Energy Consumption Evaluation of Completcly Recycling System for Industrial and Domestic Wastewaters

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Water recycling is an effective countermeasure to meet the increasing need of water for industrial and economic activities. But in some cases, the promotion of water recycling may put energy consumption up because an advanced treatment process of wastewater is usually necessary for this purpose, leading to an increase in pollution load to the environment. The aim of this study was to give a procedure for the establishment of completely water recycling system with low energy consumption. The following results were obtained.1) The present situation of energy consumption for industrial wastewater treatment and recycling was investigated based on the results of a questionnaire. The relationships between energy consumption and treatment techniques used, characteristics of raw wastewater to be treated, quality of treated water, recycling status, etc.were analyzed. A guide to select advanced treatment process for the recycling of industrial wastewater was suggested.2) The recycling system of domestic wastewater, especially of building wastewater was evaluated with life cycle assessment in term of carbon dioxide emission. It was shown that the impact to the environment of membrane filtration process, the effluent water quality of which is very high, is relatively higher than other techniques. A rainwater using system was also evaluated in terms of cost and energy consumption.3) The energy efficiency of acrobic biological treatment processes (such as activated sludge process, oxidation ditch method, sequencing batch reactor process, etc.), biological activated carbon process and membrane filtration system were evaluated and compared. The techniques for nitrogen and/or phosphorus removal from wastewater werc also evaluated.