Sludge Concentration Research Articles

Enhanced wastewater treatment with an AnF-AAO system for improved internal carbon source utilization

The main challenge in removing nutrients from municipal wastewater in China is the lack of available carbon sources. While hydrolysis acidification tanks can improve wastewater biodegradability by effectively utilizing internal carbon sources, high sludge concentrations are difficult to control in traditional tank variants. In this study, an innovative anaerobic filter (AnF) hydrolysis acidification reactor composed of a continuously stirred tank reactor (CSTR) and cloth media filter was designed to regulate and maintain high sludge concentrations in the hydrolysis acidifier. The reactor was used as a pretreatment unit for the anaerobic/anoxic/oxic (AAO) units and combined into an AnF-AAO system to explore the effectiveness of internal carbon source utilization in wastewater. The results indicate that as the sludge concentration in the hydrolysis acidifier increased, the hydrolysis and acidification processes became more efficient. The optimal sludge concentration was 40 g/L, which significantly increased the production of soluble chemical oxygen demand and volatile fatty acids. Above this concentration, the efficiency decreased. Compared to traditional AAO processes, the AnF-AAO system achieved superior total nitrogen and phosphorus removal with shorter hydraulic retention times and reduced sludge production by a significant amount of 35%. Due to its capacity for enhancing internal carbon source utilization, the AnF-AAO system constitutes a promising approach for sustainable urban wastewater treatment.

Surveillance of PFAS in sludge and biosolids at 12 water resource recovery facilities.

Per- and polyfluoroalkyl substances (PFAS) are refractory anthropogenic chemicals and current treatment processes at municipal water resource recovery facilities (WRRFs) cannot efficiently degrade them, hence, these chemicals cycle through the environment. Certain PFAS can be concentrated in biosolids from WRRFs and are commonly land applied for beneficial reuse. Given recent advances in measurement of PFAS, documentation of the range of concentrations in pre-stabilized sludge and stabilized biosolids is critical to evaluating treatment best practices and assessing potential human health and ecological risks. In this study, pre-stabilized sludge and post-stabilized biosolids samples were collected from 12 major WRRFs across the United States. PFAS were analyzed using Environmental Protection Agency (EPA) Method SW846-3500C/537.1, and Draft EPA Method 1633, by one commercial laboratory and two university research laboratories, respectively. Results comparison among laboratories demonstrated statistical differences in PFAS concentrations among split samples. For example, 5:3 FTCA (fluorotelomer carboxylic acid) concentrations in post-stabilized sludge at Lab 1 were measured at 21ng/g (dry), while they were detected at 151ng/g (dry) in Lab 3. Further, higher PFAS concentrations were observed in post-stabilized biosolids compared to pre-stabilized sludges, regardless of the laboratory or analysis method, even when solids destruction through solids stabilization was considered. Further research is required to refine methods for analyses of PFAS in sludge and biosolids samples from WRRFs prior to being used for development of regulatory actions as well as understanding how various treatment protocols could impact concentrations of PFAS in land-applied biosolids.

Fast hydrothermal co-liquefaction of high-ash sludge and Chlorella for biocrude production

Fast hydrothermal liquefaction (HTL) shows great potential for producing biocrude. This research examined the influences of mixing ratios of sludge and Chlorella during both isothermal (300 °C, 1800 s) and fast (500 °C, 20 s) co-HTL. Adding Chlorella could efficiently retard repolymerization reaction and increase the biocrude production. The highest co-liquefaction effect was achieved from a sludge to Chlorella ratio of 2:6 by fast HTL, producing a biocrude yield of 29.65 wt%, closely approaching the calculated yield of 29.39 wt% and demonstrating an additive effect. However, for the high ash content of sludge, all isothermal and other fast HTL conditions presented an antagonistic effect on biocrude production. Meanwhile, co-liquefaction also exhibited a slight antagonistic effect on the heating value and energy recovery of biocrude, with experimental values reaching 32.73 MJ·kg−1 and 52.74 %, respectively. FT-IR and maturity analyses indicated that compared to isothermal co-HTL, fast co-HTL biocrude was more favorable for the conversion into gasoline/diesel due to its lower paleo-temperature. GC–MS analysis identified amides (isothermal co-HTL) and nitrogen heterocycles (fast co-HTL) as the dominant components, suggesting that the holding time significantly influenced the competition of Maillard and amidation reactions. Besides biocrude, the major composition of aqueous phase products (APs) was also nitrogen heterocycles. Notably, fast co-HTL induced a substantial decrease in COD, NH3-N, and TN contents of APs, reducing the discharge challenge of the by-products.

Effect of combined dialysis method on dewatering of coagulant pretreated sludge

The unique composition and condition of sludge pose significant challenges in water removal. Therefore, it is crucial to investigate a cost-effective and highly efficient approach for dehydrating sludge. In this paper, the domestic sludge was respectively pretreated with ferric chloride, polyaluminum chloride, and cationic polyacrylamide. Then the pretreated sludge was performed on gravity dehydration, centrifugal dehydration, dialysis dehydration and mixed method. The effect mechanism of coagulant and dewatering method on sludge dehydration was analyzed from micro perspective. Finally, the influence range of the dialytic solution was tested by model experiment. The results indicate that the dehydration efficiency of the pretreated sludge with PAC is slightly better than that pretreated with FeCl3 and CPAM, and the optimal dosage of PAC is 8 %. The effect of dialysis dehydration is the best, which can significantly change the final moisture content of sludge (much less than 60 %), effectively achieving the requirements of subsequent processing. The water content of the sludge treated by gravity dehydration, centrifugal dehydration and dialysis dehydration can reach 38 %, which is much smaller than that of the sludge treated by a single dehydration method. The free water, occlusion, coating water, and bounding water are dehydrated by gravity, centrifugal force, and dialysis. The influence range of dialysis dehydration is less than 10 cm. When the distance is more than 10 cm, the difference of sludge moisture content at different relative heights is larger. The study has certain theoretical guidance significance for improving the performance of sludge concentration and dewatering.

Evaluating the effect of antibiotics on aerobic granular sludge treatment of pharmaceutical wastewater.

Aerobic granular sludge (AGS) has been widely applied in pharmaceutical wastewater treatment due to its advantages such as high biomass and excellent settling performance. However, the influence of commonly found antibiotics in pharmaceutical wastewater on the operational efficiency of AGS has been poorly explored. This study investigated the effects of tetracycline (TE) on AGS treating pharmaceutical wastewater at room temperature and analyzed the related mechanisms. The results demonstrate a dose-dependent relationship between TE's effects on AGS. At concentrations below the threshold of 0.1 mg/L, the effects are considered trivial. In contrast, TE with more than 2.0 mg/L reduces the performance of AGS. In the 6.0 mg/L TE group, COD, TN, and TP removal efficiencies decreased to 72.6-75.5, 54.6-58.9, and 71.6-75.8%, respectively. High concentrations of TE reduced sludge concentration and the proportion of organic matter in AGS, leading to a decline in sludge settling performance. Elevated TE concentrations stimulated extracellular polymeric substance secretion, increasing polymeric nitrogen and polymeric phosphorus content. Intracellular polymer analysis revealed that high TE concentrations reduced polyhydroxyalkanoates but enhanced glycogen metabolism. Enzyme activity analysis disclosed that high TE concentrations decreased the activity of key enzymes associated with nutrient removal.

Treatment of Reactive Orange 16 Dye-Bearing Wastewater by Electro-Fenton Process with Stainless-Steel Electrodes: Statistical Optimization and Operational Analysis

Abstract: In the current work, the Electro-Fenton (EF) based Reactive Orange 16 (RO16) dye treatment was studied and compared with central composite (CC) and Taguchi design (TD) statistical optimization tools. Color removal (RC) and COD decay (RCOD) were chosen responses for the effect of pH (A), electrolysis time (B), initial dye concentration (C), and current density (D). The facecentred CC design and L16 orthogonal array were used in the experimental procedures. At optimal conditions, the coefficient of determination (R2) values of 0.99 for CC and 0.97 for TD suggest statistical significance and good model agreement. The results of the ANOVA and Prob. > F values supported the model’s successful experimental data fitting. Taguchi method was found as an appropriate methodology for parameter percentage contributions with fewer experimental runs. Moreover, the S/N ratio charts proved to be a successful CC design replacement. The current density and pH were found to be the most important factors for the EF process. A higher biodegradability (BOD5/COD) and minimum iron concentration (0.45 mg/L) in the effluent sludge demonstrated good environmental disposal suitability. In the last, the effect of various inhibitors/scavengers (SO4 −2, PO4 −3, EDTA, etc.) on the EF process performance was also carried out.

Mechanical and Microstructural Analysis of Lightweight Subgrade Bricks Synthesized from Mixtures of Coal Fly Ash and Sewage Sludge

Abstract The massive discharge of coal fly ash and sewage sludge has placed great pressure on the environment and society. This study proposes a feasible method for producing lightweight subgrade bricks from coal fly ash and sewage sludge. The results show that the lightweight subgrade bricks mainly consist of mullite (3Al2O3·2SiO2), hematite (Fe2O3), sillimanite (Al2SiO5), aluminum phosphate (AlPO4), and a small amount of cristobalite (SiO2). The formation of AlPO4 improved the sintering and mechanical properties of the sintered samples. The formation of voids and cracks in the sintered samples was primarily attributable to the combustion and sintering shrinkage of the organic matter in the mixture. The maximum compressive and flexural strengths were observed when the sewage sludge content was 40 wt. %, and the corresponding compressive strength and flexural strength were 19.86 and 8.57 MPa, respectively. An appropriate amount of sewage sludge improves the connections between coal fly ash particles and promotes the densification of the lightweight subgrade bricks. These results provide a direction for the development of applications for coal fly ash and sewage sludge in the field of building materials.

Investigation of PAH content and hazard assessment in sewage sludge in Gwangju

Investigation of PAH content and hazard assessment in sewage sludge in Gwangju

Evaluating Technical properties of fired clay Brick production with mosaic sludge: A comprehensive study on heavy metal leachability for sustainable environmental and economic benefits

Mosaic sludge, generated from mosaic industrial activities such as cutting, polishing, and grinding, is often disposed of in landfills or discharged into drainage systems without adequate treatment. This study aims to reuse mosaic sludge from the mosaic industry by incorporating it into fired clay bricks. This approach offers an alternative disposal method, improves brick quality, and minimizes heavy metal leachability, contributing to environmental and economic sustainability. X-Ray Fluorescence (XRF) was conducted to determine the heavy metal concentration from two types of mosaic sludge bodymill mosaic sludge (BS) and polishing mosaic sludge (PS). The result indicates that the highest element concentration in mosaic sludge (BS and PS) shows that barium is the highest with 3253 ppm and 3260 ppm. Meanwhile, the lowest element concentration obtained in BS and PS is cesium with 14 ppm and 17 ppm. SPLP and TCLP also conducted in this study and the result show that, even though the element such as ferum (Fe) and cadmium (Cd) was not detected in XRF but in SPLP and TCLP, it shows that these two elements exist in clay, BS and PS with low concentration. In order to evaluate the compressive strength conducted by incorporating with different proportions 0 %, 1 %, 5 %, 10 %, 20 % and 30 % of BS and PS into fired clay brick. The result shows that compressive strength BS brick was stronger than PS brick. The maximum sludge percentage used in BS brick is 5 % with value of compressive strength is 28.10 MPa. Meanwhile, PS brick had the higher value of compressive strength at 30 % sludge percentage with the value 23.46 MPa. Static Leachate Test (SLT) was performed to evaluate heavy metal leachability from bricks containing different proportions of BS and PS sludge. In the SLT results, Fe exhibits the highest concentration of heavy metals at various proportions of BS and PS: 2.11 mg/L and 2.27 mg/L at 1 %, 1.77 mg/L and 1.88 mg/L at 5 %, 2.34 mg/L and 3.29 mg/L at 20 %, and 2.79 mg/L and 3.64 mg/L at 30 % respectively, among other elements. On the other hand, elements including Cr, Ni, Cu, As, Cd, and Pb demonstrated lower concentrations ranging from 0.00 mg/L - 1.0 mg/L. The result for control brick, BS brick and PS brick shows the same pattern. However, overall results show that the concentration still under limit set by USEPA.

Utilization of Livestock Manure as Biogas and Liquid Organic Fertilizer (LOF) in Sumbermulyo Village, Pesanggaran, Banyuwangi

Biogas is a natural gas produced through anaerobic bacteria breakdown of organic materials. Organic materials can include livestock manure, domestic waste, and other organic waste that bacteria can decomposeunder anaerobic conditions. Sumbermulyo is one of the villages in the Pesanggaran sub-district of Banyuwangi Regency, where the majority of the population works as dragon fruit farmers and goat herders. The current phenomena in the area include the scarcity of subsidized urea fertilizer and Liquified Petroleum Gas (LPG). An alternative approach is to utilize goat manure as a source of methane gas, which can be used as a substitute for LPG. The objective of this community service project is to establish a biogas processing pilot project in the Sumbermulyo Village, Pesanggaran sub-district, which the community can implement. Additionally, it aims to analyze the total N, P, K content in the wet sludge from the digester as liquid organic fertilizer. The method used involves constructing a biogas digester on the land owned by one of the farmer groups and evaluating the gas production. The digester is built using a concrete model (fixed dome) in the shape of an airtight dome. The construction of the digester takes 14 days until it is ready for use. Up to the 10th day of use, thehighest pressure is obtained on day -10, with a pressure of 107,486.76 N/m2 or 1.06 atm. Chemical analysis of the liquid organic fertilizer shows that the total N, P, K content is as follows: 0.032%, 0.009%, 0.144% for the sample from the test digester, and 0.044%, 0.005%, and 0.195% for the sample from the reference digester

The resistance of hydrogenotrophic methanogenic microorganisms to ofloxacin in sludge anaerobic digestion process

Ofloxacin (OFL) is a commonly used antibiotic that can enter wastewater treatment plants and be adsorbed by the sludge, resulting in a high OFL concentration in sludge and affecting the subsequent sludge anaerobic digestion process. However, the micro mechanisms involved in this process have not been thoroughly studied. Therefore, this study focuses on the effect of OFL on the sludge anaerobic digestion of sludge to provide such support. The experimental results showed that the maximal methane yield decreased from 277.7 to 164.7 mL/g VSS with the OFL concentration increased from 0 to 300 mg/L. Additionally, OFL hindered the intermediate biochemical processes of hydrolysis, acidogenesis, acetogenesis, and acetoclastic methanogenesis. However, it promoted hydrogenotrophic methanogenesis process, using H2 as substrate, with the concentration of 300 mg/L OFL was 5.54 fold methane production of that in the control. Further investigation revealed that the negative effect of OFL was likely due to the induction of reactive oxygen species, which led to a decrease in cell activity and interference with the activity of key enzymes. Microbiological analysis revealed that OFL reduced the relative abundance of hydrolysis and acidogenesis bacteria, and Methanosaeta archaea, while increasing the relative abundance of hydrogenotrophic methanogenesis microorganism from 36.54% to 51.48% as the OFL concentration increase from 0 to 300 mg/L.

Experiment study on particle pulverization-assisted convective air drying of sewage sludge

Sewage sludge drying is a pivotal step in sludge reduction, harmlessness, and resource utilization. Pulverizing sewage sludge can significantly increase the surface area of sludge particles available for contact with the air medium, consequently strengthening the convective drying process of the sludge. In this paper, the adopted deep drying system mainly combined sewage sludge pulverization and sewage sludge drying functions. Parametric studies were carried out to investigate the effects on the drying process. The moisture content of the sewage sludge decreased from 50.3% to 26.8% when the linear speed of the rotating blade tip of the pulverizing dryer and induced draft fan reached 28.3 m·s−1, 62.8 m−1, and air velocity reached 9.5 m·s−1, respectively. Furthermore, this work also preliminarily reveals the mechanism of the pulverizing dryer. The pores on the sludge particle surfaces are destroyed during the drying process. As the linear speed of the rotating blade tip in the pulverizing dryer increased, the hydrophilicity and the average particle size of the sewage sludge particles decreased, with the particle size representing the highest volume fraction being reduced by 62% in the particle size distribution. The pulverizing dryer not only breaks up the sludge to increase the surface area of the sludge in contact with the air but may also have a centrifugal effect. As the intensity of the pulverizing dryer increases, Nuclear Magnetic Resonance (NMR) measurements show a leftward shift in the peak of the weakly bound water in the sludge and a noticeable shortening of the transverse relaxation time. Overall, the results suggested that pulverizing is a suitable assistive method to improve the drying effect of the sewage sludge.

Solventless recovery of lipids from urban sewage sludge: How to sustainably turn a waste into a valuable source of oleochemicals

For the first time, the recovery of lipids from urban sewage sludge was investigated through a solvent-free process based on elementary operations validated on a pilot scale (2 tons per hour). Sedimented sewage sludge was dewatered through centrifugation, acidified (and in the case treated with hydrogen peroxide), heated to 80 °C and centrifuged to obtain three different streams: i) raw grease, ii) exhausted aqueous phase, and iii) dewatered sludge.The recovery yield of grease from sludge could reach a very high value (70 wt%), depending essentially on the initial lipid content in sewage sludge, which was monitored and found to range between 1.1 and 6.6 wt% (13–25 wt% with respect to TS). The use of H2O2 played a crucial role in the recoverability of lipids and the relevant pureness in free fatty acids content (>89 wt%). In addition, the total solids content in the exhausted aqueous phase and the final residual sludge were sensibly affected by using H2O2. Final dewatered sludge had a very high content of solids (TS 31.0 ± 2.3 wt%) and resulted in 15 % less of the amount of sludge conventionally obtained from anaerobic digestion. According to these figures, for medium wastewater treatment plants, a selling price of 800–900 Euro per ton of grease would guarantee a return on investments within three years of operations. This simple procedure represents a quick and proficient way to treat sewage sludge, turning it into a valuable feedstock for fine chemicals, in agreement with Circular Bioeconomy principles.

Microplastics in wastewater and sludge from centralized and decentralized wastewater treatment plants: Effects of treatment systems and microplastic characteristics

Domestic wastewater treatment plants (WWTPs) play a vital role in limiting the release of microplastics (MP) into the environment. This study examined MP removal efficiency from five centralized and four decentralized domestic WWTPs in Bangkok, Thailand. MP concentrations in wastewater and sludge were comparable between centralized and decentralized WWTPs, despite these decentralized WWTPs serving smaller populations and having limited treatment capacity. The elimination of MPs ranged from 50 to 96.8% in centralized WWTPs and 14.2–53.6% in decentralized WWTPs. It is noted that the retained MPs concentrations in sludge ranged from 20,000 to 228,100 MP/kg dry weight. The prevalence of synthetic fibers and fragments could be attributed to their pathways from laundry or car tires, and the accidental release of a variety of plastic wastes ended up in investigated domestic WWTPs. Removal of MPs between the centralized and decentralized WWTPs was influenced by several impact factors including initial MP concentrations, longer retention times, MP fragmentation, and variations of MP concentrations in sludge leading to different activated sludge process configurations. Sewage sludge has become a primary location for the accumulation of incoming microplastics in WWTPs. The MPs entering and leaving each unit process were varied due to the unique characteristics of MPs, and their different treatment efficiencies. While the extended hydraulic retention period in decentralized WWTPs decreased the MP removal efficacy, the centralized WWTP with the two-stage activated sludge process achieved the highest MP removal efficiency.

Design and Performance Prediction of a Vortex Pump Based on CFD for High Concentration Sludge Dredging

Abstract Aiming at solving the problems of clogging and severe wear of the delivery pump in the sludge dredging project, a design method for a vortex pump was summarized. An open impeller and a cross shaped blade was designed with good passing ability, simple structure, and easy maintenance. The volute flow path profile of the vortex pump was designed as a spiral, and the relationship between the width of the vaneless cavity and the diameter of the impeller was established. Based on CFD, the external characteristics of the DRC45-200-VLS vortex pump were simulated and predicted, with a flow rate of 600 m3/h, a head of 20 m, and a water efficiency of 50%. The effects of medium viscosity, solid phase distribution, and gas phase distribution on the flow field of the vortex pump were analyzed. The results showed that the designed vortex pump had good adaptability to transport high concentration sludge and aerated sludge. Combined with a municipal sludge dredging project, a vortex pump transportation scheme for high concentration sludge dredging was formed.

Insights into the effects of cobalt ferrite nanoparticles activated peroxymonosulfate on waste activated sludge dewaterability during ciprofloxacin degradation

This research delved into the effect of cobalt ferrite nanoparticles activated peroxymonosulfate (CoFe2O4/PMS) treatment on sludge dewaterability during the ciprofloxacin (CIP) degradation in waste activated sludge (WAS). When the dosage of CoFe2O4 was 80 mg/g TSS and PMS was 60 mg/g TSS, the water content (Wc) of sludge was reduced from 80.84% to 66.33% while the capillary suction time (CST) of sludge descended from 82.6 s to 55.2 s. Considering cost and follow-up operations, the favorable pH for sludge dewatering was 6.9 additionally. During the process, the sludge disintegration brought out the dissolution of organic substances and the destruction of extracellular polymer substances (EPS). The results showed that both of soluble chemical oxygen demand (SCOD) and total nitrogen (TN) dissolved in the supernatant had a remarkable positive correlation with the sludge dewaterability. The strong oxidative free radicals SO4∙- (63.6%), ∙OH (28.2%), and ·O2- (6.3%) produced by CoFe2O4/PMS destructed the EPS structure, accompanied with proteins and polysaccharides oxidization as well as the bound and intracellular water release. There was also a significant positive relationship between polysaccharide ratio to protein and sludge dewatering (CST and Wc), which was consistent with that polysaccharide is more hydrophilic than protein. At last, a mechanism involving oxidization and re-aggregation has been presented, which is beneficial to the dewatering performance of sludge. This research underlines the potential of CoFe2O4/PMS as a promising technology for enhancing the sludge dewatering efficiency and degrading CIP, with significant implication for environmental protection.

Study on the Optimization and Experimental of Fly Ash and Sludge in Ecological Slope Protection Substrate

Study on the Optimization and Experimental of Fly Ash and Sludge in Ecological Slope Protection Substrate

Analysis of microcystins in alum water treatment sludges: holding times, temperatures, linearity of response, and sensitivity to pre-coagulation cell titers

ABSTRACT ELISA assays are a potential tool to screen for dissolved or cell bound microcystins in drinking water treatment sludges. In order to evaluate this potential more thoroughly, experiments were performed in alum sludges to: (1) evaluate the impacts of sample storage times, temperatures, and sludge composition on spiked microcystin-LR recovery by ELISA; (2) examine the linearity of ELISA responses to spiked microcystin-LR as a function of sludge composition; and (3) examine the sensitivity ELISA and LC/MS/MS to five different concentrations of microcystin-producing cyanobacteria entrained in sludges of two different compositions. During storage experiments, microcystin recovery efficiencies ranged from 85% to 125% across the range of 12 storage time and temperature combinations with recovery efficiencies in 7 of the 12 combinations falling into the 90% to 110% range. During the linearity experiments, linear models fit ELISA responses in all sludge compositions with R2 values ≥ 0.95. During the sensitivity studies, simple freeze/thaw/centrifugation processing combined with ELISA or LC/MS/MS analyses resulted in detection of microcystins in thickened sludges derived from pre-coagulation cell suspensions of 102–106 cells/mL. In addition, the relationships between toxin concentrations in sludges and the original cell titers were linear regardless of analytical method.

Nitrogen recycling characteristics in multiphase transformation during municipal sludge pyrolysis

The nitrogen content of municipal sludge is as high as 2.5～9.0 wt%, which has become an important problem in pollution control during pyrolysis. Recycling nitrogen from municipal sludge not only enables resource utilization, but also reduces the nitrogen-related pollution. In this study, the transformation pathways of nitrogen to resource material and typical pollutants during the municipal sludge pyrolysis process were analyzed. The results showed that the nitrogen species in municipal sludge were mainly protein-N (64.41%), pyridine-N (19.47%) and inorganic-N (16.13%). After pyrolysis at 300 °C, the peptide bond of protein-N was gradually broken down, resulting in the formation of three nitrogenous intermediates (amine-N, nitrile-N and heterocyclic-N) were produced. These intermediates can be transformed to NH3 for resource recovery or to HCN pollutants. Moreover, the full nitrogen transformation pathways of municipal sludge pyrolysis were constructed by the method of Spearman's correlation coefficient and experiment analysis. It was found that NH3 and HCN were mostly generated from the cracking of three nitrogenous intermediates at 600–800 °C. In addition, there was a prominent effect on the transformation of HCN to NH3 with co-presence of calcium minerals in raw sludge. By adding inorganic calcium minerals, NH3 as a recyclable component was prominently improved by 10.30% at 700 °C, while HCN yield was decreased by 53.02% accordingly under the inhibitory effect. The results systematically provided a theoretical support to the possibility of nitrogen recycling for utilization during municipal sludge pyrolysis, as well as to control the transformation of nitrogen elements into pollutants.

Mechanism of stable autotrophic nitrogen removal and NOB inhibition in low-sludge PN-Anammox system under non-temperature control and low ammonia environment

PN/Anammox, as an economical and effective nitrogen removal process, is of great significance for reducing carbon emission in municipal wastewater treatment. However, municipal wastewater has mainstream characterized of low temperature and low NH4+-N concentration, and NOB activity is difficult to inhibit, so achieving a stable PN process is the biggest challenge in the application of PN/Anammox to mainstream wastewater. This study developed a method for stable and efficient PN/Anammox based on very low sludge volume (MLVSS = 65 mg/L). Even when the temperature dropped to 15℃ or there was exogenous nitrite-oxidizing bacteria (NOB) interference, the system still had good inhibition of NOB activity. The total stable operation time was 386 days, and the NO2–-N accumulation efficiency could reach more than 90 %. Ellin6067, Nitrosomonas and Candidatus_Brocadia were the dominant functional microorganisms in the system. Nitrospira was the dominant genera of NOB with very low relative abundance (<0.04 %). The mechanism of the long-term stable mainstream PN/Anammox system showed that low sludge content was beneficial to light irradiation on microorganisms in the reactor, while nxrA, the functional gene of NOB, had weak light resistance and oxidation resistance, which makes the system had strong inhibition effect on NOB. The construction of this new system which does not depend on activated sludge volume and complex NOB activity inhibition strategy can better promote the practical application of PN/Anammox under mainstream conditions.