Denitrification Filter Research Articles

Enhanced nitrogen removal from secondary effluent of municipal wastewater using denitrification filter: Feasibility of refractory organics as a carbon source

Conventional advanced nitrogen removal in municipal wastewater is hindered by the limited availability of carbon sources in the secondary effluent. However, refractory organics present in it had the potential to serve as intrinsic carbon sources after hydrolysis for nitrogen removal via simultaneous denitrification and partial-denitrification anammox (PDA) processes. To assess this potential, a denitrification filter was set up in this study to evaluate its feasibility of concurrent processes. Results showed that increasing influent ammonium (NH4+-N) from 1.0 to 7.0 mg/L increased total nitrogen (TN) removal from 52.4 % to 89.9 %. Simultaneous occurrence of PDA and denitrification process were confirmed by the actual chemical oxygen demand (COD) consumption (0.8–1.2 mg/mg TN removal) from non-fluorescent organics. The presence of the anammox, hydrolytic and denitrifying bacteria further supported the achievement of nitrogen removal through PDA and denitrification processes by utilizing hydrolytic products biodegraded from refractory organics.

A novel sulfur-based fiber carrier fixed-bed reactor for nitrate-contaminated wastewater treatment: Performance, operational characteristics and cold-tolerant mechanism

In the view of the serious prejudice of nitrates, sulfur-based autotrophic denitrification filter (SADF) has been widely used for deep nitrate removal from electron-donor-deficient water. However, it faces many challenges like slow start-up, reliance on backwashing, and poor low-temperature tolerance. For these challenges, a novel sulfur-based fiber carrier fixed bed reactor (SFFR) was developed in this study. It was found that SFFR had great film-forming ability and flow field characteristics, which promoted it to obtain superior denitrification performance, and the maximum nitrogen removal rate of 0.53 kg-N/m3/d. Meanwhile, SFFR shows significant cold tolerance, and alleviating the acidification problem of effluent to a certain extent. To sum up, the SFFR possesses the potential to be widely used in real-world wastewater treatment applications, especially as a promising solution for nitrate removal in cold regions. This study can provide an important reference for the improvement of the elemental sulfur autotrophic denitrification process.

Disinfection-residual bacteria (DRB) after chlorine dioxide treatment: Microbial community structure, regrowth potential, and secretion characteristics

This study investigates the effects of chlorine dioxide (ClO2) disinfection on the community structure, regrowth potential, and metabolic product secretion of disinfection-residual bacteria (DRB) in secondary effluent (SE), denitrification filter effluent (DFE), and ultrafiltration effluent (UE). Results show that ClO2 effectively reduces bacteria in SE and UE, achieving log removal values exceeding 3 at 1 mg/L within 30 min. A salient positive correlation (R2 > 0.95) exists between changes in total fluorescence intensity and disinfection efficacy. Post-treatment, Acinetobacter abundance increased in SE, while Pseudomonas decreased in DFE and UE. At lower ClO2 concentrations, Staphylococcus, Mycobacterium, Aeromonas, and Lactobacillus increased in DFE, but decreased at higher concentrations. After storage, bacterial counts in disinfected samples exceeded those in the control group, surpassing 105 CFU/mL. Despite an initial decline, species richness and evenness partially recovered but remained lower than control levels. Culturing DRB for 72 h showed elevated extracellular polymeric substances (EPS) secretion, quantified as total organic carbon (TOC), ranging from 5 to 27 mg/L, with significantly higher EPS in the disinfection group. Parallel factor analysis with self-organizing maps (PARAFAC-SOM) effectively differentiated water sample types and EPS fluorescent substances, underscoring the potential of three-dimensional fluorescence as an indirect measure of ClO2 disinfection efficacy.

Study on the removal of high nitrate-nitrogen concentration from pig farm wastewater by heterotrophic and sulphur autotrophic synergistic denitrification filter process

Following the anaerobic fermentation process in a lagoon, the effluent from pig wastewater exhibited elevated levels of total nitrogen and nitrate nitrogen. The utilization of simple sulphur-limestone autotrophic denitrification resulted in a sluggish reaction rate and relatively moderate removal load. To enhance the efficacy of the sulphur autotrophic denitrification process, a strategy was implemented involving the introduction of a limited quantity of corncobs as a slow-release carbon source. This addition was made to a sulphur-limestone autotrophic denitrification reactor that was being operated continuously and stably. Furthermore, the volume ratio of the corncobs added was progressively increased. This study examines the alterations in nitrate nitrogen, chemical oxygen demand (COD), sulphate, and alkali consumption within the sulphur-limestone autotrophic denitrification reactor, both prior to and after the introduction of corncobs. This study examines the operational efficiency and reaction mechanism of a sulfur-limestone autotrophic denitrification reactor that is enhanced by the utilization of corncobs as a slow-release carbon source. The findings of the study indicate that the inclusion of maize cob carbon source in the sulphur limestone autotrophic denitrification process resulted in improved effectiveness in removing nitrate and nitrogen. Additionally, when considering the three different ratios of corncob carbon source, the process exhibited a chemical oxygen demand (COD) removal rate exceeding 42%. The observed trend in the consumption of alkalinity in both the pure sulphur limestone autotrophic denitrification process and the sulphur limestone autotrophic denitrification process augmented by the three types of corncob slow-release carbon sources indicated an increase with time. The concentration of nitrate-nitrogen in the influent water exhibited a negative correlation with the length of the reactor flow-through. The addition of a slow-release carbon source derived from corncob greatly enhanced the autotrophic denitrification and denitrification impact in the three reactors. Moreover, there was an observed increase in the trend of heterotrophic denitrification as the amount of carbon source added increased. The efficacy of the mixotrophic denitrification process surpassed that of the sulphur-limestone autotrophic denitrification method in the treatment of nitrate-nitrogen wastewater characterized by a high concentration of nitrate-nitrogen. The former exhibited a higher denitrification rate and resulted in lower levels of sulphate ions and alkalinity production.

Layered double hydroxide@zeolite composite modified sponge: A versatile biocarrier for enhancing nitrogen removal in biofilters

Conventional denitrification filters exhibit limited nitrogen removal efficiency in micropolluted surface waters with high dissolved oxygen levels (6 ∼ 8 mg/L). In this study, an innovative denitrification biofilter with a novel modified sponge biocarrier, composed of a layered double hydroxide@zeolite composite (LZMC) was employed to enhance the removal of nitrogen from surface waters. Based on the response surface methodology, an LZMC with high nitrogen adsorption performance was prepared. The greatest enhancement in the denitrification efficiency in the LZMC reactor was 30.62 % compared with the control reactor, and the total nitrogen removal rate reached 91.39 % under optimal conditions. Improving the carrier surface characteristics effectively boosted biofilm formation , increased biomass accumulation, and the abundance of dominant denitrifying bacteria. Additionally, the LZMC effectively accelerated electron transfer due to its high conductivity, which promoted related gene expression and enzyme activity. In conclusion, this study presents a viable route to facilitate nitrogen removal in micropolluted surface waters.

Effect of phosphorus on the performance of sulfur autotrophic denitrification

Autotrophic denitrification, recognized as a biological denitrification method, has garnered increasing interest in the field of ecological water environment denitrification technology. This study focuses on the utilization of the sulfur autotrophic denitrification process for the deep denitrification treatment of wastewater. Furthermore, it investigates the impact of phosphorus on nitrogen removal efficiency and bacterial community structure of sulfur autotrophic denitrification. In the experiment, a column containing an autotrophic denitrification filter with a carbon-sulfur filler was constructed. This study aimed to examine the impact of phosphorus on the initiation and denitrification efficiency of the autotrophic denitrification filter column. High-throughput sequencing was used to examine alterations in the structure of the bacterial community. The experimental findings indicated that the absence of phosphorus in the influent considerably extended the initiation period of the autotrophic denitrification filter column. The average Total Inorganic Nitrogen (TIN) removal rate was determined to be 80.26%, while the effluent exhibited an accumulation concentration of NO2−-N ranging from 7 to 11 mg/L. After the addition of phosphate, the removal rate of NO3−-N in the autotrophic denitrification process increased to more than 97%, with no2−-N accumulation. As the influent phosphorus concentration increased, the ability of the sulfur autotrophic denitrification filter column to resist hydraulic impact load improved. At a NO3−-N concentration of 30 mg/L and Hydraulic Retention Time (HRT) = 2 h, the mean NO3−-N removal rate increased from 73.22% to 81.71%. The concentration of phosphorus affected the quantity and variety of primary bacteria in the sulfur autotrophic denitrification system, as their domination changed from Pseudomonas to Ferritrophicum and Thiobacillus, and from a mixed culture to complete autotrophy.

Water supply sludge-based ceramsite denitrification filter: Pollutant removal and microbial community characteristics

Using water supply sludge to prepare ceramsite for sewage treatment is one of the methods to realize resource utilization. In this study, water supply sludge-based ceramsite was prepared, and analyzed the preparation conditions, reaction conditions, and characterization of water supply sludge-based ceramsite. The results showed that water supply sludge-based ceramsite had the best adsorption performance (for NO3−-N and PO43−-P were 31.2 % and 64.5 %) when the mass ratio of water supply sludge to kaolin was 85:15, the firing temperature was 1150 °C, and the firing time was 10 min. The removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) were 67.0 % and 79.9 %, respectively, with the water supply sludge-based ceramsite as denitrification biofilter carrier, when the optimal hydraulic retention time (HRT) and carbon‑nitrogen ratio (C/N) were 0.5 h and 2:1. However, the removal efficiency of total phosphorus (TP) gradually decreased. During the biofilm formation of denitrification biofilter, the microbial community richness remained basically stable, but the microbial diversity decreased in the later stage of biofilm formation. The main dominant microbial communities were Acinetobacter and Methylophilaceae; and the relative abundance of amino acid metabolism genes increased, with the extension of biofilm formation time.

Performance and microbial communities of denitrification using construction waste as filler for nitrate removal

The increasing amount of construction waste generated by the construction industry is causing serious pollution to the environment. In our research, the feasibility of construction waste as filler for denitrification was investigated. The physical and chemical properties of ceramic pellet and construction waste were compared and analyzed using scanning electron microscopy and Fourier transform infrared spectroscopy characterization. In addition, the ability of construction waste to treat high concentrations of nitrogenous wastewater was investigated and the structure of the extracellular polymer and microbial community was analyzed. The results showed that the removal rates of NO3--N and COD of construction waste were stable at 98% and 60%, and the biofilm in the construction waste reactor is more hydrophobic and denitrification-related microorganisms are more advantageous. Experimental results demonstrate that construction waste was feasible as a filler for denitrification filters, and this study also achieve the purpose of treating waste with waste.

Abundance, characteristics, and removal of microplastics in different wastewater treatment plants in a Yangtze River Delta city of China

Microplastics (MPs) have become emerging environmental pollutants worldwide. Wastewater treatment plants (WWTPs) are considered to be the major source and sink of MPs in the terrestrial and aquatic environment. The present study has been carried out for Nanjing, a typical Yangtze River Delta city in China. In this work, the abundance and characteristics of MPs were investigated in the influent of four WWTPs, and the removal effect of different treatment processes was studied in the two advanced tertiary treatment WWTPs. In the influent, the abundance of MPs of industrial WWTPs (IWWTPs) was higher than that of municipal WWTPs (MWWTPs), with a dominant size of 38–63 μm. MP shapes were mainly distributed in fragments and fibers, with polymer species of polypropylene (PP) and polyethylene (PE). In the final effluent, MPs were removed by 93.81 % in IWWTPs versus 88.10 % in MWWTPs, which were mainly influenced by the tertiary treatment technology. The tertiary treatment showed significant differences with the removal efficiency of 61.58 % in IWWTPs, equipped with a high-density sediment tank, and 30.40 % in MWWTPs, equipped with a denitrification filter. This study provides comprehensive information about the MPs' characteristics and fate contained in different sewage of WWTPs and analyzes the tertiary treatment effect of MPs, expecting to provide constructive support for the improvement of management strategies in WWTPs technologies.

Metagenomic insight into the prevalence and driving forces of antibiotic resistance genes in the whole process of three full-scale wastewater treatment plants

The spread of antibiotic resistance genes (ARGs) is an emerging global health concern, and wastewater treatment plants (WWTPs), as an essential carrier for the occurrence and transmission of ARGs, deserves more attention. Based on the Illumina NovaSeq high-throughput sequencing platform, this study conducted a metagenomic analysis of 18 samples from three full-scale WWTPs to explore the fate of ARGs in the whole process (influent, biochemical treatment, advanced treatment, and effluent) of wastewater treatment. Total 70 ARG subtypes were detected, among which multidrug, aminoglycoside, tetracycline, and macrolide ARGs were most abundant. The different treatment processes used for three WWTPs were capable of reducing ARG diversity, but did not significantly reduce ARG abundance. Compared to that by denitrification filters, the membrane bioreactor (MBR) process was advantageous in controlling the prevalence of multidrug ARGs in WWTPs. Linear discriminant analysis Effect Size (LEfSe) suggested g_Nitrospira, g_Curvibacter, and g_Mycobacterium as the key bacteria responsible for differential ARG prevalence among different WWTPs. Meanwhile, adeF, sul1, and mtrA were the persistent antibiotic resistance genes (PARGs) and played dominant roles in the prevalence of ARGs. Proteobacteria and Actinobacteria were the host bacteria of majority ARGs in WWTPs, while Pseudomonas and Nitrospira were the most crucial host bacteria influencing the dissemination of critical ARGs (e.g., adeF). In addition, microbial richness was determined to be the decisive factor affecting the diversity and abundance of ARGs in wastewater treatment processes. Overall, regulating the abundance of microorganisms and key host bacteria by selecting processes with microbial interception, such as MBR process, may be beneficial to control the prevalence of ARGs in WWTPs.

Optimal pathways for upgrading China's wastewater treatment plants for achieving water quality standards at least economic and environmental cost

Wastewater treatment plants (WWTPs) in China must be upgraded to meet new discharge standards, but this incurs both economic and environmental costs and benefits. To select the optimal upgrade pathway, we developed ten upgrade paths based on two common decision-making scenarios for WWTP upgrade in developing countries. Using model simulation, life-cycle assessment, life-cycle cost, and multiple-attribute decision-making, we incorporated the full costs and benefits associated with the construction and operation into the decision-making process. We used a weighting scheme of attributes for the three regions and ranked the upgrade paths using the technique for order preference by similarity to an ideal solution (TOPSIS). The results showed that constructed wetlands and sand filtration were advantageous in terms of lower economic costs and environmental impacts, while the denitrification filter pathways required less land. Optimal pathways differed by region, highlighting the importance of a detailed and integrated assessment of the costs and benefits of WWTP upgrade options over the full life cycle. Our findings can inform decision-making on upgrading China's WWTPs to meet stringent discharge standards and protect inland water and coastal environments.

Molecular insights into the dissolved organic matter of leather wastewater in leather industrial park wastewater treatment plant

Leather wastewater (LW) effluent is characterized by complex organic matter, high salinity, and poor biodegradability. To meet the discharge standards, LW effluent is often mixed with municipal wastewater (MW) before being treated at a leather industrial park wastewater treatment plant (LIPWWTP). However, whether this method efficiently removes the dissolved organic matter (DOM) from LW effluent (LWDOM) remains debatable. In this study, the transformation of DOM during full-scale treatment was revealed using spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. LWDOM exhibited higher aromaticity and lower molecular weight than DOM in MW (MWDOM). The DOM properties in mixed wastewater (MixW) were similar to those in LWDOM and MWDOM. The MixW was treated using a flocculation/primary sedimentation tank (FL1/PST), anoxic/oxic (A/O) process, secondary sedimentation tank (SST), flocculation/sedimentation tank, denitrification filter (FL2/ST-DNF), and an ozonation contact reactor (O3). The FL1/PST unit preferentially removed the peptide-like compounds. The A/O-SST units had the highest removal efficiencies for dissolved organic carbon (DOC) (61.34 %) and soluble chemical oxygen demand (SCOD) (52.2 %). The FL2/ST-DNF treatment removed the lignin-like compounds. The final treatment showed poor DOM mineralization efficiency. The correlation between water quality indices, spectral indices, and molecular-level parameters indicated that lignin-like compounds were strongly correlated with spectral indices and CHOS compounds considerably contributed to the SCOD and DOC. Although the effluent SCOD met the discharge standard, some refractory DOM from LW remained in the effluent. This study illustrates the composition and transformation of DOM and provides theoretical guidance for improving the current treatment processes.

Denitrification performance and microbial community analysis of sulfur autotrophic denitrification filter for low-temperature treatment of landfill leachate

This study investigated the denitrification performance of sulfur autotrophic denitrification filter (SADF) in five low-temperature ranges (14.0–15.0 ℃, 13.1–13.9 °C, 12.0–13.0 °C, 10.1–11.9 °C and 8.8–9.8 °C) environments and the nitrogen removal contribution along the filter cells. Results showed that the average total nitrogen removal efficiency (TNRE) of the bioreactor were 90.06%, 88.49%, 86.61%, 85.71% and 74.54%, respectively. However, when the temperature was lower than 9.8 °C, the process of sulfur autotrophic denitrification was obviously inhibited, but the inhibition was slowed down after low-temperature acclimation. The bottom-filter layer (0–200 mm) contributed 50.54% of the nitrogen removal, which was the greatest. The middle- filter layer (400–600 mm), which was at 35.86%, was next. And the upper- filter layer (800–1200 mm) made the least contribution, at 13.60%. It was demonstrated by high-throughput sequencing that in addition to Thiobacillus, the genus Sulfurimonas was also found and its average relative abundance was comparable to the former (24.03% for Thiobacillus and 23.10% for Sulfurimonas). The results of microbial function prediction showed that sulfur and nitrogen metabolism played a key role in nitrogen removal. The study of substrate environmental variables showed that the key bacterial groups of nitrogen removal along the process were negatively correlated with total nitrogen (TN) and positively correlated with pH value.

Application of Deep-bed Denitrification Filter in Sewage Treatment

The combined process of A2/O oxidation ditch, high efficiency sedimentation tank and denitrification deep bed filter was adopted in Sewage Treatment Plant of Hefei City to treat municipal domestic sewage. The effluent quality could meet the discharge limit of major water pollutants in urban sewage treatment plants and industrial industries of Chaohu Lake Basin (DB34/2710-2016). In addition to the parameters of design and operation, the effect of SS and deep denitrification was summarized in detail in this paper. The results showed that the combined process SS and denitrification effect was removed very well. The operational results demonstrated SS removal efficiency 74.3%,TN removal efficiency (92.3％) in the biosystem ,in which 80.0％ and 12.3％ of TN in influent were removed in the pre-denitrif ication in oxidation ditch and post-denitrification in deep bed denitrification filter, respectively. The deep bed denitrification filter could be used as the safeguard for effluent TN with the addition of external carbon source to ensure the efficiency of TN less than 5 mg/L.

Denitrification Performance in Packed-Bed Reactors Using Novel Carbon-Sulfur-Based Composite Filters for Treatment of Synthetic Wastewater and Anaerobic Ammonia Oxidation Effluent.

To avoid nitrate pollution in water bodies, two low-cost and abundant natural organic carbon sources were added to make up the solid-phase denitrification filters. This study compared four novel solid-phase carbon-sulfur-based composite filters, and their denitrification abilities were investigated in laboratory-scale bioreactors. The filter F4 (mixture of elemental sulfur powder, shell powder, and peanut hull powder with a mass ratio of 6:2.5:1.5) achieved the highest denitrification ability, with an optimal nitrate removal rate (NRR) of 723 ± 14.2 mg NO3–-N⋅L–1⋅d–1 when the hydraulic retention time (HRT) was 1 h. The HRT considerably impacted effluent quality after coupling of anaerobic ammonium oxidation (ANAMMOX) and solid-phase-based mixotrophic denitrification process (SMDP). The concentration of suspended solids (SS) of the ANAMMOX effluent may affect the performance of the coupled system. Autotrophs and heterotrophs were abundant and co-existed in all reactors; over time, the abundance of heterotrophs decreased while that of autotrophs increased. Overall, the SMDP process showed good denitrification performance and reduced the sulfate productivity in effluent compared to the sulfur-based autotrophic denitrification (SAD) process.

Mainstream partial denitrification‐anammox in sand and expanded clay deep‐bed polishing filters under practical loading rates and backwashing conditions

AbstractThis study focused on evaluating the feasibility of expanded clay and sand as media types for mainstream partial denitrification‐anammox (PdNA) in deep‐bed single‐media polishing filters under nitrogen and solids loading rates as well as backwash conditions similar to conventional denitrification filters. The surface roughness and iron content of the expanded clay were hypothesized to allow for enhanced anammox retention, nitrogen removal rates, and runtimes. However, under the tested loading rates and backwash conditions, no clear benefit of expanded clay was observed compared with conventional sand. This study showed the feasibility of PdNA in filters with both sand and expanded clay with PdN efficiencies of 76% and 77%, PdNA rates of 840 and 843 g N/m3/d and TIN removal rates of 960 and 964 g N/m3/d, respectively. Glycerol demands were 1.5–1.6 g COD added per g TIN removed, thus indicating potential carbon savings up to 75% compared with conventional denitrification. Overall, this study showed for the first time PdNA filters performing at nitrogen removal rates double that of previous PdNA studies under realistic conditions while providing insights into the media choice and backwashing conditions. Future research on expanded clay backwash conditions is needed to provide its full potential in PdNA filters.Practitioner Points Hydraulic and TSS loading rates similar to conventional denitrification can be applied in PdNA filters. Conventional sand can be used when retrofitting conventional denitrification filters into PdNA filters. Carbon savings up to 75% can be achieved with glycerol when retrofitting conventional filters into PdNA filters

Media selection for anammox-based polishing filters: Balancing anammox enrichment and retention with filtration function.

Retrofitting conventional denitrification filters into partial denitrification-anammox (PdNA)- or anammox (AnAOB)-based filters will reduce the needs for external carbon addition. The success of AnAOB-based filters depends on anammox growth and retention within such filters. Studies have overlooked the importance of media selection and its impact on AnAOB capacity, head loss progression dynamics, and shear conditions applied onto the AnAOB biofilm. The objective of this study was to evaluate viable media types (10 types) that can enhance AnAOB rates for efficient nitrogen removal in filters. Given the higher backwash requirement and lower AnAOB capacity of the conventionally used sand, expanded clay (3-5mm) was recommended for AnAOB-based filters in this study. Owing to its surface characteristics, expanded clay had higher AnAOB activity (304- vs. 104-g NH4 + -N/m2 /day) and higher AnAOB retention (43% more) than sand. Increasing the iron content of expanded clay to 37% resulted in an increase in zeta potential, which led to 56% more anammox capacity compared to expanded clay with 7% iron content. This work provides insight into the importance of media types in the growth and retention of AnAOB in filters, and this knowledge could be used as basis in the development of PdNA filters. PRACTITIONER POINTS: Expanded clay showed the lowest head loss buildup and most likely will result in longer runtime for full-scale PdNA applications The highest AnAOB rates were achieved in expanded clay types and sand compared with smaller media typically used in biofiltration Expanded clay resulted in better AnAOB retention under shear, whereas sand could not withstand shear and required more frequent backwashing Expanded clay iron coating enhanced AnAOB enrichment and retention, most likely due to increased surface roughness and/or positive charge.

Pollution Control of Industrial Mariculture Wastewater: A Mini-Review

With the rapid development of intensive mariculture, lots of mariculture wastewaters containing residual feed and excrements are discharged into marinelands, leading to coastal pollution. Recently, the environmental problems caused by the discharge of mariculture wastewater have been paid much attention, as have other breeding industries in China. In fact, organic solid waste accounts for most of the pollutants and can be reduced by precipitation or filtration technologies, after which the supernatant can be easily treated by ecological methods. Some national guidelines and relevant local standards have been issued to strictly control the mariculture wastewater, but there are still few effective technologies for mariculture wastewater treatment due to its high salinity and extremely low pollutant concentration. This paper aims to propose feasible pollution control methods of mariculture wastewater according to the wastewater characteristics from different mariculture modes. For raw ammonia-based wastewater, it should be sequentially treated by precipitation, nitrification and denitrification and ecological methods, which would target solid waste, organic carbon/nitrogen and phosphorus removal, respectively. For the nitrate-based wastewater, this just needs denitrification filters and ecological methods for nitrate and phosphorus removal. After an overview of pollution control strategies for different types and scales of industrial mariculture wastewater treatment, some challenges are also mentioned.

Alleviating the membrane fouling potential of the denitrification filter effluent by regulating the COD/N ratio and carbon source in the process of wastewater reclamation

• Higher COD/N ratio in DNF operation led to more aggravated membrane fouling. • Fouling of DNF effluent: glucose > methanol > ethanol > sodium acetate-fed HOA and HON fractions in DNF effluent dominated subsequent UF membrane fouling. • DNF operation could alleviate UF fouling by regulating external carbon addition. • DNF-UF process should be optimized as an integrated system rather than separate units. The process of denitrification filter (DNF) followed by ultrafiltration (UF) has been widely applied for wastewater reclamation in China. The performance of DNF could have significant influences on subsequent UF membrane fouling. In this study, different chemical oxygen demand to nitrogen (COD/N) ratios and carbon sources in DNF were investigated under pilot scale, with the secondary effluent of a wastewater reclamation plant as DNF influent, to explore the impacts of DNF operation on UF membrane fouling. DNF effluent with the increased COD/N ratios from 2.9 to 6.8 rendered more aggravated membrane fouling performance, suggesting that increase of carbon source dosage could significantly increase the fouling potential of DNF effluent. In terms of four commonly-used carbon sources, the fouling potential was higher in the order of glucose > methanol > ethanol > sodium acetate-fed DNF effluent. According to the resin fractionation and fluorescence spectroscopy analysis, water samples with higher membrane fouling potential contained a larger proportion of hydrophobic components. Extended Derjaguin Landau Verwey Overbeek (XDLVO) analysis revealed fouling mechanism that hydrophobic acids (HOA) and hydrophobic neutrals (HON) exhibited both notably attractive interaction with virgin membranes and a strong tendency to aggregate on the already fouled membranes. Compared with the other fractions, HOA and HON presented significantly stronger interaction energy, demonstrating that HOA and HON dominated the membrane fouling process. Therefore, the contents of HOA and HON fractions in DNF effluent could be effectively regulated by optimizing external carbon addition, thus alleviating the subsequent UF fouling. The DNF-UF process should be considered and optimized as an integrated system rather than independent units, and appropriate external carbon addition should be regulated to achieve an optimal process from the perspective of the whole wastewater reclamation plant.

Alkalinity regulation in a sulfur autotrophic denitrifying filter substantially reduced total dissolved solids and sulfate in effluent

Sulfur autotrophic denitrification (SAD) filters are considered a promising technology due to their stable and excellent performance in nitrogen removal, affordable costs, and operational advantages. In this work, a novel operational strategy that employed sodium bicarbonate as an alkalinity source in the autotrophic denitrification filter (S-SAD) was established. With the sufficient supply of alkalinity, the S-SAD reached an excellent denitrification performance (98.01%±0.43%) with a nitrate concentration of 10 mg/L in influent and hydraulic retention time of 3 hrs. The total dissolved solids increment and sulfate concentration in effluent were significantly reduced by one-third, compared with that of the traditional SAD process under the same conditions. The analysis of microbial community indicated that Thiobacilhus, typical species with the functions of simultaneous sulfur oxidation and denitrification, was evidently enriched in the S-SAD. Thus, this present work demonstrated a feasible, relatively cost-effective and environmentally friendly approach to operate SAD towards further application.