| With the continuous increase of population as well as the acceleration of industrialization and urbanization, the following issues have become increasingly serious such as the water shortage, the deterioration of water quality, flood disaster and ecological environment deterioration. Urbanization increases the impervious area which makes urban areas lose the function of rain infiltration and water storage. For this reason, a series of problems such as urban waterlogging, runoff pollution, urban heat island effect, urban rain island effect and climate change occur. The utilization of rainwater resource plays an important role in solving urban water shortage or excess, and it has obvious benefits of urban runoff control and hydrological cycle restoration. But the rainwater utilization just stays in the natural function of water resources at home and abroad at present and the utilization of rain energy is still a blank, thus it is discussed in this paper. Electrocoagulation technology is widely used in the treatment of high concentration of industrial wastewater, domestic sewage wastewater, micro-polluted water and so on. Referring to literatures at home and abroad, the electrocoagulation technology is rarely applied to rainwater treatment, so the electrocoagulation process of rainwater treatment is discussed in this paper to explore its running effect.At first, the feasibility of rainwater collection and utilization of urban roof is discussed with Hangzhou as an example. From two aspects of rainfall and rainwater quality, the advantages of rainwater collection and utilization of Hangzhou is analyzed. Then a joint use mode of rainwater and rain energy (Rainwater&Rain Energy, RWRE) is introduced systematically. Furthermore a small rain hydro-electric station in Jinhua is taken as a study case for the feasibility analysis of rain energy utilization. Electrocoagulation batch experiments are carried out to study the decontamination effect of different cathode materials and the decontamination mechanism of electrocoagulation technology. It is concluded that the decontamination effect of electrocoagulation is good overall and pollutants are mainly removed by redox, electrocoagulation and electroflotation. Furthermore the decontamination effect of Al-Al electrocoagulation is better than Al-Ti electrocoagulation. The influence of electrode gap, initial PH, current density, reaction time, and precipitation time on the pollutants removal efficiency is determined with orthogonal tests. The comprehensive optimal condition of electrocoagulation treatment is that electrode gap is2cm, PH is8, current density is30A/m2, reaction time is30min and precipitation time is20min. The removal rate of color, turbidity, SS, COD, TP, NO3--N, Fe, Zn, Mn and Cr6+are89.29%,84.43%,89.58%,25.71%,40.63%,24.00%,77.78%,100%,63.31%and85.71%respectively and all the parameters values of effluent meet the water quality standard for urban miscellaneous water consumption (GB/T18920-2002), water quality standard for scenic environment use (GB/T18921-2002), water quality standard for domestic miscellaneous water consumption (CJ25.1-89) and environmental quality standars for surface water of class III (GB3838-2002). Electrocoagulation continuous operation for rainwater treatment runs stably. The effluent quality is good and it meets the above reuse water standards with high removal rate of color, turbidity and SS as84.95%～88.35%,76%～100%and76.19%-95.24%. Analysis shows that the energy consumption for roof runoff treatment with electrocoagulation is1.002kW·h/m3and the cost is0.539yuan/m3in Hangzhou, which is lower compared to other processing cost. So the electrocoagulation technology is suitable for rainwater treatment with advantages of good treatment effect and low cost. The small-scale water purification mode can satisfy daily miscellaneous water requirements. Follow-up the comprehensive utilization system of rainwater can be established with the proposed RWRE mode as an integration of roof rainwater collection, power generation, purification and water supply. |
PDF Full Text Request