| Discharged water treatment plant sludge (WTPS) without treatment could pollute the accepting water body and waste water resource. The current WTPS treatment situation, both in home and abroad was reviewed, and the basic chemical and physical characteristics of WTPS and relative measurement were also introduced and discussed. Furthermore the influence on the settling and condensing WTPS as well as physical and chemical conditioning of WTPS were studied. Some advanced methods of laser particle size analyzer, photometric dispersion analyzer (PDA), scanning electronic microscope and fractal theory were applied to study mechanism of the conditionings. A more comprehensive formula considering fractal dimension was deduced, and it could conduce to better understand the conditioning mechanism and the approaches of enhancing sludge's dewaterability.Settling/condensing experiments showed that inorganic flocculants had little effect on improving the WTPS's settleability, while the organic polymers such as C-PAM-1 could enhance settling velocity of WTPS obviously, implying the longer molecular chain of the organic polymers playing an important role in flocculation dewatering through absorbing and bridging functions. It was founded that SVI and turbidity were both decreased with the rise of dosage of C-PAM-1. Both the turbidity and SVI experienced a decline and then a rising periods as GT increased, thus a good settleability of WTPS was obtained when GT value was about 85860(200r/min, 3min). In the range of 5-35℃, C-PAM-1 could effectively improve the settling of WTPS. However, rise of pH from 2 to 10 deteriorated the settleability of WTPS.Application of Dick and Coe-Clevenger theories in designing gravity thickeners' area and depth based on the static settling curve for Water Treatment Plants (WTP) with consideration of its practical operation was discussed. In the application of the Dick theory, there is significant differences between the minimum solid flux values, i.e. 195kg/(m~2·d) vs. 49kg/(m~2·d), if calculated with or without considering the influence of the discharge velocity respectively. Consideration of the practical operation of thickeners in WTP, ignoring the discharge velocity was suggested as more safe way for the thickeners design. The value for the target concentration of the thickener should be determined according to the requirement of the dewatering machine when applying the Coe-Clevenger theory. In all of the tested physical conditionings, freezing-thaw was the most effective one. Freeze-thawed sludge could filter out at atmospheric pressure; and its filtered solid content increased with the decrease of the freezing temperature, sludge amount and the extension of freezing time. The influential degrees of the factors were successively ranged as: freezing time>freezing temperature>sludge amount. Microware radiation and heating/pressurization were ranked as the second most effective physical conditioning methods. Microwave can destroy the structure of sludge and enhance the dewaterability through reducing sludge's specific resistance to filtration (SRF) by 46% after 5 minutes radiation. Comparing to the results without pressurization, the pressurization heating decreased the SRF by 33% when the sludge heated for 5min at 0.14MPa and 120℃. Initial ultrasonic conditioning had negative effect on sludge's dewatering by increasing SRF. It needed further researches on its practicability, optimal operation and combination with other conditioning methods.Chemical conditionings in the study included adding polymers flocculants, surfactants, lime, and acid/base. It was found that non-organic reagents had little effects on improving the sludge's dewaterability while organic macromolecule polymers can enhance the sludge's dewatering, implying molecular weight might be an important factor determining the conditioning effect. The change of Zeta potential was slight after the reagents were added, suggesting that the flocculation dewatering mechanism of the polymers is mainly absorbing/bridging and webbing/sweeping, not electronic neutralization.The influence of surfactants of cationic CTAC and anionic SDS either act alone or with PAM together on sludge's dewaterability was tested. The results indicated that at the dosage of 50-200mg/L, no matter act alone or together with PAM, the CTAC showed a positive effect by decreased the SRF while SDS imposed an negative effects.Lime conditioning could improve the dewaterability of sludge at dosage above 1000mg/L, or 40-50% of dry sludge. However, the resulting increase of sludge's dry weight and pH in effluent at the dosage limits its application.In acid-base conditioning, with the decrease of pH, Zeta potential and SRF decreased. It is possible that H~+ changed the sludge particle's electronic nature, thus enhancing the its coagulation and also decreasing its affability to water. As a result, adding acid was benefit to dewatering while adding base had negative effect.Five conditioning operations including natural and man-made freezing-thaw, microwave radiation, adding PAM and adding PAM with acid were compared with both technical and economic aspects. The capital cost of the above 5 operations is about 1000-2000 RMB yuan/m~3 WTPS. Natural freezing-thaw conditioning is only fit to the cold region with abundant land resource. Man-made freezing-thaw is the most expensive one among the 5 operations, for its huge expense on construction, equipment and electricity consumed. However, with considering the advantage of environmental friendly, man-made freezing-thaw could be applied in the area with abundant cheap electricity resource. Microwave conditioning is a promise technology deserving research and application, not only for its operation fare is as low as 0.01 RMB yuan /m~3 sludge but also for its non reagent addition and having sterilization function which benefits to disposal of sludge cake and filtrate. The conditioning by adding PAM and by adding PAM with acid are mature in technical and also practical in economy. However the problem of disposal of sludge cake and filtrate restricts their further development.In this study, a formula including fractal dimension is deduced by applying the image technology and fractal theory.With the help of the formula and the observation of diameter and fractal dimension the sludge particles, conditioning mechanism and approaches for enhancing the sludge's dewaterability were discussed. It implies that the aim of reducing SRF could be achieved by increasingεoriginal porosity, d_e equivalent diameter of the sludge particles, D_f fractal dimension , or by decreasing s compressibility coefficient. Besides, changing the characteristics of sludge particles, reducingμthe viscosity of filtration is another effective method to decrease SRF.
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