Floc Disintegration Research Articles

Enhancing phosphorus release and recovery from waste activated sludge by citric acid treatment and cyclic extraction

Waste activated sludge (WAS) is a potential alternative supply of non-renewable phosphorus. However, improving phosphorus release from WAS is challenged by the elution of phosphorus in metal-bound phosphorus (mainly Fe-P or Al-P) due to the extreme pH condition requirement and the slow disintegration of sludge flocs. In this study, the role of citric acid (CA) in enhancing phosphorus release from WAS was investigated. Owing to its intensive chelating function, CA addition rapidly increased phosphorus release to its peak within 24 h. With the CA dosage increasing from 0.08 g/gTS to 0.32 g/gTS, the concentration of total dissolved P in the supernatant reached 698 ± 17 mg/L, significantly higher than that of the control group (154 ± 2.3 mg/L). The relative release efficiency of Fe-P and Al-P was substantially enhanced, contributing to 60.1–82.4 % and 76.0–85.6 %, respectively. Apatite P was almost completely released under acidic conditions (pH < 5), with the relative release efficiency achieving 78.5–93.1 %. Additionally, compared to adjusting pH to 3 alone, the synergistic effect of adjusting pH to 3 combined with 0.08 g/gTS CA addition boosted total solid P (TSP) release efficiency by 16 %, primarily due to the cheating function of CA with released iron and aluminum ions. Furthermore, after three continuous acid (pH = 3) recycling cycles, the release efficiency of TSP finally increased to 73.0 ± 0.9 % with the average PO43−-P recovery efficiency achieved 98 %, and the average content of P2O5 in recovered phosphorus precipitates was more than 20 %. Therefore, this study provided a research basis for the efficient recovery of phosphorus from real WAS by a cost-effective and environmentally friendly method in practice.

Impact of Doxycycline Addition on Activated Sludge Microflora and Microbial Communities

Municipal wastewater treatment plants (WWTPs) are exposed to high concentrations of micropollutants that can impact conventional activated sludge treatment. The consequences of this include failure to meet discharge standards and the disintegration of flocs, leading to poor sludge settleability. This lab-scale study focuses on the influence of doxycycline, an antibiotic widely used against human and animal diseases, on protozoa, metazoa, and bacterial communities under sludge growing conditions. Doxycycline was added to the mixed liquor of a communal WWTP up to 0, 100, 200, and 400 mg of doxycycline L−1 and incubated in batch conditions for 23 days. The regular addition of nutrient and carbon sources was preformed every 2 days to prevent sludge starvation. Sludge growth, conductivity, and settleability were measured and compared to sludge microbial community structure, determined by microscopic observations and high-throughput 16S rDNA sequencing. The high doxycycline concentration negatively impacted settleability and correlated with a decrease in bacterial diversity and floc disintegration. The addition of doxycycline promoted the enrichment of Proteobacteria Brevundimonas sp., Luteibacter anthropi, and the Bacteroidetes Chryseobacterium massoliae. These species are known to be resistant to a wide spectrum of antibiotics, including tetracyclines. A study of a larger scale may be conducted based on this study’ results.

Nitrite production mechanism and microbial evolution characteristic influenced by pH during partial denitrification (PD) process

Partial denitrification (PD) has been proved technically feasible and economically favorable to produce nitrite (NO2--N) for anammox. To obtain stable NO2--N accumulation, the effects of pH (6.0, 7.5, 9.0, 10.0) on nutrient removal mechanism and microbial community evolution were investigated. Higher pH benefited PD performance with the optimal NO2--N and nitrate-to-nitrite transformation ratio (NTR) reaching to 43.50 mg/L, 81.64% at pH= 9.0 although slight NO2--N inhibition occurred caused by biomass loss and proton deficiency at pH= 10.0. Batch testes showed the same change trends of NTR (pH=9.0 >pH=7.5 >pH=6.0 >pH=10.0), where pH and oxidation reduction potential (ORP) also proved the “NO2--N knee” as pH varied around 7.5–9.0. The denitrification kinetic proved the closely relationship among carbon consumption rate (CCR), poly-β-hydroxyalkanoates transformation rate (PTR), NO2--N accumulation rate (N2AR), NO2--N reduction rate (N2RR) and nitrate (NO3--N) reduction rate (N3RR) although COD release, nitrogen loss and floc disintegration were observed under different pH conditions. Meanwhile, more aggregated microbial compositions formed (562–605 OTUs) at the optimal pH range of 7.5–9.0, where Terrimonas, norank_f_A4b, Defluviicoccus, Hyphomicrobium, norank_f_Blastocatellaceae, and OLB13 were the main contributors for NO2--N maintenance, with the proportions accounting for 35.29–39.60%.

Improvement of waste sludge dewaterability by a novel co-conditioning approach with polyaluminum chloride-sludge based carbon-polyacrylamide

A novel sludge conditioning method incorporating sludge-based carbon (SBC) as a filter aid into the coagulation and flocculation co-conditioning process is proposed to strengthen sludge dewaterability, namely the co-conditioning of polyaluminum chloride (PAC)-SBC-polyacrylamide (PAM). The results show that the co-conditioning method can effectively reduce the specific resistance to filtration (SRF), moisture content (MC) of the filter cake and sludge compressibility coefficient (CC), meanwhile increase the net sludge solids yield (YN) of municipal sludge (MS) and textile dyeing sludge (TDS), resulting in a significant improvement in sludge dewatering performance for two types of sludge. The response of sludge dewatering performance to different conditioning agents and the variation characteristics of sludge EPS in co-conditioning process suggest that the co-conditioning mechanism involves a synergistic effect of coagulation, adsorption, and flocculation, which process includes the aggregation and disintegration of microbial cell flocs caused by PAC, the skeleton-building action and biopolymer adsorption by SBC, and sludge floc agglomeration facilitated by PAM. In addition, SBC also optimizes coagulation by electrostatic neutralization, while strengthening flocculation by bridging biopolymers and PAM. Moreover, co-conditioning exhibits a remarkable ability to eliminate dissolved organic matter from the filtrate, leading to an enhancement in the filtrate quality and a reduction in the downstream burden for sludge filtrate treatment. Consequently, the PAC-SBC-PAM co-conditioning emerges as a promising method for sludge pretreatment.

Thermal and oxidative disintegration of anaerobic digested sludge by solution plasma process

Solution plasma process (SPP) is promising for sludge disintegration, since the SPP only uses electric power and induces strongly oxidizing environments. In this study, the SPP using a capillary discharge that generating reactive oxygen species and heating solution was developed to assess the disintegration performance of anaerobic digested sludge. The SPP was compared with the thermal process (TP) which has only thermal contributions to evaluate the contributions of thermal and oxidative disintegration of sludge. Compared to the TP, under all tested conditions, the improved solubilization performance (up to 1.41, 1.84, and 6.55 times higher for overall COD, proteins, and carbohydrates, respectively) by the SPP was attributed to the oxidative effect (statistically significant, p < 0.01) with the thermal effect on the sludge disintegration. This oxidative effect became less significant as the temperature and incubation time without further plasma discharge increased. According to the particle size distributions and detailed characterization of dissolved organic matters, an increased release of biopolymers (proteins and carbohydrates), low molecular weight (LMW) substances (building blocks and neutrals), and the significant particle size reduction, suggested that the SPP induced floc disruption, cell lysis, and disintegration of sludge flocs even at the temperature of between 60 and 80 °C, while the TP was not favorable for releasing intracellular LMW substances and reducing the sludge floc size. Therefore, the SPP showed a synergistic impact of thermal and oxidative effects for improving the sludge disintegration. This study provides comprehensive insights for understanding the SPP and its possible application to sludge treatment.

Hierarchical stringent response behaviors of activated sludge system to stressed conditions

The stringent response of activated sludge systems to either stressed or harmful environments is important for the stable operation of activated sludge, which is examined by taking copper ion (Cu2+) as a stress model in this study. When weak stress was employed (Cu2+ ≤ 2.5 mg/L), the N-acyl-homoserine lactones (AHLs) of C6-, C8-, and C10-HSL increased by 30 %, 13 %, and 127 %, respectively, while the redox sensor green (RSG) intensity decreased by 28 %. Encountering the increased stress (2.5 mg/L < Cu2+ ≤ 5 mg/L), bacteria concentration in the supernatant increased by 87 %. However, the respiration rates of autotrophic and heterotrophic bacteria (SOURa and SOURh) and adenosine triphosphate decreased by 52 %, 18 %, and 27 %, respectively, and the flocs disintegrated with a diameter decreasing from 57 to 51 μm. When the stress became more serious (Cu2+ > 5 mg/L), the respiration rates continued to decline, but the quasi-endogenous respiration ratio (Rq/t) increased from 31 % to 47 %. Negligible changes occurred in the endogenous respiration rate (SOURe), adenosine diphosphate, and adenosine monophosphate. Based on these results, a hierarchical stringent response model of the activated sludge system to stressed conditions was proposed, and these responses were evaluated by respirogram. The initial response to weak stress was related to the most sensitive signals of quorum sensing and RSG intensity, well described by the quasi-endogenous respiration rate. The adaptive response to increased stress was the proactive migrations of low- and high-nucleic-acid bacteria to the supernatant, causing the looseness and even disintegration of sludge flocs, well described by SOURa, SOURh, and Rq/t. The lethal response to lethal stress was related to endogenous metabolic processes, well described by SOURe. This work provides new insights into understanding the stringent response of activated sludge systems to some stressed conditions. It helps to regulate the stability of activated sludge systems with respirogram technology.

Insight into Na+ assistant anaerobic fermentation of waste activated sludge from carbon migration, bio-transformation and recovery perspectives

Short-chain fatty acids (SCFAs) produced from anaerobic fermentation of waste activated sludge (WAS) have been regarded as the preferred carbon source, however the carbon migration pattern has rarely been reported. This work elucidated that the Na+ assistant anaerobic fermentation could facilitate carbon source release and bio-transformation towards carbon recovery from WAS. Obvious disintegration of sludge flocs and property variation of solid–liquid interface were triggered with Na+-regulation, leading to extracellular polymeric substance disruption and microbial cell apoptosis by protein structure loosening and osmotic pressure stress. Thereby, extracellular and intracellular carbon source (e.g. proteins, carbohydrates) were simultaneously solubilized, contributing to considerable carbon migration from sludge solid into liquid phase (up to 20.43 %). Meanwhile, 61.30 % of the released carbon source was bio-transformed with the improved sludge acidification in 4-day Na+ assistant anaerobic fermentation. Substantial SCFAs of 61.39 mg C/g VSS was produced, which was mainly composed by acetate and propionate (69.07 %). As such, the overall carbon recovery rate of 12.51 % was achievable. The carbon source bio-availability in fermentative liquid indeed created economic benefits and carbon-emission reduction depending on alternative carbon source utilization and residual carbon source reduction in fermented sludge disposal.

Enhanced paper sludge dewatering and in-depth mechanism by oxalic acid/Fe2+/persulfate process

As a typical advanced oxidation process, Fe2+-persulfate (PDS) oxidation technology has been widely and efficiently reported for enhancing sludge dewaterability. However, higher dosage of Fe2+ must be added, which will restrain the oxidation efficiency of Fe2+-PDS process. In this work, the oxalic acid (OA)/Fe2+-PDS process was studied to improve paper sludge dewatering. With the OA dosage of 6 μmol (g total solid (TS))−1, Fe2+ dosage of 0.3 mmol (g TS)−1, and PDS dosage of 0.6 mmol (g TS)−1, sludge dewaterability was improved more efficiently. The specific resistance to filtration and water content of sludge cake were decreased by 70.7% and 8.0%, respectively. In comparison with Fe2+-PDS process, the viscosities of sludge suspension and supernatant were further reduced by 3.73% and 51.77%, respectively, and the contents of extracellular polymeric substances fractions were increased. The improved sludge dewaterability in OA/Fe2+-PDS process was mainly contributed by the synergistic effect of oxidative disintegration by free radicals and flocs re-flocculation, the contributions of which were the orders: metal cations > sulfate radical > hydroxyl radical. OA enhanced the efficient disintegration of sludge flocs, released more bound water, generated more Fe3+-oxalate complexes, and finally increased the sludge particle size significantly, forming a larger aggregation and obvious cracks. Additionally, the stabilization of several heavy metals was improved due to the chelating capacity of OA. These works will provide a novel approach for sludge dewatering in the PDS oxidation process.

A comparison of oxidation and re-flocculation behaviors of Fe2+/PAA and Fe2+/H2O2 treatments for enhancing sludge dewatering: A mechanism study

In this study, Fe2+ activated-PAA was developed as a novel technology to enhance sludge dewatering. The result showed that the filterability (CST0/CST) enhanced by 4.20 ± 0.14 times more than the control, and the SRF and bound water content decreased from 4.58 ± 0.07 × 1013 m/kg and 2.11 ± 0.28 g/g dry sludge to 9.47 ± 0.05 × 1012 m/kg and 1.27 ± 0.18 g/g dry sludge, respectively after the sludge was conditioned by 1.20 mM/g VSS Fe2+ and 1.20 mM/g VSS PAA. The dewatering performance, physicochemical properties, aggregation behaviors, and EPS fractions of sludge were compared before and after Fe2+/PAA and Fe2+/H2O2 conditionings. The results showed that Fe2+/PAA treatment was more competitive in enhancing dewaterability under neutral and alkaline conditions than Fe2+/H2O2 treatment but slightly weaker under acid conditions. Besides, it was found that the oxidation and re-flocculation behaviors were different in those two enhanced dewatering technologies due to the difference in the generated ROS. R-O was the primary radical in the Fe2+/PAA system, while OH was the major one in the Fe2+/H2O2 system. The mechanism analysis found that the Fe2+/PAA process caused harsher disintegration of sludge flocs, meaning more generation of fine particles. However, it exhibited less effect on reducing the energy barrier between sludge particles. Therefore, the Fe2+/PAA treated sludge presented weaker aggregation behaviors. The weaker aggregation was unfavorable for sludge dewatering because the weaker aggregated flocs were more easily fragmented, which hampered the consolidation of sludge cakes and removal of bound water. Moreover, loosely-bound extracellular polymeric substances, particularly tightly-bound extracellular polymeric substances, governed the sludge dewaterability.

Integrating electrochemical pretreatment (EPT) and side-stream sulfidogenesis with conventional activated sludge process: Performance, microbial community and sludge reduction mechanisms

• Coupling EPT and sulfidogenic side-stream reactor (ESSR) with CAS process was studied. • EPT at 15 V/5min with 125 mg S/L of SO 4 2− dosage improved sludge reduction. • The ESSR could be designed with a very short SRT of 2.5 days. • The integrated process (ESSR-CAS) was operated over 200 d with good performance. • Possible reasons for fast sludge hydrolysis in ESSR-CAS were discussed. Recently, inserting an anaerobic side-stream reactor into a conventional activated sludge (CAS) process for upgrading biological wastewater treatment plants with in-situ sludge reduction function has been extensively studied. A typical example is an oxic-settling anaerobic (OSA) process, which can achieve efficient sludge reduction, but requires ample space, limiting its application potential. Optimizing the conventional OSA process towards compact and energy-efficient is necessary. This paper studied a new method by integrating electrochemical pretreatment (EPT) and sulfidogenesis-enhanced anaerobic treatment with a conventional OSA process to achieve considerable in-situ sludge reduction with a limited side-stream size requirement (i.e. short sludge retention time (SRT)). The proposed idea was verified experimentally – first, batch experiments were conducted to determine the effective sulfate concentration for the EPT and sulfidogenic side-stream reactor (ESSR); then, the ESSR-CAS process (upgrading CAS with a new ESSR) and a stand-alone CAS process (control) were operated in parallel for 200 days. The experimental results showed that: The new ESSR, with approximately 125 mg S/L of sulfate dosed and 5 min electrochemical sludge pretreatment at 15 V, can successfully accelerate anaerobic reactions, resulting in a short SRT of 2.5 days. The ESSR-CAS process can reduce sludge production by 61%, with high soluble chemical oxygen demand (SCOD) and total nitrogen (TN) removal efficiencies of 96% and 70% respectively. The possible mechanisms of ESSR for the augment of sludge hydrolysis (sludge floc disintegration, extracellular polymer destruction, and cell structure breakage) as well as the economic considerations of this new sulfur-cycle bioprocess are discussed.

Insights into the Anaerobic Hydrolysis Process for Extracting Embedded EPS and Metals from Activated Sludge.

The amount of sewage sludge generated from wastewater treatment plants globally is unavoidably increasing. In recent years, significant attention has been paid to the biorefinery concept based on the conversion of waste streams to high-value products, material, and energy by microorganisms. However, one of the most significant challenges in the field is the possibility of controlling the microorganisms’ pathways in the anaerobic environment. This study investigated two different anaerobic fermentation tests carried out with real waste activated sludge at high organic loading rate (10 g COD L−1d−1) and short hydraulic retention time (HRT) to comprehensively understand whether this configuration enhances extracellular polymeric substance (EPS) and metal solubilisation. The quantity of EPS recovered increased over time, while the chemical oxygen demand to EPS ratio remained in the range 1.31–1.45. Slightly acidic conditions and sludge floc disintegration promoted EPS matrix disruption and release, combined with the solubilisation of organically bound toxic metals, such as As, Be, Cu, Ni, V, and Zn, thereby increasing the overall metal removal efficiency due to the action of hydrolytic microorganisms. Bacteroidetes, Firmicutes, and Chloroflexi were the most abundant phyla observed, indicating that the short HRT imposed on the systems favoured the hydrolytic and acidogenic activity of these taxa.

Pretreatment of sludge with sodium iron chlorophyllin-H2O2 for enhanced biogas production during anaerobic digestion

This study investigated a novel sodium iron chlorophyllin-H2O2 (SIC–H2O2) sludge pretreatment strategy before anaerobic digestion to enhance methane production. The efficiencies and mechanism of the proposed strategy to enhance sludge biodegradability were explored. The SIC–H2O2 pretreatment could enhance the oxidation performance for sludge floc disintegration to dissociate TB-EPS into S-EPS increased SCOD to 521.38 mg/L. The increase of solubilization and release of EPS with the pretreatment facilitate the biogas production at 702 L kg−1 VS, which was 3-folds of the control and significantly higher than other pretreatments. The result of excitation–emission matrix and parallel factor (EEM-PARAFAC) analysis showed that the SIC–H2O2 pretreatment enhanced the dissociation of TB-EPS fractions, especially the protein-like and soluble microbial by-product-like substances. Electron paramagnetic resonance (EPR) results provided evidence for homolytic catalysis H2O2 for the generation OH and the production of high-valent (Por)FeIV(O) intermediates. Synergistic effects of reactive oxygen species (OH, H2O2 and ▪/HO2) and (Por)FeIV(O) enhanced the EPS disintegration during SIC–H2O2 pretreatment. The mixed-acid type fermentation provided continuous VFAs supply under the enrichment of Chloroflexi and Actinobacteria and multiplication Methanosaeta also promoted methane production. This research provides a feasible pretreatment strategy increase sludge biodegradability and enhance biogas production in the anaerobic digestion process.

COD fractionation and solubility assessment of sonicated waste‐activated sludge

AbstractUltrasonic treatment is adopted as one of the important strategies to accelerate the hydrolysis of waste‐activated sludge (WAS). This study intends to optimize amplitude and time for ultrasonic treatment of WAS using statistically designed experiments that would render a better degree of disintegration, measured in terms of chemical oxygen demand (COD) solubilization. The main and interaction effects of nonlinear regression analysis revealed a significant interaction between amplitude and time over the degree of sludge disintegration. The ultrasonic density of 0.45 W/mL for 30 min favored a 153.84% increase in COD solubilization with a 27.65% degree of sludge disintegration. This condition also favored the minimum specific energy input of 801.58 kJ/g total suspended solids compared to other sonication conditions. Besides, the sludge volume index was reduced by 45% and 26% at the ultrasonic density of 0.45 W/mL for 60 and 30 min, respectively. Microscopic examination of WAS revealed disintegration of bacterial flocs during the ultrasonication process releasing filamentous bacteria with smaller floc sizes. The results from this study indicate that higher ultrasonic density for short time could improve the sludge disintegration with minimum specific energy input.

Destroying the structure of extracellular polymeric substance to improve the dewatering performance of waste activated sludge by ionic liquid

The disposal and resource utilization of waste activated sludge (WAS) is a big challenge for its high moisture content. Ionic liquid (IL), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTf]), was innovatively used as a conditioner to improve the dewatering performance of WAS. The WAS was characterized by flocs size, three-dimensional excitation-emission matrix (3D-EEM), zeta potential, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) for the investigation of intensification mechanism. The results showed that the dewatering performance of WAS conditioned by [EMIM][OTf] was significantly improved. The moisture content was successfully decreased to 64.99±0.92 %, and the intensification mechanism was investigated. The results showed that the structures of extracellular polymeric substance (EPS) were destroyed by [EMIM][OTf]. It brought a sharp decrease of the contents of polysaccharides (PS), proteins (PN), humic acid (HA) and fulvic acid (FA) in tightly bound extracellular polymeric substance (TB-EPS) structure. The inactivation of microbial cells promoted the disintegration of flocs. Large flocs were converted into unstable small particles and biopolymers. In addition, the negative charges of WAS were also neutralized for dissolution of biopolymers in [EMIM][OTf], and the electrostatic repulsion between flocs was weakened. [EMIM][OTf] was easily recycled five times. The research results indicate that specific IL, such as [EMIM][OTf], is a potential conditioner to improve the dewatering performance of WAS.

Insight into the roles of ferric chloride on short-chain fatty acids production in anaerobic fermentation of waste activated sludge: Performance and mechanism

• The effect of ferric chloride on short chain fatty acids production was evaluated. • Solubilization, hydrolysis, and acidogenesis were promoted by ferric chloride. • Ferric chloride promoted acetogenesis and high molecular organic acids conversion. • Ferric chloride changed the acid-fermentation to propionic acid-type fermentation. • Excessive ferric chloride inhibited acid-fermentation by strong aggregation. Ferric chloride (FC) is widely used in sewage treatment and sludge conditioning, which could be inevitably accumulated in waste-activated sludge (WAS). However, its effect on short-chain fatty acids (SCFAs) production from WAS anaerobic fermentation has yet to be thoroughly investigated. This study aims to reveal how different dosages of FC affect the production of SCFAs and elucidate the corresponding mechanism. Experimental results showed that 16 mg Fe/g total suspended solids (TSS) of FC was favorable for SCFAs production, with the maximum production was 3.3 times of the control. Mechanistic study revealed that FC induced dissimilatory iron reduction (DIR) and enhanced hydrolase activities, contributing to the disintegration of WAS flocs and the hydrolysis of complex organics. Moreover, FC stimulated the productivity of HAc by promoting the release of carbon-rich substrates and accepting the intermediate electrons generated in acetogenesis process. Further study indicated FC inhibited the methanogenesis and changed the acid-fermentation type by affecting pH and ORP, which was conducive to SCFAs accumulation. Microbial community analysis confirmed that FC enriched the bacterial microorganisms related to hydrolysis and acidogenesis, and increased the abundance of Fe(III)-reducing genera. However, excessive FC (>16 mg Fe/g TSS) inhibited SCFAs production, due to the strong aggregation increased mass transfer resistance and the “over-acidification” damaged the microbial community.

Highlighting the cathodic contribution of an electrooxidation pretreatment study on waste activated sludge disintegration

AbstractIn this study, the effect of the cathodic contribution in the performance of electro‐oxidation (EO) pretreatment of waste activated sludge (WAS) was investigated using different electrode pairs, namely titanium dioxide (TiO2)/TiO2, TiO2/TiO2 coated Platine (Pt) and TiO2/TiO2 coated ruthenium dioxide (RuO2) and main operational parameters such as dosage of electrolyte solution (Na2SO4), initial pH, applied current, and electrolysis time were optimized. Disintegration degree (DD) in terms of soluble chemical oxygen demand (CODs) increased with an increase in initial pH of WAS, applied current, and electrolysis time for all pairs of electrodes. Under the optimized conditions (5 g/L Na2SO4, pH 10, 3 A of current, and 100 min of e time), a maximum DD value of 23.93 and 14.26% was obtained using TiO2/RuO2 and Pt/TiO2 electrodes, respectively. However, lower DDCOD value of 12.85% was obtained for TiO2/TiO2 electrodes at similar conditions except for 4 A current. Soluble extracellular polymeric substances analysis and their protein and polysaccharide concentrations confirmed the disintegration of WAS flocs by the EO process. The operational cost (OC) of applied processes was also calculated and OC values were found in the following order: TiO2/RuO2 (46.54 €/m3) &gt; TiO2/TiO2 (41.77 €/m3) &gt; TiO2/Pt (32.99.54 €/m3) from the point of energy consumption.

Simultaneous heavy metal removal and sludge deep dewatering with Fe(II) assisted electrooxidation technology

A hybrid sludge conditioning strategy with electrooxidation and Fe(II) addition was used for heavy metal removal from sewage sludge and industrial sludge, with simultaneous sludge dewatering and stabilization. With the addition of 82 mg/g DS Fe(II) and treatment time of 4.5 h, heavy metal removals of 72.95% and 78.49% for Cu, 66.29% and 84.26% for Zn, and 36.52% and 36.99% for Pb were achieved from sewage sludge and industrial sludge samples respectively. The system pH decreased to 2.33 and 2.98 and the oxidation–reduction potential (ORP) values increased to 435.90 mV and 480.60 mV in sewage sludge and industrial sludge samples, respectively, which was conducive to the desorption and dissolution of heavy metals from sludge structures and the degradation of the organic compounds that complexed with heavy metals. In addition, the hybrid conditioning process demonstrated excellent dewatering performance due to the efficient electrochemical disintegration of sludge flocs together with the coagulation of sludge particles by Fe(III) generated via electrooxidation. The strong acidic and oxidative environment produced by the enhanced electrooxidation process was also responsible for pathogen inactivation.

Potassium permanganate (KMnO4)/sodium sulfite (Na2SO3) rapidly disintegrates waste activated sludge by reactive Mn(III) species and shapes microbial community structure

Using potassium permanganate (KMnO4) as a reagent to pretreat waste activated sludge (WAS) is subject to limitations owing to high cost for large-scale facilities, as well as secondary manganese pollution. Permanganate/bisulfate (PM/BS) processes have been effectively used to eliminate pollutants from water treatment. However, this technology as an advanced oxidation process for pretreating WAS is relatively unexplored. In the present study, we investigated an adjustable permanganate/sulfate (with KMnO4 and Na2SO3) method to enhance disintegrable performance with in situ-generated reactive Mn(III) species. The results showed that this method could degrade WAS at extremely fast speed (10 s). The concentration of SCOD and VFAs of the KMnO4 + Na2SO3 co-treated WAS notably increased, up to 3125 mg/L and 2276 mg/L, respectively, by 10 s. KMnO4 + Na2SO3 co-treatment could enhance the sludge floc disintegration, release proteins and polysaccharides to soluble EPS fraction, and promote nutrient release. Phosphorus release by the KMnO4 + Na2SO3 co-treatment reached 4498.3 mg/L, which was 3-fold higher than that obtained by the KMnO4 pretreatment. No surplus soluble manganese was found with this method during the operation. Additionally, Illumina HiSeq sequencing of 16S rRNA gene amplicons showed that microbial diversity decreased after KMnO4 + Na2SO3 co-treatment. The predominant phyla of treated sludges belonged to Bacteroidetes, Proteobacteria, Firmicutes, and Chloroflexi. Anerolineae, Clostridia, and Deltaproteobacteria had a positive correlation with WAS hydrolysis and anaerobic digestion. Archaeal communities were not distinct in all sludge samples, and predominant populations were affiliated with Methanothrix and Methanobacterium. This study describes a rapid and efficient process for enhancing WAS degradability and shaping microbial communities with the KMnO4 + Na2SO3 co-treatment.

Investigation of a Gas Hydrate Dissociation-Energy-Based Quick-Freezing Treatment for Sludge Cell Lysis and Dewatering.

A gas Hydrate dissociation-energy-based Quick-Freezing treatment (HbQF) was applied for sewage sludge cell rupture and dewatering. Carbon dioxide (CO2) and water (H2O) molecules in sewage create CO2 gas hydrates, and subsequently the sludge rapidly freezes by releasing the applied pressure. Cell rupture was observed through a viability evaluation and leachate analysis. The decreased ratios of live cell to dead cells, increased osmotic pressure, and increased conductivity showed cell lysis and release of electrolytes via HbQF. The change in physicochemical properties of the samples resulting from HbQF was investigated via zeta potential measurement, rheological analysis, and particle size measurement. The HbQF treatment could not reduce the sludge water content when combined with membrane-based filtration post-treatment because of the pore blocking of fractured and lysed cells; however, it could achieve sludge microbial cell rupture, disinfection, and floc disintegration, causing enhanced reduction of water content and enhanced dewatering capability via a sedimentation post process. Furthermore, the organic-rich materials released by the cell rupture, investigated via the analysis of protein, polysaccharide, total organic carbon, and total nitrogen, may be returned to a biological treatment system or (an) aerobic digester to increase treatment efficiency.

Fate of proteins of waste activated sludge during thermal alkali pretreatment in terms of sludge protein recovery

Proteins are the major organic component s of waste activated sludge (WAS); the recovery of sludge proteins is economically valuable. To efficiently recover sludge proteins, WAS should undergo hydrolysis pretreatment to fully release proteins from sludge flocs and microbial cells into aqueous phase. One of the most widely used chemical methods for that is thermal alkali hydrolysis (TAH). Here, the soluble protein concentration achieved the highest level over 90 min of TAH pretreatment at 80°C; the sludge floc disintegration and microbial cell destruction were maximized according to the content profiles of bound extracellular polymeric substance (EPS) and ribonucleic acid (RNA) of sludge. Both less proteins broken down to materials with small molecular weight and less melanoidin generated were responsible. TAH pretreatment at 80°C for 90 min resulted in the solubilization of 67.59% of sludge proteins. 34.64% of solubilized proteins was present in soluble high molecular; 1.55% and 4.85% broke down to polypeptides and amino acids. The lost proteins via being converted to ammonium and nitrate nitrogen accounted for 9.44% of solubilized proteins. It was important to understand the fate of sludge proteins during TAH pretreatment in terms of protein recovery, which would be helpful for designing the downstream protein separation method and its potential application.