Composite Conditioner Research Articles

Insights into the Synergistic Effect and Inhibition Mechanism of Composite Conditioner on Sulfur-Containing Gases during Sewage Sludge Pyrolysis.

Sewage sludge odorous gas release is a key barrier to resource utilization, and conditioners can mitigate the release of sulfur-containing gases. The gas release characteristics and sulfur compound distribution in pyrolysis products under both single and composite conditioning strategies of CaO, Fe2O3, and FeCl3 were investigated. This study focused on the inhibition mechanisms of these conditioners on sulfur-containing gas emissions and compared the theoretical and experimental sulfur content in the products to evaluate the potential synergistic effects of the composite conditioners. The findings indicated that at 650 °C, CaO, Fe2O3, and FeCl3 inhibited H2S release by 35.8%, 23.2%, and 9.1%, respectively. Notably, the composite of CaO with FeCl3 at temperatures ranging from 350 to 450 °C and the combination of Fe2O3 with FeCl3 at 650 °C were found to exert synergistic suppression on H2S emissions. The strongly alkaline CaO inhibited the metathesis reaction between HCl, a decomposition product of FeCl3, and the sulfur-containing compounds within the sewage sludge, thereby exerting a synergistic suppression on the emission of H2S. Conversely, at temperatures exceeding 550 °C, the formation of Ca-Fe compounds, such as FeCa2O4, appeared to diminish the sulfur-fixing capacity of the conditioners, resulting in increased H2S emissions. For instance, the combination of CaO and FeCl3 at 450 °C was found to synergistically reduce H2S emissions by 56.3%, while the combination of CaO and Fe2O3 at 650 °C synergistically enhances the release of H2S by 23.6%. The insights gained from this study are instrumental in optimizing the pyrolysis of sewage sludge, aiming to minimize its environmental footprint and enhance the efficiency of resource recovery.

Deep dewatering of activated sludge using composite conditioners of surfactant, acid and flocculant: The mechanism and dosage model

To address the problem of difficult disposal caused by poor dewaterability of high-organic sludge in wastewater treatment plant, this study developed a sludge composite conditioner (SCC) consisting of sodium dodecyl sulfate (SDS), HCl and FeCl3. It has the potential to significantly improve the dewaterability of the high-organic sludge with the VSS/MLSS of 80%. The moisture content (MC) and bound water content of sludge were reduced from 98.00 to 59.65% and from 3.42 to 0.91 g/g dry sludge (DS) after being conditioned, respectively. The surfactant (SDS) promoted the dissolution of extracellular polymeric substances (EPS). The acid (HCl) enhanced the decomposition of the sludge flocs, making the insoluble EPS peel off and turn into the liquid phase. As a result, total EPS decreased by 52.70% compared to the original sludge. In addition, due to the neutralization effect of protons and FeCl3, the Zeta potential increased remarkably from −13.80 mV to −1.72 mV and the dispersed sludge particles formed during EPS dissolution process were re-flocculated, which increased the average size of the sludge particles. The ratio of proteins (PN)/polysaccharides (PS) also increased from 1.69 to 3.81. And a quantitative model of optimum dosage of SCC agents based on the influence of the sludge PS, PN and EPS content has been established, aiming to determine the dosage of each conditioner according to the properties of target sludge. In general, the SCC provided an effective pathway for sludge deep dewatering.

Adaptability of organic matter and solid content to Fe2+/persulfate and skeleton builder conditioner for waste activated sludge dewatering.

Sludge conditioning is important for improved dewatering, with the sludge characteristics impacting the effect of conditioning. A composite conditioner, Fe2+-activated sodium persulfate (Fe2+/SPS) combined with phosphogypsum (PG), was used to examine its impact on sludges with different organic contents (34.6-43.8%) or different solid contents (2.8-5.9%). Response surface optimization analysis shows that when the best conditioning is achieved, the reduction of the specific resistance to filtration (SRF) is not sensitive to organic matter content, but the dewatering performance of the sludge is greatly affected by the solid content. The oxidation role of Fe2+/SPS and the skeleton builder role of PG together affect the conditioning, oxidation playing a major role in conditioning, especially for greater organic matter content. The organic content (maximum ηSOL value was 0.32) also affects the effectiveness of the skeleton builder more than the solid content (Maximum ηSOL value was 0.25). Changes in PG significantly impacts the optimal molar ratio and dosage of Fe2+/SPS. Sludge with greater solid content requires greater Fe2+/SPS dosage to provide stronger oxidation to destroy flocs, and the maximum Fe2+:SPS molar ratio was 1.14 with solid content of 5.9 wt%. The composite conditioning decreases the content of extracellular polymeric substances and proteins/polysaccharides. This study provides new insight into the relationship between the oxidation role of Fe2+/SPS and the skeleton builder role of PG for sludge conditioning strategies according to the optimal conditions.

Improving waste activated sludge dewaterability with sodium periodate pre-oxidation on extracellular polymeric substances.

The efficiency of sludge dewatering is affected by the structure and composition of hydrated extracellular polymeric substances (EPS). Degrading EPS can improve the sludge dewatering performance. As an oxidizing agent, sodium periodate (NaIO4 ) has ability to oxidize organics, which is expected to decompose the protein and polysaccharide in EPS and improve the efficiency of sludge dewaterability. This study adopted NaIO4 , for the first time, as an advanced oxidation agent to regulate EPS of waste activated sludge and was combined with anionic polyacrylamide (APAM) as a flocculant to subsequently enhance sludge dewatering. Response surface methodology (RSM) was used to determine the optimal conditions of pH, NaIO4 , and APAM. The results showed that the composite conditioner's specific resistance of filtration (SRF) and the water content of the vacuum-filtered cake (Wc) were highly enhanced compared with those of the raw sludge (RS) under pH 6.5, a NaIO4 concentration of 50mg/g dry solids (DS), and an APAM concentration of 5mg/gDS. Owing to the pre-oxidation achieved by NaIO4 under a mildly acid environment, sludge flocs were broken. Subsequently, chemical coagulation (APAM) agglomerated the smaller particles into larger flocs of sludge by adsorption and bridging, thus improving sludge dewaterability. PRACTITIONER POINTS: A novel conditioner, pH/NaIO4 /APAM, was explored for sludge dewatering. IO3 • and HO• oxidized extracellular polymeric substances (EPS). Degradation of the protein content of EPS released bound water. Highly enhanced sludge dewaterability was achieved under optimal conditions.

Phosphorus recovery from incinerated sewage sludge ash (ISSA) and reutilization of residues for sludge pretreated by different conditioners

• Effect of different sludge conditioners on P recovery from ISSA was first studied. • Fe and Ca elements in sludge conditioner influenced the P speciation in ISSA. • Higher Ca content in ISSA resulted in lower P leaching efficiency. • Heavy metals mainly existed in residual specie with low mobility risk in ISSA. • Acid-leaching residue of ISSA could be reused as cement mortar additives. Phosphorus (P) recovery from incinerated sewage sludge ash (ISSA) has attracted increasing attentions in recent years. In this study, the P recovery was comparatively investigated on two types of ISSA for sewage sludge pretreated by Fenton's reagent, and a composite conditioner of Fenton's reagent and lime (referred to as ISSA-F and ISSA-FL, respectively). ISSA derived from raw sludge (referred to as ISSA-RS) was studied as the control group. The P species results showed that the proportions of AP (Ca-bound P) and NAIP (Al/Fe-bound P) in the ISSA samples were significantly affected by the added Fe and Ca elements in the sludge conditioner. The order of leaching efficiency of P in different ISSA samples was ISSA-F (100%) > ISSA-RS (94.4%) > ISSA-FL (83.1%), which was significantly related to the Ca content in those ISSA samples. Higher Ca content in the ISSA-RS and ISS-FL samples induced calcium oxalate precipitation during leaching process, which hindered the release of P from ISSA. P recovery product mainly composed of aluminum hydroxyphosphate was prepared from the purified solutions leached from different ISSA samples. Moreover, acid-leaching residues of different ISSA samples after P recovery were proposed to be reutilized as cement mortar additives by replacing 15 wt% of cement. The mechanical strength of the test cement mortar specimens with acid-leaching residues was comparable to that of the control cement mortar specimen without residue.

Enhancement of the sewage sludge dewaterability by using ethanol and Fe(III)-rice husk.

Proteins of extracellular polymeric substances (EPS) in sewage sludge play a key role in the sludge dewatering. Ethanol can denature proteins and improve sludge dewaterability. In this study, ethanol was used to precondition and combined with Fe3+ and rice husk (RH) for dewatering enhancement. The experimental results of the capillary suction time (CST) reduction efficiency indicated that the sewage sludge pretreated with ethanol and Fe3+-RH revealed well cooperative formation mechanism with regard to dewatering performance. Using the response surface methodology (RSM) determined that CST reduction efficiency of sewage sludge reached 78.5% under optimal conditions of ethanol 25.21 g/g dry solid (DS), Fe3+ 185.70 mg/g DS, and RH 406.02 mg/g DS, respectively. Moreover, the results showed that the composite conditioner is effective for the specific resistance to filtration decreased from initial 1.66E + 13 m/kg to 2.44E + 11 m/kg. The analysis of EPS showed that extractable proteins in EPS increased to maximum when the sludge was pretreated by Fe3+-RH because EPS were destroyed and proteins in EPS were released. After the addition of ethanol, extractable protein content was reduced because of protein precipitation and released interstitial water and bound water. The sludge morphology analysis indicated that the RH as a skeleton builder provided the outflow passages, which enhanced the dewatering performance of sludge. From these results, the combination treatment of ethanol and Fe3+-RH is a promising synergetic strategy to enhance the dewaterability of sewage sludge.

A highly efficient conditioning process to improve sludge dewaterability by combining calcium hypochlorite oxidation, ferric coagulant re-flocculation, and walnut shell skeleton construction

High levels of extracellular polymeric substances (EPS) and bound water in sludge negatively impact sludge dewaterability. This study applied a novel sludge conditioning process involving calcium hypochlorite (Ca(ClO)2) oxidation, ferric coagulant re-flocculation, and walnut shell (WS) skeleton construction to remove EPS and bound water and improve sludge dewaterability. The study also described the underlying mechanisms for this activity, by investigating the changes in EPS distribution, morphological structure, flocs morphology, rheological behavior, and bound water. Using single factor experiments, the optimal dosages of the composite conditioner included 10 mg/g dry solid (DS) of Ca(ClO)2, 60 mg/g DS of ferric chloride (FeCl3) or 100 mg/g DS of polymeric ferric sulfate (PFS), and 600 mg/g DS of WS. Using a novel pressure filtration system, the moisture content of the dewatered sludge cake conditioned with Ca(ClO)2/ferric coagulant/WS was reduced to below 50 wt%. The study described a three-step mechanism for the composite conditioning of sludge. First, protein-like substances and polysaccharide-like materials in the EPS and bound water were degraded by Ca(ClO)2 oxidation. Second, the porous structure and compact flocs were re-flocculated using high charge neutralization and the bridging ability of ferric coagulant. The flowability increased and the viscosity decreased compared with raw sludge. Third, a rigid networked structure was formed by adding the WS skeleton. The combined Ca(ClO)2/ferric coagulant/WS treatment had a significant synergistic effect supporting dewatering. The filter liquor of the combined treatment has a lower impact on the environment. The combined treatment is an appropriate was to treat sludge prior to landfilling and incineration. Furthermore, the economic analysis showed that using the Ca(ClO)2/FeCl3/WS treatment had economic advantages over other treatments.

Citric acid assisted Fenton-like process for enhanced dewaterability of waste activated sludge with in-situ generation of hydrogen peroxide

Fenton's reagent has been widely used to enhance sludge dewaterability. However, drawbacks associated with hydrogen peroxide (H2O2) in Fenton's reagents exist, since it is a hazardous chemical and shows carcinogenicity, explosivity, instability, and corrosivity. Moreover, initial acidification and subsequent neutralization are needed as optimal conditions for homogeneous Fenton conditioning and final filtrate discharge. In this study, a Fenton-like process for the enhanced dewaterability of waste activated sludge with in-situ generation of H2O2 and without extra pH adjustment was firstly proposed, namely citric acid (CA)-assisted oxygen activation in an air/nano zero-valent iron (nZVI) system and chemical re-coagulation with polydiallyldimethylammonium chloride (PDMDAAC). Using the response surface methodology (RSM), the optimal doses of CA, nZVI, and PDMDAAC were determined to be 13, 33, and 9 mg g−1 dry solids (DS), respectively. This composite conditioner showed a good dewatering capability compared with the raw sludge, e.g. the capillary suction time decreased from 130.0 to 9.5 s. The enhanced sludge dewaterability was further confirmed by laboratory-scale diaphragm filter press dewatering tests, which produced a lower cake moisture content compared with the raw sludge, and the final pH of the filtrate was close to neutrality. The citric acid promoted the production of H2O2 and Fe(II)/Fe(III) species, the degradation of protein in tightly-bound extracellular polymeric substances, and the decomposition of protein-N in the solid phase of sludge, resulting a greater conversion of bound water to free water. The results of electron spin resonance indicated that the hydroxyl radicals were mainly responsible for the decomposition of proteinaceous compounds. The subsequent chemical re-coagulation with PDMDAAC can make the zeta potential of sludge samples less negative, reduce the repulsive electrostatic interactions, and agglomerate the smaller particles into larger aggregates, thus enhancing sludge dewaterability.

Improving the Dewaterability of Sewage Sludge Using Rice Husk and Fe2+-Sodium Persulfate Oxidation

Physical conditioners or skeleton builders are usually used to improve the dewaterability of sewage sludge. In this study, low-cost rice husk (RH) was evaluated as an alternative skeleton builder and combined with Fe2+ and sodium persulfate (SPS) for sewage sludge conditioning. The results show that the sewage sludge conditioned with RH and Fe2+/SPS showed good dewaterability, and the capillary suction time was reduced by 92.8% under optimal conditions. With use of response surface methodology, the optimal composite conditioner concentrations were 151.5 mg/g dry solid (DS) of SPS, 46 mg/g DS of Fe2+, and 333 mg/g DS of RH. After the sludge was conditioned with Fe2+/SPS, some extracellular polymeric substances (EPS) were destroyed, which resulted in the dissolved protein and polysaccharide amounts in the filtrate increasing. The water content analysis indicated the bound water was converted to free water because of the EPS degradation. The particle size analysis showed that the sludge flocs became smaller....

Synergistic effect of water content and composite conditioner of Fenton's reagent combined with red mud on the enhanced hydrogen production from sludge pyrolysis

This study investigated the synergistic effect of water content and a composite conditioner of Fenton's reagent combined with red mud (Fenton-RM) on the pyrolytic products (fuel gas, tar, and solid char) of deep-dewatered sludge. The catalytic effect of metal oxides in Fenton-RM could be promoted by the presence of water during sludge pyrolysis, showing higher gas yield with increased water content. Maximum gas outputs of the deep-dewatered sludge conditioned with Fenton-RM (S-Fenton-RM) and the conventional dewatered sludge conditioned with polyacrylamide (S-PAM), both appeared at 900 °C with a water content of 65 wt%, and were 0.257 and 0.189 L/g dry solid (DS), respectively. At the same temperature and with the same water content, the hydrogen (H2) yields of the S-Fenton-RM samples were always higher than those of the S-PAM samples. At 900 °C, the maximum H2 yield of the S-Fenton-RM samples was 0.102 L/g DS, which was 85.5% higher than that of the S-PAM samples. The results indicated that water in the wet sludge provided the steam atmosphere for pyrolysis, and the water vapor then involved in secondary cracking reformation of tar and char gasification reactions, which would be catalyzed by the presence of metal oxides in the Fenton-RM conditioner, thus increasing the yield of fuel gas, especially hydrogen. The H2 production cost from the S-Fenton-RM system is less than that from the S-PAM system. The results suggest that pyrolysis of the wet deep-dewatered sludge conditioned with Fenton-RM is an economical and promising alternative for sewage sludge dewatering and disposal/reuse.

Mechanism and Parameter Optimization of Fenton's Reagent Integrated with Surfactant Pretreatment to Improve Sludge Dewaterability.

Sludge dewatering can effectively reduce the volume and mass of sludge for subsequent treatment and disposal. The work validated the potential of Fenton’s reagent combined with dodecyl dimethyl benzyl ammonium chloride (DDBAC) in improving sludge dewaterability and proposed the mechanism of joint conditioning. The composite conditioner dosage was optimized using response surface methodology. Results indicated the good conditioning capability of the composite conditioners. The optimum dosages for H2O2, Fe2+, and DDBAC were 44.6, 39.6, and 71.0 mg/g, respectively, at which a sludge cake water content of 59.67% could be achieved. Moreover, a second-order polynomial equation was developed to describe the behavior of joint conditioning. Analysis of the reaction mechanism showed that Fenton oxidation effectively decomposed extracellular polymeric substance (EPS), including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), into dissolved organics, such as proteins and polysaccharides. The process facilitated the conversion of the bound water into free water. Furthermore, DDBAC further released the bound water through solubilization of TB-EPS and LB-EPS after the Fenton reaction. The bound water content of the sludge conditioned with Fenton’s reagent decreased from 3.15 to 1.36 g/g and further decreased to 1.08 g/g with the addition of DDBAC. High-performance liquid chromatography analysis verified that the composite conditioning could oxidize and hydrolyze EPS into low-molecular-mass organics (e.g., formic and acetic acid), thereby facilitating the release of bound water.

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.

Roles of iron species and pH optimization on sewage sludge conditioning with Fenton's reagent and lime

Conditioning sewage sludge with Fenton's reagent could effectively improve its dewaterability. However, drawbacks of conditioning with Fenton's reagent are requirement of acidic conditions to prevent iron precipitation and subsequent neutralization with alkaline additive to obtain the pH of the filtrate close to neutrality. In this study, roles of pH were thoroughly investigated in the acidification pretreatment, Fenton reaction, and the final filtrate after conditioning. Through the response surface methodology (RSM), the optimal dosages of H2SO4, Fe2+, H2O2, and lime acted as a neutralizer were found to be 0 (no acidification), 47.9, 34.3 and 43.2 mg/g DS (dry solids). With those optimal doses, water content of the dewatered sludge cakes could be reduced to 55.8 ± 0.6 wt%, and pH of the final filtrate was 6.6 ± 0.2. Fenton conditioning without initial acidification can simplify the conditioning process and reduce the usage of lime. The Fe3+ content in the sludge cakes showed a close correlation with the dewaterability of conditioned sludge, i.e., the water content of sludge cakes, SRF (specific resistance to filtration), CST (capillary suction time), bound water content, and specific surface area. It indicated that the coagulation by Fe3+ species in Fenton reaction could play an important role, compared to traditional Fenton oxidation effect on sludge conditioning. Thus, a two-step mechanism of Fenton oxidation and Fe(III) coagulation was proposed in sewage sludge conditioning. The mechanisms include the following: (1) extracellular polymeric substances (EPS) were firstly degraded into dissolved organics by Fenton oxidation; (2) bound water was converted to free water due to degradation of EPS; (3) the sludge particles were disintegrated into small ones by oxidation; (4) Fe3+ generated from Fenton reaction acted as a coagulant to agglomerate smaller sludge particles into larger dense particles with less bond water; (5) finally, the dewatered sludge cakes were obtained, with less small pores (1–10 nm) that contributed to water affinity, but with more large pores (>10 nm) that contributed to a permeable, rigid lattice structure. Morphology of the Fenton-conditioned sludge cake exhibited a porous structure. The estimated cost of the composite conditioner, Fenton's reagent and lime, is USD$ 43.8/t DS, which is less than that of ferric chloride and lime (USD$ 54/t DS). Furthermore, pH of the final filtrate using this composite conditioner is about 6.6. Comparatively, that using ferric chloride and lime is as high as 12.4.

Synergetic conditioning of sewage sludge via Fe2+/persulfate and skeleton builder: Effect on sludge characteristics and dewaterability

High water affinity of extracellular polymeric substances (EPS) and high compressibility of sewage sludge solids have negative impacts on sludge dewatering. In this study, a composite conditioner, Fe2+–activated sodium persulfate (denoted as Fe2+/SPS) combined with thermal–pretreated phosphogypsum (PG), was used to improve the sludge dewaterability. The mechanism of the composite conditioning of sewage sludge was elucidated: the proteins in tightly bound EPS were transferred into the filtrate and loosely bound EPS, and the polysaccharides in loosely and tightly bound EPS were transferred into the filtrate; the bound water was released and reduced from 2.60g/gDS (dry solid) initially to 0.81g/gDS; specific resistance to filtration and capillary suction time were reduced by 91.6% and 88.4%, respectively. Radical quenching experiment indicated that sulfate radical (SO4−) is the dominant free radical and plays an important role in determining the oxidation–reduction potential during conditioning. Moreover, both the XRD and SEM results clearly showed that Fe2+/SPS combined with PG promoted the generation of column–shaped dihydrate gypsum in the conditioned sludge. Thus, the dihydrate gypsum crystals could act as skeleton builders, which create a more permeable and rigid lattice structure of the sludge cake. The improvement of sludge dewatering was confirmed by diaphragm filter press dewatering process, which yielded 45.7wt% cake moisture content and 91.7% dewatering efficiency.

Enhanced Dewatering of Waste Sludge With Polyacrylamide/Montmorillonite Composite and Its Conditioning Mechanism

In order to improve the waste sludge dewaterability of polyacrylamide (PAM), the composite conditioner of PAM/montmorillonite (MMT) was prepared. The structure and intermolecular hydrogen bonding of the composite were studied, and the effects of PAM/MMT weight ratio and dosage on the dewaterability of the waste sludge were systematically investigated. The results revealed that the MMT platelets were in an exfoliated state in the PAM matrix, and hydrogen bonding between –OH groups of MMT and –NH groups of PAM led to relatively high elastic modulii (G') values and low tan δ values, indicating the possible formation of a physically cross-linked network in aqueous solution. The addition of MMT significantly reduced the specific resistance to filtration (SRF) of the waste sludge, with a minimum value being achieved at a 1:1 PAM/MMT weight ratio. The UV transmittance and the turbidity of the supernatant of the waste sludge were also improved at a proper PAM/MMT weight ratio. The synergistic effect of the two components in the composite through the charge neutrality and bridging action of PAM as well as the adsorption capacity of MMT resulted in an enhanced dewaterability of waste sludge.

Mechanism of red mud combined with Fenton's reagent in sewage sludge conditioning

Red mud was evaluated as an alternative skeleton builder combined with Fenton's reagent in sewage sludge conditioning. The results show that red mud combined with Fenton's reagent showed good conditioning capability with the pH of the filtrate close to neutrality, indicating that red mud acted as a neutralizer as well as a skeleton builder when jointly used with Fenton's reagent. Through response surface methodology (RSM), the optimal dosages of Fe2+, H2O2 and red mud were proposed as 31.9, 33.7 and 275.1 mg/g DS (dry solids), respectively. The mechanism of the composite conditioner could be illuminated as follows: (1) extracellular polymeric substances (EPS), including loosely bound EPS and tightly bound EPS, were degraded into dissolved organics, e.g., proteins and polysaccharides; (2) bound water was released and converted into free water due to the degradation of EPS; and (3) morphology of the conditioned sludge exhibited a porous structure in contrast with the compact structure of raw sludge, and the addition of red mud formed new mineral phases and a rigid lattice structure in sludge, allowing the outflow of free water. Thus, sludge dewatering performance was effectively improved. The economic assessment for a wastewater treatment plant of 370,000 equivalent inhabitants confirms that using red mud conditioning, combined with Fenton's reagent, leads to a saving of approximately 411,000 USD/y or 50.8 USD/t DS comparing with using lime and ordinary Portland cement combined with Fenton's reagent, and approximately 612,000 USD/y or 75.5 USD/t DS comparing with the traditional treatment.

In situ polymerization of cationic polyacrylamide/montmorillonite composites and its flocculation characteristics

In order to improve the waste sludge dewaterability of polyacrylamide (PAM), composite conditioner of cationic PAM/montmorillonite (CPAM/MMT) was synthesized by in situ polymerization. The structure and property of the composite were studied in terms of intermolecular hydrogen bonding, melting behavior, intercalation behavior, and dewaterability of the waste sludge. The results revealed that the molecular weight and cationic degree of CPAM/MMT composites decreased with the increase of MMT content. The hydrogen bonding between –OH groups of MMT and –NH groups of CPAM was confirmed by Fourier transform infrared spectroscopic analysis, which led to a relatively high elastic modulus values and low tan δ values at 5 wt% MMT content, indicating the possible formation of a physically cross-linked network in aqueous solution for the composite. The melting temperature of the composites presented decreasing trend first and then became higher as the content of MMT increased. The MMT platelets dispersed well with an intercalated state in CPAM matrix as indicated by x-ray diffraction analysis and transmission electron microscopic observation. The addition of MMT reduced the specific resistance to filtration of the waste sludge, with a minimum value being achieved at 5 wt% MMT content, while the ultraviolet transmittance of the supernatant of the waste sludge was also improved, and the turbidity was reduced. This synergistic effect of the two components in the composite through charge neutrality and bridging action of CPAM as well as the adsorption capacity of MMT resulted in an enhanced dewaterability of waste sludge.

Emission characteristics of nitrogen- and sulfur-containing odorous compounds during different sewage sludge chemical conditioning processes

Chemical conditioners are often used to enhance sewage sludge dewaterability through altering sludge properties and flocs structure, both affect odorous compounds emissions not only during sludge conditioning but also in subsequent sludge disposal. This study was to investigate emission characteristics of ammonia (NH3), sulfur dioxide (SO2), hydrogen sulfide (H2S) and carbonyl sulfide (COS) generated from sewage sludge conditioned by three representative conditioners, i.e., organic polymers, iron salts and skeleton builders, F-S (Fenton's reagent and skeleton builders) composite conditioner. The results demonstrate that polyacrylamide (PAM) has an insignificant effect on emission characteristics of nitrogen- and sulfur-containing odorous compounds, because the properties, sulfur and nitrogen speciations are similar in PAM-conditioned sludge and raw sludge (RS). Significant increases of SO2 and H2S emissions in the H2SO4 conditioning process were observed due to the accelerated decomposition of sulfur-containing amino acids in acidic environment. Fenton peroxidation facilitates the formation of COS. CaO can reduce sulfur-containing gases emission via generation of calcium sulfate. However, under strong alkaline conditions, free ammonia or protonated amine in sludge can be easily converted to volatile ammonia, resulting in a significant release of NH3.

Conditioning of sewage sludge by Fenton’s reagent combined with skeleton builders

Physical conditioners, often known as skeleton builders, are commonly used to improve the dewaterability of sewage sludge. This study evaluated a novel joint usage of Fenton’s reagent and skeleton builders, referred to as the F–S inorganic composite conditioner, focusing on their efficacies and the optimization of the major operational parameters. The results demonstrate that the F–S composite conditioner for conditioning sewage sludge is a viable alternative to conventional organic polymers, especially when ordinary Portland cement (OPC) and lime are used as the skeleton builders. Experimental investigations confirmed that Fenton reaction required sufficient time (80min in this study) to degrade organics in the sludge. The optimal condition of this process was at pH=5, Fe2+=40mgg−1 (dry solids), H2O2=32mgg−1, OPC=300mgg−1 and lime=400mgg−1, in which the specific resistance to filtration reduction efficiency of 95% was achieved.