Moisture Content Of Sludge Cake Research Articles

Response surface optimization of sludge dewatering process: synergistic enhancement by ultrasonic, chitosan and sludge-based biochar.

Due to the colloidal stability, the high compressibility and the high hydration of extracellular polymeric substances (EPS), it is difficult to efficiently dehydrate sludge. In order to enhance sludge dewatering, the process of ultrasonic (US) cracking, chitosan (CTS) re-flocculation and sludge-based biochar (SBB) skeleton adsorption of water-holding substances to regulate sludge dewaterability was proposed. Based on the response surface method, the prediction model of the specific resistance to filtration (SRF) and sludge cake moisture content (MC) was established. The US cracking time and the dosage of CTS and SBB were optimized. The results showed that the optimal parameters of the three were 5.08 s, 10.1 mg/g dry solids (DS) and 0.477 g/g DS, respectively. Meantime, the SRF and MC were 5.4125 × 1011 m/kg and 76.8123%, which significantly improved the sludge dewaterability. According to the variance analysis, it is found that the fitting degree of SRF and MC model is good, which also confirms that there is significant interaction and synergy between US, CTS and SBB, and the contribution of CTS and SBB is greater. Moreover, the process significantly improves the sludge's calorific value and makes its combustion more durable.

Analysis of the effect of using divalent and trivalent iron compounds on sludge dewatering performance in thickening units

Abstract Sludge is one of the by-products of wastewater treatment plants (WWTPs). To assist biological processes, part of the produced sludge is returned to the treatment process and the excess is removed from the treatment plant whereby it undergoes thickening and dewatering. Numerous studies have been conducted to investigate the effect of different coagulants on dewatering from sludge, but the effect of using divalent iron for this purpose has not been investigated so far. In this research, the effect of divalent and trivalent iron compounds (ferrous sulfate and ferric chloride) on the dewatering of excess sludge of the first module of the Bojnourd WWTP (Iran) has been investigated. In this regard, first, the effect of different doses of each coagulant to optimize the dewatering characteristics of sludge was investigated and then the effect of pH change by adding lime was investigated. The results showed that the addition of optimal doses of FeSO4 (0.6 and 0.4 g/l) and lime (0.664 and 1.5866 g/l) reduced the capillary suction time of sludge by 30.6 and 32.7%, respectively, while reducing the moisture content of sludge cake by 26 and 30.6%.

Self-recycling of sewage sludge as a coagulant and mechanism in sewage sludge dewatering

The properties of sewage sludge-derived biochar (BC) pyrolyzed at 300–900 °C were characterized, and which exhibited the basic properties of coagulant. When 1 g BC500 was added to 100 mL waste-activated sludge (WAS), the maximum mean settlement rate reached 8.20 mL min−1 within 10 min, and the volume of the settlement with settling time decreased to 13 mL. The capillary suction time of BC500 (12 s) was superior to those of municipal solid waste incineration (MSWI) fly ash (13.40 s), coal fly ash (14.20 s), and activated carbon (12.20 s). In addition, added BC may reduce the moisture content of sludge cake, especially for BC500. It can be that soluble cations and organic functional groups neutralize the negative charge of WAS which is helpful to shorten settling time. Meanwhile, the pore structure is beneficial for reducing moisture content of sludge cake. As results shown, BC was feasible to improve sewage sludge dewatering used as a coagulant.

Comparative study of Fenton, Fe2+/NaOCl and Fe2+/(NH4)2S2O8 on tannery sludge dewaterability, degradability of organics and leachability of chromium

In this work, a comparative analysis of Fenton, Fe2+/NaOCl and Fe2+/(NH4)2S2O8 assisted advanced oxidation processes was carried out to study its efficacy in enhancing tannery chemical sludge dewaterability. Experimental results showed that, after conditioning of sludge at optimum pH, oxidant and catalyst dosage, capillary suction time (CST) was decreased by 75 ± 5 % and moisture content of sludge cake (M.Ccake) was reduced to 74 ± 2 % for all processes at 10 min reaction time. Among the three processes, Fe2+/(NH4)2S2O8 process was noted to have larger impact on the breakdown of sludge cells, which is reflected in terms of its highest amount of total organic carbon, protein and total dissolved solids present in the separated sludge fractions. In addition, Fe2+/(NH4)2S2O8 process was also observed to leach out largest fraction say 73.3 % of chromium present in the raw sludge into the treated sludge filtrate. The investigation carried out through zeta potential and scanning electron microscopy reveals the role of a two-step mechanism, namely oxidation followed by coagulation in enhancing the sludge dewaterability. Further studies on the possibility of utilizing dried treated sludge as biomass fuel could be carried out.

Cation-exchange resin regeneration waste liquid as alternative NaCl source for enhancing anaerobic fermentation of waste activated sludge: Compositions of dissolved organic matters and chemical conditioning performance

This study reported the NaCl-enhanced anaerobic fermentation with cation-exchange resin regeneration waste liquid (CRWL) as alternative NaCl source for waste activated sludge (WAS) disposal and carbon recovery. Through 4-day CRWL-enhanced anaerobic fermentation at Na+ concentration of 0.34 mol/L, the Na+-caused sludge disintegration triggered numerous release of dissolved organic matters (DOMs), i.e. 371.6 mg/g VSS, with composition distribution: acetic acid (28.2%) > butyric acid (16.1%) ≈ valeric acid (17.8%) ≈ proteins (16.4%) > propionic acid (14.4%) > unknown (3.2%) > carbohydrates (3.9%). Satisfying chemical conditioning performance for the fermented sludge was observed at the FeCl3 dosage of 0.3 g/g DS, attributing to the roles of double-layer compression and electric neutralization. The capillary suction time (CST) and sludge cake moisture content were decreased to 60.3 s and 75.1%, against those of 607 s and 93.5% before conditioning, respectively. Such “treating waste by waste” strategy could provide numerous environmental and economic benefits.

Meso-mechanism of mechanical dewatering of municipal sludge based on low-field nuclear magnetic resonance

Both huge volume and high moisture content of municipal sludge have brought great troubles and attracted extensive concerns in the world. In this paper, the mechanical press filtration (MPF) dewatering was performed under ultrahigh pressure in order to improve the dewatering performance of municipal sludge. Low-Field Nuclear Magnetic Resonance (NMR) technique was used to study the effect of MPF parameters on dewatering performance. Based on the pore characteristics of municipal sludge, a capillary bundle model was developed to explore the mesoscopic mechanisms of MPF dewatering. The results indicate that moisture content of sludge cake decreases gradually with the increase of compressed pressure and dewatering time as well as the decrease of sludge weight , and the moisture content of municipal sludge can be reduced to as low as 30% with MPF dewatering. According to the peak and envelope area of relaxation time curve in NMR, it can be found that the size of pores decreases and the percentage of small pores increases during the dewatering process. Therefore, the capillary water cannot be removed by MPF method because the capillary pressure in very small pores increases evidently. Furthermore, the compaction degree of the outmost layer is generally higher than that of the middle layer, and the difference of moisture content between the middle and outmost layers of cake is 25%–28.4%. The present work may be helpful to understand the MPF dewatering mechanism and shed light on the new dewatering techniques of municipal sludge.

Study on the effect of chitosan conditioning on sludge dewatering.

The difficulty of residual sludge dehydration is the major problem in sewage treatment. The reduction of moisture content in sludge can reduce the sludge volume significantly and is conducive to the subsequent disposal of sludge. As an organic polymer flocculant, chitosan (CTS) is widely used in water and waste water treatment. In this study, CTS was used in sludge treatment to improve the sedimentation and dehydration properties of sludge. When treated with CTS, the moisture content of sludge cake decreased from 85.9% to 83.0%, the SV30 decreased to about 1/2, and the sludge volume reduced to 82.9%. Further analysis showed that the zeta potential (ζ-potential) of the sludge changed from negative value to positive value, and the D50 of the sludge was larger than that of the raw sludge. In addition, when the moisture content of the sludge cake was reduced to the lowest, the concentration of extracellular polymeric substances (EPS) and SCOD was the largest and the |ζ| decreased to the lowest. CTS improved the dehydration and sedimentation performance of sludge mainly by factors of electrical neutralization, adsorption bridging and dissolution of EPS.

Effects of Moringa Peregrina and Ferric Chloride (FeClƒ ) On Water Treatment Sludge Dewatering

In the present study, an active component of Moringa peregrine (MP) was used in comparison with ferric chloride (FeCl₃) for the conditioning of water treatment sludge. The comparison was based on dewatering characteristics of the conditioned sludge determined by capillary suction time (CST), specific resistance to filtration (SRF), tests of time of filtration (TTF) and sludge cake moisture content. The results indicated that MP showed relatively comparable conditioning effect as ferric chloride. Sludge conditioned with ferric chloride, showed better results than MP. According to CST, SRF and tests of time of filtration (TTF) and sludge cake moisture content results, optimum dose for MP, and ferric chloride was 100 ml/l. From the results of the study it could be concluded that MP alone could be effectively used and replace ferric chloride for dewatering of water treatment sludge.

Combined sludge conditioning with NaCl-cationic polyacrylamide-rice husk powders to improve sludge dewaterability

Strong water binding ability of extracellular polymeric substances (EPS) and high compressibility of sludge during compression dewatering have greatly hindered the improvement of sludge dewaterability. In this paper, a novel combined conditioning method was proposed to enhance the sludge dewaterability. The sludge was firstly disintegrated by NaCl, then the sludge particles were re-flocculated by cationic polyacrylamide (CPAM), meanwhile the sludge filter cake was modified with rice husk (RH) as filter aid. The results showed that combined NaCl-CPAM-RH conditioning greatly improved the sludge dewaterability compared with that of raw sludge. The optimal NaCl pretreatment lasted 120 min with a dosage of 0.25 mol/L, the optimal CPAM and RH dosage was 30 mg/L and 50 wt%, respectively, which led to a moisture content of sludge cake of 65.44%. The changes of sludge liquid and solid phase conditioned by NaCl-CPAM-RH were analyzed. The NaCl pretreatment disintegrated the sludge floc structure with the release of protein and polysaccharide from EPS and Ca2+ and Mg2+ from sludge flocs to liquid, accompanying with the release of water trapped in sludge matrix. The addition of CPAM and RH reconstructed the sludge flocs with a big mean diameter d(0.5) of 126.84 μm, and the sludge filter cake showed a porous and rigid structure with a porosity increment of 138.62% and a compressibility reduction of 39.62% compared to that of raw sludge.

Feasibility of sludge deep-dewatering with sawdust conditioning for incineration disposal without energy input

Sludge deep-dewatering could be realized by adding inorganic and chemical conditioners. However, once for the purpose of incineration disposal, the uses of inorganic and chemical conditioners would not only bring about incomplete combustion, equipment corrosion and secondary pollution, but also greatly reduce the heat value of sludge cake. Therefore, the feasibility of sludge deep-dewatering with sawdust conditioning was investigated for incineration disposal without energy input. Firstly, the performance and mechanism of sludge deep-dewatering were studied when conventional conditioners, lime and polyacrylamide, were substituted by sawdust. Then, the superiorities of sawdust conditioning in sludge cake air drying and calorific value increase, as well as economic efficiency were analyzed by comparing with lime conditioning. Results indicate the moisture content of sludge cake can be greatly reduced by sawdust conditioning, which could decrease sludge compressibility, reduce bound water content, improve the porosity of sludge cake, but scarcely influence sludge particle size. Moreover, sawdust conditioning presented high efficiency in further dewatering of sludge cake during natural air drying. The moisture content of sludge cake conditioned with sawdust could decrease to 31.6% after 36h air drying and its calorific value reached as high as 2239kcal/kg. By comparing with lime conditioning, sawdust conditioning exhibited slightly higher expense for the conditioner, but much greater profit from energy recovery.

Enhanced dewatering of excess activated sludge through decomposing its extracellular polymeric substances by a Fe@Fe2O3-based composite conditioner

Efficient sludge dewatering methods are highly desired by municipal wastewater treatment plants. In this study, Fe@Fe2O3 nanomaterial, combined with polydiallyldimethylammonium chloride (PDMDAAC) and H2SO4, was used for sludge dewatering. This composite conditioner exhibited an excellent dewatering capability. By using uniform design, the optimized dosages of Fe@Fe2O3, H2SO4 and PDMDAAC were determined to be 40, 136 and 4.8mg/gDS (dry solids), respectively. The moisture content of sludge cake decreased from 78.1% to 64.8%, and the capillary suction time from 56 to 21s. The sludge extracellular polymeric substances (EPS) were decomposed, resulting in greater conversion of the bound water into free water and the release of free water. The electron spin resonance results show that the molecular oxygen activation process induced by Fe@Fe2O3 produced hydroxyl radicals, which were mainly responsible for the EPS decomposition. In this way, an efficient composite conditioner for enhancing sludge dewatering was developed.

Possibility of sludge conditioning and dewatering with rice husk biochar modified by ferric chloride

Rice husk biochar modified by FeCl3 (MRB–Fe) was used to enhance sludge dewaterability in this study. MRB–Fe preparation conditions and dosage were optimized. Mechanisms of MRB–Fe improving sludge dewaterability were investigated. The optimal modification conditions were: FeCl3 concentration, 3mol/L; ultrasound time, 1h. The optimal MRB–Fe dosage was 60% DS. Compared with raw sludge, the sludge specific resistance to filtration (SRF) decreased by 97.9%, the moisture content of sludge cake decreased from 96.7% to 77.9% for 6min dewatering through vacuum filtration under 0.03MPa, the SV30% decreased from 96% to 60%, and the net sludge solids yield (YN) increased by 28 times. Positive charge from iron species on MRB–Fe surface counteracted negative charge of sludge flocs to promote sludge settleability and dewaterability. Meanwhile, MRB–Fe kept a certain skeleton structure in sludge cake, making the moisture pass through easily. Using MRB–Fe, therefore, for sludge conditioning and dewatering is promising.

A Fenton-like process for the enhanced activated sludge dewatering

The presence of high moisture content in sewage sludge aggravates the disposal costs and restricts its application. Sewage sludge is traditionally conditioned by dosing organic/inorganic chemicals. However, after the treatment, the moisture content and inorganic solid mass remain to be a high level. In this work, a Fenton-like dewatering process, i.e., a combination of sulfuric acid, hydrogen peroxide and ferric sulfate, was developed. Uniform design was used to optimize the composite conditions, and the effects of Fenton-like treatment on sludge dewatering were examined. The results show that, after the treatment of the Fenton-like reaction, the moisture content of sludge cake and the dry solid mass decreased from 80.0% to 66.1% and from 12.9 to 10.6g/L, respectively. The mechanism for the enhanced dewatering performance was explored, and the degradation of abundant extracellular polymeric substances, the lysis of the sludge cells, and the release of bound water and typical metals within the sludge flocs were found to be mainly responsible for the enhanced dewatering performance. In addition, a surface thermodynamic analysis with the extended DLVO theory shows that the higher hydrophobicity and the less stable sludge flocs also contributed to the decrease in moisture content. Our results confirm that such a Fenton-like treatment exhibited excellent performance in enhancing sludge dewatering and metal leaching and is a promising pretreatment approach for sludge disposal.

Mechanism and Application Prospects of Sewage Sludge Conditioning with Fly-Ash

The effects of fly-ash on dewatering of sewage sludge were studied according to sludge specific resistance (SSR), dehydrated speed, and moisture content of sludge cake as investigation indexes through single-factor experiments by contrasting to cationic polyacrylamide (PAM). The results showed that SSR kept decreasing with the rising of fly-ash dosage. When the dosage of fly-ash was 0.02 g/(ml sludge), SSR reduced by 65.2%. When the dosage of fly-ash was over 0.03 g/(ml sludge) adding with PAM, the dehydrated speed will be increased by three fourths. Through the analyses of Zeta potential, scanning electron microscope (SEM) observation, combined with the dehydration experiments, it was thought that the mechanism of fly-ash on dewatering of sewage sludge was that their particles evenly dispersed in sludge floc skeleton structure and thus decreased the SSR and improved the permeability of the sludge cake. The disposal of dewatering sludge and recycling approaches after fly-ash condition were also discussed. They can be used as landfill or as raw materials in building fields.

Relationship between the Characteristics of Cationic Polyacrylamide and Sewage Sludge Dewatering Performance in a Full-Scale Plant

To identify the key characteristics of cationic polyacrylamide (c-PAM) for evaluating sewage sludge dewatering performance, we examined the properties of 13 types of c-PAMs that come from different manufacturers via a laboratory assay. The sludge dewatering performance was determined through a full-scale test at a large wastewater treatment plant in Beijing. We checked the cationic degree, solution viscosity, dissolution time, and 1 mm sieve residue of c-PAM. The 1 mm sieve residue was found to affect the dissolution time, solution viscosity, and conductivity. The full-scale test indicated that the cationic degree is the most important factor that affects the dosage and treatment capacity of the belt filter press when the cationic degree ranges from 25% to 45%. However, the moisture content of sludge cake is mainly relevant to raw sludge organic content. The sludge dewatering performance of the 13 types of c-PAMs showed that the c-PAM should be selected based on cationic degree, solution viscosity, and 1 mm sieve residue. The dosage should then be adjusted at the appropriate time according to the status of the equipment and facilities during sludge dewatering.