With the expanding scale of urban wastewater treatment, the resulting excess sludge quantity is also growing. Excess sludge treatment and disposal has become an important part of the sewage treatment. Sludge itself is rich in essential nutrients of plant growth such as nitrogen and phosphorus, so it's a good organic fertilizer; but it often also contains harmful substances such as heavy metals. If the sludge treatment is not good, it not only can bring secondary pollution to the environment, but also can cause the waste of resources. Luminescent bacteria tests are conducted in this research by comparing the effects on the absorption and transformation of toxic substances between traditional sludge drying bed and reed bed. The study finds that the biological toxicity of surface layer sludge either in reed bed or in traditional drying bed has little change with the seasons and maintains in low level. While the biological toxicity in the bottom of sludge has change with the seasons and achieves the lowest level in summer and fall, and the biological toxicity of sludge in reed bed is lower than that of traditional drying bed.
Abstract. In a photovoltaic (PV) system that consists of multiple series-connected PV modules with bypass diode, multiple peak points could exist in the P-V curve of the PV system under partially shaded conditions (PSC), causing conventional MPPT methods sometimes unable to track the true global maximum power point (GMPP). In view of this problem, we propose in this paper a new two-stage global maximum power point tracking (GMPPT) method based on the distribution characteristic of the GMPP voltage and the dividing point voltage. The method proposed finds all the possible peak power points and compares the power of those points to find the GMPP in the first stage. In the second stage, the method sets the operation point to the point of the maximum power found in the first stage and uses the hill climbing (HC) method to keep the operation point at that point. The method proposed is validated by simulation. Simulation result shows that this method can track the GMPP effectively.
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