Long-term performance of UASB in treating N, N-dimethylformamide-containing wastewater with a rapid start-up by inoculating mixed sludge

Anaerobic treatment of nitrogenous industrial organic wastewater by carbon-neutral processes integrated with anaerobic digestion and partial nitritation/anammox: Critical review of current advances and future directions

Anaerobic digestion combined with partial nitritation/anammox technology holds promising potential for the carbon-neutral treatment of nitrogenous industrial organic wastewater, boasting remarkable advantages in effective removal of both organic matters and nitrogen, bio-energy recovery and carbon emission reduction. This study provides a concise overview of the development and advantages of anaerobic digestion combined with partial nitritation/anammox technology for treating nitrogenous industrial organic wastewater. The process excels in removing organic matter and nitrogen, recovering bio-energy, and reducing carbon emissions, compared to traditional physicochemical and biological methods. Case studies highlight its energy-saving and efficient attributes, especially for carbon-neutral nitrogen removal. Challenges for achieving stable operation in the future are discussed, and the study offers insights into the broader application of this integrated process in industrial wastewater treatment.

Treatment of cosmetic wastewater containing N, N-dimethylformamide and high concentration of chloride salt by chemical precipitation and electrochemical method

High-strength wastewater containing elevated levels of chloride salt and N, N-dimethylformamide (DMF) solvent was collected from manufacturing of sunscreen cream (for UVA/UVB protection) at a cosmetic factory. In evaporation process, precipitates, formed due to the high chloride content (around 160 g/L), clog the pipeline, seriously reducing the treatment efficiency. This study aimed to develop a two-stage process integrating chemical precipitation and electrochemical oxidation to specifically remove the concentrated chloride salt and organic compounds (COD >100 g/L). Chloride ions were initially recovered as insoluble Friedel's salt using calcium hydroxide (Ca(OH)2) and sodium aluminate (NaAlO2) as the precipitants. The [Cl]/[Ca]/[Al] ratio and solution pH were optimized to obtain a pure crystallized phase of Ca2AlCl(OH)6•2H2O. Afterwards, the organic compound were treated by a Fered-Fenton with the addition of H2O2 and FeSO4 to degrade the remaining COD. The cost and energy consumption of this integrated processes were evaluated, compared to the conventional evaporation method.

Impact analysis of hydraulic residence time and dissolved oxygen on performance efficiency and microbial community in N, N-dimethylformamide wastewater treated by an AnSBR-ASBR

Suitable operating parameters are one of the key factors to efficient and stable biological wastewater treatment of N, N-dimethylformamide (DMF) wastewater. In this study, an improved AnSBR-ASBR reactor (anaerobic sequencing batch reactor, AnSBR, and aerobic SBR, ASBR, run in series) was used to investigated the effects of operating conditions such as hydraulic residence time (HRT), AnSBR stirring speed and ASBR dissolved oxygen (DO) for DMF wastewater treatment. When HRT decreased from 24 h to 12 h, the average removal rates of COD by the AnSBR were 34.59% and 39.54%, respectively. Meanwhile, the removal rate of NH4+-N by ASBR decreased from 88.38% to 62.81%. The DMF removal rate reached the best at 18 h and the expression of dehydrogenase was the highest in the AnSBR. The abundance of Megasphaera, the dominant sugar-degrading bacteria in the AnSBR, continued to decline due to the decrease of HRT. The relative abundance of Methanobacterium gradually increased to 80.2% with the decrease of HRT and that hydrotrophic methanogenesis dominated the methanogenic process. The HRT decrease promoted butyrate and pyruvate metabolism in anaerobic sludge, but the proportion of glycolysis and methane metabolism decreased. The AnSBR-ASBR reactor had the best operation performance when HRT was 18 h, AnSBR speed was 220 r/min, and ASBR DO content was 3-4 mg/L. This study provided an effective reference for the reasonable selection of operating parameters in the treatment of DMF-containing wastewater by the AnSBR-ASBR.

Anaerobic membrane bioreactor for carbon-neutral treatment of industrial wastewater containing N, N-dimethylformamide: Evaluation of electricity, bio-energy production and carbon emission

The feasibility of anaerobic membrane bioreactor (AnMBR) for the treatment of N, N-dimethylformamide (DMF)-containing wastewater was theoretically compared with the conventional activated sludge (CAS) process in this study. The electricity consumption and expenditure, bio-energy production and CO₂ emission were investigated using the operational results of a lab-scale AnMBR operated in a long-term operation. The AnMBR was capable of producing bio-methane from wastewater and generated 3.45 kWh/m³ of electricity as recovered bio-energy while the CAS just generated 1.17 kWh/m³ of electricity from the post-treatment of excessive sludge disposal. The large quantity of bio-methane recovered by the AnMBR can also be sold as sustainable bioresource for the use of household natural gas with a theoretical profit gain of 29,821 US$/year, while that of the CAS was unprofitable. The AnMBR was also demonstrated to significantly reduce the carbon emission by obtaining a theoretical negative CO₂ production of -2.34 kg CO₂/m³ with the recycle of bio-energy while that for the CAS was 4.50 kg CO₂/m³. The results of this study demonstrate that the AnMBR process has promising potential for the carbon-neutral treatment of high-strength DMF-containing wastewater in the future.

Chemical oxygen demand and nitrogen removal from real membrane-manufacturing wastewater by a pilot-scale internal circulation reactor integrated with partial nitritation-anammox

A pilot-scale system integrating internal circulation and partial nitritation-anammox successfully treated real high-strength membrane-manufacturing wastewater in this study. With this pilot-scale system, a high chemical oxygen demand (COD) removal efficiency of 85 % and a nitrogen removal of 90 % are achieved at an organic loading rate of 6.0 kg COD/m3/d. The nitrogenous organic matters in the internal circulation zone are degraded into ammonia nitrogen. In the partial nitrification zone, nitrite accumulation is achieved, providing a suitable NH4+-N/NO2--N ratio for anammox reaction. Partial nitritation is achieved by maintaining an operational temperature at 30-35 °C, free ammonia concentration at 5-7 mg/L and dissolved oxygen at 0.4-0.7 mg/L with a reflux ratio of 150 %. The COD to nitrogen ratio in the internal circulation effluent is maintained below 3.0 to inhibit nitrite oxidizing bacteria. This study demonstrates that a pilot-scale system can efficiently remove organic matters and nitrogen from wastewater of membrane-manufacturing industry.

Carbon-neutral treatment of N, N-dimethylformamide-containing industrial wastewater by anaerobic membrane bioreactor (AnMBR): Bio-energy recovery and CO2 emission reduction

High-strength industrial wastewater containing approximately 2000 mg/L of N, N-dimethylformamide (DMF) was treated by the anaerobic membrane bioreactor (AnMBR) during a long-term operation with the concept of carbon neutrality in this study. Bio-methane was recovered as bio-energy or bio-resource from DMF-containing wastewater along with the CO₂ emission reduction. The results are clear evidence of the feasibility of carbon-neutral treatment of DMF-containing wastewater by the AnMBR. With an effective degradation under the organic loading rate of 6.53 COD kg/m³/d at the HRT of 12 h, the AnMBR completely covered the energy consumption during long-term operation by saving electricity of 4.16 kWh/m³ compared with the conventional activated sludge process. The CO₂ emission of the AnMBR was just 1.06 kg/m³, remarkably reducing 1.45 kg/m³ of CO₂. The treatment of DMF-containing wastewater by the AnMBR perfectly realized the goal of carbon neutrality, and was considered as an alternative to the conventional activated sludge process.

Sludge yield and degradation of suspended solids by a large pilot-scale anaerobic membrane bioreactor for the treatment of real municipal wastewater at 25 °C

Sludge yield and suspended solid are important factors concerned in the anaerobic treatment of municipal wastewater. In this study, a large pilot-scale anaerobic membrane bioreactor (AnMBR) was constructed for effectively treating real municipal wastewater at an ambient temperature of 25 °C. The sludge yield and the degradation of influent suspended solids were evaluated during the long-term operation of the AnMBR. This reactor with 5.0 m³ effective volume is the largest one-stage submerged AnMBR that has ever been used to treat municipal wastewater. During the long-term operation of 217 days, this AnMBR obtained excellent COD and BOD₅ removal efficiency over 90%. Stable biogas production was also successfully obtained from treating municipal wastewater. The sludge yield of the AnMBR was approximately 0.19-0.26 g MLSS g^-1 COD removed for the treatment of real municipal wastewater. The shortest SRT of the AnMBR was calculated as 29 days for an HRT of 6 h at an empirical MLSS of 10 g L^-1. While the influent suspended solid (SS) contained in the municipal wastewater was completely removed by the AnMBR, only 57%-66% of the influent SS was degraded. The rest of influent SS was directly converted to MLSS instead of being degraded. The AnMBR maintained a stable membrane filtration using a hollow-fiber membrane with a total area of 72 m², realizing a flux of 2.75-17.83 LMH, and the mean transmembrane pressure (TMP) was 0.9-23.5 kPa. An online chemical backwash cleaning system helped to lower the TMP timely using sodium hypochlorite and citric acid when the TMP increased rapidly and reached the rated limit of membrane. This is the first report on demonstrating the successful operation and detailed performance of a large pilot-scale AnMBR applied to the treatment of real municipal wastewater.

Large pilot-scale submerged anaerobic membrane bioreactor for the treatment of municipal wastewater and biogas production at 25 °C

The aim of this work was to demonstrate the operation of a large pilot-scale submerged anaerobic membrane bioreactor (5.0 m³) for biogas production from municipal wastewater at ambient temperature of 25 °C. To the best of our knowledge, this is the largest one-stage submerged AnMBR that has ever been reported. This AnMBR realized a hydraulic retention time (HRT) of 6 h and a treatment capacity of 20 m³ d^-1, obtaining excellent effluent quality with COD removal efficiency over 90% and BOD₅ removal over 95%. The biogas yield of the AnMBR was 0.25-0.27 L g^-1 removed COD and 0.09-0.10 L L^-1 raw wastewater. The methane content of the biogas was at the range of 75%-81%. The COD and nitrogen mass balance were also identified based on long-term operation. The hollow-fiber membrane module realized a flux of 2.75-17.83 LMH. An online backwash chemical cleaning system helped to lower the transmembrane pressure timely.

Coupling of Fe-C and aerobic granular sludge to treat refractory wastewater from a membrane manufacturer in a pilot-scale system

A novel pilot-scale system based on aerobic granular sludge (AGS) as a biological treatment step was proposed to treat refractory wastewater from a membrane manufacturer. The components of the system included a microelectrolysis Fe-C filter, a hydrolysis acidification bioreactor (HA), sequence batch reactor 1 (AGS SBR1), sequence batch reactor 2 (AGS SBR2), and a membrane bioreactor (MBR). The Fe-C filter effectively improved the biodegradability of the wastewater components and introduced some byproducts (such as Fe²⁺, Fe³⁺, and Fe minerals) that are beneficial for the cultivation and stability of the AGS. Ideal conditions for aerobic granulation were maintained in the SBR, such as alternating feast and famine conditions. A selection pressure, including a hydraulic shear force and settling time, was also created therein. The results showed that the AGS was formed successfully in both SBR1 and SBR2, the sludge volume index after 30 min (SVI₃₀) and mean particle size reached 34.2 mL/g and 720 µm, and 36.7 mL/g and 610 µm, respectively, and a satisfactory nutrient removal capacity was achieved in the system. During the entire experimental period, the microbial community changed significantly; enrichment of microbes with the secretion of extracellular polymeric substances (EPS), granule stabilization functions in the AGS, and the differentiation of microbes corresponding to the function of each unit were observed. The use of Fe-C, application of SBRs, and use of dewatered sludge as an inoculant played key roles in the cultivation and stability of the AGS.

Activated sludge and other aerobic suspended culture processes

This paper provides an overview of activated sludge related to suspended growth processes for the year 2019. The review encompasses process modeling of activated sludge, microbiology of activated sludge, process kinetics and mechanism, nitrogen and phosphorus control, design, and operation in the activated sludge field. The fate and effect of xenobiotics in activated sludge, including trace organic contaminant and heavy metal xenobiotics, which had influence on the growth of suspended sludge, are covered in this review. Compared to past reviews, many topics show increase in activity in 2019. These include, biokinetics process of aerobic granular sludge formation, pyrolysis kinetic mechanism of granular sludge. These topics are referred to formation and disintegration of granular sludge. Other sections include activated sludge settling model, toxicity resistant microbial community, nitritation-anammox processes for nitrogen removal, and respirometry used in the operation of real wastewater treatment plant are especially highlighted in this review. PRACTITIONER POINTS: Biokinetics process of aerobic granular sludge formation Toxicity resistant microbial community in activated sludge Nitritation-anammox processes for nitrogen removal in activated sludge.

Investigation of hydrolysis acidification process during anaerobic treatment of coal gasification wastewater (CGW): Evolution of dissolved organic matter and biotoxicity

Coal gasification wastewater (CGW) contains several types of aromatic pollutants, which impart high biotoxicity and reduce the quality of anaerobic treatment. Two types of hydrolysis acidification processes, namely microaerobic hybrid reactor (HA-1) and upflow anaerobic sludge blanket reactor (HA-2), were developed for pre-treatment before the anaerobic treatment. The changes in the dissolved organic matter and biotoxicity were investigated to comprehensively understand the degradation process. The results showed that HA-2 coupled with an anaerobic reactor achieved a 12.3% and 13.4% higher removal efficiency for chemical oxygen demand and total phenols, respectively, compared with the coupled process with HA-1. Furthermore, HA-2 could transform macromolecules into small molecules more efficiently and produce fewer intermediates. The coupled process with HA-2 preferentially removed complex aromatic substances with absorption wavelengths of 285 and 254 nm, according to the sequential orders interpreted from two-dimensional correlation spectroscopy. In addition, the results of fluorescence excitation-emission-matrix with regional integration analysis revealed that the contents of typical cyclic compounds in CGW, such as phenolic, heterocyclic, and polycyclic aromatic compounds were remarkably reduced by HA-2. In addition, HA-2 reduced the toxic unit value of CGW by 67.5% and increased the resazurin dehydrogenase activity of the sludge by 37.5% during CGW treatment, thus improving the biotoxicity removal and biodegradability. However, the coupled process with HA-2 did not significantly affect the "indirect estrogenic activity" of CGW. A Pearson correlation analysis indicated that spectral indicators, such as UV₂₅₄ and Φ_T,n, presented a high positive correlation with the reduction of acute toxicity and organics.

Performance of an up-flow anaerobic bio-electrochemical system (UBES) for treating sulfamethoxazole (SMX) antibiotic wastewater

This paper focused on the feasibility and performance of an up-flow anaerobic bio-electrochemical system (UBES) for treating sulfamethoxazole (SMX) antibiotic wastewater at different COD loading rates (LRs) from 2.02 ± 0.13 to 6.09 ± 0.14 kgCOD/(m3·d). Open-circuit UBES had a lower average COD removal rate of 62.4 ± 4.7% in Run2, and the accumulation of volatile fatty acid (VFA) was occurred. However, closed-circuit UBES can alleviate the accumulation of VFA (which was decreased from 720.4 to 102.4 mg/L), the highest average COD, SMX removal rates were 85.7 ± 3.2% and 73.7 ± 2.0%, respectively. The closed-circuit UBES can withstand more than 3 times LR than open-circuit UBES, which proved that the ability of microorganisms to resist toxic substance stress was strengthened. And the mathematical models for pollutants removal rate were established and well interpreted the results, which also can guide the operation of UBES.

New insights into the cultivation of N, N-dimethylformamide-degrading methanogenic consortium: A long-term investigation on the variation of prokaryotic community inoculated with activated sludge

The cultivation of the N, N-dimethylformamide (DMF)-degrading methanogenic consortium is considered difficult. In this study, an up-flow anaerobic sludge blanket (UASB) was inoculated with activated sludge in order to culture the DMF-degrading anaerobic sludge under a constant DMF concentration of approximately 2000 mg L^-1. While the UASB realized a nearly 100% degradation of DMF and a high methane production of 1.03 L d^-1 for the first two months, both the removal efficiency and methane production continued to decrease until the end. The characterization of the prokaryotic community reveals that those DMF-hydrolyzing bacteria (DHB) originating from the activated sludge were responsible for the effective degradation of DMF. However, even when fed with a constant concentration of DMF, the DHB kept decreasing all the time while methane-producing archaea were rapidly cultivated. The variation of prokaryotic community suggests that the DHB could not proliferate anaerobically without utilizing the intermediate products from the hydrolysis of DMF, resulting in an unstable DMF-degrading consortium. The cultivation of DHB under the anaerobic condition of the UASB was therefore difficult. The reason it was not possible to culture a DMF-degrading methanogenic consortium in this study is that the DHB are denitrifying bacteria which require nitrate for their cell growth under the anaerobic condition. The solution to maintain the abundance of these DHB is to add doses of nitrate into the system. Nitrate is likely to help these DHB recapture intermediates from methanogens, enabling them to perform a heterotrophic denitrification by using a small proportion of DMF as the carbon source while simultaneously maintaining the cell growth of DHB.

Dissection and characterization of the prokaryotic community during the long-term operation of a submerged anaerobic membrane bioreactor for the anaerobic treatment of N, N-dimethylformamide-containing wastewater with a co-cultured inoculum

A submerged anaerobic membrane bioreactor (SAnMBR) was operated for the anaerobic treatment of wastewater containing approximately 2000 mg L^-1N, N-dimethylformamide (DMF). Inoculated with a co-cultured inoculum, the SAnMBR obtained an excellent DMF removal under a low organic loading rate (OLR) of 3.14-4.16 g COD L^-1 d^-1. However, the elevation of OLR limited hydrolysis. While the co-cultured inoculum initially contains abundant DMF-hydrolyzing bacteria with potential to hydrolyze DMF into intermediates, such as Paracoccus, Hyphomicrobium, Burkholderia, Catellibacterium, Bacillus and Bradyrhizobium, since these bacteria are facultative anaerobes which survive anaerobically, they kept decaying rather than proliferating, resulting in the weakening of the DMF-hydrolyzing ability. Each re-inoculation of new sludge only temporarily revitalized hydrolysis activity for a short period. Due to the lack of nitrate, these bacteria were unable to proliferate. This suggests that a small dose of nitrate would help to enrich these bacteria and establish a stable DMF-degrading consortium.

Anaerobic treatment of N,N-dimethylformamide-containing high-strength wastewater by submerged anaerobic membrane bioreactor with a co-cultured inoculum

The anaerobic treatment of wastewater containing approximately 2000 mg L^-1N,N-dimethylformamide (DMF) was conducted by a lab-scale submerged anaerobic membrane bioreactor (SAnMBR). The inoculum consisted of aerobic DMF-hydrolyzing activated sludge (DAS) and anaerobic digested sludge (ADS). A rapid start-up was achieved with thorough DMF methanogenic degradation on the first day. The results of a 250-day long-term experiment demonstrated that under a low organic loading rate (OLR) of 3.14-4.16 g COD L^-1 d^-1, SAnMBR maintained excellent DMF removal efficiency along with high methane conversion. However, the elevation of OLR significantly limited DMF hydrolysis. When OLR exceeded 6.54 g COD L^-1 d^-1, both removal efficiency and methane production dramatically dropped. The DMF-hydrolyzing bacteria originating from the DAS gradually decayed under the anaerobic condition, resulting in the weak hydrolysis of DMF. The shortening of hydraulic retention time (HRT) is not recommended for the SAnMBR because severe membrane fouling occurred when HRT was shortened to 8 h. To handle high OLRs, an appropriate solution is to maintain a low F/M ratio by increasing both the influent DMF concentration and sludge concentration. The high CH₄ content in the biogas, exceeding 85%, was shown to be the reason for the suitability of anaerobic treatment to DMF. Some improvements which would help to maintain the effective hydrolysis are proposed: a side-stream system to replenish DAS to the SAnMBR is helpful; slight dosage of nitrate could also help to enrich the DMF-hydrolyzing bacteria; and the co-digestion of DMF and other organics might be convenient to establish a stable DMF-degrading consortium.