Antibiotics have become a new kind of organic pollutant as they are widely used in the water environment of China. Tetracycline (TC) is a class of broad-spectrum antibiotics produced or semi-synthesized by actinomycetes. Metronidazole (MTZ) is the first generation of typical nitroimidazoles. The content of nitroimidazoles is relatively high in medical wastewater, and their ecotoxicity is worthy of attention because they are difficult to completely eliminate. In this paper, the effects of TC and MTZ on the growth, cell morphology, extracellular polymer and oxidative stress of Chlorella pyrenoidosa (C. pyrenoidosa) were studied, and the toxic interactions between TC and MTZ mixture components were analyzed. The results showed that the 96h-EC₅₀ of TC and MTZ was 8.72 mg/L and 45.125 mg/L, respectively. The toxicity of TC to C. pyrenoidosa was higher than that of MTZ, and the combined toxicity effect of TC and MTZ was synergistic after the combined action of a 1:1 toxicity ratio. In addition, the algal cells of C. pyrenoidosa died to varying degrees, the membrane permeability of algal cells was increased, the membrane was damaged, the surface of algal cells exposed to higher concentration of pollutants was wrinkled, and their morphology was changed. The extracellular polymer of C. pyrenoidosa was affected by a change in concentration. The effect of pollutants on the reactive oxygen species (ROS) level and malondialdehyde (MDA) content of C. pyrenoidosa also had an obvious dose–effect relationship. This study contributes to the assessment of the possible ecological risks to green algae due to the presence of TC and MTZ in aquatic environments.

Bisphenol A (BPA) is an important industrial chemical; bisphenol S (BPS) is a substitute for BPA. Both are frequently detected in rivers, sewage, and surface water, and have a great impact on the water environment. The effects of BPA and BPS on cell growth, chlorophyll a content, and oxidative stress of Chlorella pyrenoidosa (C. pyrenoidosa) were studied. When BPA and BPS acted alone or in combination, compared with the blank control group, the growth of C. pyrenoidosa in the experimental group showed a pattern of “low promotion and high inhibition”, and the inhibition rate reached the maximum on the 6th day. Under the combined action, the reactive oxygen species (ROS) level of C. pyrenoidosa first increased, and then decreased. In addition, the activity of superoxide dismutase (SOD) and peroxidase (POD) increased with the increase in combined concentration. In the 0.5 P treatment group, SOD and POD activity reached peak values of 29.59 U/mg∙prot and 1.35 U/mg∙prot, respectively. The combined toxicity of BPA and BPS to C. pyrenoidosa was evaluated as a synergistic effect by using toxicity unit and additive index methods. This study evaluated the effects of BPA and BPS on algae in the aquatic environment, providing some data support for their potential ecological risks.

The transformation of organic pollutants by stabilized nano-FeS in oxic conditions is far less understood than in anoxic states. Herein, carboxymethyl cellulose-stabilized FeS (CMC-FeS) nanofluids are prepared at a CMC-to-FeS mass ratio of 1/2 and their performance of tetracycline hydrochloride (TC) degradation under oxic conditions was investigated. Here, we showed that TC could be efficiently removed by oxygenation of CMC-FeS nanofluids at neutral initial pH. We found that CMC-FeS dosages as low as 15 mg/L can achieve the TC removal efficiency as high as 99.1% at an initial TC concentration of 50 mg/L. Oxidative degradation plays a predominated role in TC removal (accounting for 58.0%), adsorption has the second importance (accounting for 37.0%), and reduction has minor impact (accounting for 4.1%) toward TC removal. Electron spin resonance assays, fluorescent detection using coumarin as a probe, and radical scavenging experiments confirm that hydroxy radicals (•OH), both in free and surface-bound forms, contribute to oxidation of TC. Humic acids brought detrimental effects on TC removal and therefore should be biologically degraded in advance. This work offers a facile and cost-effective solution to decontaminate TC in natural and engineered water bodies.

Microcystis blooms and microcystins caused by eutrophication are harmful to the environment. At present, algicide based on allelochemicals is widely used in algae control. Environment-friendly sustained-release salicylate chitosan microspheres (SA-CS) were prepared by acylation of chitosan and glutaraldehyde. SA-CS was characterized by scanning electron microscopy, Fourier transform infrared spectral analysis, and laser particle sizer. The inhibitory effects of SA-CS on Microcystis aeruginosa at different stages, and the environmental impact of the inorganic index, were studied. The results showed that the mean size of SA-CS was 53.3 μm, the encapsulation rate was 40.66%, and SA-CS had a good sustained-release effect (stable release within 25 days). On the seventh day, a 90% inhibition rate in the lag phase required 105 mg/L of SA-CS, whereas a 90% inhibition rate in the log phase required 675 mg/L of SA-CS. The sensitivity of Microcystis aeruginosa at the lag phase to salicylic acid was about 1.4 times that of the log phase, thus, it is recommended to control the algae in the lag phase. The long-term inhibition effect of SA-CS on algae was detected after adding sufficient SA-CS. In terms of salicylic acid, pH, and dissolved oxygen, no lousy effect was observed for the addition of SA-CS. SA-CS could effectively reduce the concentration of microcystin-LR by 50%. SA-CS is an environment-friendly sustained-release microsphere with good algal inhibition performance for Microcystis aeruginosa.

In this study, we used chitosan/sodium alginate hydrogel as a carrier to prepare berberine sustained-release capsule materials that can inhibit algae for a long time and safely. The preparation conditions of the material were optimized by the response surface method, and the optimized capsule material was characterized and the sustained release characteristics were analyzed to study the change of the algae inhibition effect of the material within 30 days. The results showed that the optimum preparation parameters of the material were 0.54% chitosan content, 2.46% sodium alginate content and 1.09% anhydrous calcium chloride content by response surface optimization design, which was consistent with the parameters set by each factor at the central point. The algae inhibition rate of the material under this preparation condition was 93.75 ± 1.01%, which was similar to the predicted value. The release characteristics analysis showed that the material continuously released up to 90% of berberine within 24 days, and its release characteristics were sustained release after burst release, with good sustained release effect. The results of material characterization showed that chitosan/sodium alginate hydrogel could effectively load berberine and was beneficial to the loading and release of berberine. The results of algae inhibition experiments showed that low concentration materials could control the outbreak of cyanobacterial blooms in a short time, while under high concentration conditions, the materials could inhibit Microcystis aeruginosa efficiently and for a long time.

Fe(II)-activated potassium periodate (KIO₄) oxidation was used to improve the dewaterability of waste-activated sludge for the first time. Compared with those of raw sludge, the capillary suction time (CST), specific resistance filtration (SRF), and water content of filter cake (W_C) of sludge treated using the Fe(II)/KIO₄ process under the optimal conditions (i.e., the initial pH = 6.8, KIO₄ dose = 1.4 mmol/g volatile suspended solids, Fe(II)/KIO₄ molar ratio = 1.2) decreased by 64.34%, 84.13%, and 6.69%, respectively. For conditioned sludge flocs, the Zeta potential and particle size were increased, and hydrophilic proteins in extracellular polymeric substances (EPS) were partly degraded, accompanied by the transformation of tightly bound EPS into soluble EPS and the conversion of dense sludge flocs into loose and porous ones. During Fe(II)/KIO₄ oxidation, Fe(IV) and the accompanying ^•OH were determined as the predominant reactive species and the underlying mechanism of sludge EPS degradation was proposed. This work provides a prospective method for conditioning the sludge dewaterability.