Enhanced removal of humic substances in effluent organic matter from a leachate treatment system via biological upgradation of molecular structure.

Biological upgradation (BU) process was proposed, with the goal of converting the molecular structure, for improving the coagulation effect on humic substances (HS) in effluent organic matter from the membrane bioreactor of a leachate treatment system. Enhancement of coagulation effect was observed with the improvement of chemical oxygen demand and HS removal efficiency from 45.5% and 56.5% to 80.0% and 92.6% (Fe dosage was 400 mg·L-1), respectively, which was approximately 30-40% higher than the other available researches. Variations in molecular weight (MW) and carboxyl contents of fulvic acid (FA) and humic acid (HA) were analysed by size exclusion chromatography coupled with dissolved organic carbon detection, potentiometric titration and Fourier transform infrared spectroscopy. The obtained results indicated that BU process led to the growth of MW of HS, of which the larger MW (1650 Da) FA and HA raised from 19.07 and 0.34 mgC·L-1 to 71.67 and 1.58 mgC·L-1, respectively, as well as increases in the carboxyl contents of FA and HA from 6.70 and 6.28 meq·gC-1 to 11.84 and 8.71 meq·gC-1, respectively. Because of this, a stronger binding effect between Fe and HS might be formed that improved the coagulation effect.

Interaction-sedimentation strategy for highly efficient removal of refractory humic substances in biologically treated wastewater effluent: from mechanistic investigation to full-scale application.

Based on the accurate characterization of the binding sites of humic substances (HS) and their binding coefficients with ferric ions (Fe(III)), a coupled interaction-sedimentation (CIS) technology was proposed for dealing with HS in the biologically treated wastewater effluent (BTWE) from a full-scale antibiotic production wastewater treatment plant. The infrared spectral and carbon-13 nuclear magnetic resonance characteristics showed that (i) protonated carboxyl groups in HS were the main binding sites for Fe(III) and HS, (ii) one carboxyl group of HS interacted with one ferric ion, (iii) the Fe(III)-binding ability of fulvic acids (FA) was 2.8 times as much as that of humic acids (HA) when FA and HA coexisted, and (iv) the presence of non-humic substances in the effluent organic matter (EfOM) amplified the Fe(III)-binding ability difference between FA and HA to 4.9 times. Afterwards CIS technology was successfully optimized and applied in engineering-scale and superior HS and EfOM removal efficiencies of 94.2% and 84.0% were reached, respectively. The CIS technology and its engineering application in this study not only fulfill the direct discharging standard for antibiotic production wastewater, but also have the potential for replication in broader advanced treatments for BTWE.

Highly efficient AgBr/h-MoO3 with charge separation tuning for photocatalytic degradation of trimethoprim: Mechanism insight and toxicity assessment.

A highly solar active AgBr/h-MoO3 composite was constructed by a facile precipitation method, and the charge separation tuning was achieved by photoreduction of AgBr. The photoreduced Ag0 on AgBr/h-MoO3 acted as charge transfer bridge to form Z-scheme heterostructure, while the high degree of Ag reduction converted the material into type-II heterostructure. The synthesized optimal material promoted charge separation and visible light activity due to the incorporation of highly solar active AgBr, which showed ca. 2 times activity on trimethoprim (TMP) degradation than h-MoO3. The contribution of reactive species on TMP degradation followed the order of O2- >1O2 > h+, which agree well with the proposed charge separation mechanism. The photocatalytic degradation mechanism of TMP was proposed based on the radical quenching, intermediate analysis and DFT calculation. The toxicity analysis based on QSAR calculation showed that part of the degradation intermediates are more toxic than TMP, thus sufficient mineralization are required to eliminate the potential risks of treated water. Moreover, the material showed high stability and activity after four reusing cycles, and it is applicable to treat contaminants in various water matrix. This work is expected to provide new insight into the charge separation tuning mechanism for the AgX based heterojunction, and rational design of highly efficient photocatalysts for organic contaminants degradation by solar irradiation.

Investigating the potential origin and formation of humic substances in biological wastewater treatment systems from the forms of phosphorus.

Origin of the humic substances formed in biological wastewater treatment system (abbreviated as bio-HS) still remains inconclusive. In this study, the bio-HS that contained humic acid (HA) and fulvic acid (FA) from effluent and activated sludge were isolated and purified with XAD-8 resin and ion exchange resin, and then the molecular weight, functional groups, contents and forms of phosphorus (P) using gel permeation chromatography (GPC), fourier transform infrared (FTIR), element analysis and P nuclear magnetic resonance (31P-NMR) were investigated. The results showed that HS was formed in biological wastewater treatment systems, and had a lower degree of humification than soil, peat, or marine HS, and mainly comprised diester and monoester P fragments. Specific signal peaks of intracellular materials and cell membranes (nucleic acid, phospholipids, and sugar phosphate) showed that microbial cell debris was the precursor of bio-HS. HA comprised diester P fragments and monoester P fragments that formed when diester P fragments degraded, while FA contained only diester P fragments. The monoester P fragments in HA may result from microbial degradation of diester P fragments, and FA may simultaneously condense into HA. These results show that microbial cell debris was first transformed into FA and then into HA.

Inhibitory effect of thiourea on biological nitrification process and its eliminating method.

Thiourea is a typical nitrification inhibitor that shows a strong inhibitory effect against the biological nitrification process. The 50% inhibitory concentration (IC50) of thiourea on nitrification was determined to be 0.088 mg g VSS-1, and nitrifiers recovered from the thiourea inhibition after it was completely degraded. The thiourea-degrading ability of the sludge system was improved to 3.06 mg gVSS-1 h-1 through cultivation of thiourea-degrading bacteria by stepwise increasing the influent thiourea concentration. The dominant thiourea-degrading bacteria strain that used thiourea as the sole carbon and nitrogen source in the sludge system was identified as Pseudomonas sp. NCIMB. The results of this study will facilitate further research of the biodegradation characteristics of thiourea and similar pollutants.

Efficient nitrogen removal via simultaneous nitrification and denitrification in a penicillin wastewater biological treatment plant.

Nitrogen-removal performance was investigated in a penicillin wastewater biological treatment plant (P-WWTP) reconstructed from a cyclic activated sludge system (CASS) tank designed for simultaneous nitrification and denitrification (SND). Good performance was obtained during a 900-day operation period, as indicated by effluent chemical oxygen demand (COD), total nitrogen (TN) and ammonia nitrogen (NH3‒N) values of 318 ± 34, 28.7 ± 2.4 and<0.2 mg L⁻¹ when the influent COD, total Kjeldahl nitrogen (TKN) and NH3‒N were 3089 ± 453, 251.4 ± 26.5 and 124.8 ± 26.8 mg L⁻¹, respectively. Nitrification and denitrification occurred at different spaces, that is, 71.4% of TN removal occurred in the first 40% of the aeration tank, while 68.8% of the TKN removal occurred in 40-100% of the aeration tank. Sufficient easily biodegradable organics (EBO) in wastewater were key to the occurrence of SND. The denitrification rate under aeration conditions was 10.7 mg N g VSS⁻¹ h⁻¹ when EBO were sufficient, but 0.98 mg N g VSS⁻¹ h⁻¹ when EBO were completely degraded. Nitrification primarily occurred in the rear of the aeration tank owing to the competition for oxygen between carbonaceous oxidation and nitrification. The nitrification rate was only 7.13 mg NOD g VSS⁻¹ h⁻¹ at the beginning of the reaction, but 14.7 mg NOD g VSS⁻¹ h⁻¹ when EBO were completely degraded. These results will facilitate the improvement of nitrogen removal by existing WWTPs.

A control strategy for promoting the stability of denitrifying granular sludge in upflow sludge blankets.

The nitrate removal rate of denitrifying granular sludge in an upflow sludge blanket reactor is very high and reaches up to 3.6 gNO3-N-gVSS-1 d-1 at a nitrate loading rate (NLR) of 32.0 gNO3-N L-1 d-1. However, the granular sludge exhibits flotation under high NLR conditions, where the granules become large in size (of approximately 3-5 mm), light, and easily adhere to gas bubbles. In order to decrease the flotation potentiality of granular sludge, three measures were taken as follows: reducing the size of the granules, increasing the density of the granules, and weakening the adhesion effect of sludge to bubbles. While, these measures did not completely eliminate the granular sludge flotation. The way to solve sludge flotation namely instability was to slow down the biomass growth rate. The main factors to reduce denitrifying bacteria growth rate were verified as relatively low operating temperature, carbon source with comparatively slow degradation rate, and low NLR. Therefore, controlling denitrifying biomass growth rate via reducing temperature, replacing methanol with glucose as carbon source, and decreasing NLR was able to improve the stability of the granular sludge.

Successful startup of a full-scale acrylonitrile wastewater biological treatment plant (ACN-WWTP) by eliminating the inhibitory effects of toxic compounds on nitrification.

During the startup of a full-scale anoxic/aerobic (A/O) biological treatment plant for acrylonitrile wastewater, the removal efficiencies of NH(3)-N and total Kjeldahl nitrogen (TKN) were 1.29 and 0.83% on day 30, respectively. The nitrification process was almost totally inhibited, which was mainly caused by the inhibitory effects of toxic compounds. To eliminate the inhibition, cultivating the bacteria that degrade toxic compounds with patience was applied into the second startup of the biological treatment plant. After 75 days of startup, the inhibitory effects of the toxic compounds on nitrification were eliminated. The treatment plant has been operated stably for more than 3 years. During the last 100 days, the influent concentrations of chemical oxygen demand (COD), NH(3)-N, TKN and total cyanide (TCN) were 831-2,164, 188-516, 306-542 and 1.17-9.57 mg L(-1) respectively, and the effluent concentrations were 257 ± 30.9, 3.30 ± 1.10, 31.6 ± 4.49 and 0.40 ± 0.10 mg L(-1) (n = 100), respectively. Four strains of cyanide-degrading bacteria which were able to grow with cyanide as the sole carbon and nitrogen source were isolated from the full-scale biological treatment plant. They were short and rod-shaped under scanning electron microscopy (SEM) and were identified as Brevundimonas sp., Rhizobium sp., Dietzia natronolimnaea and Microbacterium sp., respectively.

Inhibitory effect of cyanide on nitrification process and its eliminating method in a suspended activated sludge process.

Inhibition of nitrification by four typical pollutants (acrylonitrile, acrylic acid, acetonitrile and cyanide) in acrylonitrile wastewater was investigated. The inhibitory effect of cyanide on nitrification was strongest, with a 50% inhibitory concentration of 0.218 mg·gVSS-1 being observed in a municipal activated sludge system. However, the performance of nitrification was recovered when cyanide was completely degraded. The nitrification, which had been inhibited by 4.17 mg·gVSS-1 of free cyanide for 24 h, was recovered to greater than 95% of that without cyanide after 10 days of recovery. To overcome cyanide inhibition, cyanide-degrading bacteria were cultivated in a batch reactor by increasing the influent cyanide concentration in a stepwise manner, which resulted in an increase in the average cyanide degradation rate from 0.14 to 1.01 mg CN-·gVSS-1·h-1 over 20 days. The cultured cyanide-degrading bacteria were shaped like short rods, and the dominant cyanide-degrading bacteria strain was identified as Pseudomonas fluorescens NCIMB by PCR.

Characteristics of denitrifying granular sludge grown on nitrite medium in an upflow sludge blanket (USB) reactor.

While inoculating pre-acclimatized floccular sludge, nitrite-denitrifying granular sludge was obtained after approximately 40 days of cultivation in a 10 L upflow sludge blanket (USB) reactor. The nitrite removal efficiency was approximately 95% when the nitrite concentration was 50 mg L(-1)at an influent flow rate of 20 L h(-1). The nitrite granular sludge had several notable features including good settleability (110 m h(-1)), high ash content (79%), and high density (1.248 g cm(-3)). The mixed liquor suspended solids (MLSS) of the sludge bed remained at 130.04 g L(-1), at a hydraulic upflow velocity of 2 m h(-1). These interesting characteristics were attributed to a high effluent pH (9.7) caused by the release of alkalinity during the nitrite denitrification process. The surfaces of the granules were dominated by cocci bacteria with a diameter of approximately 3 µm, which could be classified as Nitrosomonas-like species based on our analysis of 16 S rDNA sequences.