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The secondary fermentation stage is critical for stabilizing composting products and producing various secondary metabolites. However, the low metabolic rate of mesophilic bacteria is regarded as the rate-limiting stage in composting process. In present study, two indoleacetic acid (IAA)-producing bacteria (Bacillus safensis 33C and Corynebacterium stationis subsp. safensis 29B) were inoculated to strengthen the secondary fermentation stage to improve the plant-growth promoting potential of composting products. The results showed that the addition of IAA-producing bacteria promoted the assimilation of soluble salt, the condensation and aromatization of humus, and the accumulation of dissolved organic nitrogen (DON) and dissolved organic carbon (DOC). The bioaugmentation strategy also enabled faster microbial community succession during the medium-late phase of secondary fermentation. However, the colonization of Bacillus and Corynebacterium could not explain the disproportionate increase of IAA yield, which reached up to 5.6 times compared to the control group. Deeper analysis combined with physicochemical properties and microbial community structure suggested that IAA-producing bacteria might induce the increase of salinity, which enriched halotolerant bacteria capable of producing IAA, such as Halomonas, Brachybacterium and Flavobacterium. In addition, the results also proved that it was necessary to shorten secondary fermentation time to avoid IAA degradation without affecting composting maturity. In summary, enhancing secondary fermentation of composting via adding proper IAA-producing bacteria is an efficient strategy for upgrading the quality of organic fertilizer.

The safe disposal of antibiotic mycelial residue (AMR), a hazardous waste, is a pressing problem owing to the spread of antibiotic and heavy metal pollution. In this study, AMR pyrolysis at different temperatures and heating rates was investigated to prepare valuable biochar for heavy metal immobilization. The results showed that AMR decomposition mainly involved three pseudo-reactions, with average activation energies of 252.4, 149.8, and 219.7 kJ/mol, that fitted a three-dimensional diffusion model. Increasing the pyrolysis temperature and heating rate decreased the yield and volatile matter content of biochar, but the ash content, fixed carbon content, and aromaticity increased. The AMR-derived biochar had a favorable fuel property (18.1-19.8 MJ/kg) and stability against degradation in soil. Calcium oxalate hydrate, a major mineral in AMR, degraded during biochar formation. Furthermore, high pyrolysis temperature promoted the residual fractions of Cr, Cu, Zn, Cd, and Pb in biochar, more so than did the heating rate, inducing a low potential ecological risk. In particular, the leaching rate of Zn decreased from 46.9% in AMR to 0.3% in biochar obtained at 700 °C with a heating rate of 10 °C/min. This study elucidates the formation process and physicochemical properties of AMR biochar, which helps in the harmless utilization of AMR as a carbon resource.

Supplementing nano zero valent iron (nZVI) is an attractive technology for wastewater treatment due to its advantages in accelerating the hydrolysis, fermentation and anaerobic digestion (AD) process. In this present study, nZVI was added to investigate its effects on enhancing tetracycline (TC) wastewater anaerobic treatment and the changes of microbial community, especially for underestimated syntrophic-methanogenic associations. The TC concentrations were 1, 10, 30, 50, 80, 100 and 150 mg/L with 0.38 g nZVI (with iron g/g VS of 0.50) complemented into reactors. Results revealed that nZVI could enhance AD process in both control and TC dosed systems, and the promoting effect on methanogenesis was more significant in systems of high concentration TC, with 100 and 150 mg/L. In addition, cumulative CH4 production for all TC added systems without nZVI were higher than the control indicating TC had positive effect instead of expected negative effect on AD process, high TC concentration of 100 and 150 mg/L only affecting the increase factor rather than causing inhibitory effect. After digestion, TC was largely removed in with/without nZVI systems. And also, nZVI evidently altered the bacterial and methanogenic community structure, with an increase abundance of syntrophic-methanogenic associations (Syntrophobacterales and Methanosarcinales) and resulting in the enhancement of methane generation. This research provides an efficient method for TC wastewater anaerobic treatment.

Physical structures of sludge are critical factors determining the performance of the anaerobic digestion process, especially for the rate-limiting step, methanogenesis. Thus, to evaluate the effect of granular physical structure on methanogenesis and methanogenic community variation, intact and disintegrated granules were applied as inocula with formate, hydrogen and acetate as sole substrates in batch reactors. Kinetics results revealed that the physical structure of sludge had little impact on methane yield potential from three substrates, while a significantly different impact on methanogenesis rates of formate, hydrogen and acetate. The methanogenesis rate of formate in disintegrated granules was higher than that in the intact granular system, the methanogenesis rate of H2/CO2 in the intact granular system was higher than that in the disintegrated granules and the methanogenesis rate of acetate was similar with the in intact and disintegrated granular systems. Besides, in both intact and disintegrated granular systems, methanogenesis rates of formate were the highest, then followed the H2/CO2 and acetate was the lowest, indicating formate consumption has an advantage over hydrogen in the studied system. A microbial assay indicated that Methanobacteriales, Methanosarcinales and Methanomicrobiales are dominant methanogens on the order level, and the physical structure of granular sludge has little influence on methanogenic communities on the order level but showed significant influence on the species level. It enlightens us that the physical structure of sludge could be considered for regulating the anaerobic digestion via influencing the methanogenesis rates.

In this study, an anaerobic baffled reactor (ABR) coupled with a microbial electrolysis cell (MEC) was set up to treat carbohydrate-containing wastewater at 55 ± 1 °C. The MEC was employed to accelerate the degradation of volatile fatty acids (VFAs). The removal of chemical oxygen demand (COD) and production of methane and the corresponding kinetics were determined for different organic load rates (OLRs). The highest COD removal rate was 95.8% at an OLR of 7.0 kg COD m−3 d−1, but it declined to 90.4% when the OLR was 19.4 kg COD m−3 d−1 and finally stabilized at 65.3% when the OLR was increased to 34.3 kg COD m−3 d−1. The volumetric production of methane was 1.5 L (L−1 d−1) when the OLR was 7.0 kg COD m−3 d−1 and increased to 4.1 L (L−1 d−1) at an OLR of 34.3 kg COD m−3 d−1, when the methane yield stabilized at 0.20-0.25 L g−1 CODremoved. The kinetics and predictions according to the Stover-Kincannon and Van der Meer-Heertjes models closely agreed with the experimental data for the removal of COD and volumetric production of methane, respectively. An analysis of the microbial community suggested that hydrolytic bacteria, syntrophic fatty acid-oxidizing bacteria (SFOB), exoelectrogens and hydrogenotrophic methanogens achieved a significant synergistic effect and enhanced the degradation of VFAs, which made the thermophilic anaerobic system stable and efficient at high OLRs.

The anaerobic bio-treatment of lower COD/SO42- ratio wastewater constitutes a bottle-aqneck due to the limited carbon source. In this type of environment, interactions between acidogenic fermentation bacteria and methane-producing bacteria (MPB) are aided by syntrophic fatty acid oxidation bacteria present in the functional niche; MPB and sulfate-reducing bacteria (SRB) compete with each other due to the availability of sulfate. Therefore, introduction of syntrophic fatty acid oxidation bacteria into an SRB dominated culture can achieve maximum utilization of the substrate, weakening the competition of MPB. In this study, the mixed culture of dominant syntrophic propionate oxidation bacteria (SPOB) and SRB was established and characterized at 35°C. The dominant SPOB and SRB were enriched in a continuous flow stirred-tank reactor and in batch experiments, respectively. Subsequently, an equal proportion of the enriched sludge was mixed and incubated in conical flasks with propionate as the sole substrate. S...

For evaluating the methanogenesis from typical methanogenic precursors (formate, acetate and H2/CO2), CH4 production kinetics were investigated at 37±1°C in batch anaerobic digestion tests and stimulated by modified Gompertz model. The results showed that maximum methanation rate from formate, acetate and H2/CO2 were 19.58±0.49, 42.65±1.17 and 314.64±3.58NmL/gVS/d in digested manure system and 6.53±0.31, 132.04±3.96 and 640.16±19.92NmL/gVS/d in sewage sludge system during second generation incubation. Meanwhile the model could not fit well in granular sludge system, while the rate of formate methanation was faster than from H2/CO2 and acetate. Considering both the kinetic results and microbial assay we could conclude that H2/CO2 methanation was the fastest methanogenic step in digested manure and sewage sludge system with Methanomicrobiales as dominant methanogens, while granular sludge with Methanobacteriales as dominant methanogens contributed to the fastest formate methanation.

Antibiotics and antibiotic resistance genes (ARGs) pollution in animal feeding farms received more public attention recently. Livestock wastewater contains large quantities of antibiotics and ARGs even after traditional lagoon treatment. In this study, the performance of vertical up-flow constructed wetlands (VUF-CWs) on swine wastewater containing tetracycline compounds (TCs) and tet genes was evaluated based on three aspects, TCs and tet genes removal efficiencies, residual TCs and tet genes in soils and plants, and the effect of TCs accumulation on nutrients removal and tet genes development. High removal efficiencies (69.0-99.9%) were achieved for oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC) with or without OTC spiked in the influent additionally. TCs concentrations in surface soils increased at first two sampling periods and then decreased after plants were harvested. Satisfactory nutrients removal efficiencies were also obtained, but TN and NH4-N removal efficiencies were significantly negative correlated with total concentration of TCs (∑TCs) in the soils (p 0.01). The absolute abundances of all the target genes (tetO, tetM, tetW, tetA, tetX and intI1) were greatly reduced with their log units ranging from 0.26 to 3.3. However, the relative abundances of tetO, tetM and tetX in some effluent samples were significantly higher than those in the influent (p 0.05). The relative abundances of tet genes except for tetO were significantly correlated with ∑TCs in the soils (p 0.05). In summary, the proposed VUF-CWs are effective alternative for the removal of TCs and tet genes. But it is of great importance to prevent large accumulation of TCs in the soils.

Four pilot-scale constructed wetlands (free water surface, SF; horizontal subsurface flow, HSF; vertical subsurface flows with different water level, VSF-L and VSF-H) were operated to assess their ability to remove sulfamethazine (SMZ) and tetracycline (TC) from wastewaters, and to investigate the abundance level of corresponding resistance genes (sulI, sulII, tetM, tetW and tetO) in the CWs. The results indicated that CWs could significantly reduce the concentration of antibiotics in wastewater, and the mass removal rate range of SMZ and TC were respectively 11%-95% and 85%-95% in the four systems on the basis of hydraulic equilibrium; further relatively high removal rate was observed in VSF with low water level. Seasonal condition had a significant effect on SMZ removal in the CWs (especially SMZ in SF), but TC removal in VSFs were not considered to have statistically significant differences in winter and summer. At the end period, the relative abundances of target genes in the CWs showed obvious increases compared to initial levels, ranging from 2.98 × 10(-5) to 1.27 × 10(-1) for sul genes and 4.68 × 10(-6) to 1.54 × 10(-1) for tet genes after treatment, and those abundances showed close relation to both characteristic of wastewater and configuration of CWs.

In the process of fermentative bio-hydrogen production, organic matter is degraded into volatile fatty acids and ethanol, and consequently thermodynamic constraints prevent the further spontaneous reactions. Moreover, the anaerobic baffled reactor (ABR) with the advantage of phase separation could realize the acetic acid accumulation via acid-producing bacteria. The microbial electrolysis cell (MEC) could convert the acetic acid into hydrogen furthermore. Considering this, the ABR coupled with MEC has been operated to strengthen the hydrogen production. This study was designed regarding orthogonal experiments to operate the four-compartment ABR with a hydraulic retention time (HRT) = 24 h, influent COD ∼ 4600 mg/L, temperature = 35 ± 1 °C, and discovered the optimal parameters with pH = 7, C/N = 44, and 2-bromoethanesulfonate (BES) concentration = 20 mmol/L to achieve the high acetic acid accumulation of effluent. The single-chamber membranless MEC with carbon anode and Ni-catalyst stainless steel cathode (liquid volume = 85 mL) fed with the ABR effluent with applied voltage = 0.6 V and electric conductivity = 7.45 mS/cm, achieved 99.0 ± 0.3% total COD removal efficiency, 1.31 ± 0.04 m 3 H 2 /m 3 d hydrogen production, 2.78 ± 0.11 mLH 2 /mgCOD hydrogen yield and 138.63 ± 3.11% electrical energy efficiency. Therefore the ABR-MEC system could overcome the “fermentation barrier” to achieve higher hydrogen production and organic matter degradation.

This paper investigated the efficiency of two vertical flow constructed wetlands characterized by volcanic (CW1) and zeolite (CW2) respectively, at removing three common antibiotics (ciprofloxacin HCl, oxytetracycline HCl, and sulfamethazine) and tetracycline resistance (tet) genes (tetM, tetO, and tetW) from swine wastewater. The result indicated that the two systems could significantly reduce the wastewater antibiotics content, and elimination rates were in the following sequence: oxytetracycline HCl>ciprofloxacin HCl>sulfamethazine. The zeolite-medium system was superior to that of the volcanic-medium system vis-a-vis removal, perhaps because of the differing pH values and average pore sizes of the respective media. A higher concentration of antibiotics accumulated in the soil than in the media and vegetation, indicating that soil plays the main role in antibiotics removal from wastewater in vertical flow constructed wetlands. The characteristics of the wetland medium may also affect the antibiotic resistance gene removal capability of the system; the total absolute abundances of three tet genes and of 16S rRNA were reduced by 50% in CW1, and by almost one order of magnitude in CW2. However, the relative abundances of target tet genes tended to increase following CW1 treatment.

This study evaluated the physicochemical properties and phosphorus adsorption capacities for oyster shell (OS), broken bricks, volcanics, and zeolite when used as substrates for swine wastewater treatment. All substrates, with the exception of volcanics, proved to be appropriate for microorganism and plant growth enrichment within water treatment systems. Meanwhile, phosphorus adsorption tests indicated that OS was most effective in phosphorus removal. Significant phosphorus removal was achieved in pilot tests when OS was used as a substrate in vertical-flow wetlands treating swine wastewater from an anaerobic tank. The pilot tests also indicated that both soluble reactive phosphorus (SRP) and total phosphorus (TP) removal rates increased when the HRT was prolonged. Overall, the study results showed that OS could be used for phosphorus removal in constructed wetlands, and such use carries the added benefits of reuse of a by-product that promotes sustainability.

Potential effect of ciprofloxacin HCl (CIP), oxytetracycline HCl (OTC) and sulfamethazine (SM2) on the common wetland plant (Phragmites australis) was evaluated by measuring root activity, antioxidant enzymes and chlorophyll in leaf, and a study of the accumulation of antibiotics in plant was also included. Plants were incubated in six containers for 62 days and exposed to antibiotics at concentrations of 0, 0.1, 1, 10, 100, and 1000 μg/L in nutrient solutions. Results illustrated that high antibiotics concentrations (>10 μg/L) had a toxic effect on root activity and leaf chlorophyll, while hormesis occurred at low antibiotics concentrations (0.1–1 μg/L). As antibiotics dosages increased, superoxide dismutase and catalase activity significantly declined (5–55% and 9–58%), while peroxidase activity significantly increased. P. australis accumulated antibiotics via passive absorption, exposure to 1000 μg/L concentrations led to higher CIP, OTC, and SM2 contents in plants (13,834, 6901 and 2047 ng/g dry weight, respectively) than did exposure to 0.1 μg/L concentrations (345, 165, and 24 ng/g dry weight, respectively). The total antibiotics content in all plants followed the sequence CIP > OTC > SM2, and the distribution of all antibiotics followed the sequence root > leaf > stem. These preliminary results indicated that P. australis could both absorb and tolerate antibiotics concentrations typically found in wastewater.

Correction for ‘Impact of physical structure of granular sludge on methanogenesis and methanogenic community structure’ by Xiaofang Pan et al., RSC Adv., 2019, 9, 29570–29578.

Purified terephthalic acid (PTA) processing wastewater was evaluated as a fermentable substrate for hydrogen (H 2 ) production with simultaneous wastewater treatment by dark-fermentation process in a continuous stirred-tank reactor (CSTR) with selectively enriched acidogenic mixed consortia under continuous flow condition in this paper. The inoculated sludge used in the reactor was excess sludge taken from a second settling tank in a local wastewater treatment plant. Under the conditions of the inoculants not less than 6.3 gVSS/L, the organic loading rate (OLR) of 16 kgCOD/m 3 d, hydraulic retention time (HRT) of 6 h and temperature of (35 ± 1) °C, when the pH value, alkalinity and oxidation–reduction potential (ORP) of the effluent ranged from 4.2 to 4.4, 280 to 350 mg CaCO 3 /L, and −220 to −250 mV respectively, soluble metabolites were predominated by acetate and ethanol, with smaller quantities of propionate, butyrate and valerate. Stable ethanol-type fermentation was formed with the sum of ethanol and acetate concentration ratio of 70.31% to the total liquid products after 25 days operation. The H 2 volume content was estimated to be 48–53% of the total biogas and the biogas was free of methane throughout the study. The average biomass concentration was estimated to be 10.82 gVSS/L, which favored H 2 production efficiently. The rate of chemical oxygen demand (COD) removal reached at about 45% and a specific H 2 production rate achieved 0.073 L/gMLVSS d in the study. This CSTR system showed a promising high-efficient bioprocess for H 2 production from high-strength chemical wastewater.

Lignin terpolymer has been obtained by grafting copolymerization of both dimethyl diallyl ammonium chloride (DMDAAC) and acrylamide (AM) onto lignin. The corrosion inhibition properties of the terpolymer were tested. The results showed that the highest corrosion inhibition percentage was over 95% in 10% HCl acid medium at 25 °C and 80 °C. The lignin terpolymer inhibitor adsorption followed Temkin isotherm at 25 °C and 80 °C, and the adsorption capability was in reverse proportion to the temperature according to −ΔGads. The effects of corrosion inhibition are the comprehensive synergistic effect through the graft reaction among lignin, AM and DMDAAC.

A laboratory-scale anaerobic baffled reactor (ABR) with four compartments using soybean protein processing wastewater as organic loading rates (OLRs) was investigated for the performance and phase separated characteristics. It was found that the chemical oxygen demand (COD) removal efficiencies were 92–97% at 1.2–6.0 kg COD/m 3 d feeding. The dominated species, propionate and butyrate, were found in the 1st compartment. Acetate was dominated in the 2nd compartment and then decreased in the 3rd and 4th. Meanwhile, 93% volatile fatty acids (VFAs) were removed in the 3rd and 4th compartments. In the 1st compartment, biogas revealed carbon dioxide (CO 2 ) and hydrogen (H 2 ). The highest H 2 yield was found in the 2nd compartment, thereafter decreased from the 2nd to 4th which corresponded to the increased of the methane (CH 4 ) yield. It indicated that the proper anaerobic consortium in each separate compartment was developed along with substrate availability and specific environmental conditions.