Frequent outbreaks of harmful algal blooms (HABs) represent one of the most serious outcomes of eutrophication, and light radiation plays a critical role in the succession of species. Therefore, a better understanding of the impact of light radiation is essential for mitigating HABs. In this study, Chlorella pyrenoidosa and non-toxic and toxic Microcystis aeruginosa were mono-cultured and co-cultured to explore algal responses under different nutrient regimes. Comparisons were made according to photosynthetically active radiation (PAR), UV-B radiation exerted oxidative stresses, and negative effects on the photosynthesis and growth of three species under normal growth conditions, and algal adaptive responses included extracellular polymeric substance (EPS) production, the regulation of superoxide dismutase (SOD) activity, photosynthetic pigments synthesis, etc. Three species had strain-specific responses to UV-B radiation and toxic M. aeruginosa was more tolerant and showed a higher adaptation capability to UV-B in the mono-cultures, including the lower sensitivity and better self-repair efficiency. In addition to stable μ_max in PAR ad UV-B treatments, higher EPS production and enhanced production of photosynthetic pigments under UV-B radiation, toxic M. aeruginosa showed a better recovery of its photosynthetic efficiency. Nutrient enrichment alleviated the negative effects of UV-B radiation on three species, and the growth of toxic M. aeruginosa was comparable between PAR and UV-B treatment. In the co-cultures with nutrient enrichment, M. aeruginosa gradually outcompeted C. pyrenoidosa in the PAR treatment and UV-B treatment enhanced the growth advantages of M. aeruginosa, when toxic M. aeruginosa showed a greater competitiveness. Overall, our study indicated the adaptation of typical algal species to ambient UV-B radiation and the stronger competitive ability of toxic M. aeruginosa in the UV-radiated waters with severer eutrophication.

Nitrophenols are toxic substances that present humans and animals with the risk of deformities, mutations, or cancer when ingested or inhaled. Traditional water treatment technologies have high costs and low p-nitrophenol (PNP) removal efficiency. Therefore, an ultraviolet (UV)-activated granular activated carbon supported nano-zero-valent-iron-cobalt (Co-nZVI/GAC) activated persulfate (PS) system was constructed to efficiently degrade PNP with Co-nZVI/GAC dosage, PS concentration, UV power, and pH as dependent variables and PNP removal rate as response values. A mathematical model between the factors and response values was developed using a central composite design (CCD) model. The model-fitting results showed that the PNP degradation rate was 96.7%, close to the predicted value of 98.05 when validation tests were performed under Co-nZVI/GAC injection conditions of 0.827 g/L, PS concentration of 3.811 mmol/L, UV power of 39.496 W, and pH of 2.838. This study demonstrates the feasibility of the response surface methodology for optimizing the UV-activated Co-nZVI/GAC-activated PS degradation of PNP.

In order to solve the problems of poor tolerance of traditional algal-bacterial symbiosis system to high ammonia wastewater and biomass recovery, a new symbiosis system combining biological agents of nitrifying bacteria and ordinary Chlorella vulgaris was proposed. The results showed that adjusting the volume ratio of algae and bacteria had an effect on the wastewater treatment performance, microalgae growth and flocculation effect. At the optimal algal-bacterial volume ratio of 1:3, the TN, NH4+-N and COD removal rates were 50%, 70%and 83%, respectively. The high concentration of ammonia nitrogen would have some inhibitory effect on microalgal photosynthesis, but the appropriate inoculation ratio could alleviate this pressure and improve the growth rate of microalgae. Under the optimal inoculation ratio, the PN and PS contents of extracellular polymers were 125.16 and 73 mg/L, respectively, which induced a stronger protective mechanism and enhanced the synergistic effect between algae-bacteria. In addition, the flocculation efficiency of the algal-bacterial system increased from 15% to 30% with the decrease of the initial inoculum of microalgae. The results provided a theoretical basis for the construction of an efficient algal-bacterial symbiosis system for the treatment of livestock and poultry wastewater as well as the efficient flocculation of the algal-bacterial system.

Degradable plastics, the substitute for conventional plastics, are becoming the new pollutant in the ocean. However, studies investigating the impact of freshwater and seawater on the basic aging process of microplastics and involving degradable plastics are still lacking. To accurately compare the potential hazards of degradable microplastics aging in seawater and freshwater, the role of salinity in the ultra-violet ray (UV) aging process of degradable microplastics (MPs) was explored in this study. Polylactic acid (PLA) aged under UV and 0‰, 10‰, and 40‰ salinities was taken as the subject. The results showed that salinity combined with UV accelerated the aging process, and PLA had more holes and cracks on the surface, larger specific area ($S_{\mathrm{BET}}$ ), and significantly more oxygen-containing functional groups and negative charges. The $S_{\mathrm{BET}}$ of PLA aged under UV and 40‰ salinity was $2.97\pm 0.11$ , 33% more than that aged by UV only. Additionally, salinity increased the adsorption capacity of PLA. The adsorption quantity of oxytetracycline (OTC) and ${\mathrm{Cu}}^{2+}$ by 40‰ salinity-aged PLA were 4.822 and $9.606\mathrm{mg}/\mathrm{g}$ , 30% and 32% more than that aged by UV only. There was a drop in the desorption rate of OTC but a rise in that of ${\mathrm{Cu}}^{2+}$ by PLA aged in salinities. Moreover, the desorption quantity and rate of pollutants on PLA in simulated intestinal fluid were greater than those in water, and PLA might have a higher carrier effect on pollutants after aging under salinity conditions. These results showed that the potential hazard of PLA existing in seawater may be more serious than that in freshwater. This study also revealed the effect of salinity, enabling the environmental risk assessment of degradable MPs to be more scientific and more comprehensive.