Changle Pang

Performance of two laboratory-scale horizontal wetlands under varying influent loads treating artificial sewage

The performance of two laboratory‐scale horizontal subsurface‐flow constructed wetlands(CWs) treating artificial sewage in response to varying influent components and loads was investigated. Acidification with a pH of 3.0 was detected under an organic carbon load of 100 mg/day, which further inhibited the activity of the denitrification process. With an increase in the carbon load to 240 mg/day, the pH was significantly elevated to 6.0. However, a negative effect of sulphide as a product of sulphate reduction was observed on the removal of ammonium, the plants (Juncus effusus), and the organic carbon degradation. With a produced sulphide concentration of about 3.5 mg/L, the ammonium removal decreased from 100% to 30% under an inflow load of 100 mg/day, and the number of healthy stalks of J. effuses was reduced from about 14 000/m2 to less than 6000/m2. The removal of organic carbon decreased from 94% to 68% under an influent load of 240 mg/day, when the sulphide concentrations reached up to about 8–10 mg/L. The production of sulphide was not immediately controlled by stopping the inflow sulphate load to remove the negative effect of the sulphide toxicity, thus indicating an immobilization of the deposited reduced sulphur compounds. Moreover, the effect of a nitrate dosage on the sulphide control was also examined, but was shown to be only evident under the conditions of a low organic carbon input.

Leaching and transformation of nitrogen in soil fertilized with digestate: A soil column study

Abstract. The trend of rapid promotion of anaerobic digestion technology has stimulated and increased the application of digestate. The sustainability of anaerobic digestion systems depends largely on the appropriate utilization of the digestate. There is therefore a need to assess the environmental benefits and risks of digestate application. The purpose of this study was to improve the understanding of leaching and transformation of nitrogen in digestate-fertilized soil. Nitrogen leaching was studied during three plant (Pakchoi) growing cycles in a soil column of 31.5 cm diameter and a 100 cm height. In the first plant growing cycle, 200 mL digestate was surface-applied on the column soil. In the second and third cycles, 400 mL was applied each cycle. Leachate from 6 different soil depths was sampled every 3 days and analyzed for pH, ammonium, nitrate and nitrite. There were no significant differences in the pH value of leachate during the plant growth. The high ammonium contents present in the digestate were not found in the soil column system probably due to ammonia emission; and absorption, immobilization and nitrification in the soil during the study. The average concentrations of nitrate in the leachate from 80-cm soil depth were 14.8, 26.7 and 30.1 mg L -1 for the three growing cycles, respectively. They exceeded the standard on the environmental quality for groundwater in China (GB/T14848-1993). This study showed that inappropriate digestate application could present a risk of nitrite pollution to groundwater. To avoid nitrate leaching and ammonia volatilization, there is a need to select and implement digestate application techniques and application rates that can reduce nitrogen leaching.