[Preliminary analysis on COVID-19 case spectrum and spread intensity in different provinces in China except Hubei province]

Objective: To analyze the characteristics of COVID-19 case spectrum and spread intensity in different provinces in China except Hubei province. Methods: The daily incidence data and case information of COVID-19 were collected from the official websites of provincial and municipal health commissions. The morbidity rate, severity rate, case-fatality rate, and spread ratio of COVID-19 were calculated. Results: As of 20 March, 2020, a total of 12 941 cases of COVID-19 had been conformed, including 116 deaths, and the average morbidity rate, severity rate and case-fatality rate were 0.97/100 000, 13.5% and 0.90%, respectively. The morbidity rates in Zhejiang (2.12/100 000), Jiangxi (2.01/100 000) and Beijing (1.93/100 000) ranked top three. The characteristics of COVID-19 case spectrum varied from province to province. The first three provinces (autonomous region, municipality) with high severity rates were Tianjin (45.6%), Xinjiang (35.5%) and Heilongjiang (29.5%). The case-fatality rate was highest in Xinjiang (3.95%), followed by Hainan (3.57%) and Heilongjiang (2.70%). The average spread ratio was 0.98 and the spread intensity varied from province to province. Tibet had the lowest spread ratio (0), followed by Qinghai (0.20) and Guangdong (0.23). Conclusion: The intervention measures were effective in preventing the spread of COVID-19 and improved treatment effect in China. However, there were significant differences among different regions in severity, case-fatality rate and spread ratio.

Influence of ignited sediments on external phosphorus adsorption and sedimentary phosphorus forms

Phosphorus (P) adsorpted by sediments, when covered by and mixed with ignited sediments from Meiliang Bay in Tai Lake, was analyzed in the laboratory. Potassium dihydrogen phosphate (KH₂PO₄) was added to the parallel experimental units to simulate periodic external P input. Based on the Langmuir model, the sediments after ignition had a greater S_max (maximum P adsorption), a lower equilibrium phosphorus concentration at zero adsorption (EPC₀), and a lower degree of phosphorus saturation in comparison with sediments without ignition. This was confirmed by the variation in the dissolved inorganic phosphorus in the overlying water. When sediments were mixed with or covered by the ignited sediments, 5.985 and 5.978 mg of input P disappeared from the overlying water, respectively. However, when the sediments were mixed with the ignited sediments, 84.18% of the input P was converted to HCl-P, whereas when they were covered by the ignited sediments, sedimentary P was released, mainly from Fe/Al-P (up to 87.50%). This was attributed to differences in the microenvironments where less-intense anaerobic conditions were formed in the mixed sediments than in the sediments covered by the ignited sediments. This suggests that the injection of ignited sediments into existing sediments enhances their P adsorption and retention. It is favor of the control of the eutrophication with a simple technology.

[Effect of Different Adding Means of Ignited Water Purification Sludge on Phosphorus Adsorption and Forms]

The adsorption of external phosphorus (P) and the distribution of dissolved inorganic P (DIP) in the sediment interstitial water and sedimentary P forms were researched under the ignited water purification sludge (IWPS) addition (mixing and capping). The results showed that the adsorption ability of the IWPS increased obviously, compared with the water purification sludge (WPS). It indicated that the S_max increased by 43.7%, the EPC₀ decreased by 69.1% and the DPS decreased by 54.4%. The contribution of P disappearance in the overlying water had almost no difference between the mixing and capping with IWPS, but it was obviously higher than the control in both cases. Under the mixing condition, the adsorption of external P by unit IWPS was 2.3 times of that under the capping condition, if the contacting probability between the IWPS and the overlying water was considered. Under the capping condition, the DIP in the sediment interstitial water (1-2 cm) was 33.17 times (average) of that under the mixing condition. It was attributed to the decrease of the dissolved oxygen penetration due to capping. Under the mixing condition, the external P tended to form Ca-P, while the percentages of NH₄Cl-P and Fe/Al-P to Tot-P were bigger under the capping condition. It was suggested that the improvement of the sedimentary microenvironment by mixing with the IWPS was favorable for the adsorption of the external P and the immobilization of the internal P.