Low-temperature anaerobic treatment of low-strength pentachlorophenol-bearing wastewater

Impact of benzalkonium chloride on anaerobic granules and its long-term effects on reactor performance

This study assessed the inhibitory and performance-degrading effects induced by the cationic surfactant benzalkonium chloride (BAC) on anaerobic granules during the long-term operation of a laboratory-scale expanded granular sludge bed (EGSB) reactor. To address the critical scientific problem of how BAC affects the efficiency of EGSB reactors, this research uniquely evaluated the long-term stress response to BAC by systematically comparing continuous and discontinuous inhibitor exposure scenarios. The novel comparison demonstrated that inhibitor concentration is of minor relevance compared to the biomass-specific cumulative inhibitor load in the reactor. After exceeding a critical biomass-specific cumulative inhibitor load of 6.1-6.5 mg BAC/g VS, continuous and discontinuous exposure to BAC caused comparable significant deterioration in reactor performance, including accumulation of volatile fatty acids (VFA), decreased removal efficiency, reduced methane production, as well as the wash-out, flotation, and disintegration of anaerobic granules. BAC exposures had a more detrimental effect on methanogenesis than on acidogenesis. Moreover, long-term stress by BAC led to an inhibition of protein production, resulting in a decreased protein-to-polysaccharide ratio of extracellular polymeric substances (EPS) that promoted destabilizing effects on the granules. Finally, hydrogenotrophic methanogenesis was triggered. Reactor performance could not be restored due to the severe loss of granular sludge.

Synthesis of zero-valent iron supported with graphite and plastic based carbon from recycling spent lithium ion batteries and its reaction mechanism with 4-chlorophenol in water

Graphite and plastic recycled from spent lithium ion batteries were used to synthesize zero-valent iron/graphite (ZVI/G), zero-valent iron/plastic-based carbon (ZVI/P), and zero-valent iron/graphite and plastic-based carbon (ZVI/GP) with iron oxide through carbothermic reduction. The aim of preparing these catalysts is to improve the performance of ZVI in the removal of 4-chlorophenol (4-CP) in water through heterogeneous Fenton reactions. The structural and textural properties of materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption/desorption, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The synthesis procedure successfully disperses ZVI particles on the synthesized materials. The combination of graphite and plastic-based carbon in ZVI/GP resulted in the best 4-CP removal performance. The degradation data fitted pseudo-first-order kinetic well. The Increase in the ZVI/GP dosage and the hydrogen peroxide concentration enhanced the 4-CP removal due to the increase in the amount of Fe²⁺ ions and reactive sites. Acidic pH increased the 4-CP removal percentage due to the high H⁺ concentration. The increase in the temperature favored the •OH formation and facilitated the 4-CP removal. The reaction energy of ZVI/GP reaches 53.54 kJ mol^-1, which is competitive among the iron catalysts reported in literatures, and showing the 4-CP removal is reaction-controlled process. This study shows a promising way of recycling graphite and plastic in spent LIBs to prepare ZVI materials for wastewater treatment with the advantages of improved conductivity by graphite and added functional groups by plastic based carbon.

Acidification inhibition, biodechlorination, and biotransformation of chlorinated acetaldehydes on acidogenic sludge and microbial community changes

Chlorinated acetaldehydes (CALs) are typical chlorinated organic compounds that posing a great threat to biological wastewater treatment plants. In this study, volatile batch acid (VFA) tests were employed to investigate the acidification inhibition, biodechlorination, and biotransformation of high-strength CALs on hydrolytic acidification. The results indicated that the optimum parameters were 4 g/L sludge, pH = 8, and glucose as an electron donor. Moreover, the acidification inhibition and biodechlorination showed a strongly positive correlation with the degree of chlorination and CAL concentrations. Extracellular polymeric substances (EPS) decreased dramatically, while DNA increased sharply under higher CAL concentrations, which was the result of cell death caused by the toxicity of the CALs. Additionally, the relative toxicities of the CALs were as follows: trichloroacetaldehyde > dichloroacetaldehyde > chloroacetaldehyde. Furthermore, Excitation-Emission-Matrix (EEM) spectra of EPS revealed that aromatic protein-like substances I interacted with CALs to achieve a slight removal of CALs. The detected products revealed that some of the chlorine atoms and aldehyde groups in the CALs were removed by microbes to certain degree. Moreover, microbial community analysis indicated that the dominant phyla were Actinobacteria, Bacteroidetes, and Synergistetes, which had a stronger tolerance to CALs. Notably, biodechlorination was closely related to a remarkable increase in members of the genus Trichococcus.

Degradation of chlorine dioxide bleaching wastewater and response of bacterial community in the intimately coupled system of visible-light photocatalysis and biodegradation

Intimate coupling of visible-light photocatalysis and biodegradation (ICPB) offers potential for degrading chlorine dioxide bleaching wastewater. In this study, we reported a TiO₂-coated sponge biofilm carrier with significant adhesion of TiO₂ and the ability to accumulate biomass in its interior. Four mechanisms possibly acting in ICPB were tested separately: adsorption of chlorine dioxide bleaching wastewater to the carrier, photolysis, photocatalysis, and biodegradation by the biofilm inside the carrier. The carrier had an adsorption capacity of 17% and 16% for CODcr and AOX, respectively, in the wastewater. The photodegradation rate of wastewater was very low and could be ignored. Both biodegradation (AOX 30.1%, CODcr 33.8%, DOC 26.2%) and photocatalysis (AOX 65.1%, CODcr 71.2%, DOC 62.3%) possessed a certain degradation efficiency of wastewater. However, the removal rate of AOX, CODcr, and DOC in wastewater treatment by protocol ICPB reached 80.3%, 90.5%, and 86.7%. FT-IR and GC-MS analysis showed that the ICPB system had photocatalytic activity on the surface of the porous carrier in vitro, which could transform organic into small molecules for microbial utilization or complete mineralization. Moreover, the biofilm in the interior of the TiO₂-coated sponge carrier could mineralize the photocatalytic products, which enhanced the removal of AOX, CODcr, and DOC by more than 15.2%, 20.0%, and 24.0%, respectively. The biofilm in the carrier of the ICPB system evolved, enriched in Proteobacteria, Chloroflexi, Bacteroidetes, and Actinobacteria, microorganisms known to play active roles in the biodegradation of papermaking wastewater.

Exogenous N-acyl-homoserine lactones promote the degradation of refractory organics in oligotrophic anaerobic granular sludge

For refractory industrial wastewaters, anaerobic granular sludge technology cannot be widely used because of its limited treatment capacity, so strengthening the anaerobic degradation of refractory organics should be discussed. In this paper, the feasibility of adding exogenous N-acyl-homoserine lactones (AHLs) to promote the degradation of refractory organics in oligotrophic anaerobic granular sludge was addressed. The results showed that, after easily-degradable organics were completely metabolized, exogenous AHLs strengthened the further degradation of refractory organics and improved the methanogenic activity of anaerobic granular sludge. In addition, adding AHLs could promote the secretion of more extracellular polysaccharides and proteins by anaerobic microorganisms to resist the oligotrophic environment. Microbiological analysis showed that adding AHLs significantly optimized the microbial community in oligotrophic anaerobic granular sludge. With the regulation of AHLs, the abundance proportion of hydrolytic acidifying bacteria for refractory organics in bacterial community and the abundance proportion of acetotrophic methanogens in methanogens community increased obviously. Exogenous AHLs showed concentration-related effects on the optimization of bacteria and methanogens, and AHLs of higher concentration were beneficial to the succession of community structure in a better direction. Exogenous regulation of AHLs-mediated QS provided an attractive strategy for enhancing the anaerobic degradation of refractory organics, and proposed a technical idea for the application of anaerobic granular sludge technology in refractory industrial wastewaters.

Low-temperature anaerobic digestion enhanced by bioelectrochemical systems equipped with graphene/PPy- and MnO2 nanoparticles/PPy-modified electrodes

Bioelectrochemical systems (BESs) with graphene (Gr)/polypyrrole (PPy)- and MnO₂ nanoparticles (NPs)/PPy-modified electrodes were developed to enhance low-temperature anaerobic digestion (LTAD) of low-strength wastewater. At 20 °C, the chemical oxygen demand removal efficiencies and CH₄ yield of the BESs with Gr/PPy (R2) and MnO₂ NPs/PPy (R3)-modified electrodes were 12.7% and 25.6%, and 43.9% and 66.3%, respectively, higher than those of the control (R1, without modification). Although the performance of all reactors decreased as temperature dropping to 12 °C, the CH₄ yield rates of R2 and R3 were still 22.8% and 39.0% higher than that of R1. Further analysis indicated that the modified electrodes might stimulate the metabolic activity of the anaerobic digester sludge. Scanning electron microscopy observation showed that the modified electrodes had higher specific surface area, favoring the attachment and formation of dense biofilms on the surface of electrodes. 16S rRNA gene-sequencing results demonstrated that H₂-consuming methanogens dominated in the BESs and the influence of Gr/PPy and MnO₂ NPs/PPy differed on the microbial community structure of biofilms. These findings justify the wider use of Gr and MnO₂ NPs in electrode modification to assist LTAD using BESs.

Occurrence and profiles of halogenated phenols, polybrominated diphenyl ethers and hydroxylated polybrominated diphenyl ethers in the effluents of waste water treatment plants around Huang-Bo Sea, North China

Halogenated organic pollutants (HOPs), as ubiquitous environment contaminants, have attracted increasing concerns due to the potential adverse health impacts on organisms and even humans. Waste water treatment plants (WWTPs) are one source of HOPs to the environment through their discharge of treated effluent. In this study, the presence and profiles of 6 halogenated phenols (HP), 17 polybrominated diphenyl ethers (PBDE) and 11 hydroxylated polybrominated diphenyl ethers (OH-PBDE) were investigated in 12 WWTP effluent samples collected near Huang-Bo Sea in Dalian, China. These targeted organohalogen pollutants were found in all the effluent samples with the total concentrations of ΣHPs, ΣPBDEs and ΣOH-PBDEs ranging from 77.2 to 168.5ng/L, from not-detected to 5.3ng/L and from 0.08 to 0.88ng/L, respectively. The most abundant congeners of HPs and PBDEs in the effluents were pentachlorophenol (PCP), BDE-47 and BDE-99, while for OH-PBDEs, 6-OH-BDE-47 and 5-OH-BDE-47 were the most abundant. In addition, the statistical analysis showed that a significant (p<0.05) positive correlation was observed between BDE-47 and its metabolite 6-OH-BDE-47, indicating that PBDEs may be a source of OH-PBDEs detected in the effluents.

Enhanced anaerobic degradability of highly polluted pesticides-bearing wastewater under thermophilic conditions

This work presents a sustainable and cost-competitive solution for hardly biodegradable pesticides-bearing wastewater treatment in an anaerobic expanded granular sludge bed (EGSB) reactor at mesophilic (35°C) and thermophilic (55°C). The reactor was operated in continuous mode during 160days, achieving an average COD removal of 33 and 44% under mesophilic and thermophilic conditions, respectively. The increase of temperature improved the biomass activity and the production of methane by 35%. Around 96% of pesticides identified in raw wastewater were not detected in both mesophilic and thermophilic effluents. A dramatic selection of the microbial population in anaerobic granules was caused by the presence of pesticides, which also changed significantly when the temperature was increased. Pesticides caused a significant inhibition on methanogenesis, especially over acetoclastic methanogens. Aerobic biodegradability tests of the resulting anaerobic effluents revealed that aerobic post-treatment is also a feasible and effective option, yielding more than 60% COD reduction.

Effect of co-substrates on biogas production and anaerobic decomposition of pentachlorophenol

This study aims to examine the effect of different co-substrates on the anaerobic degradation of pentachlorophenol (PCP) with simultaneous production of biogas. Acetate and glucose were added as co-substrates to monitor and compare the methanogenic reaction during PCP degradation. During the experiment, a chemical oxygen demand (COD) removal efficiency of 80% was achieved. Methane (CH₄) production was higher in glucose-fed anaerobic reactors with the highest amount of CH₄ (303.3µL) produced at 200ppm of PCP. Scanning electron microscopy (SEM) demonstrates the high porous structure of anaerobic sludge with uniform channels confirming better mass transfer and high PCP removal. Quantitative real-time PCR (qPCR) revealed that methanogens were the dominating species while some sulfate reducing bacteria (SRBs) were also found in the reactors. The study shows that strategic operation of the anaerobic reactor can be a feasible option for efficient degradation of complex substrates like PCP along with the production of biogas.

Sequential UASB and dual media packed-bed reactors for domestic wastewater treatment - experiment and simulation

A wastewater treatment system composed of an upflow anaerobic sludge blanket (UASB) reactor followed by a packed-bed reactor (PBR) filled with Sorbulite(®) and Polonite(®) filter material was tested in a laboratory bench-scale experiment. The system was operated for 50 weeks and achieved very efficient total phosphorus (P) removal (99%), 7-day biochemical oxygen demand removal (99%) and pathogenic bacteria reduction (99%). However, total nitrogen was only moderately reduced in the system (40%). A model focusing on simulation of organic material, solids and size of granules was then implemented and validated for the UASB reactor. Good agreement between the simulated and measured results demonstrated the capacity of the model to predict the behaviour of solids and chemical oxygen demand, which is critical for successful P removal and recovery in the PBR.

The potential of using low cost naturally available biogenic substrates for biological removal of chlorophenol

This study details the application of naturally available biogenic substrates (NABS) in microbial degradation of 2-chlorophenol (CP). Jatropha deoiled cakes (JDC) and Karanja deoiled cakes (KDC) are used as NABS. The potential of NABS is compared with standard biogenic substrate, glucose. The study was carried out with both acclimatized mixed culture and pure culture, Pseudomonas putida. Microbial activity of the culture was monitored by measuring reduction in chlorophenol concentration, COD, toxicity and Cl(-) ions evolution. The study was carried out for a total of 42days. It was observed that culture having NABS has shown similar chlorophenol reduction but higher COD and toxicity reduction. Amongst NABS, Jatropha deoiled cake (JDC) has shown superior results of 71% COD reduction compared to glucose and KDC. This study is one of the first kind illustrating the potential of these substrates in removing toxic chemicals from wastewaters.

Effects of triclosan, diclofenac, and nonylphenol on mesophilic and thermophilic methanogenic activity and on the methanogenic communities

In this study, a toxicity assay using a mesophilic wastewater treatment plant sludge-based (SI) and a thermophilic manure-based inoculum (MI), under different biomass concentrations was performed to define the effects of diclofenac (DCF), triclosan (TCS), and nonylphenol (NP) on anaerobic digestion (AD) process. Additionally, the influence of DCF, TCS, and NP on the relative abundance of the methanogenic populations was investigated. Results obtained demonstrated that, in terms of methane production, SI inoculum was more resistant to the toxicity effect of DCF, TCS, and NP, compared to the MI inoculum. The IC50 values were 546, 35, and 363 mg L(-1) for SI inoculum and 481, 32, and 74 mg L(-1) for MI inoculum for DCF, TCS, and NP, respectively. For both inocula, higher biomass concentrations reduced the toxic effect of TCS (higher methane production up to 64%), contrary to DCF, where higher biomass loads decreased methane yield up to 31%. Fluorescence in situ hybridization analysis showed that hydrogenotrophic methanogens were more resistant to the inhibitory effect of DCF, TCS, and NP compared to aceticlastic methanogens.