Xi Beidou

In situ simultaneous organics and nitrogen removal from recycled landfill leachate using an anaerobic–aerobic process

An anaerobic-aerobic process including a fresh refuse landfill reactor as denitrifying reactor, a well-decomposed refuse reactor as methanogenesis reactor and an aerobic activated sludge reactor as nitrifying reactor was operated by leachate recirculation to remove organic and nitrogen simultaneously. The results indicated that denitrification and methanogenesis were carried out successfully in the fresh refuse and well-decomposed landfill reactors, respectively, while the nitrification of NH(4)(+)-N was performed in the aerobic reactor. The maximum organic removal rate was 1.78 kg COD/m(3)d in the well-decomposed refuse landfill reactor while the NH(4)(+)-N removal rate was 0.18 kg NH(4)(+)-N/m(3)d in the aerobic reactor. The biogas from fresh refuse reactors and well-decomposed refuse landfill reactors were consisted of mainly carbon dioxide and methane, respectively. The volume fraction of N(2) increased with the increase of NO(3)(-)-N concentration and decreased with the drop of NO(3)(-)-N concentration. The denitrifying bacteria mustered mainly in middle layer and the denitrifying bacteria population had a good correlation with NO(3)(-)-N concentration.

Assessment of lakes ecosystem health based on objective and subjective weighting com-bined with fuzzy comprehensive evaluation

This study investigated 37 lakes of the Jianghan lake group in the middle reach of the Yangtze River. Trophic state index (TSI) was applied to define the trophic status of the lakes. According to water quality, sediment quality and aquatic biological communities, the analytic hierarchy process ( AHP) and entropy weight method combined with fuzzy comprehensive evaluation based on fuzzy mathematics methods were applied to evaluate the aquatic ecosystem health. The lakes trophic evaluation showed that Lake Haikou was in the mesotrophic status, 18 lakes were in eutrophic status, and 18 lakes were in hyper⁃eutrophic status. The as⁃ sessment of lake ecosystem health turned out that only Lake Haikou was in the “high” health status. Five lakes were in “ good” health status: Lakes Dongxicha, Huama, Liangzi, Tongjia and Zhangdu. The rest 31 lakes were all in “poor” health status. Ac⁃ cording to the TSI, for the ecosystem health assessment of the Jianghan lake group, AHP combined with fuzzy comprehensive evalu⁃ ation was proved to be a better method than the entropy weighting method.

Effects of different forms of nitrogen on chlorophyll-a and microcystin production of Microcystis sp.

Adopting the method of batch culture,the effect of ammonia nitrogen and nitrate nitrogen at different concentrations on the production of chlorophyll-a and microcystin of Microcystis sp.isolated from Yanghe Reservoir was investigated.Results showed that,when Microcystis sp.was cultured with ammonia nitrogen,contents of chlorophyll-a increased with ammonia nitrogen concentration in the logarithmic growth phase.However,the high concentration inhibited the growth of algae cells.The productions of MCRR fluctuated with the increase of ammonia nitrogen concentration.There was a remarkable rise of microcystin productions,reaching to 6.345×10-8μg/cell,when the concentration of ammonia nitrogen was 10.0 mg/L.This was significantly different with other treatments.When Microcystis sp.was cultured with nitrate nitrogen condition,contents of chlorophyll-a increased undulately with the increasing of nitrate nitrogen concentration,and there was no difference among different groups.The productions of microcystin under high concentration increased with the concentration during the logarithmic growth phase.They increased to 1.223×10-8μg/cell when the concentration was 5.0 mg/L,and reached the maximum value which was far less than that of the ammonia nitrogen group.There was no significant difference on the growth of algae between the two nitrogen sources.Ammonia nitrogen was more beneficial to the synthesis of chlorophyll-a in algae cells with nitrogen concentration increasing under lower concentration(1.5-5.0 mg/L) during the logarithmic growth phase.The productions of microcystin under ammonia nitrogen condition were far larger than nitrate nitrogen group at the range of 1.0-10.0 mg/L,and there was significant difference among the groups.Overall,ammonia nitrogen was more easily to lead to the secretion of MCRR in algae cells.