Study On The Design Of Distirbuted Wastewater Treatment Systems

With the water scarcity and stricter environmental regulations on industrial effluents discharging, the wastewater treatment strategies have become the research focus recently. The synthesis of the wastewater treatment system has been regarded as an effective way to minimize initial capital investment and operating costs, as well as the discharge in the wastewater treatment. Compared to the centralized treatment, distributed treatment systems can reduce the capital and operating costs, therefore, the design of the distribute wastewater treatment will be the main development tendency in the future. This paper analyzes the research status and development trends of the networks of distributed treatment processes based on summarizing relevant researches of treatment systems, and presents a new design method for the wastewater treatment networks, the main contents are listed as follows:Firstly, targeting procedure for single contaminant systems with one treatment process. The determination of the pinch point is the key for the calculation of the target of wastewater treatment systems with single contaminant. In this paper, a new method is proposed to determine the pinch point based on the insight that the pinch stream(s) is partially treated. With the known pinch point, it is only necessary to carry out detailed calculation for the allocation of the pinch stream. Besides, a new bypassing fraction formula is developed for the calculation of the pinch stream, which can reduce the calculation effort for design of the treatment systems.Secondly, targeting procedure for single contaminant systems with multiple treatment processes. In most situations, one treatment process will not accomplish the treatment task because of concentration constraints and/or performance constraints of the treatment processes. In these situations, two or more treatment processes might be required. In the design and targeting procedure, the perform order should be determined first, which is related to the constraints. Then the allocations of the streams to the treatment units are determined. The flowrate of the process with high cost should be as small as possible.Thirdly, targeting and design for multiple contaminants with multiple treatment processes. This section mainly includes two cases: one process can remove one contaminant and that can remove multiple contaminants. The total treatment flowrate is often related to treatment cost, therefore, an indicator, which can reflect treatment flowrate, is required. The new concepts: the Pseudo-Minimum Treatment Flowrate (PMTF) and the Total Treatment Flowrate Potential (TTFP), are proposed. The PMTF is a measurement of the minimum treatment flowrate when contaminant j in stream i is treated by process k, without considering the influence of the other streams and other contaminants. The TTFP is the sum of the PMTFs for process k to remove contaminant j in all the streams.If the treatment cost is directly proportional to the total flowrate of wastewater which flows through the treatment, the total treatment flowrate of the processes will be taken as the main factor for the design. In order to reduce the total treatment flowrate, the treatment process with the minimum value of the TTFP should be performed first. Besides, when one treatment process can remove multiple contaminants, there is the corresponding TTFP value for each contaminant. In order to meet the environmental limit of all the contaminants, the TTFP of a treatment process should be the maximum value of the TTFPs for the contaminants treated by the process.When the relationship between the treatment cost and the treatment flowrate is not directly proportional, the design of distributed wastewater treatment processes is more complex. Generally speaking, if possible, the expensive process should be performed first to avoid increasing its treatment flowrate, and a few heuristic rules are proposed for this situation. This simplifies the design procedure significantly compared to the literature methods.