therefore, the original ecological ditch was reinforced through a combination of fine-textured soil substrates, native emergent plants with large biomass and ecologically permeable dams to enhance the removal efficiencies of TN and TP in agricultural drainage. Following reinforcement and evaluation in 2020, the removal efficiencies of TN, TP, ammonia nitrogen (AN) and nitrate nitrogen (NN) in the strengthened ecological ditches increased to 58.1 %, 56.5 %, 56.8 % and 54.2 %, respectively. In this study, a scientific foundation for enhancing the efficacy of ecological ditches in mitigating nonpoint source pollution from agricultural drainage in mountainous and hilly regions of subtropical and developing countries is established.