The advanced treatment of textile printing and dyeing wastewater by hydrodynamic cavitation and ozone: Degradation, mechanism, and transformation of dissolved organic matter.

The emission standards for textile printing and dyeing wastewater are stricter due to serious environmental issues. A novel technology, hydrodynamic cavitation combined with ozone (HC + O3), has attracted wide attention in wastewater advanced treatment, whereas the contaminants removal mechanism and transformation of dissolved organic matter (DOM) were rarely reported. This study investigated the removal efficiency and mechanism of HC + O3. The maximum removal rates of UV254, chrominance, CODCr, and TOC were 64.99%, 91.90%, 32.30%, and 36.67% in 60 min, respectively, at the inlet pressure of 0.15 MPa and O3 dosage of 6.25 mmol/L. The synergetic coefficient of HC + O3 was 2.77. The removal of contaminants was the synergy of 1O2, ·OH and ·O2-, and high molecular weight and strong aromaticity organic matters were degraded effectively. The main components in DOM were tryptophan-like and tyrosine-like, which were effectively removed after HC + O3. Meanwhile, most DOM had decreased to low apparent relative molecular weight (LARMW) compounds. Additionally, the HC + O3 effluent can reach the emission standard in 60 min for 8.07 USD/m3. It can be concluded that HC + O3 is an effective technology for the advanced treatment of industrial wastewater. This study will provide suggestions for the engineering application of HC + O3.

Degradation of acid red 73 wastewater by hydrodynamic cavitation combined with ozone and its mechanism.

Many azo dyes are consumed in the textile and dyeing industry, which makes the wastewater recalcitrant and toxic to the aquatic environment. Dye degradation by the combination of hydrodynamic cavitation and ozone (HC + O3) has caused extensive interest. The degradation mechanism of the hybrid system needs further investigation. This study investigated the degradation of acid red 73 (AR73) by HC + O3. Meanwhile, the degradation pathways and mechanisms were present. The optimal operation parameters were: inlet pressure of 0.15 MPa, O3 dosage of 45 mg/min, initial dye concentration of 10 mg/L, and initial pH at 7.5. As a result, the decolorization rate, removal of UV254 and NH3-N were 100%, 71.28%, and 87.36% in 30 min, respectively. Humic acid and most of the co-existing anions (HCO3-, SO42-, Cl-, PO43-, NO3-) played a positive role in the degradation of AR73, while NO2- restrained. The reactive species of singlet oxygen (1O2), hydroxyl radicals (·OH) and super oxygen radicals (·O2-) showed synergism in the hybrid system, and the decolorization was attributed to the fracture of azo bonds by 1O2. Meanwhile, aromatic amines were generated and further degraded into small molecule compounds. The research certificated that the HC + O3 can be an effective technology for azo dye degradation.

[Impact of Starvation Conditions on Biological Community Structure in Sulfur Autotrophic Denitrification Reactor].

Sulfur/dolomite and pyrite/dolomite autotrophic denitrification reactors were applied to treat the secondary effluent of wastewater treatment plant to explore the removal effect, the changes of microbial community, and recovery time of reactors after starvation period. It was shown in the results that after 30 d non-water starvation endurance, the effluent concentrations of NO3--N in sulfur/dolomite and pyrite/dolomite reactors increased from 1.78 mg·L-1, 11.32 mg·L-1 to 27.87 mg·L-1, 26.56 mg·L-1 respectively at the low temperature of 12-14℃. In addition, sulfur/dolomite and pyrite/dolomite reactors recovered within 5 d and 11 d since restarted and could maintain a good effect of nitrogen removal at low temperature. MiSeq high throughput sequencing results showed that the abundance and diversity of the bacterial communities in starvation period in both reactors were lower than those in recovery period. The dominating phylum was Proteobacteria in both reactors while the dominating class was ß-Proteobacteria. Thiobacillus was identified as the main genus for denitrification in sulfur/dolomite reactor.

Prolonged starvation and subsequent recovery of nitrification process in a simulated photovoltaic aeration SBR.

The ability of a new SBR (sequencing batch reactor) based on simulating photovoltaic aeration for maintaining nitrification activity under a 25-day starvation period was studied. The activity and abundance of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) and the diversity of AOB were investigated. The measured biomass decay rates were 0.017 day(-1) and 0.029 day(-1) for AOB and NOB, respectively. These decay rates correlated well with AOB and NOB population quantified by real-time PCR. The recovery of ammonia oxidation rate and nitrite oxidation rate needed 4 and 7 days, respectively, indicating that NOB was more affected than AOB by starvation conditions. According to the real-time PCR results, Nitrospira was the dominant NOB in the reactor. Phylogenetic analysis indicated that Nitrosomonas oligotropha cluster was the dominant major cluster before and after starvation. Moreover, Pareto-Lorenz evenness distribution curves were plotted to interpret the interspecies abundance of AOB; the results suggested that AOB community possessed a balanced structure with medium Fo (Functional organization). Thus, the community can potentially deal with changing environmental conditions (e.g., starvation) and preserve its functionality according to the concept of functional redundancy.