Specific Resistance To Filtration Research Articles

Influence of Sludge Initial pH on Bioleaching of Excess Sludge to Improve Dewatering Performance

pH has an important effect on the physiological activity of eosinophilic microorganisms. Therefore, this study used excess sludge produced by the mixed treatment of leachate and municipal sewage to explore the impact of different sludge initial pH on microbial biochemical reactions associated with the performance of excess sludge dehydration. Shake-flask tests were performed using inoculated microorganisms and fresh excess sludge in 500 mL Erlenmeyer flasks at a ratio of 1:4, with the addition of 2 g/L S0 and 6 g/L FeS2 as energy sources. Erlenmeyer flasks were shaken for 72 h at 180 rpm and 28 °C, in a reciprocating constant homeothermic oscillating water-bath. Results show that the specific resistance to filtration (SRF) of the bioleached excess sludge decreased from (1.45~6.68) × 1012 m/kg to (1.21~14.30) × 1011 m/kg and the sedimentation rate increased from 69.00~73.00% to 81.70~85.50%. The SRF decreased from 1.45 × 1012 m/kg to 1.21 × 1011 m/kg and the sedimentation rate increased from 69.00% to 85.00%, which both reached the highest level when the initial pH of the excess sludge was 5 and the bioleaching duration was 48 h. At this time, the rates of pH reduction and oxidative redox potential (ORP) reached the highest values (69.67% and 515 mV, respectively). Illumina HiSeq PE250 sequencing results show that the dominate microbial community members were Thiomonas (relative abundance 4.59~5.44%), which oxidize sulfur and ferrous iron, and Halothiobacillus (2.56~3.41%), which oxidizes sulfur. Thus, the acidic environment can promote microbial acidification and oxidation, which can help sludge dewatering. The presence of dominant sulfur oxidation bacteria is the essential reason for the deep dehydration of the bioleached sludge.

Evaluation of the combined effect of sodium persulfate and thermal hydrolysis on sludge dewatering performance.

This innovative study makes use of a thermal hydrolysis process (THP) and the conditioner sodium persulfate (SPS) to improve the dewaterability of sewage sludge. The best-operating conditions were optimized using response surface methodology (RSM): 100mg/g of dry solids (DS) of SPS, 101min of reaction time of THP, and a temperature of 200°C. Distribution of extracellular polymeric substances (EPS), zeta potential, bound water, and solid characters were analyzed to reveal the mechanisms involved in the dewatering process. These results indicate that the sewage sludge after treatment (SPS combined with THP) had a superior dewaterability. The specific resistance to filtration (SRF) under the best conditions was 0.51 × 1011m/kg, decreasing by 91.65% compared to the raw sludge (RS) (6.11 × 1011m/kg). This mechanism could be explained as follows: (1) Aromaticity and hydrophobicity of sludge cake after SPS + THP treatment was increased; (2) sludge flocs were re-flocculated by charge neutralization, giving rise to a loose and porous structure; (3) the structure of extracellular polymeric substances and cells was destroyed, and the bound water was released. Overall, the conditioning by combination of SPS and THP is an effective mean to improve sewage sludge dewaterability. Graphical abstract.

Temperature-induced modification of the dewatering behaviour of Ferri-Oxyhydroxide precipitates formed from low tenor solutions

Mining activities generate Acid Mine Drainage (AMD) and wastewater streams rich in dissolved inorganic species that negatively affect water quality. Conventional lime treatment of AMD leads to the precipitation of a voluminous sludge, comprising mainly of Ferri-Oxyhydroxide (Fe-O-OH) and gypsum, whose matrix renders it difficult to dewater. Such precipitates also show poor post-precipitation stability, and they are disposed of to landfills where metal remobilization can occur over time. This paper proposes that temperature assisted structural maturation of primary precipitates results in aged precipitates with improved dewatering behaviour (in terms of settleability, specific resistance to filtration (SRF) and filterability). A precipitate produced from the neutralization of aqueous acidic Fe2(SO4)3 (ferric concentration of 100, 300 and 800 mg/L) by sub-stoichiometric Ca(OH)2 solutions at room temperature was continuously matured in a holding mixed tank reactor kept at 30, 40 and 50 °C. The aged precipitates were analysed for particle size distribution, number of particles formed, mass moment and surface area moment mean particle size, crystal habit, morphology and zeta (ζ)-potential. The results demonstrate that(i)at [Fe(III)] = 100 mg/L, discernible spherical agglomerated Fe-O-OH particles are formed, whose surface area moment mean size and filtration rate attain a maximum at 40 °C, beyond which the particles experienced re-dissolution leading to size reduction. These particles exhibited poor settleability at all ageing temperatures, implying that continuous ageing had no noticeable effect on settling;(ii)at [Fe(III)] = 300 mg/L, a transition zone exists where there is maximum settleability of 2.7 ± 0.2 mm/min at 40 °C, a near neutral surface charge (ζ-potential = +1.1 mV) that favours agglomeration, the largest mean particle sizes (D4,3 = 26.27 μm, D3,2 = 17.0 μm) but a crystal habit that hindered filterability. This [Fe(III)] and ageing temperature (40 °C) showed potential for enhanced dewatering behaviour, should the ageing time be increased;(iii)at [Fe(III)] = 800 mg/L, formation of small densely packed spherulites whose degree of interlocking and interconnected layers decreased whilst the particle size increased with temperature leading to improved filterability.Based on these results, the operational implications for lime neutralization plants are that there is a temperature and [Fe(III)] trade-off at which higher throughput of sludge with improved settling characteristic is realized. However, additional ageing time is required in order for the structural maturation to effect changes in particle size, packing and morphology that yield increases in the filtration rates – as was shown by the [Fe(III)] of 300 mg/L at 40 °C.

Improving primary sludge dewaterability by oxidative conditioning process with ferrous ion-activated peroxymonosulfate

Enhancement of sludge dewaterability is key for sludge management and disposal of wastewater treatment plants (WWTP). In this study, the Fe2+-peroxymonosulfate (PMS) conditioning approach was first used to oxidize the primary sludge from the primary sedimentation tank of a full scale WWTP. The combination of Fe2+ (0.05–0.5 g/g TSS) and PMS (0.05–0.5 g/g TSS) could significantly improve the dewaterability of primary sludge. The optimal addition amount of Fe2+ and PMS was 0.1 g/g TSS and 0.25 g/g TSS, respectively, under which the capillary suction time (CST) and specific resistance to filtration (SRF) of the sludge was reduced by 79% and 95%. The physicochemical properties (particle size, zeta potential, EPS composition) of the primary sludge before and after oxidative conditioning were measured. Results showed that sulfate radicals generated from Fe2+-PMS system effectively reduced organic matter in different EPS fractions, further destroying sludge floc cells. Then the bound water in the sludge flocs was released, thereby improving the sludge dewaterability. The microscopic morphology also indicated that the sludge flocs have a blocky structure with tight texture before conditioning. After conditioning, the sludge flocs become smaller, and many irregular pores are formed on the surface, which facilitates the passage of internal moisture. Economic analysis showed that Fe2++PMS conditioning is more economical than the traditional Fenton method.

Improvement of sludge dewaterability by ammonium sulfate and the potential reuse of sludge as nitrogen fertilizer

A novel method to enhance sludge dewaterability with ammonium sulfate ((NH4)2SO4) was proposed, and the potential reuse of dewatered sludge cake and filtrate as nitrogen fertilizers was evaluated. Compared with raw sludge, 87.91% reduction of capillary suction time (CST) and 88.02% reduction of specific resistance to filtration (SRF) after adding 80% (m/m) (NH4)2SO4 were achieved, with 38.49% of protein precipitated simultaneously. The (NH4)2SO4 dose destroyed cell membrane, resulting in the release of intracellular water by converting bound water into free water, thus enhancing sludge dewaterability. In the solid phase, the content of protein-N increased, and larger protein aggregates were formed. The (NH4)2SO4 dose destroyed the hydration shell, making proteins to exhibit hydrophobic interactions, and to be aggregated, and precipitated from the liquid phase. When incubated Pennisetum alopecuroides L. with the dewatered sludge cake and filtrate after dewatering and conditioning with (NH4)2SO4, the germination rate of grass seed and shoot lengths both increased while compared with those incubated with dewatered sludge cake and filtrate of the raw sludge. This study might provide insights into sustainable sludge treatment by integrating sludge dewatering and the potential reuse of dewatered sludge cake and filtrate as nitrogen fertilizer via treatment with (NH4)2SO4.

Optimisation for enhancing sludge dewaterability using different conditioners

Dewatering of alum sludge from drinking-water plants is proving to be a major challenge because of the large amounts of residual sludges produced annually. In the last few years, most studies have focused on improving the dewatering process to reduce costs of alum sludge management and transport. In the present study, three different types of conditioners were tested. Lime was used as an example of an inorganic conditioner, ferric chloride (FeCl3) was used as an example of a chemical conditioner and chitosan was used as an example of a biopolymer. The performance of a conditioner was evaluated with respect to its effect in reducing the resistance of the conditioned sludge to filtration, namely the specific resistance to filtration (SRF). Tests are run using different concentrations of the conditioners, different speeds of rotation and different pH values to investigate the maximum value of percentage reduction in SRF. The response surface methodology was chosen from the Design-Expert program (version 12), and the Box–Behnken design was employed to find factor settings that optimise the output response – that was, percentage reduction in SRF (Red. %). The model obtained proved to be significant enough but with varying degrees. Chitosan showed to be the most favourable conditioner with a maximum percentage reduction in SRF of 98.57%. This was followed by ferric chloride, which gave a value of 89.2% for percentage reduction in SRF, and lastly came lime with a percentage reduction of 79.81%. Besides, a lower concentration of the conditioner and a lower speed of rotation are required when using chitosan as a conditioner.

Integration of electrochemical and calcium hypochlorite oxidation for simultaneous sludge deep dewatering, stabilization and phosphorus fixation

A hybrid electrochemical process with Ca(ClO)2 addition for simultaneous sludge dewaterability, stabilization and phosphorus fixation was proposed. Under optimal conditions (150 mg/g VS Ca(ClO)2, 15 V), the capillary suction time (CST) and specific resistance to filtration (SRF) were decreased by 88% and 92%, respectively. Efficient sludge stabilization with E. coli colonies of less than 1000 MPN/g TS was achieved. Phosphorus of 99% was removed from the filtrate and successfully fixed in the sludge cake and on the electrode surface. The integration of electrochemical and hypochlorite oxidation could effectively degrade the tightly bound extracellular polymeric substances (TB-EPS) structure with a total organic carbon (TOC) reduction of 52%. Besides, the disintegration of microbial cell envelopes was also achieved, with a reduction of living cell fraction of 98%. Furthermore, system pH could be maintained at near neutral (7.45) and the conversion of Fe(II) to Fe(III) was also facilitated with the addition of Ca(ClO)2, resulting in improved electrocoagulation process for enhanced sludge dewatering and phosphorus fixation. The multifunctional effects were achieved with the cooperated extracellular electrooxidation for EPS destruction and the active chlorine for intracellular microbial cell disintegration. This research provides a promising strategy for integrated sludge treatment and recycling for possible land utilization.

Investigation on the variations of sludge water holding capacity of electro-dewatering process

Since the effect of electro-dewatering (EDW) on sludge water holding capacity was unknown, tests were conducted in this study to investigate the water holding capacity of EDW sludge and the potential mechanism related to the sludge physicochemical characteristics, EPS properties and sludge structure. Sludge was dewatered to the average moisture content (AMC) of 80%, 70% and 60% with different applied voltages at 20, 30 and 40V in EDW, respectively. Then the dewatered sludge near the anode and cathode were rewatered. The variation of sludge water holding capacity in EDW process was evaluated in terms of filterability and saturated moisture content (SMC), and the filterability was assessed by the specific resistance to filtration (SRF) of rewatered sludge. The results indicated that SRF of rewatered sludge near the cathode increased greatly. The proteins/polysaccharides (PN/PS) of loosely bound extracellular polymeric substances (LB-EPS) was significantly positively correlated with SRF (r = 0.891, p < 0.01). Moreover, the exposure of hydrophobic sites or groups in PN near the cathode improved the surface hydrophobicity of sludge, which reduced the filterability. In addition, higher voltage could destroy the sludge structure near the anode at the later stage of EDW process, leading to the decrease of SRF and SMC. These results expanded the knowledge about changes in sludge properties and water holding capacity during EDW process.

Impact of persulphate mixed with paper sludge on activated sludge dewaterability

AbstractFeSO4 was used to activate K2S2O8 mixed with paper sludge to condition activated sludge, and its effect on sludge dewaterability was investigated. Interaction effects of various parameters on sludge dewaterability were investigated and analysed by considering the moisture content of cake, specific resistance to filtration (SRF) and capillary suction time (CST) as indicators and the Box–Behnken design of response surface methodology (RSM). Results indicated that the moisture content of cake, SRF and CST decreased from 74.52 to 69.57%, 25.39 × 1012 to 11.80 × 1012 m/kg and 199.8 to 146.4 s, respectively, under optimal conditions. RSM results presented that only 0.13% of the response values cannot be interpreted with this model, and the three‐factor interaction was observed to be significant. Additionally, sludge dewaterability mechanism observed that K2S2O8 mixed with paper sludge used the strong oxidising properties of SO4−• to crack sludge flocs. Fine fibres and calcium carbonate in the paper sludge played important roles as the skeleton support in the sludge filtration process, and the internal moisture was rapidly eliminated.

The influence of different sludge concentrations on its dewaterability during bioleaching.

Bioleaching, a technologically and economically feasible technology, is considered as the high efficiency method to improve dewaterability in sewage sludge. The objective of this study was to investigate the effect of different sludge concentrations on bioleaching dewaterability and understand the mechanism of the effect of bioleaching on sludge dewaterability. Variation in pH, oxidation-reduction potential (ORP), capillary suction time (CST), specific resistance to filtration (SRF) and different fractions of extracellular polymeric substances (EPS) including slime EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS) were determined. Different sludge concentrations (5, 10, 15, 20 and 30 g·L-1) were selected to investigate during bioleaching. Results indicated that sludge buffering capacity significantly inhibited bioleaching efficiency as sludge concentrations increased. Optimum enhancements in sludge dewaterability were observed during the 10 g·L-1 sludge concentration treatment, and reached a maximum when the pH was 2.11. The variation of different fractions of EPS revealed that the ratio of S-EPS/TB-EPS significantly affected sludge dewaterability. Principal component analysis and Pearson's correlation analysis both provided evidence that the higher TB-EPS followed by a very large reduction was positively correlated with sludge dewaterability. However, the increase of protein and DNA in S-EPS content was negatively correlated with sludge dewaterability.

Enhanced sludge dewaterability with sludge-derived biochar activating hydrogen peroxide: Synergism of Fe and Al elements in biochar

Reuse of sludge-derived Fe-rich biochar as sludge conditioner is an attractive route for management of waste activated sludge at source. Homogeneous and heterogeneous Fenton reactions have been proved in sludge conditioning with Fe-rich biochar activating H2O2 to enhance sludge dewaterability. The FeAl2O4 phase in Fe-rich biochar was first identified during pyrolysis of sewage sludge after adding both Fe2O3 and Al2O3, since Fe and Al elements are two of major metal elements in Fe-rich sludge. Compared with the Fe-rich biochar that did not comprise FeAl2O4 phase, the capillary suction time (CST) and specific resistance to filterability (SRF) of the sludge conditioned with the Fe-rich biochar comprising FeAl2O4 phase could be efficiently decreased by 23% and 44%, respectively. The results indicated that FeAl2O4 phase in Fe-rich biochar could improve sludge dewaterability by enhancing heterogeneous Fenton reaction. Synergistic effect between Fe and Al in FeAl2O4 contributed to weak the O–O bond in H2O2 and reduce the activation energy of H2O2 decomposition for enhancing ·OH generation, which could be explained by density functional theory (DFT) calculations for the first time. Thus, the decomposition rate of H2O2 and the amount of ·OH generation were obviously promoted by FeAl2O4 phase in sludge-derived biochar during sludge conditioning, attributing to the destruction of sludge flocs, the release of bound water, and the improvement of sludge dewaterability.

Synthesis of Hydrophobic Cationic Polymeric Flocculants by the Introduction of a Hydrophobic Monomer, Cationic Monomer and the Application in Sludge Dewatering

Dewatering pre-treatment, chemical conditions for sludge are practical approaches to advance the performance of sludge-dewatering, hence lessen the cost of sludge transportation and treatment. Cationic polymeric flocculants are used as chemical regulators because of their excellent performance and economic advantages. Current research focused on synthesizing flocculants Polyacrylamide, methacrylamido propyl trimethyl ammonium chloride, Lauryl acrylate, and Poly Acrylamide, methacrylamido propyl trimethyl ammonium chloride (PAT). The synthesis was achieved by ultraviolet initiated (UV-initiated)-induced polymerization technique. The chemical composition of the samples was investigated using Fourier transform infrared (FTIR) spectroscopy and hydrogen nuclear magnetic resonance (1H NMR). This study also evaluated the thermal stability of PATL and PAT by using thermogravimetric/differential scanning calorimetry (TGA). Moreover, the results of scanning electron microscopy (SEM) confirmed the strong floc structure has the ability to form porous and channel construction, making the filter cake a constructive drainage way. It is able to be used for water release and therefore helps to improve dehydration capacity. The hydrophobic flocculants properties in water were investigated by initiator concentration, initiation time and urea concentration. The experimental results confirmed that the optimal values for preparation of PATL were composed of initiator concentration of 0.4 wt.‰, urea level of 1.2 wt.‰; molar ratio of MPTAC to AM (5:95), irradiation time of 60 min and flocculants intrinsic viscosity of 1350 mL/g. Furthermore, it was found that PATL had stronger hydrophobic collaboration with satisfactory water solubility and also improved the dewatering performance. Sludge dewatering experiments confirmed that filter cake moisture content (FCMC) and specific resistance to filtration (SRF) for PATL flocculants reached to 65% and 6 × 1012 m/kg, respectively at the optimal dosage of dry solids about 30 mg · L–1 of sludge, exhibiting better performance than the conventional cationic flocculants (PAT).

A comparative study of waste activated sludge conditioning with Fe(II)-peroxymonosulfate oxidative process

Improving sludge dewaterability is a key step of waste sludge recycling. The effect and mechanisms on two kinds of waste activated sludge (WAS) with Fe(II)-peroxymonosulfate (PMS) oxidation were compared. For WAS-A, the optimum capillary suction time (CST) and specific resistance to filtration (SRF) reduction rates were achieved (56.5% and 89.3%, respectively) with PMS 0.1 g/g TSS and Fe(II) 0.05 g/g TSS. For WAS-B, the optimal results were PMS 0.1 g/g TSS and Fe(II) 0.1 g/g TSS, and the reduction in CST and SRF was 64.6% and 90.1%, respectively. After conditioning, the particle size decreased slightly while the zeta potential increased dramatically. The proteins and polysaccharides analysis indicated the destruction in extracellular polymeric substances (EPS) and microbial cells resulted from the sulfate radicals. Microtopography showed that the original structure was changed with irregular pores formed on the surface, thus facilitating the passage of internal water and further improving the sludge dewaterability.

Membran Biyoreaktör ve Dinamik Membran Biyoreaktör Performansının Aynı Koşullarda Kıyaslanması

This study aims comparative evaluation of two different membrane modules, 0.45 µm and non-woven dynamic membrane, in AeMBR for synthetic wastewater treatment. Filtration performances of both membrane materials were compared under same operational conditions. Throughout the filtration process, 99% and 95% COD removal efficiencies were achieved relying upon 0.45 µm and non-woven dynamic membrane, respectively. AeMBR was successfully operated at 10 LMH and no chemical cleaning was employed for 30 days. It was perfectly operated up to 15 LMH and then 20 LMH. The turbidity and trans-membrane pressure (TMP) of 0.45 µm was usually higher at the begging compared with the dynamic membrane despite membrane clogging rates were comparable. Capillary suction time (CST), soluble microbial product (SMP), extracellular polymeric substances (EPS), specific resistance to filterability (SRF), attenuated total reflectance fourier transformed-infrared spectroscopy (ATR FT-IR) and denaturing gradient gel electrophoresis (DGGE) analyzes were performed to understand the characterization of the cake deposited on membranes. 16S rDNA region shown significant result in terms of air/ambient temperature change. For both membrane modules, offline chemical cleaning employment with NaOCl and sulfuric acid, respectively, almost completely eliminated foulants and it was found that chemically washed membranes showed pressure close to that of the new membrane.

Alum sludge conditioning with ferrous iron/peroxymonosulfate oxidation: Characterization and mechanism

Alum sludge produced by drinking water plants needs to be conditioned and dewatered before final disposal. In this study, a novel ferrous iron/peroxymonosulfate (PMS) oxidation process was employed to enhance alum sludge dewaterability The effect of oxidative sulfate radicals generated by Fe2+ activated HSO5− on alum sludge was studied. The results showed that the optimal conditioning conditions for addition of Fe2+ and PMS were 0.5 g/g and 0.1 g/g TSS, respectively. Meanwhile, the capillary suction time (CST) and specific resistance to filtration (SRF) of alum sludge was reduced by 66% and 88%. Also found was that the absolute value of the zeta potential increased and the particle size decreased in alum sludge after Fe2+-PMS conditioning, which indicated that oxidative sulfate radicals destroyed the floc structure of alum sludge and smaller particles were generated. At the same time, the water contained in sludge flocs was released and enhanced sludge dewaterability, while leaching of aluminum ions also characterized decomposition of alum sludge.

Insight into conditioning landfill sludge with ferric chloride and a Fenton reagent: Effects on the consolidation properties and advanced dewatering

The landfill sludge in storage reservoirs needs to be dewatered and disposed of for environmental and engineering purposes. The key factors are the high organic matter content and low permeability. Chemical conditioning is considered an efficient method for adjusting the properties of sludge. In this paper, two typical chemical agents, FeCl3 and a Fenton reagent with different additive amounts, are studied and compared for dewatering and consolidation purposes. Compression experiments and consolidation experiments are compared, and the coefficient of compressibility and compression index are obtained and compared. Then, the sludge permeability, grain size distribution variations, specific resistance to filtration (SRF) and morphology observations are considered to analyse the treatment mechanism. The results indicate that the properties of landfill sludge will change as the curing time increases. FeCl3 and Fenton are both effective in improving the consolidation and permeability properties of sludge. For the conditioning process, the optimum FeCl3 content is 20%, and the process is dominated by coagulation if FeCl3 is less than 20%; otherwise, it is dominated by hydrolysis. For the Fenton reagent, the optimum Fe2+ content and H2O2 content are 4% and 12%, respectively. The depolymerization effect of the Fenton reagent leads to the oxidation and recombination of the polar group on extracellular polymeric substances (EPSs). The results can be used to explain the conditioning mechanism of the effective agents of FeCl3 and Fenton and compare the corresponding consolidation properties. The consolidation characteristics provide a reference for further application of vacuum preloading in the sludge disposal process.

A combined ultrasonic and chemical conditioning process for upgrading the sludge dewaterability

ABSTRACT Dewatering is of paramount step in sludge management, and conditioning with coagulant is considered as the commonest way to improve the sludge dewaterability. Sludge disintegration process was examined through Ultrasound (US) to strip the water from the sludge flocs and accordingly four coagulants: aluminium sulphate (Alum), iron (III) chloride (FeCl3), cationic polyacrylamide (CPAM) and combined ferric chloride and lime (CC) with optimum dosages were employed to improve the sludge dewaterability in terms of capillary suction time (CST), specific resistance to filtration (SRF) and moisture content (MC). The ultrasonic sludge disintegration with 1 min exposure with an energy dosage of 700 kJ/kg TS realises the best sludge dewatering efficiency. In addition, the effects of CPAM and CC conditioning on sludge dewaterability were higher compared with two other conditioners. The combined US-CPAM and US-CC with optimum dosages 8 and 101 mg/kg DS significantly improved sludge dewaterability parameters (MC: 68.50%, SRF: 1.03 × 1010 m/kg and CST: 31.82 s) and (MC: 72%, SRF: 1.08 × 1010 m/kg and CST: 31.82 s) compared with when conditioning experiments were performed alone. Scanning electron microscopy (SEM) images showed that the combined US-CPAM and US-CC conditioning formed a more porous structure and low compressible sludge filter cake which are desired to sludge dewatering. Therefore, the ultrasonic-assisted conditioning with CPAM and combined coagulant (lime + Ferric chloride) could significantly improve the sludge dewaterability indices.

Profiling of amino acids and their interactions with proteinaceous compounds for sewage sludge dewatering by Fenton oxidation treatment

During advanced oxidation treatment for enhancing sludge dewaterability, the peptide chains of protein can be decomposed into amino acids. Protein exhibits a great impact on sewage sludge dewaterability. However, the role of amino acids in sludge dewatering remains unclear. In this study, among the 23 types of amino acids investigated, tryptophane (Trp) and lysine (Lys) were identified as the key amino acids affecting sludge dewaterability during Fenton oxidation treatment. The content of lysine showed positive correlations with capillary suction time (CST), specific resistance to filtration (SRF), and bound water content, and the concentrations of total protein, low molecular weight protein, amines and amides, and 3-turn helix of proteinaceous compounds in bound extracellular polymeric substances (EPS), while the content of tryptophane showed negative correlations with the above parameters. The amino acids may be sourced from damage of the membrane and ribosomal proteins by hydroxyl radicals, and the peptide bonds connected with tryptophane were more inclined to be decomposed than other amino acids. Particularly, more amino acids of tryptophane can result in more hydrophobic interaction, and less necessary energy barrier for aggregation of particles. As such, regulating protein degradation towards production of tryptophane may be related with enhanced sludge dewaterability by Fenton oxidation treatment.

Integrating alum sludge with waste-activated sludge in co-conditioning and dewatering: a case study of a city in south France.

The unique geographical location of waterworks and wastewater treatment plant (WWTP) in Graulhet (France) profited the environmental resource integration and "Circular Economy." Alum sludge from a local waterworks was introduced to co-conditioning and dewatering with waste-activated sludge from a nearby WWTP to examine the role of the alum sludge in improving the dewaterability of the mixed sludge. Experiments demonstrated that the optimal mixing ratio was 1:1 (waste-activated sludge/alum sludge, v/v). Alum sludge has been shown to beneficially enhance mixed sludge dewaterability, by decreasing both the specific resistance to filtration (SRF) and the capillary suction time (CST). Moreover, the optimal polymer (Sueprfloc-492HMW) dose for the mixed sludge (mix ratio 1:1) was 200mg/L, highlighting a huge savings (14 times) in polymer addition without alum sludge involvement. In addition, cost-effective analysis of its potential full-scale application has demonstrated that the initial investment could be returned in 11years. The co-conditioning and dewatering strategy can be viewed as a "win-win" strategy for the Graulhet, France, water and wastewater industry. Graphical abstract.

Modifying the dewatering behaviour of iron solids from ferric sulphate solutions during lime treatment

In the continuous lime neutralization treatment of iron-laden wastewaters, such as acid mine drainage (AMD), the solid-liquid separation of iron solids formed is difficult to effect. The particle formation mechanisms, the ensuing particle size and size distribution – which in turn shape the dewatering process – are strongly influenced by the OH/Fe molar feed ratios since they dictate the supersaturation level. This work describes tests using a stoichiometric and sub- stoichiometric OH/Fe molar ratio (R = 3 and 2.5 respectively) to establish settleability and filterability variations of a slurry precipitated at steady state in a mixed-suspension-mixed-product-removal (MSMPR) reactor at 15 min residence time. Three initial ferric concentrations ([Fe(III)]) of 100, 300 and 800 mg/L were used. The results revealed that particle-particle repulsion and product dewatering characteristics were dependent on the relationship between supersaturation, pH and ionic strength. The best product performance, as seen in fastest settling rate of 3.3 ± 0.2 mm/min, an increase in the filtration rate from 3.7 ± 0.4 to 5.1 ± 0.5 cm3/cm2 min and a decrease in the specific resistance to filtration (SRF) from 1.42 × 1012 to 6.71 × 1011 m/ kg, was observed for particles formed at R = 2.5 and a [Fe(III)] of 300 mg/L. The product performance was attributed to reduced supersaturation and minimal particle-particle repulsion due to the proximity of the steady state pH and point of zero charge. This favoured a neutral surface charge resulting in the dominance of large (D4,3 of 48.3 ± 0.05 μm and D3,2 of 30.8 ± 0.05 μm), regular shaped agglomerates which had a narrow, unimodal distribution and a notable decrease in the peak number of fine particles from 3.5 × 1013 to 1.7 × 1012 / m3. Sub- stoichiometric molar ratios produced insignificant filterability changes at [Fe(III)] of 100 and 800 mg/L but the latter showed significant settling rate changes (the largest change of threefold - from 0.8 to 2.4 ± 0.2 mm/min). These results suggest that AMD treatment plants that employ lime neutralization should be operated at lower OH concentrations than is the current practice, as this ensures improved iron removal as well as settling and filtration properties of the sludge. This may have the added benefit of decreased neutralization costs as less lime will be required.