螺旋压榨式脱水机对污泥脱水的试验研究

考察了螺旋压榨式脱水机对污泥的脱水性能.结果表明:对于含水率为97.9%的消化污泥,在絮凝剂投配率为0.51%、螺杆转速为0.25 r/min的条件下,脱水后泥饼含水率最低可达70.3%、固形物回收率为98.89%、污泥处理量为24.84 kg/h;对于含水率为99.7%的剩余污泥,在絮凝剂投配率为0.94%、螺杆转速为0.75 r/min的条件下,脱水后泥饼含水率为82.5%、固形物回收率为92.46%、污泥处理量为8.64 kg/h.螺旋压榨式脱水机对污泥的处理效果较带式脱水机有很大提高.     

上海市竹园第二污水处理厂污泥脱水性能的研究

上海市竹园第二污水处理厂的泥饼含水率为78%左右,不能达到设计值(65%),为了分析其原因,对污泥的脱水性能进行了研究.结果表明,由于产生的剩余污泥脱水性能较差,且使用的是板框压滤机与PAM调理剂,使泥饼含水率降至65%是不可能实现的;根据该厂目前的运行状况及今后污泥的出路,泥饼含水率设定为75%左右较合理.     

Optimization of sewage sludge conditioning and pressure dewatering by statistical modelling

By using a quadratic model, an assessment was made of the relative importance of different sludge and polyelectrolyte variables with respect to sludge pressure dewatering. It was seen that the polyelectrolyte characteristics and dose dominated the cake dry matter content and that sludge properties were less important, especially the electrophoretic mobility of the sludge, which showed a restricted natural variability over the 10-month sampling period. The developed quadratic model in this study appeared very well suited to quantitatively predict the pressure dewatering properties of sludge, allowing the selection of the dose and polyelectrolyte type that yield the best dewatering result. It was further shown that relatively small deviations from the optimal polyelectrolyte dose caused only small changes in cake dry matter values. The model appeared to be applicable on a long-term basis, as it was able to predict the dewaterability of several sludge samples from the studied wastewater treatment plant after more than 3 years. Finally, the model also allowed an (simplified) economic evaluation, indicating that for high cake disposal costs, the polyelectrolyte should be taken that guarantees the best dewatering results, even if it has to be applied in high doses.     

影响污泥深度机械压力脱水因素的探讨

根据污泥处理处置技术在实际应用中存在的缺陷,指出污泥的深度脱水是污泥处理处置的关键环节。因此,污泥深度脱水技术面临着巨大的技术需求和市场需求。介绍了污泥深度脱水性能的表征方法,指出模拟恒压压滤脱水后泥饼的含水率能够较好地表征污泥深度脱水性能。同时,从污泥性质、调理剂预处理、过滤压力及操作、过滤介质等方面分析了污泥深度机械压力脱水的影响因素。     

Pressurised electro-osmotic dewatering of activated and anaerobically digested sludges: electrical variables analysis

Pressurised electro-osmotic dewatering (PEOD) of two sewage sludges (activated and anaerobically digested) was studied under constant electric current (C.C.) and constant voltage (C.V.) with a laboratory chamber simulating closely an industrial filter. The influence of sludge characteristics, process parameters, and electrode/filter cloth position was investigated. The next parameters were tested: 40 and 80 A/m², 20, 30, and 50 V—for digested sludge dewatering; and 20, 40 and 80 A/m², 20, 30, and 50 V—for activated sludge dewatering. Effects of filter cloth electric resistance and initial cake thickness were also investigated.The application of PEOD provides a gain of 12 points of dry solids content for the digested sludge (47.0% w/w) and for the activated sludge (31.7% w/w). In PEOD processed at C.C. or at C.V., the dewatering flow rate was similar for the same electric field intensity. In C.C. mode, both the electric resistance of cake and voltage increase, causing a temperature rise by ohmic effect. In C.V. mode, a current intensity peak was observed in the earlier dewatering period. Applying at first a constant current and later on a constant voltage, permitted to have better control of ohmic heating effect. The dewatering rate was not significantly affected by the presence of filter cloth on electrodes, but the use of a thin filter cloth reduced remarkably the energy consumption compared to a thicker one: 69% of reduction energy input at 45% w/w of dry solids content. The reduction of the initial cake thickness is advantageous to increase the final dry solids content.     

壳聚糖与硅藻土调理市政污泥

以污泥比阻为评价指标,综合考虑脱水率、泥饼含水率及过滤时间因素,研究使用壳聚糖与硅藻土对污泥单独调理的最佳条件及联合调理改善污泥脱水性能的效果,并与聚丙烯酰胺调理污泥的效果进行了对比。结果表明,先投加0.5g/g硅藻土调理污泥,再投加5 mg/g壳聚糖以30r/min搅拌反应150s,污泥比阻下降了95.43%,脱水率上升至91.02%,泥饼含水率降至83.13%,过滤时间降至29.5s。壳聚糖与硅藻土联合调理的效果明显优于壳聚糖或硅藻土单独调理的效果,且其联合调理改善污泥脱水综合性能的效果优于聚丙烯酰胺调理污泥的效果。     

绍兴污水处理厂污泥处理工程改扩建设计

介绍了绍兴污水处理厂污泥处理工程的改扩建设计,设计中对现有污泥处理脱水构筑物及设备进行了改造,解决了其污泥脱水性能较差的问题,充分发挥了现有设施的处理能力,污泥预处理能力达到350 tDS/d(83%含水率污泥为2 059t/d),新建处理能力为370 tDS/d(80%含水率污泥为1 850t/d)的污泥处理设施,全厂污泥全部处理后外运处置.     

污水厂絮凝剂耗药量对污泥脱水性能影响研究

通过离心机上机试验,研究絮凝剂耗药量对污泥脱水性能的影响。研究结果表明：离心机差速维持在4 r/min～5 r/min,扭矩在30%～40%,进泥干固体负荷在1 700 kg TDS/h～2 200 kg TDS/h的条件下,药耗在低至3.93 kg/t干污泥时仍能取得泥饼含水率不大于77%、污泥回收率不小于97%的优良脱水效果。     

厦门城市污泥深度脱水处理及资源化利用研究

结合厦门污水处理厂污泥深度脱水工艺的应用情况,考察了预浓缩—FeC l3和CaO调质—高压隔膜厢式压滤机对污泥的深度脱水效果,并研究了泥饼的处理、处置和资源化利用情况。结果表明,污泥经深度脱水后,泥饼含水率60%,自然放置7 d后,含水率可进一步降至45%左右,满足填埋的要求,另外还可用于制砖和作园林绿化的土壤基质,也可作焚烧处置。污泥深度脱水过程中产生的滤液可循环利用,回流至进水处时,对出水水质影响很小,且可为脱氮过程提供碳源和碱度;回流至重力浓缩池时,可改善污泥沉降性能,提高脱水效率。与传统污泥脱水工艺相比,该工艺具有经济优势。     

Lignite aided dewatering of digested sewage sludge

Mechanical dewatering is commonly used to increase the solids content of municipal sludge prior to its disposal. However, if the rate of filtration is slow, mechanical dewatering can be expensive. In this study, the use of lignite to improve the sludge dewatering is investigated. The effectiveness of lignite conditioning of polyelectrolyte-flocculated sludge is examined using mechanical compression tests. Results show that lignite conditioning in conjunction with polyelectrolyte flocculation gives much better dewatering than the polyelectrolyte flocculation alone. Using Darcy's filtration theory, the specific cake resistance and permeability of the compressed cakes are obtained. Both of these parameters are significantly improved after lignite conditioning. Mercury porosimetry tests on compressed cakes show that the porosity of the lignite-conditioned sludge cake is much higher than that of the polyelectrolyte-flocculated sludge and it increases with increasing doses of lignite. The mercury porosimetry results show that the lignite pore volume of pores greater than 0.5 μm are reduced with increasing sludge ratio indicating that sludge is trapped within these pores, whereas smaller pores are unaffected. The yield stress curves for sludge, lignite and sludge-lignite mixtures show that the sludge filter cake is very compressible, but the lignite-conditioned cake has a range of compressibility which although more than lignite indicate that the cake is relatively incompressible at low pressures. Thus, lignite conditioning acts to maintain the permeability of the filter cake during compression dewatering by resisting cake compression. This leads to a trade-off between the rate of dewatering and the solids content of the compressed cake. With lignite conditioning, the dewatering rate can be increased by a factor of five for the same degree of water removal.     

硝酸钠强化污泥电渗透脱水的试验研究

在污泥中加入硝酸钠可提高电渗透脱水速率,考察了投药量、机械压力、电压和脱水时间等因素对电渗透脱水效果的影响。结果表明,在加入硝酸钠后,电渗透脱水速度加快、脱水程度增强、泥饼含固率在短时间内明显提高。分析认为,这主要和电渗透脱水过程中电流密度和温度的升高有关。在不同电压及脱水时间下,硝酸钠的加入更有效地提高了污泥含固率,且效果显著。     

Electro-dewatering of wastewater sludge: influence of the operating conditions and their interactions effects

Electric field-assisted dewatering, also called electro-dewatering (EDW), is a technology in which a conventional dewatering mechanism such a pressure dewatering is combined with electrokinetic effects to realize an improved liquid/solids separation, to increase the final dry solids content and to accelerate the dewatering process with low energy consumption compared to thermal drying. The application of these additional fields can be applied to either or both dewatering stages (filtration and/or compression), or as a pre-or post-treatment of the dewatering process. In this study, the performance of the EDW on wastewater sludge was investigated. Experiments were carried out on a laboratory filtration/compression cell, provided with electrodes, in order to apply an electrical field. The chosen operating conditions pressure (200-1200 kPa) and voltage (10-50 V) are sufficient to remove a significant proportion of the water that cannot be removed using mechanical dewatering technologies alone. A response surface methodology (RSM) was used to evaluate the effects of the processing parameters of EDW on (i) the final dry solids content, which is a fundamental dewatering parameter and an excellent indicator of the extent of EDW and (ii) the energy consumption calculated for each additional mass of water removed. A two-factor central composite design was used to establish the optimum conditions for the EDW of wastewater sludge. Experiments showed that the use of an electric field combined with mechanical compression requires less than 10 and 25% of the theoretical thermal drying energy for the low and moderate voltages cases, respectively.     

Pilot scale study on the ex situ electrokinetic removal of heavy metals from municipal wastewater sludges

In order to remove toxic heavy metals from municipal wastewater sludges, the ex situ electrokinetic technique was studied at pilot scale. This study focused on the feasibility of the electrokinetic removal of heavy metals from sludge and the effectiveness of this technique on the variations of abiotic (physicochemical) and biotic (intracellular and extracellular) speciations of heavy metals using several analytical methods. Even though the sludge used was taken from a municipal wastewater treatment plant, the sludge contained relatively high concentrations of target metal contaminants (Cd = 6.8 mg/kg, Cr = 115.6 mg/kg, Cu = 338.7 mg/kg, and Pb = 62.8 mg/kg). The removal efficiencies of heavy metals were significantly dependent on their speciations in the sludge matrices. The electrokinetic removal efficiencies of abiotic heavy metals exceeded 70% for the mobile and weakly bound fractions, such as, the exchangeable and carbonate fractions and were lower than 35% for the strongly bound fractions, such as, the organic/sulfide and residual fractions. In the case of the biotic heavy metals, the removal efficiencies of the extracellular fractions were slightly higher than those of the intracellular fractions.     

污泥脱水用离心机的絮凝剂耗用量调试研究

针对中山市净水二厂污泥脱水的絮凝剂耗用量大的问题,对污泥脱水用离心机进行了调试研究。结果表明,絮凝剂型号及配制浓度、离心机出水堰板半径等均会影响絮凝剂的耗用量;该厂污泥脱水系统的最佳运行参数如下:进口7652型絮凝剂、絮凝剂投配率为35%～45%、离心机出水堰板半径为128 mm、污泥处理量为25 m3/h。将此最佳运行参数应用到实际生产中,在2010年下半年该厂共减少絮凝剂耗用量为660 kg,节省絮凝剂成本为27 732元。     

Laboratory tests of electro-osmotic consolidation combined with vacuum preloading on kaolinite using electrokinetic geosynthetics

Laboratory tests were conducted on kaolinite to investigate the effectiveness of electro-osmotic consolidation combined with vacuum preloading using electrokinetic geosynthetics (EKG). The results showed that the combined method could remove more water and induce larger surface ground settlements compared with the traditional vacuum preloading or electro-osmotic consolidation. Vacuum preloading was quite effective during the first 4?h, though the electro-osmotic consolidation took a main role in dewatering process after 9?h. The combined method could also hinder the development of cracks, induce higher negative pore water pressure and hence increase the efficiency of electro-osmotic consolidation. The results showed that deep electro-osmotic consolidation technique combined with vacuum preloading could result in significant water removal efficiency along with shorter electrode length. Furthermore, both electro-osmotic consolidation and the combined method could consolidate the soil efficiently with low energy consumption.     

Effect of polyelectrolyte conditioning on the enhanced dewatering of activated sludge by application of an electric field during the expression phase

Activated sludge is known to be poorly dewaterable due to its high surface charge density and the extreme solids compressibility, even after polyelectrolyte conditioning. The application of an electric field during pressure dewatering (PDW) of sludge can enhance the dewaterability by the electroosmosis effect. A comparative study was conducted to investigate the additional effect of an electric field, applied during the expression phase, on the dewatering course of polyelectrolyte conditioned sludge, compared to mere PDW. It was found that the application of an electric field markedly improved the dewatering kinetics for all sludge samples, regardless of the conditioning treatment. Although the conditioning polyelectrolyte characteristics and dose had a major effect on the PDW of sludge, the conditioning history did not have a significant effect on the electroosmotic water transport efficiency during the sludge expression phase. By means of on-line streaming potential measurements and fractionated filtrate electrophoretic mobility measurements, it could be demonstrated that even at high polyelectrolyte doses, leading to positively charged sludge flocs, negative surface charges were still present inside the sludge matrix. During the expression of the sludge cake, when liquid is forced to move through the floc inside pores, these negative surface charges hampered PDW, but enhanced electroosmotic dewatering. Electroosmosis is therefore an appropriate technique to remove the water fraction that is associated with these negative surface charges.     

Shear sensitivity of digested sludge: Comparison of methods and application in conditioning and dewatering

Shear sensitivity of digested sludge was evaluated by two methods: a CST shear test and a strain sweep rheological method of measuring yield stress. Sludge pretreatment by an enzyme formulation was used to alter the sludge's response to shear and, potentially, to improve dewaterability. Also varied were the polymer conditioning dose and the amount of shear applied by mixing. A bench-scale device was then used to simulate dewatering by belt press in order to assess the CST shear tests and the rheological test. CST-based shear tests showed that the optimum chemical conditioner doses with low shear levels became sub-optimal with increasing mixing times. For all three polymer conditioners, longer shear times increased the dose requirements. When the polymer dose was held constant, and the extent of mixing varied, the CST test was a poor indicator of effects on dewaterability. The benefits of enzyme treatment, apparent by actual dewatering, were not predicted by the CST results. In contrast, yield stress values were significantly correlated with cake solids values, and inversely correlated with filtrate solids. Yield stress is not adequate by itself to predict final cake solids after dewatering, because enzyme pretreatment gave higher solids concentrations when both shear extent and initial yield stress were held constant.     

Monitoring the strength properties of electrokinetically treated soil by bender elements to determine the treatment period

Bender elements have been used as a non-destructive soil investigation technique by many researchers and have proven to be effective in predicting the shear strength of various soils. In this paper, electrokinetic treatment tests were performed with embedded bender elements to monitor the increase in the shear strength of a soft sandy clay during the treatment. The bender element system, designed and assembled for this study, was integrated into the electrokinetic treatment process in order to quell a common uncertainty associated with this form of soil improvement technique, namely: when is the treatment completed? The cross-correlation and first-peak arrival times were used to measure the shear wave velocity of a clayey soil under the treatment of electrokinetics using bender elements. To determine shear wave velocity before and during treatment, a variety of shear wave tests were performed every hour of treatment using frequencies ranging from 100 Hz to 2500 Hz via the use of bender element. The results show that monitoring the soil improvement during the treatment by bender elements can shorten the treatment time by 43% and reduce the energy consumption, which is a major expenditure in an electrokinetic treatment process, by 33% while consistently improving the shear strength and the load capacity by approximately 200% and 300%, respectively.     

粉煤灰调理自来水厂排泥水污泥的比阻

自来水厂污泥直排水体会使水环境恶化,为此开展了掺调理剂改善其脱水性能的试验研究。结果表明,自来水厂污泥不宜采用混凝处理,而利用电厂粉煤灰作调理剂,可使污泥比阻大幅度下降,改善了脱水性能;细粉煤灰的最佳投量是20g/100mL,粗粉煤灰的最佳投量是30g/100mL;粉煤灰与污泥混合形成的滤饼掺入一定比例的煤炭后可做成燃料,实现了自来水厂污泥的焚烧处置。     

Experimental analysis of centrifugal dewatering process of polyelectrolyte flocculated waste activated sludge

The study experimentally investigated the centrifugal separation of moisture from activated sludge subject to cationic polyelectrolyte flocculation. An arm-suspended centrifuge was employed which allowed in-situ detection on all positions of interfaces of centrifuged sludge as functions of time. Experimental results revealed that, sludge flocculation would yield a significant sedimentation effect at the first phase of centrifugation. Therefore, not as suggested in conventional centrifugal-filtration models, the most significant moisture-removal stages included filtrate to flow through a wet cake. Moreover, an optimal rotational speed exists at which the moisture-removal rate reaches a maximum value. New theories/correlations are required to describe centrifugation dewatering of polyelectrolyte flocculated sludge.