Quaternization-based graft modification of straw fibers for conditioning the sludge dewatering performance.

Extracellular polymeric substances (EPS) are a critical influencing factor in sludge dewatering. Disrupting such EPS contributes to the release of bound water in sludge, enhancing the sludge dewatering performance. In This study, quaternized straw fibers that are destructive to the EPS structure and components in active sludge were prepared useing heterogeneous free radical graft polymerization. Straw fibers, dimethyl diallyl ammonium chloride (DMDAAC), ammonium persulfate (APS), and acrylamide (AM) were taken as the substrate, grafting monomer, catalyst, and cross-linking agent, respectively.The optimal processing conditions determined for the DMDAAC-based quaternization and graft modification of straw fibers were as follows: reaction temperature of 60 °C, reaction time of 5 h, 0.100 g of catalyst APS dosage per gram of straw, and 3.000 ml of DMDAAC dosage per gram of straw. The optimal processing conditions yielded 1.335 g of modified straw fibers per gram of straw, 33.67% grafting rate, and 31.70% substitution of the quaternary ammonium groups. The capillary suction time (CST) was conditioned from 243.3 ± 22.6 s in the original sludge to 134.5 ± 34.45 s. The specific resistance to filtration (SRF) was reduced from 8.82 ± 0.51 × 1012 m/kg in the original sludge to 4.59 ± 0.23 × 1012 m/kg.

The influence of different sludge concentrations on its dewaterability during bioleaching.

Bioleaching, a technologically and economically feasible technology, is considered as the high efficiency method to improve dewaterability in sewage sludge. The objective of this study was to investigate the effect of different sludge concentrations on bioleaching dewaterability and understand the mechanism of the effect of bioleaching on sludge dewaterability. Variation in pH, oxidation-reduction potential (ORP), capillary suction time (CST), specific resistance to filtration (SRF) and different fractions of extracellular polymeric substances (EPS) including slime EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS) were determined. Different sludge concentrations (5, 10, 15, 20 and 30 g·L-1) were selected to investigate during bioleaching. Results indicated that sludge buffering capacity significantly inhibited bioleaching efficiency as sludge concentrations increased. Optimum enhancements in sludge dewaterability were observed during the 10 g·L-1 sludge concentration treatment, and reached a maximum when the pH was 2.11. The variation of different fractions of EPS revealed that the ratio of S-EPS/TB-EPS significantly affected sludge dewaterability. Principal component analysis and Pearson's correlation analysis both provided evidence that the higher TB-EPS followed by a very large reduction was positively correlated with sludge dewaterability. However, the increase of protein and DNA in S-EPS content was negatively correlated with sludge dewaterability.

Characteristics and kinetics simulation of controlled-release KMnO4 for phenol remediation.

Controlled-release KMnO4 (CRP) technology has been recently developed as an improved, highly efficient technique in wastewater treatment. In this study, batch-style experiments were conducted to evaluate this technology. The release characteristics of CRP in distilled water and the reaction between CRP and phenol were studied and fitted using MATLAB software. Results indicated that in distilled water, temperature (T) and pH value had a larger effect than dissolved oxygen (DO) concentration on the release characteristics of KMnO4, and this relationship can be accurately described by the following kinetic equation: logQ = log[1.141T(0.152)(pH)(-1.0536)(DO)(0.4674)] + [0.0048T(0.3756)(pH)(1.8854)(DO)(-0.0509)]logt. KMnO4 released from CRP can effectively degrade phenol-contaminated water with different concentrations. A simulated equation (r = -dCA/dt = -15.1705 CA(0.6840)CP(-0.1406)) characterizing phenol degradation was developed using MATLAB software. Comparison between the theoretical phenol removal rates deduced by the above two equations and the initial phenol concentration as well as the CRP dosage with the experimental data indicates that the differences between them were less than 20%. The results indicate phenol can be effectively removed by CRP and smaller dosage of KMnO4 was required compared with literature values. The models can provide guidance for CRP application in real polluted sites, which can lower the cost for site remediation.

Intimate Coupling of Photocatalysis and Biodegradation for Degrading Phenol Using Different Light Types: Visible Light vs UV Light.

Intimate coupling of photocatalysis and biodegradation (ICPB) technology is attractive for phenolic wastewater treatment, but has only been investigated using UV light (called UPCB). We examined the intimate coupling of visible-light-induced photocatalysis and biodegradation (VPCB) for the first time. Our catalyst was prepared doping both of Er(3+) and YAlO3 into TiO2 which were supported on macroporous carriers. The macroporous carriers was used to support for the biofilms as well. 99.8% removal efficiency of phenol was achieved in the VPCB, and this was 32.6% higher than that in the UPCB. Mineralization capability of UPCB was even worse, due to less adsorbable intermediates and cell lysis induced soluble microbial products release. The lower phenol degradation in the UPCB was due to the serious detachment of the biofilms, and then the microbes responsible for phenol degradation were insufficient due to disinfection by UV irradiation. In contrast, microbial communities in the carriers were well protected under visible light irradiation and extracellular polymeric substances secretion was enhanced. Thus, we found that the photocatalytic reaction and biodegradation were intimately coupled in the VPCB, resulting in 64.0% removal of dissolved organic carbon. Therefore, we found visible light has some advantages over UV light in the ICPB technology.

Factors influencing hydroquinone degradation in aqueous solution using a modified microelectrolysis method.

The discharge of hydroquinone (HQ), an important chemical raw material, to natural waters poses different ecological threats to aquatic organisms. In this study, we investigated the removal performance of traditional and modified microelectrolysis methods in aqueous solutions. The traditional microelectrolysis packing was modified by adding manganese (Mn), zinc (Zn), and copper (Cu) powder as additives. The factors affecting the removal performance of HQ, such as catalytic metal type, mass fraction of additive, reaction time, and initial pH, were examined. The results showed that the Mn modified packing exhibited the best performance compared to Zn and Cu powder. The removal rate of HQ using Mn modified packing can reach 94% after 4 h. In addition, 9% of Mn packing has a higher removal rate than other mass fractions. The acidic solution pH shows a more favorable degradation than a neutral and alkaline solution. The intermediates of HQ degradation by modified microelectrolysis were identified and then the pathway of HQ degradation was proposed. Our result indicates that Mn as catalytic metal holds promising potential to enhance HQ removal in water using the microelectrolysis method.

Eliminating partial-transformation products and mitigating residual toxicity of amoxicillin through intimately coupled photocatalysis and biodegradation.

Intimately coupled photocatalysis and biodegradation (ICPB) is a promising technology for treating wastewater containing antibiotics. While past work has documented the benefits of ICPB for removing and mineralizing antibiotics, its impacts on mitigating biotoxicity from products has not been studied. We fabricated an ICPB carrier by coating Ag-doped TiO2 on the outer skeleton of sponge carriers and allowing biofilm to grow in the internal macro-pores. We used amoxicillin (C16H19N3O5S) as the model antibiotic. The amoxicillin-removal rate contents with ICPB was greater by 40% vs. photocatalysis and 65% vs. biodegradation, based on the first-order kinetic simulation. While mineralization of amoxicillin was minimal for photocatalysis or biodegradation alone, it was ∼35% with ICPB. Photocatalysis alone led to accumulation of C14H21N3O2S; biodegradation alone resulted in accumulation of C14H21N3O3, C16H18N2O4S, and C15H21N3O3; but they were negligible after ICPB. As a result, ICPB reduced toxicity impacts measured by Staphylococcus aureas growth, Daphnia magna mobility, and teratogenicity to Zebrafish embryos. In contrast, photocatalysis alone increased each of the toxicity effects. In sum, ICPB gave greater removal and mineralization of amoxicillin, and it mitigated biotoxicity from treatment products.

Roles of an easily biodegradable co-substrate in enhancing tetracycline treatment in an intimately coupled photocatalytic-biological reactor.

Intimately coupled photocatalysis and biodegradation (ICPB) was realized in a macroporous carrier in which a photocatalyst was present on the outer surface, while a biofilm accumulated inside the carrier. In ICPB, photocatalysis products are rapidly biodegraded by a protected biofilm, leading to mineralization of the refractory organics, such as antibiotics. However, mineralization in ICPB could be compromised if the photocatalysis products remain refractory or are inhibitory. To address this, we attempted to increase metabolic activity by providing a readily biodegradable co-substrate (acetate) that could act as a source of energy and electrons to improve biotransformation and mineralization of the refractory antibiotic tetracycline (TCH). When we added acetate during ICPB of TCH, TCH removal increased by ∼5%, mineralization increased by ∼20%, and almost all photocatalysis products disappeared. Acetate addition also led to an increase in active biomass, an increase in the biomass's respiratory activity, and evolution of the microbial community to having more members able to biodegrade photocatalysis and biotransformation intermediates. Thus, providing an easily biodegradable co-substrate was an effective means for enhancing TCH removal and mineralization with the ICPB technology.

Contrasting roles of phenol and pyrocatechol on the degradation of 4-chlorophenol in a photocatalytic-biological reactor.

Intimate coupling of photocatalysis and biodegradation (ICPB) provides superior treatment for the degradation of bio-recalcitrant compounds, such as chlorophenol. Photocatalytically generated intermediates can be promptly used by the enclosed biofilms. Chlorophenol degradation can theoretically be accelerated by a co-substrate or be compromised by the competition for photocatalytic reactive oxygen species (ROS); however, studies to examine the comparison are limited in number. Non-chlorinated phenols commonly co-exist in real wastewater; thus, we evaluated the influence of phenol (hard to photo-oxidize) and pyrocatechol (easy to photo-oxidize) on the degradation of 4-chlorophenol (4CP). The removal efficiency of 4CP was 51%, which increased to 62% after phenol addition. Meanwhile, the dechlorination efficiency of 4CP increased from 47 to 63%; similarly, the living/dead cell ratio increased from 49/51 to 79/21. However, pyrocatechol addition led to a decrease in 4CP removal efficiency to 32% and a reduction in living/dead cell ratio to 35/65. The differences in the results were attributed to the extra electron donors provided by the photodegraded products of phenol to bacteria, which enhanced 4CP degradation; meanwhile, pyrocatechol competed with 4CP for ROS, thus inhibiting its degradation. Competition for ROS and co-substrate properties should be considered in the treatment of phenolic wastewater by ICPB.

Identifying the role of reactive oxygen species (ROSs) in Fusarium solani spores inactivation.

The inactivation mechanism of photocatalytic disinfectants on bacteria is well known. In contrast, the potential inactivation of fungal spores by visible-light induced photocatalysis has been recognized, but the inactivation mechanism is poorly understood. We hypothesize that photocatalytically generated reactive oxygen species (ROSs) are directly involved in this mechanism. To test this hypothesis, we identified the roles of ROSs in the inactivation of Fusarium solani spores. As the photocatalysts, we doped TiO2 with 3 typical dopants, forming Ag/TiO2, N/TiO2 and Er3+:YAlO3/TiO2. The Ag/TiO2 photocatalysis was dominated by H2O2, with the longest lifetime among the investigated ROSs. Ag/TiO2 photocatalysis yielded almost 100 % inactivation efficiency and preserved the cell-wall shape of the spores, thus minimizing the biomolecule leakage. Er3+:YAlO3/TiO2 was dominated by h+ ROSs, yielding an inactivation efficiency of 91 %; however, the severe leakage released large numbers of molecular bio-products. Severe damage to the cell walls by the h+ species was confirmed in micrograph observations. Subsequent to cell wall breakage, the Er3+:YAlO3/TiO2 nanoparticles entered the spore cells and directly oxidized the intracellular material. The N/TiO2 photocatalysis, with •O2- dominated ROSs, delivered intermediate performance. In conclusion, photocatalysts that generate H2O2-dominated ROSs are most preferred for spore inactivation.