| Contact flocculation technology with micro-flocculation– filtration as a representative process has found wide application in both water and wastewater treatment practice, which is promising to provide a new fundamental principle of separation technology in water treatment processes.This thesis aims at the development and application of contact flocculation process in water treatment technology. The basic theory of coagulation and flocculation and its recent development in polymeric flocculants of hydroxyl ployaluminum (PACl) in both the interaction mechanisms and the suitable applied technology are reviewed in the paper based on the literature survey. Comprehensive and systematic experimental study is then conducted, which is mainly focused on the following aspects:1. As an important buildup element of contact flocculation process, the speciation and distribution of hydroxyl polymeric aluminum flocculants play a significant role in the overall process performance. Therefore, the study of aluminum polymer species and their interacting mechanism is of great concern. In the first part of the thesis, the effects of basicity and different aluminum polymer species on the coagulation performance of PACl coagulants are carried out by jar test to screen out the optimized PACl flocculants with high efficiency for the contact flocculation process of micro-flocculation– filtration technology.2. Treatment of drinking water with low temperature and low turbidity is proved to be a tough task due to its high viscosity, less particulates, slow coagulation rate after dosing the flocculants, and the small flocs (alum) that are usually formed in the coagulation process are hard to settle down, causing them easy to penetrate through the filter layers in the filtration bed. In the second part of this paper, two cases of study in the drinking water treatment with low-temperature and low turbidity are experimentally performed using contact flocculation technology. By dosing a small amount of quartz sand to the raw water from the Irtysh River in Xinjiang to artificially increase the turbidity for the enhancement of coagulation performance, experiments are carried out in pilot-scale to optimize the contact flocculation reaction conditions; In the second case study, water samples with low temperature and low turbidity from the settling tank of water plant during the winter in Beijing were investigated using both the conventional and enhanced filtration process. Based on the head loss, particle counts, TOC and COD, conditions of PACl dosage, particle size of filter medium, and the coagulation time etc. of the micro-flocculation and enhanced filtration process are screened out in order to improve sewage interception capabilities of the filter bed, and to optimize the operating parameters of the overall process performance .3. To demonstrate the applicability of contact flocculation technology in the advanced treatment of typical dye printing wastewater effluents downstream in the Dongjiang river basin, both the micro-flocculation / direct filtration and the Coagulation - Precipitation - Multi-media filtration processes are investigated on the tailing wastewater discharged from a local bleaching and dyeing mill of textile industry for the purpose of water reuse and pollutants emission reduction. Jar test is performed on the dye printing wastewater effluents to optimize the coagulation conditions in the micro-flocculation / direct filtration combined process and through the dosing of the composite coadulants nano iron is introduced as an aid into the Coagulation - Precipitation - Multi-media filtration process to enhance the removal of organic pollutants for their emission reduction.The following conclusions have been reached based on the above experimental results:1. PACl with high alkalinity is usually demonstrated better coagulation performance than that with the low one; High-Alb content PACl flocculants are easy to form loose flocs to be difficult to settle down for separation, while PACl with high-level Alc often leads to compact flocs that facilitate the removal of organics and particulates by the precipitation process of flocs; HPAC flocculants are proved to be superior to the ordinary PACl coagulants in the performance.2. For the treatment of raw water with low temperature and low turbidity, optimized coagulation conditions are as follows: 20-25 min for the slow agitation reaction time(T) with 30 S-1of velocity gradient (G). The introduction of small amounts of silica particles into the low temperature and low turbidity water body can largely improve the coagulation performance due to the increase of collision efficiencies between the aquatic particles, but dosing of SiO2 particles should be precisely controlled in a small quantity, otherwise it will deteriorate the effluent water quality due to a poor residual turbidity removal. It is concluded that compared to the conventional water treatment technology micro-flocculation /direct filtration process can effectively improve the water quality in the drinking water treatment with low temperature and low turbidity3. Micro-flocculation - direct filtration, which is a representative technology of contact flocculation process, can be successfully exploited in the advanced treatment of typical dye printing wastewater effluents for the purpose of water reuse and pollutants emission reduction. The effluents by micro-flocculation - direct filtration process can meet the urban recycling water quality standard for industrial use (GB/T19923-2005), in which better results can be obtained in the multi-media filtration than that in the uniform media process; In the selection of coagulants, HPAC is better than conventional ferrous sulfate and PACl in the overall process performance. Furthermore, a novel advanced treatment process, i.e. nanoscale iron + coagulation - precipitation - Multi-media filtration, has been investigated on the dye printing wastewater to reduce the emission of toxic pollutants. The selection of high-efficient flocculants in the serious products of HPAC-9 can offer better treatment results. Dosing of a small amount of nano-iron is the key point for this process, which may facilitate the degradation of organic pollutants in wastewater and enhance the overall removal of organics by combined processes, and therefore reduce the emission of the toxic pollutants into the water body. Nevertheless, the dosage of nano- iron should not be large due to its high reactivity, otherwise small molecular weight degradation products of organic pollutants may be formed, which may complicate the performance of organic removal by the combined processes; Moreover, the slow oxidation of Fe2 + residual in the effluents may cause a color change of the effluent water when preserved for some time.
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