Advanced Treatment Of Secondary Effluent Research Articles

Advanced treatment of secondary effluent by the integration of heterogeneous catalytic ozonation and biological aerated filter.

The advanced treatment of secondary effluents was investigated by employing heterogeneous catalytic ozonation integrated with a biological aerated filter (BAF) process. The results indicated that catalytic ozonation with the prepared catalyst (MnxCuyOz/γ-Fe2O3) significantly enhanced the performance of pollutant removal and broke up macromolecules into molecular substances by the generated hydroxyl radicals. These molecular substances were easily absorbed by microorganisms in the microbial membrane reactor. In the BAF process, chemical oxygen demand (COD) (chemical oxygen demand) decreased from 54.26 to 32.56 mg/L, while in catalytic ozonation coupled with the BAF, COD could be reduced to 14.65 mg/L (removal ratio 73%). Under the same condition, NH4+-N decreased from 77.43 to 22.69 mg/L and 15.73 mg/L (removal ratio 70%) in the BAF and the catalytic ozonation coupled with BAF, respectively. In addition, the model that highly correlated influent COD to effluent COD and reactor height for filler could predict the removal ratio of COD of the BAF system. Based on the microbial community analysis, ozone in the solution had a certain screening effect on microorganisms, which helped to better adapt to the ozone-containing environment. Therefore, the integrated process with its efficient, economic, and sustainable advantages was suitable for the advanced treatment of secondary effluents.

Immobilization of phototroph-derived extracellular polymer for simultaneous removal of antibiotics and heavy metals: A sustainable approach for advanced treatment of secondary effluent

Antibiotic and heavy metal residues in secondary effluent are mainly responsible for the spread of antibiotic-heavy metal resistance genes and cannot be efficiently removed by traditional wastewater treatment processes. A sustainable approach by using alginate immobilized phototroph-derived extracellular polymer (EPS) for simultaneous inducing photolysis of antibiotic (sulfadiazine, SDZ) and adsorptive removal of heavy metal (Cd2+) from simulated secondary effluent was firstly explored. The results showed that immobilization of Rhodopseudomonas palustris-derived EPS (R-EPS-Alginate) led to the fastest SDZ photolysis due to its highest amounts of proteins (3.76 mg/g). With the optimum R-EPS-Alginate dosage of 6 g/L, 60 mg/L of immobilized EPS concentration and pH of 5.6, 86% of the SDZ was degraded within 96 h. 1O2 generated from 3EPS* was mainly responsible for the SDZ photodegradation which was decomposed into less toxic substances. 61% of Cd2+ was immediately adsorbed by R-EPS-Alginate within 60 min with a maximum adsorption capacity of 88.1 mg/g. Cd2+ adsorption moderately enhanced SDZ photolysis, probably due to the generation of CdS, while the latter almostly does not adversely impact the former.

Synthesis, characterization and application of dewatered municipal sludge-based creamsite and its phosphorus adsorption characteristics

Direct utilization of sludge-based biochar for phosphorus recovery exists numerous deficiencies (secondary pollution, poor stability, etc.). This study further explored dewatered sludge/bentonite ceramsite application for large-scale use of sludge-based biochar with low potential environmental risk. The best parameters for optimized ceramsite (SBC 900) were concluded as follows: mass ratio (dewatered sludge: bentonite: kaolin: starch) was 5:5:2:2 with 5% Na2SiO3, preheating temperature = 400 ° C, sintering temperature = 900 ° C. Batch experiments show that the optimized ceramsite could significantly remove phosphorus (Qe: 4.29 mg g−1) in a wide pH range (4–10). Column studies with quantitative analysis demonstrated that SBC 900 as fillings could effectively control phosphorus effluent during advanced treatment process. Breakthrough curves of SBC 900 from column experiments were described well by Thomas model (QT: 0.3691 mg g−1) and Yan model (QY: 0.1417 mg g−1). Compared to other factors, human acid (HA) is the key factor restricting advanced treatment of secondary effluent. Saturated ceramsite could be simply separated for subsequent utilization (fertilizer or building materials) to shift solid wastes toward marketable resources. This study provided another safer sludge resource utilization and effluent advanced treatment view which could be a beneficial and sustainable solution for sludge reclamation.

Advanced treatment of secondary effluent from wastewater treatment plant by a newly isolated microalga Desmodesmus sp. SNN1.

Secondary effluents contain considerable amounts of nitrogen and phosphorous, which if dumped untreated can cause eutrophication of the receiving water bodies. Microalgae can remove these nutrients and other pollutants from the wastewater effluents and play an effective role in the secondary effluent treatment. In this study, six microalgae strains (SNN1, SNN2, SNN3, SNN4, SNS1, and SNS2) were isolated and screened from the water and mud of Yingxue Lake of Shandong Jianzhu University, and their efficiencies for the removal of COD, NH4 +-N, TN, and TP in the secondary effluent were assessed. By comparing the growth performances and nutrient removal ability of algal strains in domestic sewage, we found that SNN1 (identified and named as Desmodesmus sp. SNN1) has the highest efficiency for biomass accumulation and sewage purification. Hence, the algal strain SNN1 was selected for further screening and optimization experiments. The strain showed higher biomass yield and better nutrient removal rate when the pH of secondary effluent was 9.0 and the initial inoculum concentration (optical density at 680 nm) of algal strain was 0.4. After 12 days of treatment, the concentrations of COD, NH4 +-N, TN, and TP in the secondary effluent were 31.79, 0.008, 8.631, and 0.069 mg/L, respectively. Therefore, SNN1 with the removal rates of 52.69% (COD), 99.99% (NH4 +-N), 89.09% (TN), and 94.64% (TP) displayed its high potential in nutrient removal. In addition, it also yielded 5.30 mg/L of chlorophyll a and 168.33 mg/L of lipids. These results demonstrated that this strain exhibited an effective treatment capacity for secondary effluent and microalgal oil production. This study is helpful to provide a strategy for the resource utilization of secondary effluent and the conservation of freshwater resources required by microalgae culture.

Advanced treatment of industrial estate effluent using ozone-membrane processes based on optimized random forest model

This study aimed to survey ozone-membrane processes for advanced treatment of secondary effluent in the industrial estate wastewater treatment plant. The performance of a pilot-scale system combining chemical treatment (coagulation, flocculation, sedimentation), sand filtration, ultrafiltration, activated carbon, and reverse osmosis were evaluated without and with ozonation at three different points of the set up. Ozone at the reaction time of 30 min and concentration of 24 ppm was injected before chemical treatment, before UF and before RO. UV254, COD, TOC, TSS, TDS, pH, turbidity and ozone efficiency were evaluated. For estimating the value of UV254, a random forest (RF) model was presented. The model uses supervised learning to estimate UV254 from an input vector consisting of step, location pH, temperature, electrical conductivity, and turbidity. The residue of organic matters, as UV254, that enter the membrane systems (UF and RO) were 0.125, 0.080, and 0.198 cm−1, respectively, which is desirable compared to the ozone-free state which is equal to 0.251 cm−1. Ozonation before UF, showed the lowest value (0.080 cm−1). TOC concentrations in the step of ozonation before UF were 12.1, 11.2, 10.8, 7.7, and 0.75 mg/l after SF, ozonation, UF, AC, and RO, respectively. Estimation of UV254 using RF-BO method represents MAE, MSE, and RMSE indexes equal to 0.01632, 0.00044191, and 0.021022, respectively. The results showed better efficiency of ozone injection before UF, compared to the other two cases. In the UV254 estimation section, the model shows enhanced accuracy in terms of error indexes in comparison with SVM-BO and GPR-BO methods.

Biochar based constructed wetland for secondary effluent treatment: Waste resource utilization

• The sustainable reuse of sludge and wetland macrophyte litter was realized. • SBC and CBC promoted nutrient removal and reduced N 2 O emissions fluxes in CWs. • Biochar-derived DOM can supplement carbon source for denitrification in CWs. • SBC significantly enhanced the key enzyme activities and ETSA in CWs. • Biochar enhanced the enrichment of nitrogen and phosphorus removing microorganisms. Constructed wetlands (CWs) are widely used to treat the effluent of wastewater treatment plants (WWTPs) due to their energy-saving and environmentally friendly advantages. Wetland macrophyte litter and sludge are wastes produced by CWs and WWTPs, respectively. However, there are few studies on the reuse of sludge and macrophyte litter as CW filling materials. In this study, sewage sludge and cattail litter were selected as raw materials to prepare biochar, which was used as CW filling materials to enhance the advanced treatment of secondary effluent. The results showed that the sludge biochar CWs (SBC-CWs) and the cattail biochar CWs (CBC-CWs) possessed better total nitrogen removal efficiency (91% and 81%, respectively) compared with the control (67%). Furthermore, SBC-CWs significantly improved total phosphorus removal efficiency by 20% than that of the control (p < 0.05), and reduced nitrous oxide emissions by 66% compared with the control (p < 0.05). The dissolved organic matter (DOM) released in the biochar was beneficial to replenish carbon sources and accommodate adaptive microorganisms. Electrochemical characterization and molecular methods revealed that the sludge biochar had stronger electron transfer capacity (ETC) than the cattail biochar, which could better promote the activities of key enzymes of the pollutant removal procedure. High-throughput sequencing showed that microorganisms such as Thaurea , Rhodocyclaceae , Hydrogenophaga and Fusibacter related to nitrogen removal were well enriched in the SBC-CWs and CBC-CWs. This research shows the potential for the simultaneous energy-saving advanced treatment of WWTP tailwater and waste resource recovery.

Enhanced photodegradation of antibiotics based on anoxygenic photosynthetic bacteria and bacterial metabolites: A sustainably green strategy for the removal of high-risk organics from secondary effluent

Antibiotic residues in effluents discharged from wastewater treatment plants (WWTPs) have been considered high-risk organics due to biorefractory property and potential toxicity. Secondary pollution and unsustainability existed in advanced treatment of secondary effluent are currently in urgent need of improvement. In this study, a sustainably green strategy based on Rhodopseudomonas palustris (R.palustris) by regulating the structure of extracellular polymeric substances (EPS) was proposed for the first time to achieve efficiently removal of sulfadiazine (SDZ). Results showed that 0.2 V was the optimal external potential for R.palustris to efficiently remove SDZ, where the biodegradation rate constant obtained at this potential was 4.87-folds higher than that in open-circuit mode and a complete removal was achieved within 58 h in the presence of EPS extracted at this potential. Three-dimensional excitation-emission matrix (3D-EEM) spectra analysis suggested that tryptophan protein-like, tyrosine protein-like, humic acid-like and fulvic acid-like substances present in EPS were the main effective components which was responsible for the indirect photodegradation of SDZ. The quenching experiments showed that 3EPS* was the dominant reactive species which accounted for 90% of SDZ removal. This study provides new implications for the advanced treatment of secondary effluent organic matters by developing eco-friendly bioaugmentation technology and biomaterials.

Immobilization of Phototroph-Derived Extracellular Polymer for Simultaneous Photosensitive Degradation of Antibiotics and Adsorptive Removal of Heavy Metals: A Sustainable Approach for Advanced Treatment of Secondary Effluent

Immobilization of Phototroph-Derived Extracellular Polymer for Simultaneous Photosensitive Degradation of Antibiotics and Adsorptive Removal of Heavy Metals: A Sustainable Approach for Advanced Treatment of Secondary Effluent

Advanced treatment of antibiotic wastewater by ionizing radiation combined with peroxymonosulfate/H2O2 oxidation

The advanced treatment of secondary effluent from an antibiotic wastewater treatment plant was investigated using ionizing radiation alone and combined with peroxymonosulfate (PMS)/H2O2 oxidation. In the effluent, 3 antibiotics, including erythromycin (ERY), tetracycline (TC), sulfamethoxazole (SMX), and 7 groups of antimicrobial resistance genes (ARGs) and 12 bacterial classes were detected. Results showed that the content of antibiotics and ARGs could be reduced greatly by radiation. The removal of ERY, TC and SMX reached 87%, 80% and 48% respectively, while the abatement of ARGs, including ermB, ermT, ermF, maA/mel, sul2, blaOXA, floR and mefA reached 63–91%. The COD removal was only 16.8% at 25 kGy. The enhancement with PMS addition was better than with H2O2 addition during radiation. With 10 mM PMS addition, the removal efficiency of antibiotics and COD increased to 70–98% and 57.6%, compared to 55–97% and 45.1% with 10 mM of H2O2 addition at 25 kGy. The PICRUSt analysis suggested that radiation at a dose of higher than 25 kGy could stimulate the bacterial activity for metabolism of amino acid, carbohydrate and energy, etc, but damage the genes coding for cellular and genetic information processing. The major ecological risk is derived from ERY (high level) and TC (medium level) in the effluent. The ecological risk of ERY and TC could be declined to medium level and low level, respectively after radiation with 10 mM PMS/H2O2 addition at 25 kGy. However, the operating cost of EB/PMS processes was more than twice higher than that of EB/H2O2 processes. Based on the tech-economic evaluation, ionizing radiation combined with H2O2 was a promising technology for the advanced treatment of pharmaceutical wastewater.

High-efficiency oxidation of fluoroquinolones by the synergistic activation of peroxymonosulfate via vacuum ultraviolet and ferrous iron

Fluoroquinolones in aquatic environments have caused worldwide concern due to the negative effects on human health and ecological environment. So far, the performance and mechanism for fluoroquinolones removal by the synergistic activation of peroxymonosulfate (PMS) via vacuum UV (VUV) irradiation and Fe2+ are still blank. Herein, compared with its sub-processes, VUV/Fe2+/PMS process significantly improved the degradation and mineralization efficiencies of three fluoroquinolones. Effect mechanisms of typical parameters (Fe2+ and PMS doses, initial pH) on norfloxacin (NOR) removal by VUV/Fe2+/PMS were elaborated and VUV/Fe2+/PMS showed excellent performance at wide initial pH (3−10). The results of fluorescence molecular probe and radical trapping experiments proved that hydroxyl radical, singlet oxygen, and sulfate radical were primary reactive oxygen species in VUV/Fe2+/PMS. The degradation pathways of NOR in VUV/Fe2+/PMS were mainly defluorination, piperazine ring transformation and quinolone group transformation, and its main inorganic by-products were F-, NO3−, and NH4+. Besides, the synergistic reaction pathways in integrated VUV/Fe2+/PMS process were elaborated. Furthermore, inorganic anions (such as Cl-, NO3-, SO42-, CO32-) hardly affected NOR removal by VUV/Fe2+/PMS, while dissolved organic matter showed slight inhibition. Finally, well-pleasing results of fluoroquinolones removal by VUV/Fe2+/PMS in actual waters highlighted its superiority in the advanced treatment of secondary effluent.

A comprehensive review on toxic petrochemical wastewater pretreatment and advanced treatment

Abstract Petrochemical wastewater is a major industrial source of pollution that produces a variety of refractory and toxic organic pollutants that are detrimental to animals and plants in natural water bodies; it is especially harmful to biological treatment systems. Regardless of these threats, studies on these specific organic pollutants are limited at present. Consequently, it is extremely essential to promote relevant problem solving efficiently. Currently, only limited processes are available for pretreatment of high-concentration wastewater, and advanced treatment of secondary effluent as compared to the conventional treatment are introduced by current studies. Therefore, in this review, we have systematically generalized the characteristics of petrochemical wastewater; we have particularly summarized and compared different methods (recent developments, influencing factors, etc.) which are applied in pretreatment and advancement of current methods. Additionally, the interaction mechanisms of microbes under a wide range of concentrations of specific organic pollutants and associated degradation pathways have been described comprehensively. Moreover, we have analyzed bioenergy recovery from the degradation/removal of specific organic pollutants with environmental-friendly and economically methods because it can help realize the goal of circular resource utilization during the process of detoxification and minimization.

Non-activated peroxymonosulfate oxidation of p-aminobenzoic acid in the presence of effluent organic matter

Non-activated peroxymonosulfate (PMS) oxidation of p-aminobenzoic acid (PABA) in the presence of effluent organic matter (EfOM) from wastewater treatment plant was investigated. The reaction kinetics of PMS with PABA exhibited a strong pH dependency, which was well described by species-specific reactions. The transformation of PABA by PMS was inhibited in the presence of EfOM at pH 3.0. Moreover, the variation of EfOM during PMS oxidation processes was tracked using excitation emission matrix (EEM) combined with parallel factor analysis (PARAFAC). The results revealed that humic-like substances and proteins in EfOM consumed a fraction of PMS and thus hindered PABA degradation, which was partly attributable to phenolic compounds widely existed in EfOM. The transformation products of PABA by PMS oxidation were identified by leveraging quadruple time-of-flight (Q-TOF) mass spectrometry (MS) coupled with ultra-high performance liquid chromatography (UHPLC), and a possible reaction pathway was also proposed. Understanding the role of EfOM in PABA oxidation by PMS is essential for providing useful insights into the application of PMS in advanced treatment of secondary effluent.

Study on Treatment of Secondary Tailwater of Wastewater Treatment Plant by New Reinforced Flocculation Sedimentation

The advanced treatment and reuse of secondary effluent from urban sewage plants is currently one of the reliable ways to solve the shortage of urban water resources. This paper proposes a new type of enhanced flocculation and sedimentation process for the advanced treatment of secondary effluent from a wastewater treatment plant. The new type of enhanced flocculation sedimentation tank is used as a main process for new advanced wastewater treatment. The combination of wing micro vortex flocculation tank, net catching flocculation, inclined plate sedimentation tank and biological filter has good effluent quality. Basically, CODCr were stable at 35 mg/L, turbidity of effluent were stable at 2 NTU, chroma were stable at 30 degrees, TP were stable at 1 mg/L.

Performance and microbial community in a combined VF-HF system for the advanced treatment of secondary effluent.

In this study, a laboratory-scale system combined a vertical flow constructed wetland (VF) with a horizontal flow constructed wetland (HF), which was used to treat the secondary effluent of a wastewater treatment plant. Removal efficiencies of 67.02%, 89.80%, 90.31% and 75.38% were achieved by the system for chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), total nitrogen (TN) and total phosphorus (TP), respectively. The VF showed much higher average loading rates of COD, TP, NH4 +-N and TN (7.96 g/m2/d, 0.076 g/m2/d, 0.31 g/m2/d and 0.99 g/m2/d) than in HF (0.65 g/m2/d, 0.016 g/m2/d, 0.25 g/m2/d and 0.50 g/m2/d), during the stable operation period. Biodegradation played a major role in pollutant removal, especially for COD and TN. The results of bacterial community analysis indicated that heterotrophic denitrifying bacteria (Hydrogenophaga and Flavobacterium) were the dominant contributors for nitrogen removal in the VF, while heterotrophic denitrifying bacteria (Rhodobacter, Flavobacterium and Dechloromonas) and the autotrophic denitrifying bacteria Sulfurimonas played the principal roles for nitrogen removal in the HF. Redundancy analyses showed that COD and NH4 +-N were the important factors affecting the distribution of nitrogen removal bacteria in the VF, while pH, dissolved oxygen and oxidation-reduction potential were the key factors influencing the distribution of nitrogen removal bacteria in the HF.

Sequential biofiltration – A novel approach for enhanced biological removal of trace organic chemicals from wastewater treatment plant effluent

Recent studies revealed the benefits of oligotrophic and oxic conditions for the biological removal of many trace organic chemicals (TOrCs) during soil-aquifer treatment. These findings indicate an unused tuning potential that might also be applicable in engineered biofiltration systems with drastically reduced hydraulic retention times for an enhanced mitigation of TOrCs during wastewater treatment. This study introduces the novel approach of sequential biofiltration (SBF) for the advanced treatment of secondary effluent using two granular media filters operated in series with an intermediate aeration step aiming for oxic and oligotrophic conditions in the second filter stage. Results from the experiments conducted at pilot-scale confirm a reduced substrate availability and predominantly oxic conditions in the second filter stage of the SBF setup. An increased removal of several TOrCs was observed in an SBF system as compared to a conventional single-stage biofiltration unit operated at the same overall empty bed contact time (EBCT). Short-term tests with varying EBCTs in the first filter stage revealed a high degree of system robustness of TOrC mitigation when confronted with sudden hydraulic load variations. Higher removal of several TOrCs at increased EBCTs in the second filter stage indicates that EBCT might play a crucial role for the degradation of certain compounds.

The nitrogen removal performance and microbial communities in a two-stage deep sequencing constructed wetland for advanced treatment of secondary effluent

The advanced treatment of secondary effluent was conducted in a two-stage deep sequencing constructed wetland (DSCW) which comprised a denitrification chamber (W1) and a nitrification chamber (W2). The results showed that a superior NO3−-N removal rate was observed in W1 with a C/N ratio of 6.5, and a high NH4+-N removal rate was obtained when the W2 was operated with 6-h duration of idle. In the long-term operation for 45days, the two-stage DSCW pilot system achieved high and stable removal of TN, NH4+-N and NO3−-N, which were 92.9%, 83.7% and 95.6% in average, respectively. The microbial communities between W1 and W2 were significant different. Rich diversity of the microbial community and the high proportion of denitrifying bacteria in the W1 were essential for nitrogen removal in this treatment system. AOB in the W2 played a major role in NH4+-N removal in W2.

Occurrence and fate of amisulpride, sulpiride, and lamotrigine in municipal wastewater treatment plants with biological treatment and ozonation

This study examines the transformation and removal of the atypical antipsychotics amisulpride and sulpiride and the anticonvulsant lamotrigine in municipal wastewater treatment plants (WWTPs). Amisulpride, sulpiride and lamotrigine were selected using a tailored non-target screening approach. In WWTPs, lamotrigine concentrations increased from 1.1 to 1.6μg/L while sulpiride and amisulpride exhibited similar concentrations, up to 1.1μg/L and 1.3μg/L, respectively. It was found that N2-glucuronide conjugates of lamotrigine were cleaved to form lamotrigine. Both lamotrigine and amisulpride were detected in groundwater with a concentration of 0.07μg/L. Sulpiride was identified but not quantified. This demonstrates that amisulpride, sulpiride and lamotrigine might be used as indicators for treated wastewater in raw waters used for drinking water production.Furthermore, it could be shown that all three pharmaceutical compounds are efficiently oxidized by ozonation, leading mainly to N-oxide oxidation products. No significant removal of the N-oxides of amisulpride, sulpiride and lamotrigine was observed in the bench-scale biodegradation experiments with activated sludge. This indicated their high biological persistence. Therefore, N-oxides might be appropriate as indicators for post-ozonation as a major technology for the advanced treatment of secondary effluent.

Upgrading secondary wastewater plant effluent by modified coagulation and flocculation, for water reuse in irrigation

In this study, the feasibility of using coagulation, flocculation, and sedimentation (CF-S) for advanced treatment of secondary effluent released from the Yazd Intermittent Cycle Extended Aeration System was investigated. Four coagulants including ferric chloride (FeCl3), polyaluminum chloride (PAC), ferrous sulfate (FeSo4), and potassium ferrate (K2FeSo4) along with Gflog C-150 as flocculant polymer were used. In this study, returned chemical sludge was considered as a modification. Preliminary CF-S processes showed that FeSO4 and K2FeO4 had low removal efficiencies. Thus, these two coagulants were abandoned and CF-S processes were continued only with PAC and FeCl3 coagulants which had higher efficiencies in the removal of biological oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), and turbidity. Removal efficiency was higher when half of the chemical producing sludge was returned as compared with using both coagulants simultaneously along with 2 mg L−1 of C-150 as flocculant. In the optimum dosage, when half of PAC and FeCl3 sludge were returned, the volume of produced sludge was reduced by 40% and 28%, respectively, as compared without returned sludge. For the PAC coagulant in the optimum dosage with half of the sludge returned, all 2012 EPA standards of irrigation were met for both ‘processed and non-processed type’ agricultural crops.

Advanced Treatment of Secondary Effluent of a Pharmaceutical Factory in Northern

A combined process of coagulation with Fenton oxidation was introduced to the advanced treatment of the secondary effluent of a pharmaceutical wastewater treatment process in northern China. Major factors affecting the treatment were investigated by lab-scale tests. The results showed that FeCl3 was the best among the tested 4 coagulants, and its optimal dose and the initial pH for reaction were 175 mg/L and 7, respectively, at ambient temperature. After the coagulation, the wastewater was treated by Fenton oxidation. An excellent treatment efficiency was obtained with H2O2/Fe2+ (M/M) of 7.5 and H2O2 dosage of 10 mM/L at 20°C reacting for 60 min. For the influent with a COD of 170~200 mg/L and a TP of 6~9 mg/L, a COD removal and TP removal as high as 71.5% and 99.5%, respectively, could be reached after treated by the coagulation combined with the Fenton oxidation under the optimized condition. The final effluent could meet the requirement of Discharge Standards of Water Pollutants for Pharmaceutical Industry Fermentation Products Category (GB21903-2008).

Performance of a tertiary submerged membrane bioreactor operated at supra-critical fluxes

A pilot-scale submerged aerobic membrane bioreactor (MBR) was run for over 3 months to assess the sustainability to operate at supra-critical fluxes. The MBR was applied as advanced treatment of secondary effluent from a conventional wastewater treatment plant. The system was successfully operated without biomass purge at hydraulic retention time (HRT) of 8.8h, resulting in a moderate liquor suspended solid concentrations range (MLSS=4.1–7.1g/l) in the bioreactor, according to the influent organic load fluctuations. Treatment performance was stable and achieved high conversion of ammonium to nitrate (96%) and dissolved organic carbon removal (53%). Short-term tests have been carried out according to a modified flux-step method to determine critical flux and evaluating optimum membrane cyclical aeration frequency. For the long-term tests, an alternative operation mode for backwashing initiation, based on a pre-selected transmembrane set-point, was applied. Under typical specific demand values (SADpnet=13.7–18.3Nm3/m3), continuous operation under different supra-critical filtration fluxes (J=60–80l/hm2) and backwashing fluxes (40–80l/hm2) can be maintained without any chemical cleaning. Analysis by means of sludge fractionation in lab-scale tests, at similar hydrodynamic conditions, indicated that the contribution of suspended solids to cake membrane fouling was estimated about 86–89%.