[Effect of SRT on Stability of Yeast-SBR in Treating Oil-containing Wastewater].

Sludge retention time(SRT) is a crucial parameter to influence the stability of biological wastewater treatment systems. Especially, the effects of SRT on yeast-wastewater treatment remain unclear. In this study, mixtures of yeast strains were applied to treat oil-containing wastewater in sequencing batch reactors(SBR) and the effects of sludge retention time(SRT as 5, 10, 20, 40 d) on the removal efficiency of pollutants, contents and composition of extracellular polymeric substances(EPS), yeast cells settleability and yeast communities were investigated. The results showed that the recommended SRT was 5-10 d for the yeast-SBR system; Higher SRT led to decrease of COD removal rate and content of EPS; the tightly-bounded EPS was the major one which consisted of polysaccharides. SRT of 5-40 d had no significant effects on the SVI of yeast cells, however, longer SRT (>20 d) resulted in the increase of mycelial cells and a tendency to produce the filamentous bulking. In the continuous operation of SBR, three extraneous yeast strains capable of utilizing or degrading oil were identified in the systems under the short and long SRT. To conclude, shorter SRT was favorable for the system stability in treating oil-containing wastewater by yeasts.

[Fertility and Environmental Impacts of Urban Scattered Human Feces Used as Organic Granular Fertilizer for Leaf Vegetables].

The disposal of urban scattered human feces has become a difficult problem for the management of modern city. In present study, the scattered human feces underwent the collection, scum removal, flocculation and dehydration, finally became the granular fertilizer; the effects of the ratio of fertilizer to soil on the growth of the pakchoi and the quality of soil and leaching water were evaluated, and the feasibility of granular fertilizer manuring the pakchoi was discussed by pot experiments. The results showed that the granular fertilizer significantly enhanced the production of the pakchoi which were not polluted by the intestinal microorganisms under the experiment conditions; meanwhile, at the proper ratio of fertilizer to soil, the concentration of these microorganisms in the leaching water was lower than that in the control check. Chemical analyses of soil revealed that the nutrient content of nitrogen, phosphorus, potassium and organic matters in soil became much richer in all treatments. In addition, the granular fertilizer improved the physical- chemical properties of soil, including raising the level of soil porosity and reducing the volume weight of soil. Application of granular fertilizer won't pollute the soil or leaching water; instead, it can also prevent nitrogen, potassium and intestinal microorganisms from leaching inio ground water at the proper ratio of granular fertilizer to soil.